Rotor Damping

[C. Beaty]

Whenever the name Magni is mentioned, the Faithful bow their heads in reverence and chant the Master’s Mantra; “The road to Everlasting Stability is paved with Harmony.”

Along comes the Irreverent Mr. Bird who says; “The bloomin’ thing drives like an overloaded dump truck with the power steerin’ busted.”

The original US importer of the VPM predecessor machines, Bill Parsons, continuously bitched about stick pressure. That’s been 20 years ago.

Other, more discreet individuals say; “It flies like it’s on rails.”

There are some that credit the horizontal stabilizer for the excellent safety record of the Magni line and dismiss out of hand the University of Glasgow windtunnel testing that showed the horizontal stabilizer, buried in the fuselage wake as it is, to be less effective than it should have been.

I think what might have been underestimated in the Glasgow studies was the effect of damping provided by the rotor.

Rotor damping is produced by the rotor lagging behind a control input, whether its spindle is tilted by the pilot manipulating the cyclic control or by a disturbance tilting the airframe. A rotor with flapping hinges (teeter hinge) exchanges its gyroscopic rigidity for damping. A rotor that lags behind airframe motion produces a force that opposes such motion and provides a restoring moment.

Cyclic stick force is a good relative measure of rotor lag and therefore damping provided by the rotor. The more the rotor disc axis lags behind the spindle axis for a given tilt rate, the greater is the stick force and damping. A rule of thumb is heavy rotor = heavy stick. Check FIG 1.

If there are no tricks involved, the lag of the rotor disc vs. spindle tilt rate is a relatively simple quantity to calculate. But I suspect the Magni rotor has some tricks that I’ve yet to uncover. Otherwise, there is no plausible explanation for a Magni having higher stick force and slower response than similar gyros with the same rotor weights.

Other gyros with similar rotor inertia and AUWs have significantly lower stick force and greater agility. I believe that an RAF-2000 fitted with a Magni rotor would behave nearly identically to a Magni and that a Magni with an RAF-2000 rotor would behave nearly identically to an RAF-2000, after due allowance for differences in horizontal stabilizer configuration.

Some of the tricks applied in the past have used auxiliary gyroscopic devices to artificially increase the apparent inertia of the rotor and its damping.

Perhaps the best known is the Bell flybar rotor. The flybar is pivoted to the mast and driven by it but maintains a fixed position in inertial space. The rotor, with respect to cyclic pitch, is tied to the flybar and also maintains its position in inertial space in the case of rolling or pitching motion of the airframe. The pilot’s input is via a differential linkage that applies input in series, between flybar and rotor.

The flybar is slowly precessed into alignment with the airframe by a pair of friction dampers but which do not respond to short term disturbances. See FIG 3.

Another artificial inertia device is the Hiller Rotomatic control system and stabilizer. With this system, the pilot “flies” the servo rotor, which in turn, controls the main rotor. It is a system related to the Bell flybar rotor but with a very different control mechanism. The response to pilot input is quite sluggish and slow. The paddle blades of the control rotor can be ballasted to have almost any control lag imaginable. There is a well known publicity photo of a Hiller hovering with sandbags strapped in the seat and with the “pilot” standing alongside; probably wouldn’t do anything but hover with the necessary amount of lead installed in the paddle blades.

The Hiller servo rotor is the device that first enabled ordinary humans to fly RC helicopter models; without such a device, model helicopters are far too twitchy to be flown by mere mortals. Now, of course, the coming of inexpensive piezo rate gyros has rendered such devices unnecessary.

The sketch of FIG 2 illustrates how a Hiller servo rotor might be applied to a tilt spindle gyro. The near side hub plate was omitted to show details. Whatever stick force and rotor response wanted could be easily obtained by proportioning mass to area ratio of the paddle blades.

There are advantages to artificial inertia devices. A low inertia autorotating rotor has some desirable features: namely its rotational speed can more quickly respond to load, suppressing cyclic flapping and the resulting excess velocity stability of rotorcraft.

An increase of load, say an upward gust, increases the angle of attack equally on both retreating blade and advancing blade but since the advancing blade has greater airspeed, its incremental lift increase is greater, causing the rotor to tilt noseup, an unstable response. If a rotor was inertialess, its rotational speed would increase instantaneously, reducing airspeed differential between the two blades and tending to suppress cyclic flapping. Excess velocity stability (rotor blowback) is a primary contributor to angle of attack instability along with propeller thrust line offset.

Airpeed stability is a different kettle of fish. It is related to angle of attack stability.

I think in the final analysis, Juan de la Cierva had it right; get rid of the gimmicks, arrange the propeller thrust line to pass through the CG and provide ample horizontal stabilizer power with surfaces centered in the propeller blast.

The first man to successfully hitch an ox to a cart must have had at least an intuitive understanding of the relationship of thrust line and CG.

[troed@aon.at]

I still do not get what this should tell us ?!

The M 24 Orion has surprisingly low stick forces compared to the M16/22. Actually the M24 feels on the stick like a heavier MT03 (and this model has VERY light stick-forces).

So there MUST be somethin´else contributing to this than only rotor-weight.

All European gyros have a similar design, esp. concerning H-Stab, based on the gyro-concept of Juka Tervamakki and Vittorio Magni. All fly stable, never heard of a non-pilot-error fatal incident.

The incidents I know caused by pilot error would have happened the same with LTL/CTL-gyros.

Please get me the POINT You are aiming at to make me FULLY understand about the issue of this discussion.

Angelo

[Doug Riley]

Chuck: I agree that rotor damping probably has a good deal to do with pitch stability. A wingless gyro's rather weak roll stability demonstrates to us that rotor damping isn't especially powerful in general.

The only PIO I've ever managed to get a gyro into is in the roll axis. The first time I got my gyroglider off the ground, I got into a wild side-to-side rolling PIO that terminated in a snow pile on the edge of the runway.

The Bensen gyro was a "perfect storm" of poor rotor damping. The blades were fast (400 RPM) and light. That may account for the Bensen's proneness to porpoising and pitchover, even though its HTL wasn't too bad by today's standards. Bensens were smoking in at almost one a month when I first got involved in this hobby.

Fast forward to the 80's. McCutchen baldes were dramatically heavier, and slower, than Bensens. The first time I flew these blades and saw the shadow of the rotor languidly coasting about overhead, it was positively weird. Slow and heavy equals more damping. McC blades probably helped blunt the effect of the increasingly high thrustlines brought on by redrives.

[bpearson]

The M 24 Orion has surprisingly low stick forces compared to the M16/22. Actually the M24 feels on the stick like a heavier MT03 (and this model has VERY light stick-forces).


Glad I wasn't imaginning it Angelo. Maybe the set up of the 24 allows for more stick to head movement (no rear seat for the back stick to hit).

The MT has much longer control sticks as the seats sit higher. Maybe that is all there is to it ! I've seen Magnis thrown around Chuck just like the Italian on your machine in the video but maybe you need bigger arm muscles.

[C. Beaty]

Just trying to flesh out opinions with some facts, Brian,

The only quantitative data we have are the 2-axis hang tests done in Australia, showing the prop thrust line/CG offset to be about 12 inches and the Glasgow data showing stagnation pressure at the horizontal stabilizer to be 50% of free stream.

If anyone wishes to dispute these numbers, he ought to come up with his own set, not dismiss it all out of hand.

I suppose everyone knows how to locate the CG from a double axis hang or weight test.

The stagnation pressure can easily be measured with an airspeed indicator and a proper pitot/static probe mounted at various locations along the stabilizer leading edge.

"When you can measure what you are speaking about, and express it in numbers, you know something about it, but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind: it may be the beginning of knowledge, but you have scarcely. . . advanced to the state of science." –Lord Kelvin

[C. Beaty]

Doug, although lateral PIO has happened, it’s pretty rare. The lower roll axis MOI and the crisper response probably account for that.

I’ve also experienced lateral PIO that was caused by too much backlash in a rotor system that had no component of thrust fed back into the stick.

It was with a rotor where the roll/pitch pivots were coplanar with the teeter bolt.

I think three of us tried to fly it, Ernie, David Seace and myself. No one could fly it until I solved the backlash problem.

The self centering action of a standard offset gimbal rotorhead mitigates control slop.

[Doug Riley]

Chuck, that probably means that I'm laterally challenged (a politically correct way of saying "retarded").

My Bensen gyroglider had a spindle head (no centering force and very weak rotor damping). The first time I had it off the ground, I got it into a wild lateral oscillation. It and and I were saved from damage by my colliding with a soft snowbank instead of hard tarmac.

The next time was nearly 30 years later, on the initial flight of my Gyrobee. It lifted off at about 18 mph and I got it wallowing around pretty nicely, though nothing like the old B-8 glider. The 'Bee has a large, slow, medium-weight Rotordyne rotor and a gimbal head... but (like the glider) it has an overhead stick with a very slow leverage ratio. The total throw in each axis is about two feet, giving a rate of over 1" per degree. It takes a measurable amount of time to physically deflect the stick far enough for anything to happen. This is a source of lag/overshoot.

Anyway, I got used to both of them after awhile.

[Lee Scatt]

Chuck, Thanks for posting such info. It really helps to understand what I have read in other threads.

Your statement concerning inertia produced velocity stability as a negative, due to angle of attack instability, is interesting.

Do you think it would be possible to fabricate a set of rotors resembling the Hiller paddles? Basically a 12 foot dia. hub bar with 5 foot airfoil sections. Filament wound tubing to resist torquing and bending. Seems it should have a lower mass.

I can't imagine the inboard 5 or 6 feet of rotor having enough airspeed to have any appreciative lift.

[bpearson]

Just trying to flesh out opinions with some facts, Brian,



I think the debate will go on Chuck until someone puts a raf rotor on a Magni or vis versa. The numbers are too much for me to follow.

I'm sure the V CofG thrustline offset was found to be around 4" by Glasgow or somebody so I suppose that figure needs to found out with some accuracy first.

I remember walking into my first A level physics lesson to be told everything I'd learnt at O level was wildly inacurate and fairly useless. I dropped out of school a few weeks later and got a job !

[Learjet]

Whenever the name Magni is mentioned, the Faithful bow their heads in reverence and chant the Master’s Mantra; “The road to Everlasting Stability is paved with Harmony.”

he he at least the Magni Faithful aren't having to bow their heads because the too heavy rotors are busy chopping off the too low tail-plane situated too far below the too high thrust line... funny that! :-)

[Chippydriver]

Arrow engined VPM M16 G-BWGI modified with air data system, inertial measurement unit, recorder, power supplies etc

Mass (zero fuel, 78 kg pilot in rear seat) 426 kg
Normal distance from propeller geometric thrust line to c.g. 1.75" (c.g. below)

Mass (full fuel, 78 kg pilot in rear seat) 459 kg
Normal distance from propeller geometric thrust line to c.g. 3.24" (c.g. below)

Results for Rotax 912 modified VPM M16 G-BUZL showed a slightly higher c.g. If I can find photos of G-BWGI it can be seen that the c.g. is likely to have been lower than normal due to the batteries from a Cessna 406 being place where the front seat used to be.

I also did a VPM M16 that was to be used for a round-the-world trip by a British Army pilot. This had c.g. nearly 6" below. This aircraft had been modified for the trip, so was non-standard, but it had other features that I hadn't seen before on 'GI or 'ZL. The Royal Air Force weighing team repeated the exercise a week later and obtained the same result I believe.

Will get the details for 'ZL and the round-the-world machine tomorrow and post here.

[Udi]

I know the Magni blades are supposed to be torsionally stiff but -- wouldn't an over balanced airfoil rotor be highly damped as well? Is it possible the Magni rotors contain a piece of lead or some other heavy metal at the leading edge, far out there - close to the tips? This may be one of the "company secrets".

Dr. Angelo and Mr. Pearson - I am not sure a light stick on the M24 is good news. If Chuck's hypothesis regarding the Magni stability is correct than the M24 may not posses the most important trait - high rotor damping.

Doug - I am not sure if I read your statement correctly, but a high-RPM light rotor is better damped than a low RPM light rotor. Whether a low-RPM heavy rotor is better damped than a high-RPM light rotor depends on the proportions. MOI is linear with weight but the square of the arm (of blade CG).

[bpearson]

Arrow engined VPM M16 G-BWGI

Mass (zero fuel, 78 kg pilot in rear seat) 426 kg
Normal distance from propeller geometric thrust line to c.g. 1.75" (c.g. below)

Mass (full fuel, 78 kg pilot in rear seat) 459 kg
Normal distance from propeller geometric thrust line to c.g. 3.24" (c.g. below)



Wildly differing numbers to the Australian test and IF right then explains a lot.

[C. Beaty]

Doug: I have always disliked a slow stick and suspect it could cause control difficulty.

Lee: On the NACA site, there is complete wind tunnel test data on rotors with various amounts of the inboard portions of the blade replaced with a streamlined spar. It doesn’t look good with too much cut away. I don’t have the URL stored on this computer but have it on another if you can’t find it.

Udi: Overbalanced blades was what I’ve been thinking about when saying there might be a secret vis-a-vis rotor damping. Greg G. has assured me there is no overbalance.

However, overbalanced (nose heavy) blades will provide an effective increase of rotor damping. I suspect that’s Wing Commander Wallis’ secret.

[Udi]

There are two ways to know whether the Magni blades are overbalanced - one is to get the manufacturer plans and the other is to dissect a blade postmortem. If only the outer section of the blade is overbalanced, it would be difficult to detect while the blade is intact. If you have a section of the blade and you don't know what part of the blade it came from, you won't be able to rule out overbalancing in other sections.

What other "secret" could there be?

[C. Beaty]

I expect an ultrasound scanner could detect lumps, Udi. The things used to scan pregnant women’s bellies or better still, the scanners used for detection of flaws in composite structures.

I wouldn’t be surprised if a smart electronics guy like Al Hammer could convert one of those ultrasound “tape” measures to the task.

But better still, I’d like to examine a trashed rotor blade.

[Udi]

An x-ray will give a perfect picture of the guts of a blade - but you still won't know weight distribution without knowing what metal is used.

Soft steel 7.9 g/cc
Lead 11.4 g/cc
Tungsten 18.8 g/cc

[C. Beaty]

It has occurred to me, Udi, that perhaps pitch/cone coupling is employed in the Magni rotor, maybe unknowingly.

Pitch/cone coupling, where an increase of coning angle pulls pitch, changes a lot of things; it reduces velocity stability and improves angle of attack stability. I think it also increases effective damping.

If the blades were swept slightly rearward, an increased rotor load would tend to twist pitch out of the blade. It’s not something one would want to do with a metal blade or even a fiberglass skinned aluminum spar blade but a blade with fiberglass spar would be OK.

It would also account for the heavy stick.

The McDonnell tip jet helicopters employed a considerable amount of pitch/cone coupling and, so it was claimed, had remarkable stability.
************
Speaking of tungsten, a young Coast Guardsman who flew gyros in the 1970s, brought me a section of whatever Sikorsky (Sea King?) helicopter the Coast Guard was using for search and rescue at the time. These blades had a hollow D shaped aluminum spar with individual blade afterbody sections about 18” long bonded to it. The noseweights were tungsten.

[birdy]

(and this model has VERY light stick-forces).
I wish there was sum way to quantify statements like this.
Its like sayn ' very rough conditions", we all have different ideas of wot very rough conditions are. Iv never flown in very rough conditions yet, but i bet iv flown in conditions that alota people wouldnt even roll their machines out for.
Everyone says these mto and ela machines aint as heavy, but how heavy are they?
Iv had people tell me the magni stick isnt heavy?!?!. Compared to a FW its not bad, but compared to wot im used to, its jamed.

A wingless gyro's rather weak roll stability demonstrates to us that rotor damping isn't especially powerful in general.
Im startn to lean towards CBs line on this Doung, coz the magni stick is just as heavy in roll as is in pitch.

Slow and heavy equals more damping. [or just higher resistance to change, which every way you look at it] But it still dont explain why the magni and wasa blades are miles apart, given they are nearly identical, cept for the wasa blades be'n 2 foot longer. [Which means they should be heavier on the stick]

The MT has much longer control sticks as the seats sit higher.
Thats interesting. ;)

I think the debate will go on Chuck until someone puts a raf rotor on a Magni or vis versa.
Id like to take the HS off a magni and give it a fist full. :)

What other "secret" could there be?
Iv never thought there was any.

[JEFF TIPTON]

If you are looking for metal in the blade, would not an metal detector be appropriate. It would not be exact, but it would indicate if something was there.

[Udi]

What other "secret" could there be?
Iv never thought there was any.
So how do you explain the heavy stick on the Magni, Birdy?

[Learjet]

yawn... well the friction control / damper for starters... but I think we've been there and discussed that...

[birdy]

Yawn............. id heard bout these too, and also heard theres no such thing on the magni.

Heavy blade- short stick Udi [ and probably a docile balance point].

[C. Beaty]

yawn... well the friction control / damper for starters... but I think we've been there and discussed that...That’s what Greg G. was initially suggesting as an explanation for the heavy stick of a Magni but as it turns out, there is no such device.

If you would like first hand experience with PIO, add a friction damper to the control system.

[birdy]

If you would like first hand experience with PIO, add a friction damper to the control system.
Funny you should say that CB.
A few years back, not long after id changed out the control systm on the ferel with a new one, one that uses those orange fiber washers as thrust bushes, i was mustering on a rainy day. The rain got too heavy for me to be of any benifit in the air so i landed for a bit and waited for it to pass.
A while later i was off again, and i noticed there seemed to be sumthn restricting the stick. It didnt take long before it was 'grabing', and took quite abit of force to make it let go, which, as you point out, makes for an interesting flight path.
I landed again and found the water had made the fiber washers swell and jam the joint, effectivly maken for a cyclic friction.

[C. Beaty]

I also have some first hand experience, Birdy.

Years ago, someone had built a new Bensen that no one could fly without PIO. I was asked to give it a try and sure enough, I had the same problem. But I recognized the cause.

The builder had wedged oversize Teflon washers between torque bar and U block, giving a good bit of friction but it wasn’t recognizable on the ground since the breakaway (static) and dynamic friction of Teflon is nearly the same (less slip-stick), almost like hydraulic friction.

With the Teflon wedges removed, the gyro flew normally.

[gyromike]

I guess I'll throw a story in here too. :)

A few years back one of our club members, a new guy, was having trouble flying his Air Command. "It's all over the place and scares the crap out of me", he said.

So Steve Alexander (who would try to fly a sheet of tin if you stuck a motor on it) went up in it, flew around a bit, landed and said, "Man, that scared the crap out of me!".

Since I'm not the sharpest tool in the shed, I decided to go up and see what the problem is. I didn't take into account that if it scared Steve, it would terrify anyone else!

As soon as I broke ground, I thought "Man, this thing scares the crap out of me!".

It was gusty and I was all over the sky trying to control it. I was afraid to try to land it in front of the hangars because of the crosswind, and the air tumbling over the hangars. Luckily Jennings has multiple runways and several taxiway intersections, so I was able to find one facing into the wind and pretty much fly it onto the ground.

The culprit? Too much friction in the controls.

[Al_Hammer]

If the blades were swept slightly rearward, an increased rotor load would tend to twist pitch out of the blade -Chuck.
If nose weights were indeed used to shift the cg of the blade, wouldn't some amount of rearward sweep be needed? This in fact might be a way to test a blade- simply hang it and see if it hangs straight down or not- see diagram, borrowed from an R/C site.

[C. Beaty]

Absolutely, Al. With a blade hung on its exact aerodynamic center, the hang angle would indicate whether over, under or dead on balance had been achieved.

Why didn’t that dawn on me?

[Udi]

Brilliant! Al comes to the rescue... :plane:

Now, who is going to hang-test a Magni rotor?

[hiphop]

Hey Chuck,

You mentioned that Wallis has large nose-weights on his flexible (wooden) rotors, and that this mag be his secret. I know I have seen him quoted somewhere as saying that he does not like the metal rotor blades, which I read as too torsionally stiff.

Can you comment a bit on what the effect would be of having a torsionally soft rotor blade with a mass distribution *ahead* of the quarter chord?

Thanks, G.

[C. Beaty]

Just like a nose heavy airplane, Gabriel. An upward gust, acting on the aerodynamic center, twists the blade nose down and airspeed dissymmetry of a translating rotor insures the rotor disc will also tilt nose down, which is what we would like.

I’ve seen literature on the subject but can’t remember where. It could have been Bensen experimenting with extra heavy noseweights, where, to the best of my memory, I recall that overbalance was carried to the point where the rotor would no longer respond to cyclic input. That would surely cause a heavy stick.

[hiphop]

Thanks for the quick reply, Chuck.

Just like a nose heavy airplane, Gabriel. An upward gust, acting on the aerodynamic center, twists the blade nose down and airspeed dissymmetry of a translating rotor insures the rotor disc will also tilt nose down, which is what we would like.

Follow my train of thought for a minute. You take a normally very light rotor (wooden), which would have very little damping and reacts almost too fast, and offset this effect by adding nose weights at 70% span. You wind up with a rotor that is no longer *twitchy* but still can accelerate quickly to absorb a gust.

This is pure speculation on my part, but it seems that this might work as a nice design compromise.

--G

[C. Beaty]

I imagine that’s the reason I’ve never seen a photo of a Wallis machine with metal blades, Gabriel.

I’m sure there is literature somewhere about overbalancing rotorblades. I believe that was one of the things explored in the early history of the helicopter when a number of people were chasing stability gremlins.

[C. Beaty]

Here’s what Google found for forward CG but I haven’t waded through it yet.

http://scholar.google.com/scholar?q=rotor+blade+with+CG+ahead+of+aerodynamic +center&hl=en&client=firefox-a&rls=org.mozilla:en-US:official&hs=TaD&um=1&ie=UTF-8&oi=scholart

[Al_Hammer]

Just thought I'd share this.

Over a delicious lunch Signor Magni gave us his views about how gyros were progressing. For example the Glasgow work on C of G. There was a danger he felt of being too academic and looking at just one aspect of the gyro phenomenon. You have to take a holistic view - "If it flies, it flies" - is very much the way he approaches the subject. And by way of reinforcement he cited the case of a helicopter and its thrust line in flight which is clearly well above the centre of gravity and creates a tremendous moment arm. "Why does it not topple over?" he inquired with suitably Italian gesticulation!
http://www.kate.aviators.net/temp4.htm

[birdy]

Big difference Al, but i know you know that.
And i assume Magni dose too.

[Al_Hammer]

As you and I know Birdy, all that matters is where the line of thrust is pointing, not where the rotor is on that line.

[troed@aon.at]

Thanks Al for the link.....

Towards the end of the afternoon Khalid and Dave were each given the chance of trying one of the Magni's by one of Vittorio's sons, Lucca. What can I say? David Beevers had told me that after an RAF the Magni would seem as smooth as silk but nothing had prepared me for the reality of this exquisitely designed machine. At every stage it was gentle but responsive. Rock steady, its suspension soaked up the imperfections of the grass strip at Spessa. Wind up the rotor on the twin belt drive at 1800 engine rpm to around 175 rpm and then roll, easing on the power. Release the prespin at 200 rpm and true to Lucca's word the machine flies itself off the ground when it is ready and climbs effortlessly upward at 50 mph powered by its Rotax 4 stroke. Use the electric trim for 60 mph in the cruise and it flies truly hands off. Pull back on the stick for 10 seconds and release, the machine climbs then dives slightly and then settles back into straight and level flight without further adjustment. And it's the same if you push the stick forward. I have never flown a more stable machine which is at the same time so responsive and manoueverable. Pushing the cruise to maximum at 100 mph and you still feel in control. Geoff Hoyle, the UK Magni agent reckons that with a following wind they may well get through The CAA's section T and have machines available in Britain by the end of 2002/beginning of 2003. If they get their fully enclosed cockpit 2 seater up and running and looking like the incredibly tidy single seat enclosed cockpit we saw at Spessa, they will have a world beater on their hands.

Nothing to be added.... it perfectly describes how the M24 flies.........

We were kindly invited to view the Magni factory to the north of Milan and after some negotiation of the Italian road system we arrived at their premises on the somewhat aptly named Strada Puccini to see how the great maestro of gyroplanes put his machines together. It's a compact operation - 3 floors of approximately 1500 square feet each. On the top floor, overseen by Vittorio's elder son Pietro, is the composite production unit with its associated specialist equipment for laying up the fibre and spray painting the final mouldings. They try to do all their mouldings themselves so they can control the quality. This includes the rotors, the die for which cost around £30,000! Pietro explained how they weighed and balanced rotors and made up matched pairs. With relatively little head adjustment available on the aircraft itself this job is critical to creating a smoothly flying aircraft.

On the next floor four gyro chassis in various states of build were being worked on by younger son Luca. It all looked very professional. This tight knit team of just ten people aim to produce roughly four aircraft a month which means that at the end of each week the latest to roll off the line has to be trailered 30 miles south to the strip at Spezza for flight testing at the weekend. The Magnis are truly dedicated to their business.

In the basement were the stores of steel, and other components. They outsource key components requiring CAD machining but try to produce everything else themselves as part of Vittorio's unceasing drive for quality.

spares me a hell of typing work, the new Magni-factory works the same but more parts fabricated by Magni itself and higher number output of gyros but still too little for the demanding customers. But Vittorio, Luca and Pietro won´t make compromises in quality. If You want to have a Magni, You have to wait.......

Angelo

[birdy]

after an RAF the Magni would seem as smooth as silk
To be fair, so would a brick. :)

[troed@aon.at]

What EXACTLY do You mean by THAT ? :plane:

Angelo

[Xavier AVERSO]

Je connais vittorio Magni depuis plus de trente ans et j'affirme que cet homme est consciencieux et ces productions sérieuses, toutefois dans la pratique commerciale les Magni's ont tendance a laisser croire que seul leur produits sont bons..!!!
J'ai volé avec de bons rotors Magni et j'ai volé avec de mauvais rotors Magni ( beaucoup de vibrations )
Il n'y a ni secret ni magie, en 1996 j'ai eu l'occasion d'ausculter un rotor Magni , voici les données: Diamètre du rotor : 854 cm ; longueur de la pale : 420,5 cm ; corde : 22 cm ; épaisseur du profil : 27 mm ; poids de la pale :18,7 kg ; CG de la pale depuis le premier trous de fixation : 185 cm , le CG de la pale est a 44% de la longueur de la pale, le longeron est fabriqué en sifflet, d'une largeur de 9 cm a l'encastrement a 4 cm au saumon, au bord d'attaque il y a du plomb sur la totalité de la longueur de la pale sauf sur les premiers 30 cm de l'encastrement, a l'encastrement l'équilibre sur la corde est a 27% , au saumon l'équilibre sur la corde est a 24% , un rapide calcul du lest en plomb donne une masse de 3800 g.
J'imagine que depuis ce produit a évolué ..???
Pour éviter les erreurs des traducteurs informatique , j'ai fais traduire par mon ami Canadien Edwin Cox que je remercie ici.

I have known Vittorio Magni for more than thirty years and can state that this man is conscientious and his products are serious ones ; nevertheless, in commercial practice, Magni have the tendency of letting you believe that only their products are any good!!!
I have flown with good Magni rotors and I have flown with bad Magni rotors (a lot of vibration).
There is no secret or magic in this, in 1996 I had the opportunity of sounding out a Magni rotor, here are its parameters: Rotor diameter: 854cm ;blade length: 420.5cm ; Chord: 22cm ; Profile thickness: 27mm ; Blade weight: 18.7 kg; Blade CG from the first fixation hole: 185 cm; the blade CG is at 44% of the blade length, the spar is tapered, 9cm wide at the hub and 4 cm at the tip, the leading edge is lead weighted over the whole blade length except for the first 30 cm from the hub, at the hub the chord balances at 27%, at the tip the chord balance is at 24% :
A rapid calculation of the lead ballast gives a mass of 3800gr.
I imagine that this product has evolved since…???
To avoid automated translation errors, I have had this translated by my Canadian friend Edwin Cox and thank him for it here.

http://img254.imageshack.us/img254/7410/magniscan2oo6.th.jpg (http://img254.imageshack.us/my.php?image=magniscan2oo6.jpg)

http://img388.imageshack.us/img388/6526/croquisfq5.th.jpg (http://img388.imageshack.us/my.php?image=croquisfq5.jpg)

[Xavier AVERSO]

http://img376.imageshack.us/img376/5892/croquis2ji6.th.jpg (http://img376.imageshack.us/my.php?image=croquis2ji6.jpg)

[C. Beaty]

Thanks, Xavier. Normally, it is impossible to find factual information about a Magni. The usual response to a technical question is a testimonial from a seduced customer.

The moment of inertia of a Magni rotor blade is considerably less than similar, uniform blades.

Magni blades are in fact over balanced at the outer ends which accounts for high stick force and greater damping.

The aerodynamic center of a NACA 8H12 airfoil lies at 26% of chord.

[All_In]

Thanks guys, this helps a great deal there is so much still to learn!

[Rotor Rooter]

The usual response to a technical question ....

Perhaps this may be of interest to some. It is by Gordon Leishman.

Development of the Autogiro: A Technical Perspective (http://pdf.aiaa.org/JournalsOnline/PDFFiles/00218669_v41n4/aiaa/00218669/v41n4/1205.pdf?CFID=99023&CFTOKEN=44104942)

Dave

[Chippydriver]

Excellent paper by an excellent University of Glasgow graduate.

Regards Magni blade data, the previously posted numbers agree broadly with what I've got. Unfortunately knowing that the c.g. lies at 44% radius will overestimate the blade inertia, hence underestimate the Lock number, hence get the rotor damping wrong. Blade mass distribution is such that quite a lot is concentrated at the root. You really need to carve the thing up.

We, and the UK CAA, tried to buy a Magni blade this year, but they refused to sell one to either of us. Personally I think they're hiding something, particularly since they still don't have Section T approval.

On the other hand I had a McCutcheon blade sliced into 20 segements. Very interesting.

BTW all that geometric property stuff is irrelevant without knowledge of torsional stiffness. That's not a trivial exercise.

[bpearson]

Personally I think they're hiding something, particularly since they still don't have Section T approval.


What, some manufacturing secret or something sinister ?

[Chippydriver]

I think that they don't know what they're hiding. That's why they're hiding it. We'd have paid over the asking price. Bit fishy.

[bpearson]

I don't suppose you care to say but what were you after finding out and is it anything to do with sec T ?

[Chippydriver]

Nothing to do with Section T. Just want to examine the role of blade elasticity in model fidelity. I've now got an elastic blade model of a McCutcheon rotor for my Montgomerie simulation. So the interest is no more than academic. VPM blade data needed just for consistency - the hostility of the reaction to the request for a Magni blade had to be read to be believed.

[C. Beaty]

Designers working in accordance with the “Infinite Monkey Theorem” always believe everything is a trade secret.

[birdy]

What EXACTLY do You mean by THAT ?
After an RAF, anythn would feel smooth as silk .

The moment of inertia of a Magni rotor blade is considerably less than similar, uniform blades.
Inreresting.

Magni blades are in fact over balanced at the outer ends which accounts for high stick force and greater damping.
Over balanced blades, short stick, no wunder its a hard mouthed yangyang.

[Murray Barker]

Here is the photo of the double hang test done at the 2007 Nationals in Australia. From memory the offset was approaching 14 inches with one person in the machine and half fuel.

[birdy]

Over balanced blades, short stick, no wunder its a hard mouthed yangyang.
Add to that the amount of down force needed on its ass to hold the COG forward of the RTV, and you have, i my oppinion, and imoveable power inefficiant gyro.

Its very stable but. ;)
[ but so is a Cessna]

[Harry_S.]

Huh????????????????????????????


Cheers :)

[Chippydriver]

14" looks as though the rotor wasn't included. If I assume an empty mass of say 260kg; reasonable bloke at 80kg then the 14 inches is consistent with a c.g. that is 3 in low (if the rotor wasn't included and the rotor mass is in reality 41 kg - our machine was 40.55)

Seems to make sense. However if it did include the rotor..........

[C. Beaty]

What appears to be the same crew measuring the CG of one of Paul Bruty’s machines.

[bpearson]

Well someones got it wrong ! Ten inches difference is a fair bit though.

[mceagle]

14" looks as though the rotor wasn't included.
The rotor mass is irrelevant to the C of G in the hang test from the teeter bolt simply because it is always directly on the C of G, and as such its mass will not effect the position of the C of G.

[Chippydriver]

What reacts the mass of the rotor then?

Took us years to knock this misconception out of the UK gyro community.

[Gyro_Kai]

The rotor mass is irrelevant to the C of G in the hang test from the teeter bolt simply because it is always directly on the C of G, and as such its mass will not effect the position of the C of G.

Hi,

let me challenge this. You need to hang the gyro twice. Once, if you like (but not necessarily), by the teeter bolt where the weight indeed does not matter. But the second "hang" will have to be from somewhere else, so then the blade definitely matters.

The Hang Test is merely a method of finding the CG easily. As far as I understand, the point of the whole CG discussion is:

If, through pilot error or gusts, you find yourself in a 0- g situation, the prop thrust pushes the now aerodynamically inactive object foward but not over. In this situation, weightless, the rotor mass is definitely contributing to the geometrical moment of inertia. The heavy rotor on the long mast may well contribute to lifting the CG, deceiving the eyball gauge of the Magnis looking very HTL.

Kai.

[Mayfield]

Hi Tim,

It seems to me that the weight of the rotor would not be relevant when determining longitudinal CG if hanging from the teeter bolt. It seems that rotor weight would be important when determining vertical CG.

On the other hand, the rotor would clearly have to be attached if determining longitudinal CG through weighing and computation.

Sound right?

Jim

[C. Beaty]

I think Tim’s statement has been misunderstood. Hanging from the teeter bolt, absence or presence of the rotor is irrelevant.

Hung from another axis, not in line with the rotor CG, rotor presence is all-important.

[Murray Barker]

All the COG tests done in OZ on that day were done with the rotor attached.

Even if there is a small error in our measurements you can see that the notion of a 4 inch offset on the Magni is just wishful thinking.

Here is another Gyro we tested on the day.

[bpearson]

Hmm. This leaves us in a bit of a situation. If Glasgow were 10" out then how can any of their report have any validity. I said IF !

And if the Magni's TL is 14" high then how come they aren't flipping inverted by the truckload.

The mystery continues.

[Murray Barker]

As we can see in the photo of the Magni there is only the weight of one person in the machine. Maybe we should have had it at gross weight but how scary would the offset be then? That horizontal tail must be working awfully hard.

Paul Bruty's Firebird was done at gross weight (probably over) and came in at a much more reasonable figure.

[C. Beaty]

I think, Brian, there is some confusion between the earlier machines with Hirth engines and the later machines with Rotax 912s. They don’t even look the same, side by side.

Or was it Arrow engines? I can't remember.

The later Magnis clearly have considerable thrust line/CG offset.

I don’t know why they’re not falling out of the sky but the purpose of this thread was to discover the nature of the prosthesis. Is it the horizontal stabilizer, mounted in the fuselage wake as it is or is it the rotor damping provided by the forward CG of the rotor blades?

I don’t have a chicken in this fight; my sole interest is scientific knowledge.
***
A note on CG measurement: Balancing on the main wheels to establish one CG axis isn’t a good idea if the suspension has travel not in line with that axis.

[mceagle]

The purpose of the hang and balance test is to arrive at two data lines, the intersection of which will determine the C of G of the gyro. The rotor mass could be 10 lbs or 100 lbs and it would not change the C of G Datum from the hang test.

[Chippydriver]

Ok. Have it your own way.

[Gyro_Kai]

The purpose of the hang and balance test is to arrive at two data lines, the intersection of which will determine the C of G of the gyro. The rotor mass could be 10 lbs or 100 lbs and it would not change the C of G Datum from the hang test.

Hi Tim

you are correct about the two lines. One, for convenience reasons usually goes through the teeter bolt. The other, and that is the one to watch out for, here, will not to through the teeter bolt. And suddenly the weight of the rotor becomes important. Please see in the attached tilted photo, where the Firebird's rotor is, when it balances on the mains: about 3 ft out to the right, pulling the machine backwards.

If the rotor was weightless, you would have to balance the contraption further back, to neutralize the weight of the manned cabin, thereby the intersection of the two lines would be much lower.

Kai.

[Gyro_Kai]

Hello,

is there some way to get the famous Glasgow Gyroplane study in the full? I have the below link, which is the summary:

http://www-legacy.aero.gla.ac.uk/Research/Fd/Project5.htm

Kai.

[birdy]

Wen balancing on the mains, the rotor should be at 9 and 3 oclock, so's theres no weight on the teeter stop.

[bpearson]

The purpose of the hang and balance test is to arrive at two data lines, the intersection of which will determine the C of G of the gyro. The rotor mass could be 10 lbs or 100 lbs and it would not change the C of G Datum from the hang test.

Surely if you are wanting to determine v cof g using the double hang method then you must have the blades (or equivelant weight) attatched.

It won't matter if one of the 'hangs' is from the t bolt but it will matter from the other 'hang'.

In fact where is the second hang attatched to. Over here they replace a blade with a length of metal, weighted the same as the blades and tied to the keel and front of the gyro. This I think is used for the second hang. Obviously you couldn't hand the machine from the blade itself.

[bpearson]

I think, Brian, there is some confusion between the earlier machines with Hirth engines and the later machines with Rotax 912s. They don’t even look the same, side by side.

Or was it Arrow engines? I can't remember.

The later Magnis clearly have considerable thrust line/CG offset.


The basic geometry remains the same I think Chuck. The Arrow engine's exhausts can't have helped things though.

I think until we get definate v cof g figures (the only two results we have are 10" out) we may....may be all wrong.

[C. Beaty]

Hello,

is there some way to get the famous Glasgow Gyroplane study in the full? I have the below link, which is the summary:

http://www-legacy.aero.gla.ac.uk/Research/Fd/Project5.htm

Kai.Jean Fourcade, a French aeronautical engineer, wrote an article that is a pretty good synopsis of the Glasgow report in easy to understand language. A copy is posted on the OZ gyro site:

http://www.asra.org.au/L_Stability.htm

[Mike G]

Chuck B
My Magni blades are currently in my garage so a decided to find the C of G (or C of M) In fact as I did it I found that the it was already marked from some previous owner.
The C of G is 1797 mm from the inner end of the blade (which is 65 mm from the center of the bearing) and 56.5 mm back from the leading edge. The blade has a chord of 220 mm so the C of G is at 25.7% of chord.

I then took the piece of an Aircopter blade that I have and did a few measurements. I must say that I was given this bit of blade by someone (who I do not wish to name) and therefore cannot guarantee that it is the latest Aircopter design. Attached are some dimensions.
The bare blade C of G is 70 mm from the leading edge and the chord is 200 mm. From other info I got from Aircopter many years ago (see a previous post that I cannot find) there are two steel bars glued into the leading edge at the outer end of the blade. Assuming that the C of G of the bare blade (without inserts) is in the middle I calculated the position of the Cof G of the total for a blade that had the same diameter as my Magni.
The attached shows that the C of G of the Aircopter blade I have with the steel inserts I was told about is 63 mm back from the leading edge, thats 31.5% of the 200 mm chord.
It is also interesting to see the thickness of the Aircopter outer skin, I seem to remember you said that anything below 3mm would be difficult to achieve. I measured 1.4 mm which suggests that either Aircopter have one hell of a extruding machine or the aluminium used is very ductile.

Someone said in one of the recent threads that the trailing edge of the Magni was very sharp unlike the trailing edge of an extruded blade. Well the trailing edge of my Magni blade has a 1.2 mm thick trailing edge section and the Aircopter is 1.4mm.

It's also interesting to note that the Aircopter blade I have is not exactly the same as that shown on the MT03 website. I'm sure I read somewhere that the MTO3 people were making there own blades which may explain the difference, or the blade section I have is no longer what Aircopter make.

Even though I'm a Magni driver I'm not a fanatic, like you I'd like to see some facts.

I hope this is of some use in the never ending quest for the facts.
Mike

[C. Beaty]

Overall, Mike G., the chordwise CG in no doubt where you have indicated. However, long flexible members such as rotorblades are sensitive to local conditions. You would have to cut them up and measure at various radial stations.

Xavier Averso in post #42 pretty well nailed it.

The prosthetic effect of overbalance is very dependent upon torsional rigidity.

[ckurz7000]

Allright, I take the worm! If you want to determine the CoG experimentally alone, you will have to have the rotor attached for that one measurement where you don't hang the gyro from the rotor's CoG. Of course you could do even the second hang without the rotor, thereby determining the CoG location for the gyro sans rotor. Then you weigh the rotor separately. It's easy to compute the compound CoG (rotor and machine combined) from knowing each one's separately. And you know, of course, where the rotor's CoG is: right at its geometric center.

If you happen to have the rotor installed, it doesn't matter in which position the blades are. You can even move them between the hangs. The only important thing is that they be as close to flying position as possible. Although I would think that the error induced by having them sag instead of straight is within the general measurement error.

-- Chris.

[Gyro_Kai]

Jean Fourcade, a French aeronautical engineer, wrote an article that is a pretty good synopsis of the Glasgow report in easy to understand language. A copy is posted on the OZ gyro site:

http://www.asra.org.au/L_Stability.htm

THanks a lot

Kai.

[C. Beaty]

If you happen to have the rotor installed, it doesn't matter in which position the blades are. You can even move them between the hangs.

-- Chris.Only if the blades are balanced.:D

There are potential errors in all these tests; compression of gear struts, flexing of mast; particularly when locating the CG of an RAF with magic rubber bushing, etc., but none of the potential errors will add up to more than an inch or so. The rotor ought to be set to proper coning angle by a cord running tip to tip with a clothesline prop in the center.

The 2-axis weight test will work as well if accurate scales are available. My experience has indicated that bathroom scales aren’t good enough.

The variation due to Stan Foster using a laser to project a vertical line is probably the most fool proof. This method eliminates parallax errors and the necessity to overlay images.

[quadrirotor]

....
The prosthetic effect of overbalance is very dependent upon torsional rigidity.

All the problem is there! For the blade, it seems there is a confusion between the Center of Gravity and the Centroïde of torsion: the distance, between the Center of Lift and the Centroïde of Torsion (and the rigidity of the blade), determines the behaviour of the blade. The relative distances between the C.o.G., the C.o.T. and the Center of lift (and the rigidity of the blade) determines the flutter and the frequency of the flutter!...
As it is easier to determine the C.o.G., it is taken for the Centroïde of Torsion, which is not the same (above all, for composite blades)!... :(

[bpearson]

Even though I'm a Magni driver I'm not a fanatic, like you I'd like to see some facts.



Same here Mike. I'd be flying a Dominator if they would let me. Just find it strange that everytime a picture of a Magni is put up we here shouts of 'deathtrap'.

In fact I'm thinking of starting a Dom because with the upcoming financial depression hopefully the bloated regulatory industries will be trimmed right back and leave us alone .

[helipaddy]

Hi Brian
Flying a Dominator in Ireland. Its a blast!
Paddy

[bpearson]

Hi Brian
Flying a Dominator in Ireland. Its a blast!
Paddy

Paddy, it seems Ireland has very sensible rules concerning amatuer built aircraft. They allow you to fly safe machines without having to go through all the hoops we have to (which effectively stops any non comercial new designs). Not to mention innovation etc.

Over here we are limited to either £40,000.00 factory clones or 40 year old designs !

Anyway, how did you buy your Dom ? Kit or plans, and how long to build ?

Brian.

[helipaddy]

I bought a kit from Ernie and made some of the bits too. You can decide on how much you want to get pre made. It makes sense buying the welded and the machined parts. Everything goes together great.
I think the Dominator wouldn't pass all the Section T Bull***t regarding the nose gear strength, but in real world Grass strip flying the Dominator gear is plenty strong enough. Its an absolutely stable flying platform, A very manoeuvrable brilliant machine, I'm really happy with it.
I think that section T has damaged the Gyroplane movement in the U.K. possibly beyond repair,while doing nothing in the interests of safety. It seems to concentrate on the certifying the strength of the airframe after the accident. The new interest in the MT03 is really good to see. does anyone know who wrote it?
Paddy

[bpearson]

I think the Dominator wouldn't pass all the Section T Bull***t regarding the nose gear strength,

I think that section T has damaged the Gyroplane movement in the U.K. possibly beyond repair,while doing nothing in the interests of safety. It seems to concentrate on the certifying the strength of the airframe after the accident.

Spot on. I approached the PFA with thoughts on a dominator years ago and yes, they said it would fail sec T on the nose leg. They seem to want a gyro that would still be flyable after a crash that no human would survive.

The costs involved also make any non comercial gyroplane impossible.

What a backward looking country I live in !

[helipaddy]

Brian,
At least you can get a gyroplane licence in the U.K.!
Paddy

[Mike G]

Chuck B
I realised my data on the Magni blade only confirmed what Xavier posted. I was hoping you'd comment on the Aircopter data, especially the thickness of the extruded skin. Was it you who said that less than 3mm was dificult to extrud or is my memory letting me down again?

Mike G

[Mike G]

Paddy
It must be cold over there with your dom and no wind protection. It's bad enough here in the north of France in the M16 winter flying for you must require lots of thick clothing.

Mike G

[helipaddy]

Mike, 10 years on bikes in Ireland and a good layer of bodyfat, you get used to it!

[C. Beaty]

I’m not an extrusion engineer, Mike, although I’ve purchased extrusions and have visited extrusion mills.

Thinner sections require more pressure from the press (it’s easier to squeeze toothpaste through a big hole than a small hole) and thin sections don’t mix well with thick sections because of differential cooling rates. There is a tendency for thin sections to sag between supporting webs.

The 500 lb. ingots of aluminum are preheated to just below the melting point before going into the press. Under pressure, the aluminum flows through the die for the desired shape.

The extruded part, after quenching, is gripped in jaws and stretched or snapped for straightening. Ends that have been skinned up by the gripper jaws are sawn off and go back into the furnace.

[Xavier AVERSO]

Ce que dit André Martin ( Quadrirotor ) est juste et c'est en fontion de ces données que les pales extrudées sont souvent plus efficaces que les pales composites trop souples en torsion

What André Martin (Quadrirotor) says is right and c' is in fontion of these data which the extruded blades are often more effective than the too flexible composite blades in torsion

[quadrirotor]

Merci Xavier, quelques fois j'ai l'impression que mes billets sont invisibles pour les autres membres de ce forum!!! :)
Je sais que tu as essayé les deux type de pale (aluminium et composite); et aujourd'hui tu ne fournis que des pales aluminium à haute rigidité, et elles ont une bonne réputation.


Thanks Xavier, sometimes i have the impression my posts are invisible for other members of this forum!!! :)
I know you have experienced both type of the blade (aluminium and composite); and today you fournish only high rigidity aluminium blades, and they have a good reputation.

[Resasi]

Andre your post along with others are certainly not invisible. Certainly for my part I forlornly attempt to follow, with great interest if not as much comprehesion as I would like, some of these discussions that are seriously beyond my abilities.

[C. Beaty]

By “Centroïde of Torsion,” I assume the meaning is shear axis, the axis about which things rotate when subjected to elastic twist.

The shear axis ought to coincide with the aerodynamic center as indeed it did with the old fabric covered Autogiro blades having a steel tube spar located at the aerodynamic center.

With a hollow, airfoil shaped thinwall tube, the shear axis will be at about 40% of chord. Bonded metal and I suppose fiberglass spar blades will generally have the shear axis forward of the aerodynamic center, not necessarily a bad thing from the aspect of flutter.

But the bottom line is that all tail heavy rotorblades will flutter or diverge at some airspeed. Extruded blades with thick skins sometimes aren’t mass balanced about the aerodynamic centers but never reach the critical speed for flutter.

I’ve watched SkyWheels blades being run on a test stand where divergence began at ~500 RPM with a 23’ set. SkyWheels blades have their center of mass at ~35% of chord from the leading edge.

Propeller blades aren’t often mass balanced about their aerodynamic centers but don’t flutter because they’re short and stiff.

[gyrogreg]

There are two ways to know whether the Magni blades are overbalanced - one is to get the manufacturer plans and the other is to dissect a blade postmortem. If only the outer section of the blade is overbalanced, it would be difficult to detect while the blade is intact. If you have a section of the blade and you don't know what part of the blade it came from, you won't be able to rule out overbalancing in other sections.

What other "secret" could there be?

Udi, no "secrets" here. I posted the following Magni rotor blade section info on a previous post. Attached is a pic of a section of the Magni rotor - same along the full length. Note the triangular metal (lead?) bar in the nose. Magni distrubuted these sections several years ago as part of their Magni's Day trophies. (The dark area inside the lower rear surface is just a gap - for mounting the section to the rest of the trophy - not a thicker lower surface - would normally be foam against the lower surface!) The spar is solid layers of composite material - the rear 3/4 is foam filled. I'm not sure what the composite materials are - but there are suggestions, and the color of the wrap suggests, and the blade stiffness suggests some use of Carbon "Fibre".

The chord is 8-5/8". The leading edge is solid composite (spar) back to the 2" from leading tip. (The spar is composite - probably fiberglass - not metal spar) The balance point (of this section on a knife edge) is at 2-3/8" from leading tip. The max chord is approximately at the 2-3/4" chord point.

This puts the balance point at 28% chord - aft of 1/4 chord. The max thickness point is about 35.% of chord. I don't know what airfoil this is - but it looks like any other gyro blade to me. Trailing edge has a bit of reflex. Does this jive with your thoughts on an "over balanced" blade?

With the balance point at about 28% of chord, I don't think it is over balanced.

Myself and others have posted the span-wise CG - I can't find that right now. But, these numbers do not suggest the rotor is weighted any differently along the entire span - except for slight differences from the metal root mount, and the tip dressing.

- Thanks, Greg gremminger

I just found time to try to catch up on the forum - still working through this thread so I'm not sure someone else had not already provided this blade section info.

[gyrogreg]

That’s what Greg G. was initially suggesting as an explanation for the heavy stick of a Magni but as it turns out, there is no such device.

If you would like first hand experience with PIO, add a friction damper to the control system.

FYI:

There is no specific friction damper in the Magni controls. But, we do add some friction by tightening the pitch and roll bolts - this is for two purposes:

- Reduces a lot of the residual rotor shake getting to the stick

- Improves the hand's off stability by forcing the rotor to follow the airframe. Note, this is not what you would want to do with an unstable airframe - force the rotor to follow the airframe when the airframe pitches in the unstable direction. Because a well stabilized airframe pitches in the correcting direction to a distrubance, it a good thing to have [b]some friction. Hand's off, or fixed stick, with a little friction in the cyclic control, it is even better in severe turbulence to just let the Magni fly itself - pilot can make a comfortable ride in wind less comfortable if you try too hard - does better on its own!

The friction we put in the stick essentially provides that the gyro flies essentially "fixed stick" with even hand's off - only large wind transients force the stick to actually move! To be fair, the Magni factory may not apply quite as much friction as we do here in the U.S. - and some Magni fliers choose to set in less stick friction.

We have never had reports of PIO - slow or fast rate. I have managed to create over-control PIO in both roll and pitch on my Magni by much over tightening the pitch and roll pivot bolts - but this is because this forces the pilot to over control to break the "stiction" in moving the stick - done this on other aircraft as well. This is not the rapid "PIO" that kills people - but it is not comfortable if the "stiction" is too much.

At any rate, the "heavy" stick on a Magni is not from the friction in the controls - "heavy" stick is still just as "heavy" with no friction set in the cyclic control!

- Thanks, Greg Gremminger

[Doug Riley]

Another contributor to "heavy" stick is the undersling of the gimbal pivots. As the vertical distance from the pivots to the rotor itself gets greater, the centering forces in the controls go up. This increases the stick pressures at a given G load -- but, unlike friction, it does not create a need for a "breakaway" force.

(Jim Mayfield stated in his article about the Groen Bros. Hawk IV development that this effect moved Groen to abandon the gimbal head in favor of a swashplate. That's a shame, I think. It's possible to control this vertical distance by design, and therefore preserve the great handling qualities of the gimbal head, even on a heavy gyro.)

[C. Beaty]

Quite true, Doug, but the Magni’s side plate hub style permits the spindle bearings to be located within the hub confines and leads to considerably less distance between gimbal pivots and teeter bolt than on comparable gyros.

Also, as pointed out by Xavier Averso, the CG of the Magni rotor is at 44% of radius, resulting in lower moment of inertia than rotors having uniform mass distribution.

About the only explanation left for the slow response is overbalance. I don’t understand clearly how overbalance of 2% (CG at 24% chord) can lead to that much damping unless the rotor is much softer in torsion than imagined.

[gyrogreg]

Too much going on in this thread for me to get into too deeply. But, I commend any efforts to find ways to improve gyroplane safety - whether they are "secrets" or not. I suspect some of the important elements are "secrets" to even those who provide very safe gyros! We should learn from both safe examples and from mistakes or unsafe examples! Since the accident rate may be the best indicator of what is working and not working, I still do consider the Magni gyro to be something we can learn from.

I would just like to again express my difficulty with presuming the big tail on a Magni is not part of the dynamic stability. I do not trust the Glascow report - especially the wind tunnel report - which I have never seen - that suggests the HS is 50% as effective as would be expected from such an airfoil. I do not agree that the Magni HS is shaded (much) by the body and engine - it is mounted well below the body in mostly free air stream!

I do agree that the rotor dynamic damping is a BIG element of the stability of a Magni gyro - even of the "heavy" cyclic - I'd like to understand why this is so too! But, the dynamic damping of the airframe is probably equally a part of how this gyro flies. The rotor may be dynamically damped so as to help avoid PIO and divergent static reactions, but the airframe attitude MUST follow the flight path quickly and tightly and without overshoot. The rotor changes the flight path, but the airframe attitude must follow!!! The airframe dynamic damper (HS) provides both resistance to distrubances and quick following (without over-shoot) of a flight path change from a rotor disk AOA change.

When the responses of both the rotor and the airframe are properly matched (what I think Vittorio calls "harmony"), the "harmony" of control is better than if either the rotor or the airframe have different response rates. "Harmony" of control is an element that aircraft designers are always striving for - and that is what I consider to be so excellent on the Magni configuration.

I cannot at all agree that an RAF would fly like a Magni if it had a Magni rotor!!! I can also not agree that a Magni would fly like an RAF it it had an RAF rotor!!! This just does not make sense! Without a HS, the RAF airframe attitude just simply cannot follow the flight path as quickly or accurately, or even always in the same direction! With a strong HS, the Magni airframe attitude would follow the divergent antics of even an unstable rotor - but that would be even much better than misleadingly presenting wrong attitude cues to the pilot! Of the two mutations, I'd much rather fly the one with a stable airframe (effective HS) that at least accurately presents an accurate flight path indication to the pilot.

I do believe that the reports that the MT03 and ELA "feel" differently than a Magni - but apparently with similar PIO and buntover resistance - are probably from the differences in rotor dynamics. The airframe aerodynamics is very similar between these three models - suggesting the airframe is the common thead for such PIO and buntover resistance. The common thread for "feel" is the rotor! From all this anectotal evidence, I just cannot dismiss the airframe HS as being an essential element in this PIO and buntover resistance!!

- Thanks, Greg Gremminger

[Aviomania]

Quite true, Doug, but the Magni’s side plate hub style permits the spindle bearings to be located within the hub confines and leads to considerably less distance between gimbal pivots and teeter bolt than on comparable gyros.

Also, as pointed out by Xavier Averso, the CG of the Magni rotor is at 44% of radius, resulting in lower moment of inertia than rotors having uniform mass distribution.

About the only explanation left for the slow response is overbalance. I don’t understand clearly how overbalance of 2% (CG at 24% chord) can lead to that much damping unless the rotor is much softer in torsion than imagined.

What about the geometry of the rotor system? Did somebody string the rotor (carefully)?

Maybe there are some geometry reasons (intentional or unintentional).

Is the feathering axis of the blade inline with the aerodynamic center of pressure or more forward?... how much?... if the string runs from the tip center of pressure to the other, is the leading edge parallel to the sting or does it a "sweepback"..

Wait........ I know it shouldn’t be like that but you never know!!!!!! :noidea:

[gyrogreg]

About the only explanation left for the slow response is overbalance. I don’t understand clearly how overbalance of 2% (CG at 24% chord) can lead to that much damping unless the rotor is much softer in torsion than imagined.

It looks like the "heavy" stick is not consistent with the rotational inertia of the rotor - compared to other rotors. That would have been my explanation for the "heavy" stick and high rotor damping!?!? But, some other rotors with lighter "feel" have even higher MOI? - is this the determination?

Just to make sure some other characteristics toward "heavy" stick and rotor damping are not overlooked:

Blade torsional stiffness: Despite proclamations that "composite" rotor blades are not torsionally stiff, the Magni rotor blades are somehow extemely torsionally stiff. Could this be explained with use of Carbon "fibre"? I have physically twisted many blades - but I cannot get ANY twist deflection in my Magni blades!

Blade coning angle: Magni does several things to keep coning angle low - higher RRPM, flapping stiffness. Starting with a shallower coning angle means that load transients result in less coning response and therefore less RRPM response to load transients.

Blade over (or under) balance: The blade section I measured - posted below - showed the Chord-wise CG to be at about 28%. This differs from some other postings here that suggest an overbalance! But I have triple checked this on the blade section I have. Interestingly, the blade root aluminum connector (heavy) is also almost exactly centered on this 28% chord point. Also, Magni sometimes adds a small metal weight near the root (for span balance matching to other blades) - this also closely matches the 28% point. It looks to me like they are shooting for the CG for the whole blade to be on the 28% chord location. This would suggest an underbalanced blade!

If an "overbalanced" torsionally softer rotor blade could lead to high rotor damping, could an underbalanced blade with a torsionally stiffer blade result in higher damping also?

"Slow Response": I would not say the Magni rotor has a "slow response". It is a heavy stick, but, as evidenced by a lot of Magni fliers*, if you use the muscle to move the stick, the gyro responds very quickly. I don't think the rotor response is really slow - just "heavy". IMO, the airframe, although the tandem configuration has a high MOI, responds very quickly to a new flight path because the airframe is so highly damped in pitch by the large HS. (I temper this a bit by saying a lighter gyro is naturally going to be a bit more responsive - but compared to other "heavy" gyros, I would not say the Magni response is "slow".)

* European gyro fliers - I think the Magni fliers in Europe have probably got a lot more experience with hard maneuvers in a Magni than we do have in the U.S. I have watched GiPi in Italy literally tear up the air with his M16! I have seen experienced gyro fliers, even Bensen fliers, remark at the maneuvers GiPi has demonstrated - not that I endorse these! Any of you guys and gals in Europe have any testimonials to this maneuverability? Or, do you disagree that the Magni is as highly maneuverable (with muscle) as I suggest?

Thanks, Greg Gremminger

[gyrogreg]

Is the feathering axis of the blade inline with the aerodynamic center of pressure or more forward?... how much?... if the string runs from the tip center of pressure to the other, is the leading edge parallel to the sting or does it a "sweepback"..


It appears, from the measurements I made for my last post, the root connector which is centerd on both the chord CG and the spindle, the feathering axis is aligned with the CG of the blades (28% of chord) - not necessarily with the CP of the blades.

The "string" runs exactly to the 28% point on the chord - no "sweepback".

Could the CP of this airfoil be at the 28% chord point? The max thickness point is at about 35% chord. I don't know exactly what this airfoil is!

- Greg

[C. Beaty]

The chordwise CG location doesn’t stay in the same place along the span with a tapered spar, Greg.

Photo by Xavier:

[Aviomania]

So.... from the data we have from Xavier, Mick G and Greg G.

chord wise CG (root) 27% from LA
chord wise CG (tip) 25% from LA
Span wise CG 44% from root
Feathering axis 28% from LA

given these numbers we can see that the blades under centrifugal force will tent to bend backward (sweptback) and the way that the blades connect to the hub plates ( my opinion) will allow for that, as well as the flexibility of the blades to lead lack direction. if this happens it will require more force for feathering the blades as well as the blades will want to follow any AOA change of the airflow over them. ( like having the pivot point of an airfoil almost at the leading edge.).

Is this correct or am i wrong? I am to tired now to think straight, after a full days of work and 4 days of antibiotics. :)

[gyrogreg]

The chordwise CG location doesn’t stay in the same place along the span with a tapered spar, Greg.

Photo by Xavier:

Chuck, you are correct - Didn't catch that on Xavier's pics, and wasn't aware that the spar is tapered. When I watched the blade lay-up maybe about 2001? - through a window to their clean room - I did not see that the spar was different along its length. It looked like they were taking care to make the spar uniform along the whole length - using standard cut lengths of fiberglass strips. But, maybe I assumed this wrongly. These pictures show otherwise, so it does look like the CG does change with the span - if these are the current versions! This suggests the tip ends are way overbalanced

- I still maintain they are very torsionally stiff. Any new thoughts?

Xavier, you mentioned your observations were in 1996. Do you know if these are pictures of a newer or older rotor.

Thanks, Greg

[Xavier AVERSO]

Greg, les profils photographiés sont des morceaux d'une pales détruite en 1996 , et nous reconnaissons tous le style de construction deTervamaki, je ne sais pas si les pales construites aujourd'hui sont identiques??
Greg tu dis que les pales Magni sont raides en torsion, c'est vrai mais les pales
extrudées de mêmes dimensions sont encore plus raides.
J'ai personnellement du respect pour ce que Vittorio a fait pour notre activité et je ne critique pas cet homme, je dis ce que j'ai vu et ce que je pense.
J'espére que vous comprennez mon traducteur informatique ( moi je ne parles pas Anglais ), je serais heureux que la réponse soit : OUI?? comme ça je vous parlerais de mes expériences de pilote et de constructeurs.

Greg, the profiles photographed are pieces d' blades destroyed in 1996, and we recognize all the style of construction deTervamaki, I do not know if the built blades aujourd' today are identical?? Greg you say that the Magni blades are stiff in torsion, c' is true but the blades extruded of same dimensions are even stiffer. J' personally have respect for what Vittorio did for our activity and I do not criticize this man, I say what j' saw and what I think. J' hope that you include/understand my data-processing translator (me I do not speak English), I would be happy that the answer is: YES?? as that I would speak to you about my experiments of pilot and manufacturers.

[troed@aon.at]

* European gyro fliers - I think the Magni fliers in Europe have probably got a lot more experience with hard maneuvers in a Magni than we do have in the U.S. I have watched GiPi in Italy literally tear up the air with his M16! I have seen experienced gyro fliers, even Bensen fliers, remark at the maneuvers GiPi has demonstrated - not that I endorse these! Any of you guys and gals in Europe have any testimonials to this maneuverability? Or, do you disagree that the Magni is as highly maneuverable (with muscle) as I suggest?

I had two occasions to copilot an explicit gyro-crack:

once the instructor and European reknowned extreme-aviationist Andi Siebenhofer on an M16 and 2 weeks ago Luca Magni himself on the M24.

Both smashed the gyro around in maneuvres I could not repeat with my limited experience and inborne fear not to risk anything.

The maneuvres were: very high banked curves following each other left-right in short intervals, very low-G-maneuvres (lacking a G-meter I can only tell: my a.. felt VERY light), sudden throttle off and max, 720° vertical turns, PIOs, the rotor sometimes going up to 450 rpm.

All these maneuvres felt the same as done in an MT03 which is considered to be a very agile gyro, but forgetting my fear during these maneuvres at the end I had the feeling: still always on the safe side. Dunno if we reached the limits or if there could be even more but I wouldn´t like to know.

Maneuvres were done in various weather conds, with M16 in heavy autumn winds and turbulances.

Remark: Eric Changeur said stick feels heavy also in the M24, another one said geometry of rotor head differs between first serial mods and following mods. Maybe Eric refers to the first serial "proto"-mod and following serial-mods are lighter in stick ? I´ve flewn only one M24 thus I can tell only how THIS one feels on the stick and it was definitely MUCH lighter than the M22 I´ve flown 2 days before in comparable weather conds alone (w/o PAX).

So my comparison is only valid for the single M16, the M22 and M24 I have flown.

Tx Angelo

[birdy]

Any of you guys and gals in Europe have any testimonials to this maneuverability?
Angelo, im not in Europe, but ill say this.
ANY gyro, no matter wot its configuration, weight, or power supply, can do the same as any other.
The thing that gets you close to the edge/limits is the RATE at which you perform the maneuvers.

[troed@aon.at]

True birdy :D

My experiences as PAX during these flights were: a roller-coaster is a bunny-fart in comparison. Sorry for the unprecise "report" on this but just held me tight in my seat with no time to look at the instruments.

Another problem is: most pilots won´t live to tell if they exceed specific limits....... and if they survive, how to tell it wasn´t a pilot error. :wave:

(remember the acrobatic Heli-video on Youtube - link somewhere in this forum - and some days/weeks ? later we had the report that the pilot fatally crashed. He does not live to tell if it was a pilot err or malfunction of the heli)

TX Angelo

[quadrirotor]

[I]....the edge/limits is the RATE at which you perform the maneuvers.

You have understood what autorotation is all about!...

[papacharlie]

As said by Xavier, I do confirm that aluminium extruded blades are stiffer than composites blades, at same physical conditions (chord).

[C. Beaty]

ANY gyro, no matter wot its configuration, weight, or power supply, can do the same as any other.
The thing that gets you close to the edge/limits is the RATE at which you perform the maneuvers.Birdy is a physicist posing as a SCG. The key to survival in a Magni is the limited rotor response rate.

The horizontal stabilizer configuration provides no resistance to torque roll, yet there isn’t a single reported instance of torque over. Rotor damping provides a solution at the expense of a heavy stick and reduced agility.

I’m not certain where the damping comes from; overbalanced blades or blade sweep; perhaps a combination of both.

[bpearson]

Birdy is a physicist posing as a SCG. The key to survival in a Magni is the limited rotor response rate.


Chuck, would that stop a HTL machine pushing over when the rotor thrust reduced ? If the rotors were unloaded and slowed then surely they would just become lumps of plastic and the HTL would take over.

[Doug Riley]

Brian, may I interfere for a minute? The primary problem in PPO (POWER pushover) is not loss of RRPM. The event happens too fast for much loss of RRPM.

Rather, the really vicious culprit is the self-accelerating effect. As the rotor unloads (or more accurately, as its angle of attack decreases a little and rotor thrust decreases with it), the HTL is no longer fully opposed by rotor thrust. The machine begins pitching down. This further reduces rotor AOA and thrust, the frame pitches down further and faster and so on.

A rotor that responds relatively slowly to cyclic inputs won't follow the frame immediately, and so the rotor will preserve more of its AOA for longer. This allows it to more effectively hold back the development of down-pitching rotation of the frame.

In an airframe-stable gyro (i.e. one that can't, by design, PPO), unloading the rotor for a long enough time will, in fact, result in a loss of RRPM. However, that's a different (and much less likely) phenomenon than PPO in a HTL gyro.

People who sell HTL gyros confuse these two different phenomena, whether intentionally or through ignorance. PPO involves an explosive loss of rotor AOA that occurs faster than a loss of RRPM could happen. Loss of rotor AOA for an instant is not a "coffin corner" unless the gyro is frame-unstable.

(The usual advice given to pilots of PPO-prone gyros, "float the stick," is a way of decoupling the frame and rotor and thereby creating a sort of enhanced rotor damping. It actually works most of the time.)

[C. Beaty]

Imagine this scenario, Brian. With the rotor unloaded, the airframe begins its nosedown tumble because rotor blades with a fast following rate follow the airframe without much lag and reduce rotor angle of attack even more, farther unloading the rotor.

On the other hand, a rotor with a slow following rate doesn’t follow the airframe as closely and as the flight path becomes more downward, the slow following rotor develops thrust that resists the forward tumble. Since the attitude of the fuselage is more downward than that the rotor, the rotor’s thrust line is ahead of the CG which tends to yank the nose of the aircraft up.

A slow following rotor resists fuselage excursions, which is damping.

The behavior of the Magni rotor is more nearly like that of a Hiller Rotor (in the first post) than like, say Dragon Wings rotors.

I see Doug beat me to a response but we don't disagree.

[bpearson]

Thanks Doug. So, unless I'm wrong can't the rotor AOA be reduced due to severe air movement? That would not be an actual stick input but something like how a props pitch reduces at higher airspeed. So that in theory could put the aircraft into a low rotor AOA even with the slow response rate thing Chuck was talking about.

I don't care what anyone says there is NO aircraft I would rather be in if the weather turned nasty than my VPM.

I have a feeling I'm talking crap here......its late and I'm tired.

[bpearson]

Thanks Chuck. I follow the theory but have to admit that some of the lunatics in Italy don't make it look like the Magni's have slow rotor response.

[C. Beaty]

A bit off topic Brian: one set of my great grand parents, the only known foreigners amongst my ancestors, came from near your corner of Olde Blighty. A village near Louth in Lincolnshire. My sister has their wedding certificate, issued in 1863 by the vicar of Fulstow Parish.

When I was a boy, some of the old timers in these parts remembered my great grandfather as a “an eccentric old Englishman with a long red beard.”

[bpearson]

A bit off topic Brian: one set of my great grand parents, the only known foreigners amongst my ancestors, came from near your corner of Olde Blighty. A village near Louth in Lincolnshire. My sister has their wedding certificate, issued in 1863 by the vicar of Fulstow Parish.

When I was a boy, some of the old timers in these parts remembered my great grandfather as a “an eccentric old Englishman with a long red beard.”

I will be travelling through Louth tomorrow on my way to work. The place is full of red bearded eccentrics.

A few of your countrymen stayed a while in my village during the war. We had the largest onshore oil wells in the country and needed men who knew what they were doing to extract it.

The nodding donkeys are still in the local woods and an eight foot bronze statue was put up in memory of the priceless work that helped so much towards the war effort. There is talk of drilling again due to the oil price. Unfortunately the price of metal is also high and the brass plaque underneath was recently stolen.

[birdy]

A rotor that responds relatively slowly to cyclic inputs won't follow the frame immediately, and so the rotor will preserve more of its AOA for longer. This allows it to more effectively hold back the development of down-pitching rotation of the frame.

I dissagre.
A slow rate rotor will react slower to the gimble offset reaction to a low G situation.
IOW, wen the offset tryes to apply more AOA wen the spring pulls, the rotor will be slower than regular blades to regain AOA, so the effect is actualy LESS damping.

[gyrogreg]

Imagine this scenario, Brian. With the rotor unloaded, the airframe begins its nosedown tumble because rotor blades with a fast following rate follow the airframe without much lag and reduce rotor angle of attack even more, farther unloading the rotor.

On the other hand, a rotor with a slow following rate doesn’t follow the airframe as closely and as the flight path becomes more downward, the slow following rotor develops thrust that resists the forward tumble. Since the attitude of the fuselage is more downward than that the rotor, the rotor’s thrust line is ahead of the CG which tends to yank the nose of the aircraft up.

A slow following rotor resists fuselage excursions, which is damping.

The behavior of the Magni rotor is more nearly like that of a Hiller Rotor (in the first post) than like, say Dragon Wings rotors.

I see Doug beat me to a response but we don't disagree.

Hi Chuck,

I really don't know why you so dismiss the dynamic response and effect of the large tail - do you really believe the large HS is not effective? I agree a slow response rotor can help temper an airframe nose-down tumble – but that is only if the airframe starts to tumble more forward than the rotor AOA. With a large dynamically damping tail, the airframe quickly and accurately follows the flight path dictated by the rotor AOA – not past it. A "slow response" rotor is not necessary then! If an unstable airframe or poorly dynamically stabilized airframe sustained the nose-down moment from the reduced AOA, it may indeed “tumble” past the rotor AOA. But, with the airframe dynamically damped to quickly and accurately follow the flight path, there is no tendency for the airframe to accentuate the reducing AOA by providing even more spindle/cyclic nose-down action - the spindle matches the rotor disk - not past it!

This is easily demonstrated in the Magni encountering a strong down gust. Stick fixed or stick free, encountering a strong down gust causes the airframe to pitch up just slightly, if even noticeable (causing the rotor to follow with just enough increased AOA to counter the down gust reduced rotor load.) The result, as in all highly stable gyros, very little airframe attitude response – just enough to provide adequate cyclic to the rotor to counter the turbulence. Free stick, even without friction in the cyclic, the stick moves only a small amount – if at all during any turbulence – indicating the airframe attitude is matching the rotor AOA, not leading it or lagging it!

• Since the sudden down gust actually causes the gyro to pitch up, that indicates the “effective” RTV is aft of the CG (Sorry Udi!) – even if the “real” RTV might be forward of the CG as the HTL believers are implying.

• If the gyro were AOA unstable, a downgust would cause it to pitch nose-down – AOA unstable.

• If the rotor were slow to correct for the downgust (from airframe/spindle pitching cyclic action), as you maintain the Magni rotor must be, the airframe would be pitching rather wildly in severe turbulence – airframe attitude and rotor disk AOA not matching! In severe turbulence, stick free or stick held tightly (with or without normal cyclic friction), the M16 airframe attitude changes only minutely and the stick may barely move in severe turbulence - IMO, the airframe pitch is just enough to input adequate cyclic to the rotor to counter the wind disturbances. (As Doug R. posted, and as we all know, in an unstable gyro it is best to allow the stick to float free and move around in turbulence as the airframe attitude does not match the rotor disk AOA. In the Magni, the stick does not move around, so the skill to allow the stick to “float” is not needed and this indicates a stable, rather than unstable response to that turbulence.)

I’m simply saying, Chuck, that the airframe pitch attitude reaction is quick to match flight path – and quick to match free air (turbulence) direction change because the airframe is so highly damped. I’m also saying that the rotor reaction is not sluggish – as indicated in testimonial after testimonial on these threads. It is just heavey and muscel must be used to make the rotor move quickly! If the rotor were sluggish to react to cyclic inputs, the airframe would be pitching a lot in turbulence and the stick would be moving around a lot in turbulence – it does neither.

In my understanding, airframe dynamic response from the HS dynamic action has two effects:

• Its dynamic damping resists pitching motion relative to the free airstream – this slows the pitch acceleration when the airframe is subjected to a pitching moment such as a reduced rotor load moment (or changing prop HTL moment when the power is changed rapidly).

• It causes the airframe to quickly and accurately align with a new flight path to maintain its HS trimmed AOA to the free airstream. This is what helps the airframe align quickly to a gust of wind, but also to a new flight path dictated by a new rotor AOA.

I maintain that it is the matched dynamic rate responses of both the rotor and the airframe that make it work so well in the Magni. When the rotor AOA changes the vertical flight path, the airframe follows it quickly and accurately – essentially keeping up with the rotor disk AOA. When the airframe changes pitch due to a vertical wind gust, the rotor quickly follows it through rotor spindle action to counter the effect of the gust. I have another perception of what this is and feels like – it feels like a Fixed Wing! Essentially, the rotor and airframe responses are matched (harmony?) so that the rotor is essentially “fixed” to the airframe and vice versa! I consider this to be one of the “secrets” in the “harmony” of the control of a Magni. It flies like, and as easily as a FW (so does any really stable gyro when it is really stable!)

Now, after saying this feels like a “fixed Wing”, I can hear the complaints that we want it to fly like a gyro! Such a stable gyro still does maneuver like a gyro – BECAUSE the pilot can still directly move the “wing” through cyclic stick input – you cannot do this in a FW! So, essentially, when the pilot is not “commanding” the rotor to change the flight path the gyro is taking care of the business of canceling out the turbulence disturbances - without need for pilot action or interference. It is doing this better than a FW because the rotor is less sensitive to turbulence (very high wing loading), and because the airframe/spindle is using its powerful cyclic action to adjust the “wing” – high loop feedback gain! But, when the pilot wants it to do something else – a new flight path - the gyro responds quickly like a gyro should – because you are moving the “wing” directly. When the pilot “commands” a rotor disk AOA change, he/she IS changing the relative pitch attitudes of the rotor disk and the airframe – until the airframe quickly re-adjusts to match the new “commanded” flight path. The result is that the airframe pitch attitude to the horizon is always closely matching the actual flight path – also as in a stable gyro and a FW.

I agree that the rotor has a dynamic response (inertia and damping) that contributes to the stability. But, I also maintain that the airframe has a matching dynamic response to produce the "harmony" that makes it both so easy to fly and resistant to turbulence. True, any stable gyro does this same thing - but, a lot of people here are trying to say the Magni CANNOT be stable for overly-simplistic reasons. But it is obviously at least as stable as those other "stable" gyros - and it maintains that same strong stability margin through the full range of of power and airspeed. (A gyro that depends on propwash augmentation of its HS and LTL augmentation of its RTV/CG moment, cannot maintain that same margin of stability when the propwash is not there - now I know that is what pushes a lot of buttons - but HTL, CLT or LTL does not matter when power is low or off - no or little thrust or prowash. Maybe that's not an important condition of flight, but I bet that everyone that has propwash augmented stability in their gyro (LTL and/or highly embedded HS) avoids high speed, low power dives - it just does not "feel" the same! And if you tested it for dynamic stability in that mode, you would find it does have an airspeed where it doesn't handle trubulence as well as when the prop was producing propwash! I think this is a "secret" that is not politically correct, but it should not be a "secret"!)

Chuck, say the word and I will fly my Magni to Florida to let you fly it. You really need to fly it to see what myself and others are describing. I promise the Magni HTL won’t kill you. I promise you i won't do low or negative G maneuvers (Udi's request). I need an excuse to visit my Sister in Florida anyway! I’ve got my gyro decked out with XM radio and transponder now – so I need a good excuse to use all that while I am paying for the XM subscription! Say the word, and maybe several of us will fly down to visit you!

- Thanks, Greg

[chuter]

Trying to keep up with this thread:

In a HTL gyro with a slow-following rotor, sudden down draft causes a significant loss of rotor thrust (from the loss in angle of attack on the rotor), it seems that there would still be a good chance of PPO.

I know it depends on a lot of variables (degree of rotor thrust loss, amount of forward tumble force from the HTL), but can this really explain the lack of PPO accidents with Magnis?

Of course we seem to have conflicting info on the amount of HTL; 14 inches in one report and 4 inches in another. If it's really 4 inches I can see how this and the HS on a long arm may be the "secret".

Edit: Greg posted the same time I did.

[gyrogreg]

I know it (PPO) depends on a lot of variables (degree of rotor thrust loss, amount of forward tumble force from the HTL), but can this really explain the lack of PPO accidents with Magnis?

I don't agree with the common perception that it is the loss or reduction of rotor drag that causes a HTL to "tumble". Chuck B. has long described the more accurate mechanism that happens in a buntover (or PPO). But, adherence to this over-simplified “rotor drag loss” visualization of the prop pushing over the airframe loses sight of what an unstable AOA buntover static divergence really is. This over-simplified description suggest that all buntovers are PPO - not true, even a LTL or CLT can buntover. (Some like to call it a "dragover", but this is also an overly simple visualization that does not describe the real action!) You could not properly describe a buntover on a LTL as a “PPO” - it would not be a "push"! But that does not mean a LTL cannot buntover.

A HTL or a lot of drag and other aerodynamic moments that cause the nose to fly low - "effective” RTV forward of the CG - are simply the situations that can set up for the real mechanism of a buntover. The real buntover action is when the “effective” RTV is forward of the CG, a reduction of rotor lift presents a nose-down moment – the RTV to the CG, that forces the nose further down in a statically divergent progressively worsening buntover. Chuck has emphasized this mechanism for many years. We need to consider the composite rotor lift vector and its moment to the CG. The rotor drag is only one part of this rotor lift vector (RTV). In the interest of technical accuracy, I wish we could clearly appreciate this mechanism in terms of the RTV and CG moment – not just the prop thrustline and the rotor drag forces.

Now I’ll push a few more buttons! Certainly a LTL has fewer, if any incidents of a “buntover”. That may only be because it spends a lot less of its flight time, with lower power applied, in the unstable mode ( “effective” RTV forward of the CG.) But a significant LTL is probably capable of a flight condition where the “effective” RTV is forward of the CG. This would be when the power (and prop thrust) is low or off. Most LTL have a lot of draggy things down low – to get the CG up high and the prop low. Most of the flight time, when power is abundantly applied, a LTL is AOA stabilized by the fact that the LTL is forcing the CG well forward of the CG (nose-up). But, this LTL is not augmenting this static AOA stability when there is no prop thrust! When there is no prop thrust to force the CG forward (nose up), the draggy wheels and things down low can “Drag” the nose down and the CG possibly aft of the “effective” RTV. This LTL gyro, and possibly any prop thrustline gyro can be set up for this “dragover” buntover condition at low power. The situation for an unstabilized HTL certainly presents a buntover risk for more of the flight time than does a LTL – but it is not just a PPO that we should understand can result in a buntover!

LTL and/or propwash stability augmentation may have other issues to deal with: The stability margin (control and handling feel and required pilot proficiency) changes with power setting. This may not be a really desirable trait – especially if most of the stability is from prop thrust and/or propwash augmentation. A LTL will be super stable at normal power settings - normal stability augmentation. But reduce that power, or worse, cut that power, and the stability picture changes significantly and possibly rapidly – not to mention the likely sudden nose-down pitch motion at exactly the same time the gyro is suddenly less stable. I suggest an aircraft’s stability margin, and its control and handling “feel” should be fairly consistent over the full range of airspeed and power settings – including zero power! It might be especially undesirable for the gyro to unexpectedly switch from a docile Cessna to a twitchy Pitts just because the engine quit at high speed! The pilot of a stable aircraft probably does not have the proficiency to have to fly a suddenly more unstable one!

For any gyro with a significant prop offset, there is really only one way to get away from a sudden pitch attitude change with a sudden reduction of power (prop thrustline moment). That is to use a strong dynamic damper (HS) that resists sudden pitch attitude changes upon power changes. This is another reason to employ a large HS mounted far aft of the CG. There is a double multiplier for dynamic damping power with a longer tail! - not just a single multiplier of the lever arm! It may also be preferred that this dynamic damper HS not be so dependent on propwash augmentation (highly embedded), because it won’t help as much if it suddenly loses a lot of its effectiveness when propwash suddenly disappears – doesn’t as well prevent a sudden pitch reaction to power change. Call me biased, but this is the reason for the very large Magni tail placed below most of the propwash in free air far back on a long tail. This dynamic damping strongly resists any sudden nose-down moments, and buntover – even if that gyro would happen to be statically AOA unstable. The strong pitch dynamic damper augments the static AOA stability – buntover resistance. (Udi, this is another factor that goes into the “effective” RTV “K-factor”.)

I still believe that the real “secret” to a truly stable and buntover resistant and PIO resistant gyro is a large efficient HS on a long tail – and the absence of PIO and buntover incidents in such gyros is a testament to that “secret”! With such a large tail dynamic damper, it probably (apparently on a Magni, ELA, and MT03) makes the distinction between HTL, CLT and LTL a mute issue! The “secret” may be as simple as that!

Thanks, Greg Gremminger

Sometimes I actually have fun with these posts - they do help me clarify my concepts and probably help ward of Alzheimer’s with all the brain excercise! I hope they are helpful to others as well!

[chuter]

Greg,

Not sure if you were talking to me, but I do understand the RTV is a combination of rotor lift and drag, and the RTV being ahead of the CG in is a force resisting a bunt.

We can turn the tables a bit regarding your theory that LTL gyros can bunt during a loss of power at high speeds; as far as I know there is only one accident that could be a result of this, and there wasn't conclusive evidence that this is what happened.

So, as with the Magni, we have a theory that doesn't seem to be supported by real life accident records.

(Greg, I really appreciate you and all the others taking time to add to these discussions; makes me think!)

[C. Beaty]

Greg, the only attempt at measuring the prop thrust line offset of a current Magni was done in Australia. An offset of 14” does seem high but compare a Magni and an RAF side-by-side. Both have the engine underslung below the prop and both have the propeller thrust line parting the pilot’s hair. Both have rotors of similar weight on a mast of similar height. Similar offsets shouldn’t be a surprise.

And of course the Magni’s tail is beneficial but I believe the Glasgow measurements showing dynamic pressure at the horizontal stabilizer to be 50% of freestream. That means airspeed at the tail is 70% of freestream, something I don’t find at all strange. If you don’t believe Glasgow’s numbers, then you ought to mount an airspeed probe on the horizontal stabilizer’s leading edge and produce your own numbers.

The location of the Magni’s tail surfaces can provide absolutely no propeller torque compensation. I believe the Zenon’s designers have things about right for the case of a conventional rotor; horizontal stabilizer centered in the propeller slipstream and CLT or thereabouts.

[birdy]

I find it amusing, with all these Magni drivers calln us bashers.
Yet nun of them has gon to the effort to take two fotos. :(
Maybe they know they wont like wot they were told they dont know. ;)

All you clowns that think we are all magni bashers, shut us up and post the pix.
Afterall, a few busted ass Ozzys in a shed did it a coulpa years ago, so who's sepeculating now?

[Greg Mitchell]

With respect.....I can not in all fairness stand by and say nothing every time I hear the so called AUSTRALIAN result of 12-14" high thrust line of the Magni.

The Butterfly was calculated to be 1 - 2" HTL........load of rubbish and I still am waiting for someone to forward me copies of the pics.
My Butterfly at the time was likely 1" - 1 1/2" LTL.

By my calcs, this could put the Magni at anywhere from 8" to 10" high. I think this is more reasonable.

I concur with Birdy, how come no-one ever did the calcs on the Magni or if they did why hold back the result.

I said at the time of the Aussie Tests that the process was to hit and miss to be reliable. That was me in PB's Firebird.

[birdy]

I said at the time of the Aussie Tests that the process was to hit and miss to be reliable.
Sure it wasnt a proper controled test Mitch, but it is accurate , give or take an inch.

More accurate than the speculation you'll get over ere. ;)

[ckurz7000]

You'd think that by now someone would have gotten three scales and a measuring stick together and determined the location of the CG by double weighing.

-- Chris.

[C. Beaty]

The problem with the double axis weight method Chris, is the scales. Bathroom scales are inconsistent and are sensitive to how the load is applied. Load at dead center will produce a different reading than a load not centered. We’re dealing with small angles so weight errors are compounded.

Now if someone has 3 doctor’s office balance beam scales, the weight method should be fine.

I put the trig on spreadsheet years ago and anyone who wants a copy is welcome.

[Gyro_Kai]

The Butterfly was calculated to be 1 - 2" HTL........load of rubbish and I still am waiting for someone to forward me copies of the pics.
My Butterfly at the time was likely 1" - 1 1/2" LTL

Greg,

to fix your "too high CG" I sugget to put on some weight! :)

Kai.

[Resasi]

For a serious thread that has to raise a smile.

Still following and learning, or trying to, late though it is.

Mr Beaty does that mean you are red haired and eccentric??

[C. Beaty]

No, but my Italian ex-wife is a redhead. Auburn, to be precise. At least she was when I last saw her about 20 years ago.

[SamL]

Here is the pic of the Aussy Magni test 1 up.
The origional test didnt take into account Parallax, so I have updated it.
I dont have the balance test photo, as I wasnt their, so cannot check its accuracy.
I have added a keel reference line, as the origional thrust line was wrong.

Sam...

[birdy]

Thanxs Sam.
Now, the rest of you 'speculaters' can shutup, unless you have other FACTS.

BTW, 2 up would have the TL even higher.

[Greg Mitchell]

Hey Birdy,

I agree whole heartedly on your position, that we get little by way of real world calcs on the thrustline C of G offset from Magni.
For nearly 5 years, I have asked Greg G for such a number. The response is usually a page of discussion regarding "harmony" and well etc, etc....
Please do not misinterpret. I value Greg G's dedication and willingness to enter discussions and his obvious work with the ATSM (sp?) thingy.
I am at a loss to understand why no attempt has been made by Greg to clarify this debate with a double hang test.....at least this might 'de-ice';) the debate somewhat, if the figures were 'favourable' to Magni. The suspicion I have is that the offset will be large and difinitive, that indeed the Magni is a very HTL...the M24 scares me.

No to the Aussie result. I must disagree again.
The day way warm and a little windy. Some test were done in one hangar, with a block and tacle arrangement, others were done in the big shed, hung from a big frontend loader/tractor. There was a considerable draft and the pendulum, was constantly in motion. Even the hanging gyros, were having to be steady and when the Magni tail was being steady/held, one needs to account for human error.

The Butterfly was not 1-2" high thrustline given my weight at the time.
Kai:yo:
I had actually put on weight from my initial solo and first build Butterfly, so if anything I would have already put the relationship into more of a lower offset.

I trust the figures determined by Larry Neal. I have never met anyone who tests more extensively or represents the results more honestly.
Birdy says the results were within 1" or so and they were accurate. I again will have to disagree with my friend. As I said I had gained considerable weight from solo. Yes, weight was added by the removal of the Bensen Blades and addition of the Patroneys. I acknowledge that this would have placed the thrustline closer to the C of G. The amount of personal weight gained was within a couple of pounds of weight gained at the head, so I discount the accuracy of the hang tests. Though I would give weight to a 8-10" magni offset. Again why doesn't Greg G do a hang test?

Birdy, the 10 gallon seat tank you sent me (Thanks Buddy) now has a welded frame on which to mount it to the new Monarch 582, I can assure you that I will do the hang tests and report back soon.

I believe these tests, should be done in nil wind conditions, without the need for a humanbeing to hold a long pole, with a string and weight hanging off it (pendulum/plumb bob) after, maybe having too many the night before...:tape::lol: Tim Mate....I wasn't necessarily referring to you. Nice photo Mate.LOL!

All of the Butterfly/Monarch/Aurora's are hung in closed workshop conditions....unlike the Lameroo Hang Tests.

My two Bobs worth.

Mitch.

[Greg Mitchell]

By the way, that is me laying on the floor, attempting to get the plumb bob steady.
Earlier I was having to steady the tail and I am the dead weight in PB's FireBird.
I thought at the time we were having more trouble getting eyeball figures than a test done in nil wind. Maybe I am the only one who thought this process was a little flawed on the day.

Thanks Sam.

[C. Beaty]

That scales out to about 11 inches of offset if the guy holding the stick is 70 inches tall.

[Murray Barker]

I agree,That Main wheel on the Magni should be around 13 inches in diameter. As a scale the offset appears to be around 11 inches, in the updated photo.

The vertical line appears to be parallel to the vertical beam on the shed so I think you were doing a good job holding the string steady Mitch.

[birdy]

Birdy says the results were within 1" or so and they were accurate. I again will have to disagree with my friend.
Mitch, wen i said the test woulda been accurate , give or take an inch, i ment just that.
An inch either way, as in your machine, wouldnt mean a thing, its so close it dont matter.
Wen we [ yes, i was there with the blokes in the sheds] hung the magni, it wouldnt matter if the test was 2 inches out, the TL is still bloody high.

We can only wate for the ledgends to proove us rong ay. ;)

[Greg Mitchell]

Muzza,

I always do a good job, even when I fail, I'm good at it.:D
Now where is the hang test pics of the Blue Emperor Butterfly???????
I have never seen them....and after all the hard work I put in sitting in the FireBird and lying around on the floor:wacko: Where are they Muzza:lol:

Sam ole Mate,

Can you get hold of my gyro's hang test pics and do your magic.....:hail:

Birdy,

I agree, 8" or 12" it is bloody high. :sad: Let's hope someone from the hundreds of Magni owners out there, takes the time to do it and be done with it. What do we need.....3 comparisons to get a rough consensus? :argue:

Chuck,

You would have to ask Tim Mc how tall he is. I'd take a stab and say he's not 5' 10" tall. Tim, I'm going to guess...5' 8 1/2" to 5' 9". I know you are gonna slap me next time we are having a couple around the camp fire.:boink:

So where would that put the 11" HTL now?

Cheers,

Mitch.

[karlbamforth]

Here is the pic of the Aussy Magni test 1 up.
The origional test didnt take into account Parallax, so I have updated it.
I dont have the balance test photo, as I wasnt their, so cannot check its accuracy.
I have added a keel reference line, as the origional thrust line was wrong.

Sam...

Sam,
Thankyou for taking the time to post the pics.
How were the lines derived ? One is obviously a hang test, and it is implied the other is by balance. If so shouldn't the second line intersect the wheel axle ?

[C. Beaty]

I noticed the same thing, Karl, but the yellow line ought to have its origin at the axle center when the landing gear strut is compressed. Perhaps that’s the explanation.

[gyrogreg]

I noticed the same thing, Karl, but the yellow line ought to have its origin at the axle center when the landing gear strut is compressed. Perhaps that’s the explanation.

I'm not disputing these measurements, I''ll be trying to do this myself as soon as I can. But, I sure would like to see the pics from all the balance and hangs here. For instance, I can't see the rotor head in the hang pic to see that the hang line is going through the teeter bolt - I assume it was, but it looks a little aft to me?? I think the mast is much taller! The "balance" line should be through the main wheel axel bolt. There may be other inaccuracies involved. If the LG is compressed - which it is sitting on the ground - the "balance" line would actually be lower or more forward than shown on the pic. Was the balance line done with the rotor installed? How much fuel was in the tank? - the tank has a large volume both forward and aft of the CG - fuel will mass aft of the CG in the "balance" test, and forward of the CG when hanging - should be done with full tank or MT tank to assure the fuel it stays in one place where it would normally be in flight. Some of these questions actually suggests a larger HTL!!!

It would certainly be even harder to accept the HTL is more than the 10-11 inches we are interpreting from this - so much different than the VPM measurements by Dr. Houston at the U of G? With that much HTL, and with little propwash effect on the HS, the Static Power Stability flight test ought to make its trimmed airspeed much more a function of power setting - in normal flight, there is hardly a noticeable need to move the stick to maintain airspeed at different power settings - much less than some other CLT and LTL gyros around, or of the original Air Command.

But, this just re-inforces my argument:

If the HTL is that extreme, it simply emphasizes the point that I am trying to make - HTL does not necessarily make buntovers (or PIO) inevitable! If it did, certainly there would be incidents of such in Magni gyros. If the HTL is 10-11 inches, there must be some other explanation for the lack of these incidents. That's what I hope we might determine here. Could it be the "sum of all the parts" or the "harmony" of all the parts. Can the rotor alone do this? Is the HS (or it's dynamic damping?) part of the "secret"? It would be more difficult for me to argue there is much more than just HTL involved if the prop offset was only 2-4 inches, as I still suspect it really is. But with HTL of 10 inches or more, I think the point is made! (Udi - this is for you! ;) Maybe its just the "effective HTL" that is just 2-4 inches!) It seems this data makes it harder to argue that HTL is a "Deathtrap" - kind of destroys that argument.

Still looking for someone to provide a better explanation as to why such a HTL (if it is) does not buntover or PIO.

- Thanks, Greg

[Udi]

...Still looking for someone to provide a better explanation as to why such a HTL (if it is) does not buntover or PIO.

- Thanks, Greg
Lets see...

As you know very well, Greg, it is all about static stability and damping.

The main players in static stability are the offset gimbal rotor head and the gyro aerodynamic center of lift (CL). The gyro CL is the sum of all components that contribute to aerodynamic lift -- the rotor and the tail to the most part. As long as the tail is more lightly loaded than the rotor, it tends to move the CL backwards - i.e. in a direction that improves static stability (for this reason canards are more heavily loaded than the back wing and the tail of a FW is more lightly loaded than the main wing). A bigger tail, mounted further aft, would improve stability in comparison to a smaller tail mounted closer to the CG.

When looking at a HTL gyro, unless the tail is immersed in the prop wash, the CL is forward of the CG at very low airspeeds, when the tail is not effective. Increase airspeed, and the tail is starting to work, moving the CL back and eventually behind the CG. As long as the CL is behind the CG, the airframe is statically stable. I say the airframe and not the gyro, because the offset gimbal rotor head is adding static stability, even when the CL is forward of the CG. The offset gimbal rotor head is the only reason gyros like the old Air Command and a stab-less RAF are flyable by humans at all.

Damping is the trait that makes the gyro more sedated, or less snappy, if you will. It is the tendency of the gyro to resist change. Damping resists PIO and any other attempt to change attitude quickly (like a strong draft). Damping is achieved thru rotor damping and thru tail damping. In the case of the Magni - both are heavily damped. Rotor damping works all the time, regardless of airspeed, while tail damping is a square function of airspeed - therefore nil at very low airspeeds. That is why at high airspeed the Magni feels more like it flies on rails than at low airspeed. The damped rotor is mostly what sets the Magni apart from a RAF 2000 at very low airspeeds and is preventing PIO at all airspeeds.

What else is there to say?

Oh yes. When is the Magni not so safe? I believe the Magni is not so safe at high power - low airspeed climb - especially if the pilot were to unload the rotor at high power/low airspeed. The reasons the Magni is not safe at these conditions are 2: One - at low airspeed the CL is forward of the CG and unloading of the rotor due to any reason may trigger a PPO. Two - the prop rolling torque is highest under these conditions and the gyro might torque-over if the rotor is sufficiently unloaded and/or if the gyro is side slipped, which adds to the rolling torque. Stay away from these conditions, and the Magni will not disappoint you.

I can think of at least one fatal accident in a Magni that was probably caused by some of the conditions I described above.

[C. Beaty]

Chuck,

You would have to ask Tim Mc how tall he is. I'd take a stab and say he's not 5' 10" tall. Tim, I'm going to guess...5' 8 1/2" to 5' 9". I know you are gonna slap me next time we are having a couple around the camp fire.:boink:

So where would that put the 11" HTL now?

Cheers,

Mitch.The difference, Mitch, between 5’8.5” and 5’10” is 2%. But I was going from the bottom of his shoes to the top of his hat, which may very well have been 70 inches.

2% of 11 inches is 0.22 inches, a shade less than ¼ inch, not enough to fret about in light of other likely discrepancies.

Stan’s trick of using a laser level to project a vertical line is hard to beat. Stick a length of ½” masking along the laser line at about where the CG should be and do the same with the 2nd hang angle. Most of the parallax error is eliminated and all of it is eliminated if the machine is kept square with the laser.

[Gyro_Kai]

Udi,

that is the post I have been waiting for. Thanks a lot!

Kai.

[birdy]

What else is there to say?
Nuthn mate, youv covered it.
Trouble is, you can keep on sayn it, but if their mind is closed, it wont sink in. :(

[gyrogreg]

Lets see...

As you know very well, Greg, it is all about static stability and damping ----.

Udi, I agree with most of your explanation, but a couple of areas of "more to say":

Damping is the trait that makes the gyro more sedated, or less snappy, if you will. It is the tendency of the gyro to resist change. Damping resists PIO and any other attempt to change attitude quickly (like a strong draft). Damping is achieved thru rotor damping and thru tail damping. In the case of the Magni - both are heavily damped. Rotor damping works all the time, regardless of airspeed, while tail damping is a square function of airspeed - therefore nil at very low airspeeds. That is why at high airspeed the Magni feels more like it flies on rails than at low airspeed. The damped rotor is mostly what sets the Magni apart from a RAF 2000 at very low airspeeds and is preventing PIO at all airspeeds.

Damping is not the tendency to resist change. Damping is the tendency to decay movement, velocity or pitch RATE - like friction. Inertia or MOI is the tendency to resist change. The dynamic "response" is a combination of the effects of BOTH inertia and damping. The damping component is what stops oscillations and prevents overshoots. Damping and inertia are not the same thing, but they are both elements of the dynamic response.

IMO, it is the ROTOR inertia that does resist change in disk AOA. There is also some rotor damping which prevents the possiblility of overshoot or oscillation of the rotor disk AOA. Everyone who flies a Magni can attest to the inertia of the rotor - "heavy stick". However, anyone who flies a Magni can also attest that the rotor WILL change quickly if you provide the muscle to do so - some don't like this, but Magni does this to prevent inadvertent cyclic inputs that can lead to pilot over-control - safety is the priority! But, it will move if you intentionally make it!

IMHO, the airframe is a bit different. The large volume HS has strong static stability - strong enough to quickly overpower the rotational inertia of the airframe - so, upon a change in flight path (from the rotor input), or upon a change in HS AOA or lift (from a wind gust), the HS quickly initiates a pitch attidude change to re-align with the relative wind on it. But, the strong airframe damping both limits the rate that it can re-adjust to the new relative wind, and damps it to avoid over-shoot when it appoaches it's "trimmed" AOA again. The result is when a wind gust or the pilot's cyclic control changes the flight path, the airframe quickly follows - ideally at quick, critically damped rate to "get there" quickly and avoid overshoot. IMHO, ideally, the airframe inertia, HS static volume, and HS dynamic damping should combine so that the airframe pitch attitude "keeps up with" and closely matches what the rotor controlled flight path is. This means the airframe pitch is closely "locked" or "fixed" to the rotor. That is why the Magni feels like it flies like a FW airplane. [A telling indication of this is that, except for landings, FW pilots actually require no real familarization to fly a Magni - other than maybe 2-3 minutes to get used to the quick pitch and roll rate of a gyro upon initial takeoff. Within the first 5-10 minutes, we have FW pilots (and even non-pilots) flying at high speeds and slow speeds with no tendencies to over-control or get into trouble. The first takeoff in a Magni by a FW pilot is done by that novice gyro pilot - with verbal coaching from me! As we know, in unstable gyros, the most PIO and buntover accident prone novice gyro pilots are experienced FW pilots. The Magni presents none of these issues to a FW pilot!]

IMHO, the "harmony" between the rotor dynamic response and the airframe dynamic response is this:

- If the HS STATIC response VOLUME were low, the airframe would be sluggish to start to catch up with a changing flight path and could lead to pilot over-control because the pitch attitude (horizon ref) does not match the the actual flight path or intended controlled flight path. This pitch rate should match or nearly equal the rotor pitching response rate AND damping to avoid sluggish airframe response that lags the actual flight path. This is "harmony"!

- If the airframe was inadequately pitch damped (by the HS), it would tend to over-shoot the trimmed AOA for a newly changed flight path. This also can lead to pilot over-control as he/she tries to settle out the airframe attitude on the new and/or intended flight path.

- If the airframe was overly damped - more than "critically damped" - it would be sluggish to "settle out" on the new flight path - again leading to a mis-match of the horizon reference to the actual flight path!

The "harmony" is when the pitch inertial elements and the pitch critical damping elements of BOTH the rotor and the airframe are matched so that both keep up with changes in the other - without mis-match - so that the horizon ref matches the actual flight path. Two situations this is important for:

A) Pilot commands a flight path change - the commanded cyclic input causes a rotor disk AOA change and a subsequent flight path change. The airframe response rate and damping "keeps up" with this "commanded" flight path change.

B) Wind gust or turbulence changes the airframe attitude - un-commanded by the pilot. The aiframe attitude inputs an uncommanded cyclic input to the rotor disk to compensate for the wind gust.

Now, wind gusts come in two conditions:

1) A vertical wind gust: This is obvious, the AOA change on the HS causes the HS to rotate the airframe to point into the increasing vertical wind gust. This applies an uncommanded spindle cyclic input to the rotor to adjust its disk AOA into the increasing vertical gust - compensating the rotor lift change from the wind gust.

2) A longitudinal wind gust (increasing or decreasing - but let's just talk about an increasing horizontal longitudinal wind gust - works the same for a decreasing gust!): This is where the down-loaded HS works out best - to regulate airspeed to the "trimmed" airspeed. An increasing forward wind speed increases the down-load on a down-loaded HS and causes the airframe to pitch up - causing the rotor disk to pitch up to slow the airspeed - a corrective NEGATIVE feedback control loop that automatically maintains "trimmed" airspeed.

Consider though, if the HS has no load ("effective" CLT) or is up-loaded ("effective" LTL): An increasing forward wind speed increases the UP-load on an up-loaded HS and causes the airframe and rotor disk to pitch in the nose-down direction!!! This will add to the increased airspeed - a divergent POSITIVE and unstable control loop that can further increase airspeed progressively and divergently - Static AIRSPEED instability! An "effectively" CLT will have no airframe pitch correction to the longitudinal wind gust.

This up-loaded HS example is not so cleanly clear though. An increasing forward wind will also increase the rotor lift. The increasing rotor lift, for a stable gyro with the "effective" RTV behind the CG, will cause the airframe to pitch down - divergent POSITIVE feedback loop- tends to INCREASE airspeed while reducing rotor lift! But, the actual vertical acceleration will unload the up-lift of the HS, countering the other nose-down pitching moments - a corrective NEGATIVE feedback loop! What the final result is depends on the "balance" of all these pitching mechanisms, the dynamic reaction rates and damping, etc.

The rotor lift component of an increasing forward wind on a down-lifting HS works out similarly - but there is one less nose-down moment to have to balance. What you get in either case requires testing - but if the "harmony is right, the gyro will actually be statically AIRSPEED stable! If the moments do not work out to an "effictively" negative airspeed feedback loop, that gyro can end up statically airspeed unstable - airspeed tends to runaway!


Oh yes. When is the Magni not so safe? I believe the Magni is not so safe at high power - low airspeed climb - especially if the pilot were to unload the rotor at high power/low airspeed. The reasons the Magni is not safe at these conditions are 2: One - at low airspeed the CL is forward of the CG and unloading of the rotor due to any reason may trigger a PPO. Two - the prop rolling torque is highest under these conditions and the gyro might torque-over if the rotor is sufficiently unloaded and/or if the gyro is side slipped, which adds to the rolling torque. Stay away from these conditions, and the Magni will not disappoint you.

I sort of do this all the time in a Magni. Above the HV curve, I'll zoom climb at high power to bleed off inertia to low speed and then level out at the top. I don't propose this should be done in a less stable gyro, and I don't push it real hard - but hard enough to get light in the seat!!! (I don't get to feel light very often!) Remind me to show this to you next time we can fly together! Students do this worse sometimes: In a zero airspeed, idle power vertical descent, sometimes a student will rapidly lower the nose while applying a lot of sudden power! After experiencing this once, I explain how recovery should really be done and why not to do it that way - in other gyros! Yea, it's exciting, but about like a roller-coaster ride. Remind me to show you this sometime. (Kids, don't try this in just any gyro!)

There is obvious rolling torque if you either increase or decrease power at the top of a zoom (or at any time), but, not enough to really notice unless you watch for it. Remind me to show you this sometime too!

I think all I'm trying to say is that, although the concepts and theories have validity as a starting point, there is more to the story than just the simple theories. The whole picture requires the sum or all the elements that are at work - probably a few that we don't really understand - but the above is my best attempt to explain my thoughts.


I can think of at least one fatal accident in a Magni that was probably caused by some of the conditions I described above.

Please tell us the details - I am not aware of this.

- Thanks, Greg

[GyroRon]

I have not flown in a Magni. I can assume they fly very stable and solid, and are smooth flying ships.

I did fly in Jim Logans RAF 2000. It has a very high thrustline, and very powerful engine, and NO horizontal stabilizer. It also felt stable and solid and smooth. More stable and smooth than any other RAF I can remember flying in. It certainly did not feel as one would expect a high thrustline no stab gyro to fly like.

Does that mean Jim Logans gyro can not bunt over and kill you? Nope.... high thrustline is simple math, and it will kill you if you let it. I suspect the Magni is also a potential killer, possibly harder since the rotor and Stab tend to help stabilize the Magni more than the rotor and magic mast does for the RAF.

Why do we not see Magnis tumbling out of the sky? Maybe cause due to the serious investment a buyer has to raise to purchase a Magni, followed up with careful training by the instructor that checks them out in the Magni, that the pilots that are out there flying Magnis are just simply more careful and are more attentive at flying their gyros within the safe flight envelope.

[Xavier AVERSO]

Cette discussion est interressante et finalement Chuck et Greg ont raisons la stabilité augmente avec un CG au niveau de l'axe de poussée, et la stabilité augmente avec un HS grand et sur un long bras de levier, sauf a basse vitesse.
C'est comme ça qu'il faut faire les nouveaux gyros, j'ai testé cette solution et c'est vraiment la plus stable.

This discussion is interressante and finally Chuck and Greg are right stability increases with a CG on the level of l' thrust axis, and stability increases with a large HS and on a long arm of lever, except has low speed.
C' like that qu' is; it is necessary to make the new gyros, j' tested this solution and c' is really most stable.

[C. Beaty]

C'est comme ça qu'il faut faire les nouveaux gyros, j'ai testé cette solution et c'est vraiment la plus stable.Cierva knew that in 1929, Xavier.

Here is a drawing from Cierva’s British patent.

[gyrogreg]

---- I suspect the Magni is also a potential killer, possibly harder since the rotor and Stab tend to help stabilize the Magni more than the rotor and magic mast does for the RAF. Ron, so where are all the smoking holes? - Greg

Why do we not see Magnis tumbling out of the sky? Maybe cause due to the serious investment a buyer has to raise to purchase a Magni, followed up with careful training by the instructor that checks them out in the Magni, that the pilots that are out there flying Magnis are just simply more careful and are more attentive at flying their gyros within the safe flight envelope. I am sure the Magni factory and network on good training is part of the accident equation. Vittorio emphasizes training equally to stability. Another part is that he incourages his representatives to try to descriminate toward responsible pilots (The concept is you sell a gyro to the whole family and friends - wives who understand that safe decisions are a big part of safety help their loved ones overcome any inherent "hazardous attitudes".) I have had a few potential purchasers that I have not encouraged and/or simply discourged from even getting into gyros - but especially into Magni gyros - don't trust their attitudes and decision making.

Another potential positive is that the Magni factory has resisted the temptation to go to higher production than its representative network can properly attend to the fliers. A requirement of Magni is that representatives must continue a close relationship with all of our Magni fliers - not just the customers who originally bought the Magni gyro. This is the real work with being a representative of Magni - and the one that causes the most work for me - and why I'm not out trying to sell more than about 2 per year in the U.S. It does help me on this score when a customer actually builds their Magni - they eventually take a lot less attention - and they start helping out with this job among the Magni fliers.

So, I emphasize the safety record is not totally the stability and buntover/PIO resistance. But, if the Magnis are so dangerous as some like to infer, ANY pilot gets sloppy with their decision making and occasionally pushes into these areas where some people are sure it will kill you - adding a lot of sudden power at low or zero airspeed, pushing over the top of a zoom, etc. It is human nature - at least for human males - to push the envelope at least occasionally - some males worse than others.

Still no smoking holes! (Unless Udi can tell me where he says there was a Magni buntover as he suspects.)

- Thanks, Greg

[mceagle]

Re Magni hang test.
Mitch you were spot on. My ‘bare’ height is indeed 5ft 8 ½”, or 5ft 9 ½” with the boots on. If you add ½” for the hat then Chuck’s estimate of 70” would be within a poof-teenth of dead accurate. The original estimate of the thrust-line offset was deduced from scaleing the main wheel radius. If I were to do the test again I would include a ruler in the photo to eliminate that part of the speculation.

The photos were taken with the rotors on and I believe at the time that there was no interference from wind, and that the able bodied Mitch was steadying the plumb bob from the fine adjustment necessary at the top to align the string with the centre of the teeter bolt. After steadying the bob, Mitch released it for the photo. The hang test photo was taken from the approx C of G distance ahead of the axle centre-line to minimise parallax error (this distance is easy to judge because the string is right on the C of G and its distance from the axel centre-line is obvious.
Other contributing factors – the pilot’s weight was below the national average, there was no passenger and no appreciable ‘baggage’ in the storage compartments. If any of these factors were to change to more realistic useage, the offset would have been greater.
The Glasgow University expensive thrust-line offset measurement quoted for the Magni is totally irrelevant to this discussion because as Chuck pointed out, this was a completely different aircraft and far removed from the current Magni.

For those of you accusing others of “brand-bashing” consider this, where there is smoke there is usually fire. While there are certainly uneducated comments found here, a lot of others are based on fact and you cannot bury your head in the sand and hope it will go away.
In most circles the Magni has an enviable safety record, and the most constructive thing we can do is to find out why. This I believe is the general thrust of these posts.
Technically the MT 03 should be a safer aircraft (because of the lower thrust-line and partially immersed H/S) but records will show a bad safety record in their short life span. We would also do well to pin-point the reason for this.

BTW Chuck, what is the "Infinate Monkey Theorum"?

[C. Beaty]

The infinite monkey theorem, Tim, states that with enough time, an infinite number of monkeys randomly pounding keys on typewriters, will eventually write a Shakespearean play.

That’s the way some gyros appear to be designed.

Some of our friends have come to believe that because a Magni doesn’t tumble out of the sky, the laws of physics no longer apply.

What they’ve failed to recognize is the effect of rotor damping. If a rotor responds slowly enough to airframe pitch/roll perturbations, rotor damping can be used to mask the errors of thrust line offset.

The Hiller Rotormatic rotor system provided good stability with the penalty of sluggish response. The Magni seems to accomplish much the same thing with a nose heavy rotor. Maybe the monkeys have written Romeo and Juliet.

I have a picture around here somewhere of a Hiller hovering with sandbags strapped in the seats while the pilot stands alongside.

I couldn’t locate that particular picture but did find this one that shows you shouldn’t turn a corner too fast in a Hiller or maybe that’s just the effect of a too slow focal plane shutter.

The pilot flies the paddle blades with no direct control of main rotor cyclic. The servo rotor can be given nearly any following time desired while the main rotor is slaved to the servo rotor.

[C. Beaty]

Here’s a link that provides a mathematical analysis of the lag of a Hiller rotor by G. J. Sissingh, a guiding light of 20th century rotorcraft development.

http://naca.central.cranfield.ac.uk/reports/arc/rm/2860.pdf

If you have problems calculating gas mileage of your automobile, this may not be for you.

[Doug Riley]

Birdy's Post #122 seems to have gotten lost in the excitement.

His point is important: a slow-reacting rotor does, in fact, make the gimbal head less useful as a G-smoothing device.

The gimbal head works by using changes in rotor thrust to create servo forces in the control system. These forces push the controls in a (hopefully) G-stabilizing direction: less rotor thrust allows the spring to pull aft on the torque bar, increasing the aft tilt of the spindle and eventually of the disk... and so on. If the rotor reacts slowly because of high rotor damping, this device won't be as helpful.

This brings us back to the "float the stick" approach to unstable gyros. Floating the stick (using a very light hand grip) allows the head's servo forces to do their thing. A heavy grip on the stick tends to shut down the operation of the gimbal head by locking the controls.

Relatively large values of rotor damping, and airframe stability (using HS and CLT), enhance stick-FIXED stability. Keep in mind that, once the gimbal head reaches its control stops, you've GOT a fixed stick. The stops, in turn, are attached to the airframe and move with it (in the wrong direction if the airframe is unstable).

IOW, fixed-stick stability, not stick-free stability, is the ultimate defense against PPO. Even the most unstable and PPO-prone gyros have a fair amount of stick-free stability -- up to a point -- thanks to the gimbal head.

Personal note:

When I first started flying Dominators in rough air, I used the good old "stick float" method. I didn't realize the full benefits of a stable airframe until I gave this up in favor of a firm stick grip. This let the airframe do the work of stabilizing the craft. The effect was pretty amazing.

[gyrogreg]

When I first started flying Dominators in rough air, I used the good old "stick float" method. I didn't realize the full benefits of a stable airframe until I gave this up in favor of a firm stick grip. This let the airframe do the work of stabilizing the craft. The effect was pretty amazing.

Hi Doug,

This is exactly why we are able, and do, put some friction in the cyclic on a Magni (and also to prevent some of the residual vibrations from showing up much in the stick.) We also have learned in the Magni it is a smoother ride in rough turbulence to stop trying to respond to wind gusts - just let the gyro do it for you. With or without the friction, you can either hold the stick tight, hold it loosely, or let it go. The amazing thing is that even without the friction in the controls, the stick does not float even stick free - mostly stays put! This is why I say the rotor responses match the airframe and vice-versa - basically a fixed wing until the pilot does move the stick - then it is a gyro! Maybe there is some strong feedback between the rotor and airframe that synchronize the two, but I still feel it is basically matched dynamic response characteristics ("harmony"!) that make the two stay together - even in rough air!

Another point with this observation is that if either the rotor or the airframe had much sluggishness or "lag", I don't see how they would keep up with each other so solidly unless both are responding the same to disturbances - without depending on feedback from one to the other to initiate the synchronized reactions. From flying, and from this observation, I cannot confrim as slow of a response as is being suggested in either. If there were much "lag" between the two, the rotor and airframe out-of-phase, there would likely be some sustained oscillations as one agravated the other.

Doug, I also wish you still had the Dom - try what you explained above, but this time without engine power - in a high speed glide in turbulence. In both my old High Command (a bit LTL), and in the Dom I built and flew 60 hours in, the "float the stick" was needed in rough air in a high speed glide with idle power. Both felt twitchy without the stability augmentation of the LTL prop thrust, I always slowed down a bunch from cruise before reducing power.

Lately, some of us (Magni fliers) in the U.S. have started pitching the prop to get higher cruise speeds. I'm often cruising in the 100 - 110mph range. Descents at the end of a cruise are simply reducing power and continuing a fast power off glide back down to the airport - feels exactly the same - solid - with and without power at all airspeeds above about 50. (Below 50mph, the controls start getting "softer", but still hands-off or fixed stick stable.) I attribute this to the HS not depending on propwash augmentation, and stability not depending on power to push the nose up to achieve high static AOA stability. I think the Europeans and SAs normally cruise in the 100+ speed range they are lighter folks! - still no buntovers or PIO that I know of in Magni gyros!

Do you recall how the Dom felt at high glide speeds at idle power?

- Thanks, Greg

[Doug Riley]

Greg, I can't recall a really rough-air idling glide at high speed. With throttle back, though, the Dom devloped a more rubbery, laggy feel. I imagine this was both because the HS was no longer receiving fairly clean, fast air from the prop and because, with LTL, cutting the throttle moves the CG aft relative to the rotor thrustline.

One student did forget which way to push the a stick to slow down, shoved it forward, and got us into a 90+ mph idling dive, then hauled back and did quite the mid-air flare. No permanent harm done (just a botched inside loop on short final).

Students in general did porpoise on power-off glides until they learned the old gyro "jab-and-return" control reflexes that we used to use in Bensens and such. My advice was to move the stick half as far as you think you need to, and wait.

It was a little confusing for them to have the aircraft change its personality in this way when the throttle was closed. If I were designing a gyro trainer (God forbid), I would mimic the Dom in many ways. However, I'd try to work this split-personality characteristic OUT of the aircraft... even though it's not the end of the world to leave it in.

[Udi]

Greg - finally I have a little time to answer your very thorough post. I wish you could deliver you messages in smaller bite sizes. Generally, I agree with your analysis although I think it is time we try to connect some of your ideas with measurable facts. Most of what we know about the Magni is bits and pieces from a few people who took measurements. I think you can help a lot in this regards and since you are stating all the time that all you are trying to promote is safety and understanding of gyros, I think you are the perfect person to collect and report this data.

Do you have a SmartTool Smart Level? If you do, using three bathroom scales and some ramps you can get a close approximation of your gyros CG location. I can send you a spreadsheet to do the calculations, if you don't already have it.

Also, using the same smart level, you may determine the AOA of your stab vs. prop axis and stab vs. the keel. Then, you may mount the smart level inside the cabin and collect airframe (and thus stab) attitude in flight in several conditions. I would be interested to know what is the attitude of the stab at S/L at several airspeeds from min airspeed to max airspeed. I want to know if the stab is indeed, as you say, downloaded throughout the flight envelope. These measurements are easiest to perform during S/L flight, as verified by altimeter, because then you know that you flight path is horizontal, which gives you an easy datum for stab AOA. It would be interesting to have this information also during climb and descent, but it is difficult to determine true climb and descent angle without some sophisticated equipment.

Other interesting data would be the rotor head angle vs. airframe at the same conditions. This may be determined by measuring stick distance from the panel and correlating this distance with the known geometry of the head. In particular, I would be interested in knowing the rotor angle at low airspeed with full power, cruise power, and idle power (same airspeed). This information would tell me what effect, if any, the HTL has on airframe attitude vs flight path.

All of this information would help put some meet on the bones of your theories. We can talk more about it offline, if you wish.

.

Please tell us the details - I am not aware of this.

- Thanks, Greg

Yes. The accident I had in mind is the Italian aerobatic pilot who crashed in his friend's Magni. The accounts I have heard of this accident always sounded suspicious and maybe a little bit of positive spin control by the factory. I wouldn't be surprised if on video this accident looked a little like the Pee Wee (sp?) Judge accident - which was a direct result of unloading the rotors at low airspeed and then suffering a combination of PPO and PTO.

[gyrogreg]

Udi,

I will try to get the data you are suggesting. Should be interesting and doable. One comment on finding the CG - I understand the three scale method combined with a hang test - my problem is I do not have the facility to hang the gyro to get an accurate second line to cross with the longitudinal CG.

The three scale method for one of the lines will work, but we have been trying to figure out how to balance on the mains to get a second CG line that has more angle with the hang angle - better accuracy. I have done the three scale thing before - with certified scales, and still couldn't get repeatable numbers!! But, we are working on this wheel balance way - may be easier than even a hang test - just need to get a lot of people together to do it all.

Otherwise, I do have a Smart Level and will try to get some numbers for you. FYI: the symetrical airfoil HS is mounted exactly parallel to the keel and the keel is intended to be level in flight for the average pilot. The keel hang angle range is specified to be between 6 and 12 degrees - 9 degrees is the median. The keel angle, and HS AOA is typically level for a light to average weight pilot in the front seat, and negative (nose-down) with heavier people - like me. - so I need to find a light weight pilot who can make these keel flight angle measurements also. We have some ligher weight Magni fliers, but for consistency, we would need to use the same machine. We'll work on this.

FYI: The Italian aerobatic pilot, Paulo Lintini, who died in the Magni M14 was an aquaintance of mine. His normal gyro was an M13 - an older prototype enclosed single-seat. Paulo regularly did aerobatics in this gyro and other airplanes. Paulo was killed in a borrowed M14 with a 914 engine - more performance than he was used to in his M13. The witness reports say he apparently tried to do a hammer head maneuver from low level - a maneuver he regularly did do in airplanes - but not his gyro! Witnesses said they definitely saw him pull the stick back for a high speed vertical climb from low level. Most of these witnesses were good friends of his, and they certainly were Magni proponents - including Luca and Peitro Magni. They all said the hammer head type maneuver was certainly one that could not be done in a gyro - and it ended in certain results. They did not report it flipped over - just did not pull out. Certainly the rotors were unloaded and that maneuver is impossible in a gyro. Paulo was also an Al Italia 747 pilot, an aerobatic pilot in several aircraft types, he did loops and rolls in his M13 gyro (against Vittorio's wishes!), and he was the Safety Officer at their flying club's events - including Magni's Days events. I was part of a Safety Briefing he conducted at a Magni's Day! He was very careful and professional in his approach to safety. So, everyone is still amazed that he would have done this maneuver - he knew gyros very well! But, we can't figure how this maneuver could have been initiated without a pilot command, and the witnesses said they did see him pull aft on the stick as he flew by them and started the vertical climb! The only thoughts are that he was not use to the performance of this 914 and momentarily forgot what type of aircraft he was flying - until it was too late after the nose vertical climb was initiated! At that point, the loss of rotor RPM was probably inevitable and unrecoverable!

- Greg

[Resasi]

Sad story. Experienced pilot, moments inattention and he's gone if that is what happened.

Doug with regard to that comment of yours about jab-and-return I went to trying that after finding I was not being too successful/comfortable with the smooth slow pullback for power off landings with a steep approach which I am just doing now. Is that a cruder/old technique and should I just persevere with the smooth pull back, or is it simply another way of doing it.

Sorry about the drift

[Doug Riley]

Jab-and-return is necessary if the aircraft (or any other device you are operating) is unstable. Balance a folded umbrella upright on end on your palm: this is a simple case of static instability -- you are continually making little jabs to keep it upright. As you practice, the jabs may get smaller and smaller, but you must always use the jabbing technique.

A gyro with an ineffective H-stab (and not much rotor damping) may be weakly unstable in pitch, even with the power off. It may require a bit of jab-and-return, but it's not nearly as unstable as the umbrella. With practice, you can just about eliminate the "jabbing" element in your flare, even if your gyro is not clearly pitch-stable.

One way to progress toward this goal is to under-flare intentionally. Allow the gyro to settle onto its wheels while you hold the nose no higher than level. Do the rest of your back-pull AFTER the gyro is on the ground. Obviously, don't start this type of landing from ten feet. Fly the aircraft down to a foot or so and let the gyro settle in.

Jabbing is a prudent technique to use when first flying an unfamiliar gyro. Instructors usually want you to get beyond it, however, since it tends to make the gyro wiggle.

[Resasi]

Thank you for that advice Doug. I suppose that because it is still new that seems to be the exploratory technique, hopefully will progress with experience.

Since you are here, we are estimating that with the gyro planned for 254 and 215lb pilot we think we will be looking at 23'-24' DW's at sea level with a 503 but was wondering what governs choice of hub bar length or will that come matched to the rotor blades?

The coning angle is set in the hub bar so I guess that would effect the teeter height?

[Doug Riley]

Leigh, that diameter sounds right, but ask Ernie about DW's. Hub bar selection is a bit more involved when you are using twisted blades.

[Udi]

Greg,

The Smart Level accuracy (if calibrated, which is easy to do) is 0.1 degrees. Neglecting weigh scale accuracy, the accuracy of the VCG should be within 1 inch if you are tilting the gyro back ~11 degrees. If you are able to tilt the gyro more than 11 deg, your accuracy will improve. The accuracy of the weigh scales affects your results directly. A 5% weight error would lead to about 5% error in measured VCG (which is 2.5" if your VCG is 50" from the floor). That is why accurate weigh scales (1% or better) are crucial. Also, all wheels must be unlocked during this test - all forces must be strictly vertical. If you have scales with better than 1% accuracy and a way to tilt your gyro back 11 deg or more, than you will get good results from this test and no hang test is necessary.

Regarding the Magni stab - I am a bit confused. You said that the gyro is designed to fly with the keel level, and that the stab is mounted parallel to the keel. On another post you have said that the Magni stab is downloaded, which gives the gyro airspeed stability. There seems to be a contradiction here.

[gyrogreg]

Greg, The Smart Level accuracy (if calibrated, which is easy to do) is 0.1 degrees. ----------
Regarding the Magni stab - I am a bit confused. You said that the gyro is designed to fly with the keel level, and that the stab is mounted parallel to the keel. On another post you have said that the Magni stab is downloaded, which gives the gyro airspeed stability. There seems to be a contradiction here.

Hi Doug,

I understand your comments on the scales and determination of CG - I'm trying to figure out how to do one or the other, but I need to find both time and people and facility to help do all this. Will try.

HS downloaded: The Magni, at least at higher airspeeds and power settings, does fly a bit nose-down - this presents the HS download then.

I did get a chance to try the Smart Level tests you suggested: This may not work as we desire, but here is a first set of results, but first a little clarification on how I did this:

- I determined a place on the side of the cabin to locate the Smart Level wher I could read it in flight

- I zeroed the Smart Level on the steel keel - tail keel is the only place available - but this is a tube that continues through the forward cabin.

- The location on the side of the cabin where I could take measurements in flight was 7.4 degrees nose-up - so 7.4 degrees was my ZERO ref. (Smart Level would not ZERO with this much deviation from level - so I just used 7.4 as a reference.)

- I considered that there could be some deflection of the keel with flight loads on the frame vs, sitting on the gorund - but I could not figure out how to determine or verify that! Probably mute point with the stacked welded square tube keel structure.

- The Smart Level digital output, in flight, seemed to have a "beat" with the vibration of the cabin! The digital signal was not steady - but seemed to switch consistently up and down - about 0.5 degrees total - with successive digital samples. The numbers were consistent in range, so I used the median indication. (I do not feel this was from small deviations in aircraft attitude, just a measaurement issue with the Smart Level digital sampling rate under vibrations??)

- So, I don't believe the Smart level can provide any accuracy better than about 0.5 degrees.

Initial tests - I did this preliminary attempt just to see what issues there might be with this testing. All numbers are relative to keel level attitude. These need closer testing attempts, but they were relatively repeatable on this first try:

- 60 mph S&L, approx 4500 RPM - -1.5 degrees

- 70 mph S&L, approx 4700 RPM - -1.5 degrees

- 90 mph S&L, approx 5100 RPM - -2.0 degrees

- 110 mph S&L, approx 5500 RPM - -2.5 degrees

Between 50 and 60 mph S&L power settings, the keel was approximately level - zero AOA on the HS.

Below about 50 mph S&L, the HS AOA was progressively positive up to about +2 degrees at 25 mph at full power.

Again, I would need to take this data with more precision - but it did appear to be repeatable - and fun to do! Be aware that this was with me - max forward loading - so it tends to fly more nose down with more forward weight. Once I get the data with myself, it would be interesting to see data with a 130 Lb pilot - but that will be difficult to do. I suspect the numbers would all shift to lower airspeeds though.

This data, to me, confirms that the M16 is a bit HTL. - how much? I don't think this data would be enough to determine how much - have to take the free air HS forces into account also! To conduct this S&L test requires different airspeeds to maintain S&L at different power settings - confuses the HTL determination.

The more telling test, IMHO, is the Static POWER stability test done with a fixed stick. Again, this cannot be used to determine the amount of HTL, but at least it is done at a fixed stick position so that the HS forces due to airspeed do not vary much. I'll try to get this data on my new M16 also (my new M16 actually has about a 1 inch higher mounting of the engine!) Preliminary testing suggests about a 15 mph decrease in trimmed airspeed with reduction in power from MPRS power to idle. This also indicates HTL, but seems to be reasonably in the range with other gyros - even LTL (in the other direction). Zero airframe AOA pitch response to power changes requires an good balance of both the drag moments and the prop thrustline moments to the Hs moments from both prop thrust and free air - so this may be a rare situation!

An interesting thing to note is that the airframe does not quickly change pitch attitude upon a sudden power change. Fixed stick, the aircraft continues level attitude while speed quickly reduces with a sudden power reduction - no sudden nose up! Stick free, upon a sudden power reduction, the airframe initially remains level with quickly decaying speed, but the stick moves forward suddenly. This would also be consistent with a HTL (suddenly disappearing), but instead of an airframe quick pitch up, the rotor quickly pitches down!?!? I attribute the steady attitude airframe to the strong dynamic damping of the HS. (I'm not sure that this isn't a common reaction for a stable gyro - but, without a good HS, a HTL gyro would normally pitch suddenly nose-up (CG forward) upon a sudden power reduction - hence the old axiom to reduce power if you think the gyro is getting unstable - works for HTL at least!

Thanks, Greg

[Udi]

Greg, one of the tests I recommended is to record stick position relative to the panel at three different power levels, with the same airspeed. This test is a good measure of the HTL effect. The purpose of keeping airspeed constant is to maintain constant rotor blowback angle and airframe pitching moments. For example, climb full power at 60, fly S/L at 60 and descend at idle at 60. With this information we can determine the change in rotor/airframe relationship, thus RTV/CG relationship due to prop nose-down moment. If you know the all up weight of your gyro during this test, this information may be converted into prop nose-down moment.

Keep in mind that every gyro should fly nose-lower at higher airspeed because the rotor itself is flying with a shallower AOA at higher airspeed. The 2 to 2.5 deg nose low attitude is really not that much - but, if we know your stab area (does it have tip fins?) we can guestimate the load on the tail at these airspeeds.

This is good info, Greg. Thanks for doing it.

[Doug Riley]

Udi, I'm gonna footnote your post just a bit. I know you know these things already.

First, an immersed H-stab would complicate the constant-airspeed/variable power test you suggest. An immersed H-stab with down-load can easily make the gyro fly nose-higher as the throttle is opened. The reason, obviously, is that, while we're keeping the free-stream airspeed constant, the airspeed of the slipstream is increasing as we add engine RPM.

Second, for the same reason, not all gyros (nor even just all HTL gyros) will fly more nose-down as they go faster. Again, the presence of a down-loaded H-stab (either immersed or not) can reverse this trend, despite the fact that rotor AOA gets shallower as airspeed builds. In fact, I would argue that an airspeed-stable gyro SHOULD adopt an increasingly nose-high stance as airspeed builds; it's apt to be statically divergent otherwise, especially if it has a Bensen-style head with a trim spring secured to the frame.

I realize that the working assumptions with the Magni are that the H-stab is not immersed and is minimally, if at all, down-loaded. Under those conditions, your proposed tests should work as advertised.

[Udi]

Agreed, Counselor, on the three counts. ;)

[mceagle]

This is all good informative stuff. It would be great if others could do identical tests on different makes of gyro and report such accurate and unbiased results. This would then give us some real data that the Guru's could get stuck into and deduce some real-world results.
It is probably not beyond the capabilities of some of the smarter ones here to devise some accurate electronic recording equipment that could be independent of pilot influences and be fitted to any gyro for testing.

[gyrogreg]

Greg, one of the tests I recommended is to record stick position relative to the panel at three different power levels, with the same airspeed. ------------ If you know the all up weight of your gyro during this test, this information may be converted into prop nose-down moment.

-------------- but, if we know your stab area (does it have tip fins?) we can guestimate the load on the tail at these airspeeds.

Udi and all,

I've played with more of this - we must be thinking along the same lines. See the attached spreadsheet data and charts. I flew this last night, and I think this is what you are thinking of. I really did this last night to try the technique - but this may be data you are looking for. I hope to try to include more data when I get the technique down - maybe next time including the Rotor RPM, Smart Level keel angle data, etc. I need to make up a datasheet and rig up my tape recorder to record more data - kinda hard to fly, watch for traffic and make notes in an open cockpit - but it was FUN!

I fastened a retractable tape measure to the instrument panel forward of the stick. I fastened the tape to the stick - at the bottom of the grip. I read the stick position in inches at the exit of the tape measure housing - I'll take a picture today and send it on a future post.

I then calibrated the Smart Level to ZERO on the keel. I then checked the spindle angle (relative to the keel) at a series of stick positions (inches) - to develop the conversion chart between stick position and spindle angle.

----------------------------------------

See the attached M16 dimensions to get the stab dimensions. HS area is about [(24" + 18")/2] X 60' = 4.375 sq ft - on a moment arm of about 62 inches. Tips have an approximate area of 18" X 24" = 3 sq ft. Tips and HS are airfoil shapes.

The gross wt for these tests with myself and 10 gallons of fuel was approximately 920 Lbs. RRPM about 360.

-------------------------------------------

This data is for the spindle angle - not the actual RTV. The spindle angle data does not consider the "Blowback" disk angle - do you know how to guestimate the blowback angle at different airspeeds? RRPM approx 360. Rotor diameter 28 ft. Blade chord 8-3/4".

It would be very interesting to be able to approximate the actual RTV relative to the 11.8 degree spindle hang angle (CG) - add blowback angle to spindle angle? This could suggest whether the RTV is forward or aft of the CG at these flight conditions. ie., does free air on the HS start statically compensating the HTL moment at the higher airspeeds? (Udi, I would still suggest that there could be additional factors into the "effective" RTV such as the static margin extended by the strong dynamic damping from the HS - at all these airspeeds, and at higher airspeeds up to Vne of 115 mph, this gyro is strongly dynamically stable and therfore must have the "effective" RTV aft of the CG.) The interesting question is where is the actual RTV relative to the hang angle CG.

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My observations:

- In a vertical descent, the spindle angle is approximately what it hangs at this loading - about 11.8 degrees keel angle! Not, unexpected, but I thought the large HS in a vertical descent might try to pitch it more nose down than the hang angle.

- I first got data at the approximate hang angle on the spindle to see what airspeed at this spindle angle resulted in S&L flight. This was at 42 mph. At 42 mph, higher power settings (than S&L) resulted in a spindle axis aligned forward of the hang angle (CG), and less power resulted in a spindle axis aft of the CG.

- At 60 mph and higher, spindle axis was aft of the CG. at all power settings

- At all power settings, spindle angle was more forward for increasing power settings - indicating a static unbalanced HTL effect.

It may be a while now before I can get more data - but see if this is worth anything already.

- Thanks, Greg

[gyrogreg]

Attached is the method I used to measure stick position for the above testing. This is a retractable tape measure, stuck to to instrument panel and the tape secured to the stick. The tape release lever on the tape measure is taped depressed to allow the tape measure to always retract. The position is measured at the exit from the tape measure housing. This is pre-calibrated to the spindle angle relative to the keel per the curve on the spreadsheet above.


- Greg

[All_In]

Thank you so much guys!!!
@Greg I know Stan will help.

PS:
I liked this too: but it was FUN!

[gyrogreg]

Udi,

I thought I'd give a try at estimating the HTL from the data above:

Assumptions:

- Used 60 mph data

- Full prop thrust = 500 Lbs (500 Lbs static on the ground, so this might be a conservative worst case at 60 mph)

- @ 5400 RPM (prop thrust = 500 Lbs.)
- Thrust is square function to RPM, so prop thrust @ 4780 RPM = 386 Lb

- So, thrust change from 4780 RPM to 5440 RPM is 500-386 = 113 Lbs.

- 920 Lbs rotor lift (all up weight). Considering a 7/1 L/D, that makes rotor thrust = 1050 Lbs

- Assume rotor arm to CG (rotor to CG length) to be about 50 inches - scaled guestimate off of drawing above

Spindle angle change (RTV angle change) for 114 prop thrust change is 10.2 - 9.4 = 0.8 degrees. Trig says RTV moment arm changed is .70 inches.

So RTV moment arm change is .70 in X 1050 Lbs = 734 in-Lbs

So, 734 in-Lbs is the change in HTL moment with a 114 Lb prop thrust change.

HTL = 734 in -Lb / 114 Lb = 6.44 inches

I can believe 6.44 inches HTL. So, Udi, tell me where I might be wrong with this estimate - see what you get.

- Thanks, Greg

[Udi]

Greg,

That is indeed the calculation I was after. I don't have time today to go over the numbers but your results look very reasonable and probably, as you implied, worst case. You probably don't get 386 lbs of thrust with 4780 rpm at 60 mph. I have calculated the stab area and I got 4.6 sqft each side, for a total of 9.2 sqft. Also, the moment arm should be measured from the CG to the mean quarter chord - which I would estimate at 80 inches, not 62. This is good data - I will work on it hopefully soon.

[gyrogreg]

Udi,

I hope to get a lot more data - fill in some of the spreads, and include deck angle and constant power numbers, etc. This will take me some time, but I believe the measurement tools work.

I agree the HS moment arm should be measured to the 1/4 chord, the 62 inches was just a reference - and the longitudinal location of the CG as shown is debatable - but 80 inches looks a bit long to me. Might take a little calculus to determine the 1/4 chord of the HS also - I'm too rusty on calc to try that.

How did you figure in the tip plates - or did you? Using just the HS dimensions, I get: [(24" + 18")/2] X 30" = 630 sq in = 4.375 sq ft per side - not 4.6.

- Greg

PS:

I am confused about one measurement on the M16. The head is mounted (to the keel at 12 degrees - not the normal 9 degrees. This is the forward allowed hang limit (6 - 12 degrees to keel). But, the total spindle angle is from 1 degree aft to about 18 degrees aft. So, the nominal 9 degree spindle angle is not exactly mid range of the head travel. I'm not sure why this is - just to get the stick position and range where they want it? - or does the heavy trim spring in the tandem config work better with a more aft head angle to cover the whole front seat allowed weight (130 - 260 Lbs). Per the spindle numbers I measured with 270 Lbs in the front seat, the spindle will be centered on this 12 degrees only at high power and lower airspeeds. But, at 60 mph (MPRS), 9 degrees seems to be the number - normal? But, this is not centered in full head range.

These spindle angles will be lower for less weight in the front seat - so it will take a more forward stick for light pilots. I don't know how this might affect the stability parameters, but the HS will not be as down-loaded asmuch, and probably will be uploaded at somewhat higher airspeeds than our data indicates for the nose-heavy condition.

[Bob Gregory]

I figure the horizontal sides to be 4.375 sq ft or 8.75 sq ft without the tip plates.

The CG to quarter chord is 78 inches.

Rotor Thrust Vector sheet to follow.

[troed@aon.at]

Now this for the first time is a real scientific approach to the discussion...

Millions of thanks to You Greg ! :hail: You are really special. :first:

Could You translate Your measurements and calcs into some nice graphics for easier understanding ?

Angelo

[gyrogreg]

I figure the horizontal sides to be 4.375 sq ft or 8.75 sq ft without the tip plates.

The CG to quarter chord is 78 inches.

Rotor Thrust Vector sheet to follow.

Bob, thanks for the spread sheet - I'm still trying to understand what it is telling us. Can you summarize any conclusions this leads you to.

One question though - looks like this sheet requires a measured prop thrustline offset - 6.44 in that I had estimated above? That number actually needs to be verified, I'm not sure all my assumptions to derive that number are accurate. For instance, I assumed prop thrust of 500 Lbs - the typical static prop thrust on the ground. At some higher airspeeds, that might not be the real prop thrust - the 500 Lbs static may include some stalled prop blade area, and the reduced prop blade AOAs at higher airspeed will probably reduce the prop blade thrusts at higher airspeeds. Anyone know if the prop thrust at 60 mph can be expected to be higher or lower than static on the ground? Typically we woulkd expect prop thrust to be less and less at higher and higher airspeeds - at least after portions of the blade become unstalled at the lower airspeeds.

How did you compute the "effective" quarter chord location - take into account the varying chord effect, or just the mid point of the 1/4 chord line? Probably not a lot of difference between the two though.

(If anyone has any trouble opening Bob's file attachment above - when I saved it it is a .php file? Just change the extention from .php to xls - then it will open with Excel.)

- Thanks, Greg

[Bob Gregory]

Determine quarter chord.

[gyrogreg]

Determine quarter chord.

Bob, probably plenty close enough - better than my original number! I'm not sure this does account for the higher component of the lift at the inner - longer chord - sections of the tapered "wing". There are probably standard formulas to determine the "effective" 1/4 chord for swept and tapered wings. I think your computation accounts for the sweep, but maybe not the taper? I'll bet the difrference is not ore than 1 inch though. As a learning experience, anyone have thoughts or formulas for this?

- Thanks, Greg

[mceagle]

For instance, I assumed prop thrust of 500 Lbs - the typical static prop thrust on the ground. At some higher airspeeds, that might not be the real prop thrust - the 500 Lbs static may include some stalled prop blade area, and the reduced prop blade AOAs at higher airspeed will probably reduce the prop blade thrusts at higher airspeeds. Anyone know if the prop thrust at 60 mph can be expected to be higher or lower than static on the ground? Typically we woulkd expect prop thrust to be less and less at higher and higher airspeeds - at least after portions of the blade become unstalled at the lower airspeeds.

In-air prop thrust is something that is very difficult to determine.

At the lower end, some combinations will produce maximum thrust at zero mph while others will not reach their maximum until a large percentage of the blade is un-stalled, typically somewhere between 10 and 30 mph. In the latter case it is usually the higher horsepower engines running high pitch angles.

At the higher airspeed end of the scale there is no doubt that at some forward speed the prop thrust would be zero (it might require a steep descent to achieve this). It can even reach a negative figure (drag) if the gyro overruns propeller speed. Given the rotational speed and the pitch angle it is not too hard to work out at what airspeed the thrust equals zero.

Whether the thrust line between this maximum and minimum would be a straight line or not, I do not know.

To determine the in-air thrust at different airspeeds would ideally require the use of a large wind tunnel, but even then this would only be accurate for the given engine/prop combination. Realistically it would be out of the question and impractical to do this sort of testing.
A more practical alternative would be to do thrust testing on an open flat-bed trailer or truck at differing airspeeds. Even this would require some time, dedication and a long airstrip, but could afford some useful data.

Knowing thrust over the normal flight range could go a long way towards understanding the requirements and effectivness of a horizontal stabilizer.

[birdy]

Bloodyell, i picked the rong time to take me holiday.
Im go'n to have square eyes wen i get home waden through all this.