Control conundrum

[Vance]

My current conundrum has to do with rotor control. I will try to explain my train of thought.

I believe that one of the big advantages of an autogiro is that the rotor doesn’t stall no matter how slow the forward airspeed. I am trying to understand how the other control surfaces work with very low airspeed? If they are not working and the rotor is not producing lift because of some low g event, what keeps the aircraft from tumbling out of control? If the rotor attitude is controlled by commands from the body of the aircraft and the body has no aerodynamic control, can’t the out of control body command the rotor to do something unintended by the pilot? Could this become a self-energizing event?

It seems to take very little control force to command the rotor to take a different attitude. The question for me becomes, what makes the body of the autogiro stay still while the pilot commands a change in rotor attitude?

I have heard “fly the rotor” but I believe the commands must come from a relatively stable body for the pilot to know what he is commanding.

I am able to imagine a rolling turbulence that would produce a low G event and reduce airflow over the control surfaces to near zero. Particularly on the lee side of a mountain. What would the effect of this be on control by the pilot?

I am also able to imagine adding power if I had flared too high and have the ship want to torque roll from the accelerating mass of the prop, particularly in a CLT configuration.

I have not stated these questions well; I am hoping that someone out there who understands autogiro dynamics is also good at mind reading.

This has nothing to do with the two recent crashes, just the Vance comities having a discussion in my head.

Thank you, Vance

[birdy]

Just coz the rotors arn't producing lift in a 0g situation Vance, don't mean they loose 'airodynamic' power. They are still spinning, so air is still flowing over them, so all you have to do is apply some more positive pitch to them and you will have an airdynamic responce.
And the amount of 'feed back' to the airframe from an input command is very small, so it'd have buggerall effect on the frame coz of the frames greater mass.
Torque roll OTOH is different, and i'm not sure how many people understand wot 'could' happen in a relativly sustained 0g, full power situation.
A smart bloke will always chop the power in a 0g event, no matter wot his machines configureation.
Just yesterday, i found myself in an unnerving situation.[ well, it was unnerving 4 hours later when i was thinkn bout it.]
When i was turning tight in me 'new' ferel, i noticed the rotorhead was obsquering my vision of wot i was lookn at on the ground. This is nuthn new, but my headset/helmet is, and coz im ruged up like an eskymo and its a full face helmet, my neck movement is restricted and i have to 'lean out' of the seat in order to keep an eye on the critter. IOW, when the machine exceeds a 90* bank, i have to lean up[ like ona bike] in order to see the target.
As i sad, its nuthn new, but this occasion i happened to fly into a strong sink, and nearly fell out. But it was coz of the pitch control i still had in the 0g situation[ and full 912s power] i didn't loose control.

[RossB]

Vance

[It seems to take very little control force to command the rotor to take a different attitude. The question for me becomes, what makes the body of the autogiro stay still while the pilot commands a change in rotor attitude?
[/QUOTE]

You seem to be confusing control input and forces applied by the body of the gyro.
The control inputs are applied to the rotor head and due to the teetering action no direct forces are applied to the plane of rotation of the rotors.
The body of the gyro does not apply any direct forces to the rotor attitude, this is not a weight shift aircraft, so the body of the gyro does not have to "stay still".
The only time you can apply any direct forces to the rotor disk plane of rotation, is when you hit the teeter stops, that's a bad way to finish a good day.

Not sure if this helps...I'll think on it some more
Ross B

[Vance]

Thank you David, you correctly identified that I was asking about two different and only slightly related things. That helps. I had a feeling that I asked the questions badly.

I understand that in a low g event the rotor still has the power to change attitude when commanded, the first question has more to do with the combination of a sustained low g event combined with a loss of forward air speed. I could imagine this happening flying away from the lee side of a mountain. I imagine that the control surfaces, the rudder and horizontal stabilizer, would have very little control over the attitude of the airframe as the forward airspeed approached zero. I imagine that this might confuse the control input because it would seem to be affected by the airframes relationship to the rotor. When the pilot loses the ability to influence the attitude of the airframe I would imagine that this might confuse his commands to the rotor. This might confuse me. I would imagine that I would need to shift the tools I am using to access the response of the airframe. I would hope that this low G low forward airspeed event would be short enough to be a non-event. I am trying to be confused on a higher level.

On to what would appear to be the second part of the question;

On a motorcycle gassing it is usually the way out of trouble. This is counter intuitive, so it is something that I had to learn.

When I flair too high in a heavy machine, Steve taught me to give it power to cushion the uncontrolled decent. Sort of like a failed go-around. The Autogiros I was flying with Steve, a modified RAF and a SparrowHawk, appear to turn right and pitch nose up. The success of this action made me want to try power as the way out of other kinds of trouble.

I have a 20-knot wind limit so I have only experienced one sustained low G event and Steve cut the throttle and dropped the nose. This is in conflict with what I had learned on a motorcycle, so, for me, I need to understand it in my head so I can change the response of my body. My natural response would be to apply throttle to arrest the sink, but if I understand you correctly, that would not be the best action.

I would be grateful for further impute on either question.

Thank you, Vance

[Vance]

Thank you Ross, I did not mean to imply that the control forces to the rotor might affect the attitude of the body of the gyro. I did not ask the question well. I am speaking of cyclic control impute.

I believe that control imputes have to do with the relation ship of the body of the gyro to the rotor.

When the pilot loses his ability to control the attitude of the airframe because of low forward airspeed combined with a low G event, I would imagine it could be both disorienting and destabilizing. I like to believe that I will know what to do when something new happens so I try to think ahead.

Because of the low forces required to influence the rotor, I can imagine making unintended commands to the rotor when the control surfaces of the empennage see low airspeed and I lose my ability to adjust the attitude of the airframe.

The circular nature of the imagined challenge is; as the rotor loses it’s ability to know which way is up from a low G event and I lose my ability to control the attitude of the airframe from low forward airspeed, I still have the ability to tell the rotor to do the wrong thing. My normal frame of reference would be distorted and I might make poor decisions.

I would be grateful for further impute.

Thank you, Vance

[Doug Riley]

Vance, I'm not entirely sure I get the question, but maybe we could nibble around the edges.

In the first place, the ability of a rotor with a teeter hinge (or other central flap hinge) to affect the orientation of the fuselage in space is a direct function of the magnitude of its rotor thrust. If no thrust, then no control effect on the frame from moving the stick. Mind you, the rotor still moves, it's just that the frame doesn't follow it because there's no rotor "pull."

Second, I often find the notion of zero G too metaphysical. It implies that gravity goes away. It doesn't. "Zero G" is simply a way of identifying a circumstance that FEELS AS IF gravity went away. What actually happens in zero G flight is simply a reduction in rotor angle of attack, to zero or even less. No AOA, no rotor thrust. If no thrust, then no control, as described above.

When angle of attack and thrust go away, the net of the other, non-zero forces on the aircraft determines what happens next.

In PPO-prone craft with no HS, this net is instantaneously a strong nose-over torque.

In a craft with forces that balance WITHOUT the help of rotor thrust, this net is... zero. The gyro simply proceeds on its previous path in a straight line at its initial airspeed.

Almost. I lied a little in the previous two paragraphs. There's another force present in both situations: gravity. As we said, it doesn't really go away. When rotor AOA and thrust go to zero, the gyro starts accelerating toward earth in response to gravity.

This acceleration (OK, this FALL) will increase airspeed. It will also normally restore positive angle of attack, as long as the aircraft hasn't flipped upside down and chopped off its own tail in the meantime.

Maybe you're asking whether anything you might do with the stick during that moment of zero AOA/zero G could ruin this rosy picture. The "floaty" sensation that you get in zero G is normally interpreted by our inner ears (and outer rear ends!) as "falling." Our untrained instinct is, I think, to pull back on the stick.

Pulling back will be overkill, I think. The system's tendency is to restore AOA without your help. A more trained reflex is to hold the stick still and let the gyro settle back into pos-G flight.

[Vance]

Thank you Doug, that helps.

Do nothing is counter-intuitive, but it is also often how you save a motorcycle. Give it its head until it’s done acting badly and hope you don’t hit anything in the mean time.

After my un-commanded low G event in what appeared to be nice air, I have been doing what Jim Mayfield suggests, trying to imagine all the trouble I will get in and what to do about it. I believe in learning what to do before it happens so when it does happen I don’t have to stop and think about what to do.

From Bonneville I know that considerable wind can come through a gap and wind conditions can change during the flight. We always check the wind for the whole 7-mile coarse before we launch.

In my aeronautical knowledge book it shows a kind of tumbling air on the lee side of a hill. I imagine this wind coming on top of my rotor and from behind. It could easily drop my airspeed to near zero and take away the lift. I would imagine at this point I don’t have enough airspeed over my empennage to provide much control.

If I understand you correctly you are saying to relax and let it fall because it will catch up with the down draft shortly and I will be able to fly again. I imagine that I should reduce power to minimize torque roll. Hopefully I won’t run out of altitude before I have an in-flight collision with terrain.

I apologize for over thinking this and I appreciate your help.

Thank you, Vance

[birdy]

I can imagine making unintended commands to the rotor
Generaly, unintended commands are only the problem of pilots who 'choke' the stick. They tend to use it more as a handle than a control device, and squeeze the crap outa it whenever sumthn irregular happens. The stick should be allowed to float, so the offset can do wot its desigened to do.

The success of this action made me want to try power as the way out of other kinds of trouble.
The trouble with comparing bikes to gyros is that bikes are already on the ground[ or at least most of the time]. Gyros are 3 dimentional, and not all things are the same. Hitting the power after flareing too high will not kill you, solong as its done gently. Cracking it open at the top of the flare, when your ass is light in the seat could cause damage tho. The idea of applying power is to re establish some forward AS to coushn the landing.


As Doug said, ina 0g event, nuthn happens except a sudden virtical increase in speed, down. So the machine will only drop till sumthn stops it from droppn, like a change in airflow.
And don't worry, all down drafts stop at ground level, so thats as far as they'll take you.;)

If it makes you feel any better, i'v tightened the shoulder straps on both me gyros countless times, and am still here anoying everyone.:D

[Udi]

...In my aeronautical knowledge book it shows a kind of tumbling air on the lee side of a hill. I imagine this wind coming on top of my rotor and from behind. It could easily drop my airspeed to near zero and take away the lift. I would imagine at this point I don’t have enough airspeed over my empennage to provide much control...
Hello Vance,

I hope your question is purely theoretical because flying into wind shear is a bad idea in any kind of aircraft. Jetliners on approach for landing have crashed exactly due to the scenario you are describing. Many planes have crashed here in Colorado when they flew into the rotors caused by wind tumbling over the mountains.

When you enter a wind shear (i.e the wind is hitting you from the back and top) you lose both airspeed and lift (AOA). The only way to exit this situation is to accelerate back to your original airspeed and gain a positive climb rate before you eat rocks.

What you are more likely to encounter in a normal flight are strong down draft caused by thermals. These will make you feel light in the seat and you may lose some altitude but it is very unlikely that you will have an honest zero-G situation.

Let’s play with some numbers. At zero-G, the gyro is accelerating downwards at a rate of 9.81 m/s² or 32.2 ft/s². This means that after one second at zero G your vertical speed is 32.2 ft/s, or 1932 ft/min. 2000 ft/min down drafts are even hard to find in Colorado. Even if you hit a 2000 ft/min down draft, it would take the gyro only one second to reload the rotors. In one second you don't have enough time to do anything.

In reality, when you enter a 2000 fpm down draft the transition is more gradual. You will feel light in the seat and then maybe very light for a fraction of a second and then you won't even know your are descending anymore, unless you have a VSI or some other point of reference - the gyro will be descending but not accelerating any more.

The bottom line is that the best course of action is to have a gyro that is pitch stable, so you don't have to worry about what you have to do when you hit that down draft. An unstable gyro is on the verge of tumbling out of the sky every time they hit this kind of down draft but for a stable gyro this is not a problem. Oh, and try not to fly into mountain turbulence…

Udi

[Vance]

Thank you David,

It helps me to understand where I am when I look at where I have been. Steve taught me to apply power to cushion the touch down from a high flair. I believe that I particularly embraced the power cushion technique because of my motorcycle experience. I believe you are saying it has limited application. I suspected that, and that is why I asked the question. Thank you for your help, I love your fundamental approach.

Thank you Udi,

Yes it is hypothetical. I was trying to imagine a maximum bad situation. When I had my unintended low G event I lost about 800 feet on the backside of a thermal and the rotor lost about 50 rpm. I found it disturbing. We lost about 20 miles per hour IAS. Steve cut the power. I believe it was about a half G event. I didn’t see it coming and the beginning was like many thermals I had run into before.

We do have wind sheer near the Santa Ynez airport. There is about a 2400-foot hill within a mile of the ocean. Gliders love it.

Your answer is very helpful and succinct. Thank you, Vance

[Ga6riel]

ok now THIS is a leap of faith
for it seems to me, with the knowledge that the CG precedes the AC as it does in all stable aircraft. For it is this that ensures dynamic stability. It is also perhaps inherited from conventional aircraft design where the dictates require that the machine go nose down to recover airspeed in a stall.

Ok so what if the CG were aft of the AC, momentarily fogetting the machine would be dynamicly unstable (permitting that it matters less at low to zero speed); would that resolve the zero speed bunt? For in this instance, weight is returning the machine to nose up, more rotor AoA with a propensity to increase rotor speed not decrease.

And given that this condition is true, could dynamic stabiltiy then be regained via aerodynamic means as it is with some gliders that have aft CG conditions?

did I mention a leap of faith ?

[birdy]

I hope your question is purely theoretical because ..................
2000fpm down [ or up] drafts are not theoretical, wether its caused by thermal activity or mechanical disturbance.
Flying through them in a gyro also is not theoretical, nor dangerous.
If you insist on scareing the crap outa yourself and constantly fly on the down wind side of mountains on a windy day, then the fear is only in your mind. [ mind you, fear is the only thing that'll save sum people.]
A few years ago i spent over 2 hours in the shadow of a shear range of bout 1700' x bout 5 miles on a day that wasn't suited for joy flying.
It was bout 45*c, with a dust storm blowing with gusts of wind that had me in negative ground speed when my ASI said i was do'n 50K. The VSI isn't very quick to react to speed changes and it rearly exceeded 1500FPM in either direction coz by the time the needle started moveing, the virtical wind would swap directions. The ASI was constantly flicking from 0 to 60 odd knots.
Needless t say, i wasn't happy with the situation, but it may give an indication of what these machines will put up with, solong as you don't let go.

BTW, this happened in the ferel, back when the TL was high and the stab was non existant.[ as it still is.]

One reason why gyros are seemingly less affected by wind shear is coz if its high wing loading AND its slow AS.
On a bad day a FW will feel like rideing a scooter with rock hard suspension on a road thats not designed to be ridne on at 100mph.
On the same day, a gyro will feel like a 40mph putt on a scooter with soft sus.


Disclaimer; i strongly recomend anyone not comfortable or relaxed in a gyro to not fly in anythn near rough.

[Aussie_Paul]

Hello Vance,
The bottom line is that the best course of action is to have a gyro that is pitch stable, so you don't have to worry about what you have to do when you hit that down draft. An unstable gyro is on the verge of tumbling out of the sky every time they hit this kind of down draft but for a stable gyro this is not a problem.
Udi

Exactly correct Udi. I cannot understand why there are still people who continue to trust their own abilities:eek: rather than have an aircarft that will help them when conditions get really bad, or they make an error in judgement!!!:confused:

Aussie Paul.:)

[Chopper Reid]

Exactly correct Udi. I cannot understand why there are still people who continue to trust their own abilities:eek: rather than have an aircarft that will help them when conditions get really bad, or they make an error in judgement!!!:confused:

Aussie Paul.:)

Where's a bit of 4x2 timber......you got that needle stuck Paul.:p

[Vance]

I am not sure what that means Brian? Would you please translate that?

Thank you, Vance

[Aussie_Paul]

I am not sure what that means Brian? Would you please translate that?

Thank you, Vance

Vance, I am a Diabetic, and every now and then my mates (those with HTLMs:eek: ) give me some cheek about it!!!!:D Hi Brian.

Aussie Paul.:)

[Doug Riley]

Gabriel: Low speed bunt? What moment creates the bunting action? I trust you haven't fallen victim to the "gyroplanes inherently try to bunt over" fallacy. That is nonsense, but it's nonsense that has been promoted (in my opinion) by the ill-advised use of the vague term "bunt." We'd be better off sticking to "power pushover" and "drag-over."

Some gyros will nose over in low G because their designers made a mistake and deployed the moments and forces improperly. These "flips" are not an inherent or normal characteristic of gyroplanes. They ARE an inherent or normal characteristic of tailless aircraft with high thrustlines and/or moment-generating bits stuck out in the airstream. Flying wings and trikes are just as bunt-ish as gyros if they have unbalanced pitching moments. For that matter, if the H-stab falls off a Cessna, watch IT tumble, too.

A sharp gust from above-and-behind, in a CLT machine, is just as likely to generate a violent nose-UP moment. If actual tail-first airspeed were achieved, there'd probably be movement toward a violent yaw pirouette, as the tail feathers got back-winded. It would not be pretty. As Udi advises, stay out of mountain rotors; they're simply an unsafe place to be in a flying machine.

Something like this MAY have caused Ken Rehler's accident last December, although honestly it seems a bit far-fetched at 20 feet over a flat runway.

Vance, you're right about the potential for a torque rollover in low G, if the gyro uses rotor thrust as compensation for engine torque. Either a tall tail or differential incidence on the two sides of an immersed HS are better for this purpose, however, since they aren't G-dependent. At cruise power or more, the prop blast is much faster than the gyro's airspeed, so our hypothetical gust-from-behind isn't as likely to reduce the immersed tail feathers' airspeed to zero.

[Vance]

Vance, I am a Diabetic, and every now and then my mates (those with HTLMs:eek: ) give me some cheek about it!!!!:D Hi Brian.

Aussie Paul.:)

Thank you Paul, My wife is diabetic and she uses a needle, but what is the refrence to lumber? Is HTLMs a different kind of disease? What is cheek?

Thank you, Vance

[Vance]

Thank you Doug.

What do you think about using power to cushion a high flare? Both the modified RAF and the SparrowHawk pitched nose up and turned right. I always wondered how close I was to a dynamic rollover. I didn’t seem to have this trouble with Jim Logan’s RAF but I flew it into the ground once. I found the difference in ride height disorienting.

I believe I have had a landing challenge epiphany. I believe I was trying too hard for consistency and not listening enough to the feedback from the aircraft. I am hoping to get some more dual soon and I am looking forward to changing my priorities. Have you seen this priority challenge with students? It is both the height and the speed of my flare. I was within a few feet of my target point on my touch down and keeping it straight didn’t seem to be a challenge, but sometimes the speed of my flair was a little fast and I had trouble holding full back stick. I also had difficulty with cross wind landings. I had a 20kt limit, but even at 15kts I lacked coordination and felt awkward.

Do you ever feel that your students are trying to kill you? Jim Mayfield would always say, “He had cheated death once again.”

I called my wife after a particularly challenging flight and told her “we had cheated death once again.” She wanted me to expand on the reference and I couldn’t find the words to slow her breathing.

Thank you, Vance

[Doug Riley]

I wrote a long reply, all of which the system ate. Briefly:

Stick with one machine to avoid confusion.

Don't rely on power to save landings, practice consistently at idle. Use a consistent approach speed and watch for the "unmoving spot."

Don't flare until you have felt the ground effect. Then bring the nose no more than level. Only after the machine has slowed enough that it won't balloon should you pull back more. All this happens at a foot of altitude.

This is all done by feel. You can almost do it blindfolded once you get the hang of it. It takes everybody awhile to get it dialed in, however. It's the last basic skill most students master in my experience. Once you get it, you'll wonder what all the fuss was about.

I haven't felt that a student was trying to kill me. Some have threatened my landing gear a time or two. The only who's actually bent it, however, is me.

[Vance]

Thank you Doug, sorry it lost your long answer.

I was trying to use ground effect to calibrate my altitude, it seemed like the aircraft would go right through ground effect before I could respond unless I came in with a little power.

Dave wouldn’t let me land his Dominator, but he did five landings and I could always feel the ground effect. I believe that he was uncomfortable with my handicap. Could it be that the heavier machines take a different technique?

I will try landing with my eyes closed. That might be a good way for me to become more sensitive to the aircraft.

I have 319 landings in my logbook and it is still my week spot. I am beginning to feel dispirited. I haven’t bent anything yet, but my landings lack style and consistency.

Thank you, Vance

[Doug Riley]

Vance, I have no experience with the really big iron. My Dominator grosses around 900 and has a 28-foot rotor. I'd suspect that even the lead sleds have a detectable ground cushion if you get low enough and are travelling at the right airspeed.

[Vance]

Thank you Doug,

I have good control of my approach speed, the flare is the challenge.

I am going to work on being more sensitive to what the aircraft is telling me.

I am looking forward to trying the eyes closed landing.

Thank you, Vance

[Doug Riley]

Vance, some of the input is in the form of stick pressure. So some of the "feel" is in your hand, as well as in your posterior. The pressure is light; I'll try to get conscious of it next time I fly, but I believe it's a slight forward pull. If the instructor is also holding the stick, the input may not come through to you.

One thing you DON'T need once you "get" the process is the ASI!

[Ralph]

Vance,

Early on, the terminal portion of the landing, leading to touch-down, seems to run at warp speed. There doesn't seem to be time to do anything sophisticated and one tends to think of the "flare" as one thing which you are challenged to do at exactly the right time.

With time and practice, that terminal phase begins to run in slow-motion, stretching out for what appears to be a long time. You simultaneously perceive nuances you never had the time to notice previously and the whole thing stretches to provide lots of time to respond. Now the "flare" ceases to be an event and becomes a feedback-moderated sequence. Once you get to that point, you will wonder why you started by viewing the whole landing sequence as a rushed series of pre-programed responses.

Ralph

[Vance]

Thank you Doug,

You pined down another challenge I have. I have trouble equating the angle of the cabin with airspeed. I am inside too much. That is what I particularly liked about the Dominator, I could feel the wind and I found it cathartic.

Thank you, Vance

[Vance]

Thank you Ralph, I have found that with many things.

An unintended dismount from a motorcycle at speed seems interminable.

I will look forward to a slower and more relaxed experience.

Thank you, Vance

[Ga6riel]

Gabriel: Low speed bunt? What moment creates the bunting action? I trust you haven't fallen victim to the "gyroplanes inherently try to bunt over" fallacy. That is nonsense, but it's nonsense that has been promoted (in my opinion) by the ill-advised use of the vague term "bunt." We'd be better off sticking to "power pushover" and "drag-over."

Some gyros will nose over in low G because their designers made a mistake and deployed the moments and forces improperly. These "flips" are not an inherent or normal characteristic of gyroplanes. They ARE an inherent or normal characteristic of tailless aircraft with high thrustlines and/or moment-generating bits stuck out in the airstream. Flying wings and trikes are just as bunt-ish as gyros if they have unbalanced pitching moments. For that matter, if the H-stab falls off a Cessna, watch IT tumble, too.

A sharp gust from above-and-behind, in a CLT machine, is just as likely to generate a violent nose-UP moment. If actual tail-first airspeed were achieved, there'd probably be movement toward a violent yaw pirouette, as the tail feathers got back-winded. It would not be pretty. As Udi advises, stay out of mountain rotors; they're simply an unsafe place to be in a flying machine.

Something like this MAY have caused Ken Rehler's accident last December, although honestly it seems a bit far-fetched at 20 feet over a flat runway.

Vance, you're right about the potential for a torque rollover in low G, if the gyro uses rotor thrust as compensation for engine torque. Either a tall tail or differential incidence on the two sides of an immersed HS are better for this purpose, however, since they aren't G-dependent. At cruise power or more, the prop blast is much faster than the gyro's airspeed, so our hypothetical gust-from-behind isn't as likely to reduce the immersed tail feathers' airspeed to zero.

thanks Doug
my concerns centre around an issue that I failed to describe, that even where there is a stab airspeed can be so slight as to make the stab ineffective, ie the surface provides insufficient balance control.

Ive no idea where, but I thought I saw a description of such a condition that resulted in a bunt. It seemed feasable to me that low speed / nose down hence flatter rotor disc pitch to relative air and slowing rotor would present a dangerous condition

[Doug Riley]

"Slowing rotor" is indeed dangerous if it progresses to the point of a full blade stall in some sector of the disk. This is true of helicopters as well. We expect the gyro to "catch up" with any wind shears quickly enough to avoid catastrophic RRPM loss. In theory, a violent enough wind shear (or series of them) could put the rotor into non-recoverable, low RPM flap. This is an area where I'd like to see some numerical research... but we're talking about violent turbulence, enough to put any small aircraft in peril.

Low/zero G does not automatically induce "bunting" (hate that expression; it creates a mystery where none need be). Pitchover does not involve the rotor at all; it's caused by engine thrust or torque, or by the aerodynamics of the fuselage at higher airspeeds.

Obviously, the latter cause isn't a problem at zero airspeed. The HS and the draggy windshield, wheels or whatever both lose their force at the same rate as you slow down.

In contrast, the engine doesn't lose thrust or torque as you slow down. However, if the craft is CLT, then there's no engine-derived pitching moment to worry about at any airspeed. If the craft is HTL, then there IS a nose-down moment at zero airspeed. The logical way to counter this moment is with an immersed HS. If the HS receives slipstream air from the prop, then the HS's airspeed ISN'T zero, even if the gyro is standing still. The HS therefore continues to do its work at low airspeed, preventing pitchover.

Ditto in the roll axis. An immersed HS and/or an immersed tall tail can provide the moment needed to counter engine torque. These items will work even at zero aircraft airspeed, thanks to the prop blast.

Buntover is not a necessary concomitant of low/zero G. Low/zero G simply allows a design flaw (one that's always there, but normally masked by the rotor) to reveal itself. Fix the flaw, and pitchover is no longer an issue. RRPM is still an issue in strong turbulence.

[Brad_King]

Just yesterday, i found myself in an unnerving situation.[ well, it was unnerving 4 hours later when i was thinkn bout it.]
When i was turning tight in me 'new' ferel, i noticed the rotorhead was obsquering my vision of wot i was lookn at on the ground. This is nuthn new, but my headset/helmet is, and coz im ruged up like an eskymo and its a full face helmet, my neck movement is restricted and i have to 'lean out' of the seat in order to keep an eye on the critter. IOW, when the machine exceeds a 90* bank, i have to lean up[ like ona bike] in order to see the target.
As i sad, its nuthn new, but this occasion i happened to fly into a strong sink, and nearly fell out. But it was coz of the pitch control i still had in the 0g situation[ and full 912s power] i didn't loose control.


Man,what an interesting life the SCG has. Birdy you probably see more "unnerving" situations in a week than most pilots will see in a lifetime.:eek:

My hat's off to you sir.

Brad King
N6372K
Mad Max II LTC

[Aussie_Paul]

Thank you Paul, My wife is diabetic and she uses a needle, but what is the refrence to lumber? Is HTLMs a different kind of disease? What is cheek?

Thank you, Vance

Brian fly’s a High Thrust Line Machine (HTLM). The 4 X 2 lumber is to bash me around the ears for my stance on stable machines.:eek: He reckons maybe I have something else in the syringe!!!:rolleyes:

Any time I make reference to stable machines like I did in post #13 they give me cheek as in a cheeky, disrespectfull kid!!!:p

There are quite a few Aussies who still think the pilot is the main stability provider in a gyro. They have not flown or flown in a truly a stable gyroplane yet.

I hope that I got around all of that for you Vance. :confused:

Vance, I have been an Insulin dependant Diabetic for over 36 years and my endocrinologist, whom I see 4 times a year to keep me flying, says I am in the best shape he has ever seen for Diabetic on Insulin for that many years. This I guess is due to my commitment to control and also some luck. The same commitment I have to safer gyroplanes and good training!!!!:D

Aussie Paul. :)

[Vance]

Thank you Paul and congratulations on controling you Diabeties.

Thank you, Vance

[Udi]

...2000fpm down [ or up] drafts are not theoretical, wether its caused by thermal activity or mechanical disturbance...
I never said they are theoretical Birdy, I said they are rare. Many people have flown thru them. However - 2000 fpm up or down drafts will get your attention reall quick - even if you are Birdy :) And they may be the door to the next world if you are flying an unstable machine and lack the experience to handle it.

Udi

[birdy]

Just a tip Vance;;)
I'v found with all side by side machines that if you flare to 0 or near 0 AS at touchdown the machine will all ways yaw to the side of the lightest person. The extra weight on one side of center, when the rotors are your breaks, will make it yaw if you have it at idle.
I saw a bloke landing his SH[ the only one i'v seen] and tho his touches were very neat and gentle, he'd always roll for bout 20', with the nose wheel in the air and rudder on full lock trying to stop the yaw caused by his weight being off center of the machine. If, for wot ever reason, [ like a lull in the head wind] that nose wheel touched the ground when it was pointing one way, and traveling another, it woulda been messy.
The symple solution is to keep a little power on for rudder authority, till you get a no roll landing sorted.
[ I didn't want to see the SH fall over, so i suggested to him to keep the rpm above bout 1500 for the rudder. to my supprise he listened to this SCG:rolleyes: and i could watch him fly again without holding me breath.]
And i think he was just as supprised I gave a sh!t.:D

We expect the gyro to "catch up" with any wind shears quickly enough to avoid catastrophic RRPM loss. In theory, a violent enough wind shear (or series of them) could put the rotor into non-recoverable, low RPM flap.

I probably shouldn't post this but I'd like your thoughts on this Doug.:confused:
Whenever i fly into a sustained and streghtening down draft, that'd have the rotors looseing too much RPM, I hit full power[ if i'm not already on it] and start a hard bank to feed sum Gs in to the system.
In my small mind, this dose 2 things ,it Keeps the RRPM up and seems to lessen the 'jolt' when you exit the downer, probably coz the disc isn't being hit with such a high AOA when the airflow civilises.
This is a little unnerving at the first time, but i think its saved me ass a few times.:p

[Vance]

Thank you for the tip David. I am a zero roll landing enthusiast myself.

I have never had to use full rudder on a landing, but I always had somebody in the right seat. I suspect that Terry is 100 pounds lighter than I am, but the rudder was only to correct for cross winds unless I flared too high and gave it throttle. Then it would pitch up and turn right.

Thank you, Vance

[Chopper Reid]

Brian fly’s a High Thrust Line Machine (HTLM). The 4 X 2 lumber is to bash me around the ears for my stance on stable machines.:eek: He reckons maybe I have something else in the syringe!!!:rolleyes:

Any time I make reference to stable machines like I did in post #13 they give me cheek as in a cheeky, disrespectfull kid!!!:p

There are quite a few Aussies who still think the pilot is the main stability provider in a gyro. They have not flown or flown in a truly a stable gyroplane yet.

I hope that I got around all of that for you Vance. :confused:

Vance, I have been an Insulin dependant Diabetic for over 36 years and my endocrinologist, whom I see 4 times a year to keep me flying, says I am in the best shape he has ever seen for Diabetic on Insulin for that many years. This I guess is due to my commitment to control and also some luck. The same commitment I have to safer gyroplanes and good training!!!!:D

Aussie Paul. :)


Thanks for giving the explanation although I wasnt refering to you being a diabetic, rather that your reply on stable gyros is the same every time !:D

Paul, I agree, a stable gyro is a good thing, particularly for those who have trouble flying ,doing only a few hours a year etc, I'm fortunate enough to feel very much at home and extremely safe in my gyro. I have had most stuff that weather can throw at anyone and never felt like the gyro was out of controll or that I wasnt in controll.

[Vance]

Thank you Brian,

That is why I asked. As colorful as colloquial speech is, it doesn’t work if everyone isn’t on the same page. Clearly Paul wasn’t on the same page and I don’t even have the book. Oops, that reference to a book is a colloquialism, it is speaking of a rulebook. Thank you for explaining your reference.

I find great value in accurate communication. It is exciting that we have people of so many backgrounds here, but sometimes it makes it a little harder to understand each other because we lack a common frame of reference.

To be sure I have it right, you’re saying that Paul should be hit with a large stick because he is like a scratched phonograph record that makes the needle skip and play the same part over and over.

In my experience that only exacerbates the challenge.

Thank you, Vance

[Aussie_Paul]

Thanks for giving the explanation although I wasnt refering to you being a diabetic, rather that your reply on stable gyros is the same every time !:D

Paul, I agree, a stable gyro is a good thing, particularly for those who have trouble flying ,doing only a few hours a year etc, I'm fortunate enough to feel very much at home and extremely safe in my gyro. I have had most stuff that weather can throw at anyone and never felt like the gyro was out of controll or that I wasnt in controll.

"Any time I make reference to stable machines like I did in post #13 they give me cheek as in a cheeky, disrespectfull kid!!!"

Brian, I rest my case!!:D

Ah ha, the stuck grammaphone needle repeating the same words. We have mp3 players now!!!!

Brian, I take that as a compliment, because it is working. Just look at how the gyro pics in the magazines, forums etc. have been changing over the last few years to stable designs. Thanks. Much appreciated.;)

Aussie Paul.:)

[Doug Riley]

Birdy, I asked the first gyro guy I ever met about this "zero G" stuff. He said he'd roll into a bank in response to it. If you're talking about a simple downdraft that creates a one-time change in AOA, the event is over before you can react to it. No need to bank and no time to, either.

But I think I know what you mean --a downer in which, as you punch deeper into it, the down-airspeed increases. This is NOT a single event, it's a gradient. In effect, it forces the gyro to do through a series of tiny down-accelerations.

Like the perfect storm, a certain combination of gradient and gyro airspeed will keep the gyro in low G longer than a simple downdraft. The gyro is trying to keep up with the down air, but the down air keeps speeding up and running away from the gyro. This leads to sustained low or zero AOA, which costs you rotor RRPM.

In true zero G with a teeter hinge, you can't bank because you have no rotor thrust left to create the bank. Conversely, if you CAN bank, you're not in zero G. I agree that you ought to bank while you still can. A downer that approaches a banked rotor is attacking it slantwise rather than squarely on top. This means that it will affect rotor AOA less.

My own tactic for dealing with rough stuff (I'm sure I haven't been in 2000 fpm vertical turbulence) in my old HTL unstable rig was to slow down to, at most, the airspeed that required the least engine RPM. Often I'd go even slower than that (e.g. 30 mph) and tolerate a gentle mush. The thinking was that (a) a low airspeed means the gyro passes through any gradients at a slower pace, allowing more time for RRPM to adjust and b) a lower power setting leaves less prop thrust to power a PPO.

Now, in the Dominator, I hold the stick firmly and don't power down. I do slow down to economy cruise, though.

I'm only joyriding, not working moo-cows. Your needs may differ!

[Ralph]

With respect to "sustained" events, once the aircraft has stabilized in the moving air mass, there are no further issues until it transiitions into still another air mass with different properties. Once "inside" a moving mass of air, the machine operates normally, whether the air is rising, falling, or moving laterally at any velocity, and that includes the ability to maneuver and maintain autorotation.

It is the transitions into or out of air masses with very different properties that pose a hazard, not "sustained" conditions. Of course relativity only goes so far. If you are flying in a mass of air headed for terra firma at -2000 fpm, you had better hope that you started high and that it won't take long to fly out of the cell! :=)

Ralph

[mceagle]

In true zero G with a teeter hinge, you can't bank because you have no rotor thrust left to create the bank. Conversely, if you CAN bank, you're not in zero G.Doug, I would have thought that the "air" would have to have been falling at the same speed as the Gyro (32ft/sec sq). In any case the air does not disappear, and until the rotors wind down to stalling point, there would still be full rotor control and still be enough rotor thrust to manoeuver the aircraft, within the boundries of the moment of momentum of the mass of the fuselarge. This is fairly evident after you land and come to a stand-still in calm air. The rotor can still be manoeuvered with the joystick for some time as it is winding down. I would imagine that the only time that total control would be lost would be in a vacuum with zero G.
I believe that such a critical down draft from above and behind (such as to loose total control) would be vary rare, and would be consistent with shocking weather conditions that no sane person would fly in anyhow.
I have personally experienced what I thought was zero G but in hindsight, it probably was not. It felt like an high speed elevator in a tall building when you hit the down button. Full control was maintained, even though the pitch control only changed the attitude, not the climb or descent.
This is a fairly common occurance with mustering pilots who operate low, and sometimes over less than friendly terrain. Many times there have been accidents avoided by the instant application of full power to accelerate out of the "downdraft" before hitting the deck. Interestingly, most of these mustering pilots fly HTL machines.
This is at odds with what Vance has been taught but if I struck the same situation again, I would hit full power again rather than settle into the trees.

[birdy]

True 0g in any aircraft is rare and generaly short lived.
Its usualy less than one, but not quite 0, or sometimes negative. In the sevier stuff, you'd spend more time in negative than 0g, but both are usualy very short term events. Mainly coz its askn alot for the machine AND the air to be going the same direction at the same speed for more than a second[ which is whats happening at 0g.] Either one will out run the other pretty soon.
But like Doug said, it the gradual and extended increase in downward airflow that causes the more dangerous rrpm decay, which gives the light stomach feel for a while, not an instant.
I'm not sure how long i'v gota be dropn for before i start to load the blades by banking, but i'd hazard a gess at bout 2 secs max.[thats 2 seconds of off the seat feeling before i recon i'm in trouble]. It don't seem long, but at the time, when your only starting from 100'/200', you gota make a desicive decision pretty quick. [ iow, bugger the critter, i'm in trouble.]
I don't belive rotors loose rpm as quick in 0g as one may assume,[ i can't be sure coz i don't have/watch the tac]. Not as fast as they do when you land anyway. Once you'v landed, theres no load on the disc, as in 0g, but its still pumping air. In 0g, its only pumping air as fast as its already flowing, so there'd be less drag than there would be when its pumping air faster, as it dose when you land.
IOW, rrpm decay is faster when you land than in 0g coz its still pumping air, and this means more drag, and its drag that slows them down.

In any case the air does not disappear, and until the rotors wind down to stalling point, there would still be full rotor control and still be enough rotor thrust to manoeuver the aircraft, within the boundries of the moment of momentum of the mass of the fuselarge.
Spoton Tim, and its coz of this limited time span before the rrpm slows to a point where cyclic responce is going to be inadiquate, why i usualy respond within a couple o secs after it starts dropn.

I can't be sure of the time frames of wot i posted above, coz its the sorta thing that happens instinctivly and instantly, but i know its wots happening coz i'm sitn init.

[Al_Hammer]

I think there is some misunderstanding of what happens to control at zero g.
As I understand it, the result of being in zero g is that the angle of attack goes to zero. The blades are not able to "pump air" , only ram into it edgewise as they continue to spin. There is no autorotation to feed power into the rotor so drag begins to take effect. There is zero lift at this point, which is easy enough to understand.

You can create local lift on one blade and decrease it (negative lift) on the other blade by moving the stick.

This is what normally tilts the rotor and it will still tilt the rotor in zero g.

But if you add a pound of lift on side and subtract a pound on the other side, the net lift is still zero. So what happens is there is a differential lift across the disc and the disc tilts, but the gyro does NOT bank.

To bank, the rotor must be lifting- it pulls the mast in the direction of the bank. The teetering rotor gyro does not bank by using torque.

In my Robby training, it was taught that if you encounter zero g, there will most likely be a right rolling tendency from tail rotor thrust. Do not attempt to counter it with left stick because the rotor is not making thrust. The rotor will tilt, as I said above, and it will tilt left until it slams into the mast and most likely breaks it off.

The thing to do is to always give gentle aft stick first. this will reload the rotor system and then you can worry about the roll.

Incidently, there are Robinson factory instructors who demonstrate a power chop and without touching collective, they will slowly count to 10 and the rotor will maintain rpm. They only use back cyclic. And that's in a R22 that normally gives you less than 2 seconds until rotor stall if you do nothing.

I'm not minimizing the experience of seasoned pilots. If Birdy says he banks to reload the rotor, I believe it, but in true zero g, you ain't gonna bank until you've got SOME positive g re-established, or maybe you never got to zero g in the first place.

[birdy]

As i said Al, true 0g will only last a very shrot time in most cases, but, even at 0g you still have sum control.
Yes, at 0g,the blades are spinning in 'dead' air, and yes, the net lift[ on the machine] is still 0, but it will change the AOA of the disc, which will provide the lift/ reaction [on the machine].

The thing to do is to always give gentle aft stick first
I can only speak from experiances, but the first thing i do is let the stick drop back[ offset effect]. If its still dropn like a brick and i still can't feel the seat, thats when i start the bankn thingy.

[Doug Riley]

Tim, there is such a thing as zero thrust. You're right that it won't actually happen at exactly zero rotor AOA in most rotors. We often over-simplify by leaning too hard on the fiction that the rotor is a "disk." This can lead to the inaccurate notion that zero DISK AOA is zero lift.

A rotor isn't really a disk, it's a couple of skinny fixed wings going round in a circle. They have the same qualities as any other wings. That is, they can be cambered or not, twisted or not, and have incidence or not. They can have negative, positve or zero AOA, depending on how the air is hitting them.

Every airfoil has a zero-lift angle of attack. Check your airfoil's lift curve to see what angle it is. For cambered foils such as the ones on most gyros, this zero lift AOA is around -2 deg. IOW, the camber itself contributes the equivalent of 2 deg. of incidence. Futhermore, most gyro blades have some built-in pitch (or incidence). However, if the flow is sufficiently "down from above," even cambered blades with positive pitch are going to hit their zero-lift AOA, or even a negative-lift AOA. This won't happen until our imaginary DISK's AOA is slightly negative. But no matter -- there's a disk angle that'll do it.

At that AOA, they aren't going to pump air. As Al says, they are just going to have drag and slow down.

And, yes, the doomsday downdraft that I was picturing must be going faster and faster as you penetrate it, so that, with your penetration rate, the vertical airspeed speed the gyro experiences is increasing at the same rate as the gyro's down-speed is increasing relative to earth -- 9.8 M/sec/sec. That's some gradient!

Birdy's right about how rare and momentary these conditions are likely to be. However, if you got stuck inside a violent storm, I imagine the chaotic turbulence might approximate this doomsday downdraft closely enough to get you in serious trouble.

[Ralph]

A falling column of air is not going to continuously accelerate as it gets closer to the ground. Any gas mixture has a huge drag component, relative to its mass, so gravitational forces result in a relatively low "terminal velocity". Normal air movements are a big heat engine driven far more by pressure differentials (typically caused by thermal displacements of air masses) than gravity.

A gyro, in level flight, that cores a downdraft moving at -2000 fpm will "fall" in the air mass until the speed of the gyro matches the downward air velocity, at which point the machine will be in level flight in full control at 1G. The air moves downward at 2000 fpm but that is only 33.3 fps! When the gyro has been in free-fall for 1 second, it will have a downward velocity vector of 32 fps - essentially that of the air and the problem is almost over! By the way, it will have lost only 16 feet of altitude* in that first second. Assuming that the machine is still trimmed for level flight, it will be descending at 33.3 fps relative to the real world (0 fps relative to the surrounding air) and it will not continue to accelerate.

If airflow is turbulent rather than smooth (including fun things like microbursts), then all bets are off in predicting what the machine will do - beyond the fact that the pilot probably won't like the answer!

*That is 16 feet relative to the air mass. You have to add another 33 feet for the movement of the air mass, so the absolute altitude loss in the first second is 16 + 33 or 49 feet. After that, altitude loss will be a steady 33 fps.

[Vance]

I believe I would be afraid.

Thank you, Vance

[Vance]

As I remember, we lost about 800 feet of altitude and lost about 50 rotor RPM. I found this intimidating. Gusting winds were below 15 KTS at the time. I am sure it was only a low G event and that is why I began wondering what worse looks like and what to do if it occurs. Steve cut the power and we stayed rotor up and lost a bout 20 miles per hour of indicated airspeed. I believe that like so many things, this event becomes bigger in the re-telling.

Thank you, Vance

[Doug Riley]

To elaborate on Ralph's comment, a given blob of falling air won't automatically be continually accelerating downward. Any object falling thorugh the atmosphere has a terminal velocity -- the speed at which its air drag matches its weight.

Nevertheless, circumstances in which it MIGHT accelerate include (1) it's just beginning to fall and hasn't yet reached its "personal" terminal speed and (2) it's falling into warmer, more humid, less dense surrounding air so that its negative buoyancy is getting MORE negative (IOW, its drag is DEcreasing).

I'm no meteorologist. We probably need one here. However, the latter hypothesis is really just the inverse of the case of an unstable thermal -- an anti-thermal, you might say.

All that aside, I think an aircraft is most likely to experience a downward acceleration that lasts more than a moment if the aircraft's FORWARD speed is taking it into a large downdraft that has a velocity gradient, with the highest velocity at some distance inside the draft.

[dragonflyerthom]

Now this is the type of info that a newbie like me needs. Great thread Guys

[dragonflyerthom]

Vance did you ever get the info you were looking for? I was wondering about how long in time and how wide these microburst last????


Thom

[Vance]

Yes Thom,

I am now confused on a higher level and I have a lot more information to be confused about.

For me, this is the best possible result for a question asked.

All aspects of autogiros fascinate me and my limited experience often causes me to draw conclusions in error.

I have trained with quite a few instructors and I try to reconcile what appear to be inconsistencies about theory and style.

My background and experience raise questions that are sometimes outside the discussions on this forum. People here have been very patient and helpful.

I am arrogant enough to be designing and building an autogiro and I am hoping to not put my test pilot friend at too great a risk.

I am working on my third complete redesign after having gone quite a way down the road in construction of the first two. This progress is based on my increased flight hours and the things I learn here.

Design is about priorities and resources and I am always trying to reconcile these with my limited experience, knowledge and vision.

I try to quantify things that are subjective for most people as part of my investigative process.

I find great inspiration on this forum and reasons to reach higher and further with my dreams. I feel it adds to the quality of my autogiro adventure.

Thank you, Vance

PS. Thom, are you an accountant?

[dragonflyerthom]

Yes. This is a very slow time for me. I started using the gyro to have something to do and to fulfil a dream that I had of owning my own. It really has been an adventure. The misconceptions that I had at the beginning has further had an effect on my own ideas. I had an idea that I could make a gyro hover..I still think I can but the aerodynamics of the idea has really made me step back and reevaluate the whole concept. Ga6iel in Oz is a person that I really want to sit down with and pick his brain. He seems to understand the concepts I want to explore. Too bad he is sooo far away. And I think I have some propietary ideas that i won't discuss on the forum.

Thom

[Vance]

Hello Thom, I am puzzled. I spend a lot of time with my accountant analyzing the first two quarters towards the end of July and strategizing for the next two quarters. I am impressed you have free time. What sort of accounting is the focus of your practice?

Do you find your skill with numbers helps to quantify your gyroplane experience?

Why do you want to hover?

How do you define hover?

Why don’t you want to use a helicopter to hover?

Thank you, Vance

[dragonflyerthom]

Hello Thom, I am puzzled. I spend a lot of time with my accountant analyzing the first two quarters towards the end of July and strategizing for the next two quarters. I am impressed you have free time. What sort of accounting is the focus of your practice?

Do you find your skill with numbers helps to quantify your gyroplane experience?

Why do you want to hover?

How do you define hover?

Why don’t you want to use a helicopter to hover?

Thank you, Vance



Zero airspeed and maintaining altitude. I will have the effeciency of a gyro and the hovering ability of a heli


I specialize in tax accounting. I am very busy from jan to april and moderately busy from may to dec.

I guess you could call me a workaholic. I have 18 horses that i take care of also. that could be a 24/7 job in it self. I have a 40 acre ranch that I keep my horses.

My inquiring mind just won't let me sit still.
I am 59 this year June and I have learned that if I stagnate my health goes down. I weigh 198 lbs that is down from 265 3 years ago when I began my quest to lose weight. I am writing a book also of health related issues.
This is just a few of my interests



Thom

[Vance]

Zero airspeed and maintaining altitude. I will have the effeciency of a gyro and the hovering ability of a heli

I guess you could call me a workaholic. I have 18 horses that i take care of also. that could be a 24/7 job in it self. I have a 40 acre ranch that I keep my horses.

My inquiring mind just won't let me sit still.
I am 59 this year June and I have learned that if I stagnate my health goes down. I weigh 198 lbs that is down from 265 3 years ago when I began my quest to lose weight. I am writing a book also of health related issues.
This is just a few of my interests

Thom

Hello Thom,

What is “the efficiency of a gyroplane”?

I have shoveled more than my share of horse maintenance.

I too have weight challenges. It is very frustrating to redesign a complex part to save a pound and then to try to imagine the value of the weight savings on performance. It is exciting with the FAA normal 180-pound pilot, but when I plug in the 200+pound old fat pilot the performance improvement is muted. I eat when I am upset or frustrated, so you can see the circular nature of the challenge.

Thank you, Vance

[dragonflyerthom]

It basicly no power to the rotor. I believe I can maintain that and power the rotor temp. then return to the autogiro there by maintaining it efficiency. This will have to be done with the torq of the rotor in mind. See this is where the propietary ideas will come in.
Can I give you a clue as to the weight thing. Start looking at the labels of the prepared foods and drinks you use.

Farmers have used corn and corn by products to fatten up the calves. Dog food mfgs use it as filler to add fattening ingredients and tell you it is balanced. Corn Syrup is cheaper than sugar so the Soda Mfg use it to sweeten their beverages. Just by watching these thing you will lose weight. You see Vance The human body doesn't know what to do with corn or corn syrup so it stores it(weight gain) until it needs it(it never does). Oh by the way there is fungi in the corn and corn syrup. You know about fungi don't you. If not there is a direct corrilation between fungus and cancer.
This is just a little heads up from my book.

Thom

[Vance]

Hello Thom,

It is my understanding that power to the rotor mechanically is more efficient and wind powering the rotor is less efficient, so you can see why I am confused.

Autogiros seem to me to be particularly inefficient. They are not fast and they use a lot of horsepower for each pound lifted. Speed also seems consumptive of power in an autogiro.

Fortunately, efficiency is not the primary allure of gyroplanes for me.

I love how they fly.

I love how an engine-out is managed in an autogiro, especially compared to a helicopter.

Autogiros seem both magical and comical to me.

I enjoy the mechanical simplicity of an autogiro. Compared to a helicopter there are less things to go wrong. This is important to me if I am going to do my own maintenance. A Helicopter appears to have a lot of critical systems.

My helicopter instructors kept referring to non recoverable events.

There is great focus on the height velocity curve and this limits the value of hovering on most of my missions.

What is the allure of the hover for you?

Thank you, Vance

[Al_Hammer]

Vance,
would you agree with this overview of the situation?
The gyro has propeller losses, while the helicopter has transmission and tail rotor losses. Lets call it a wash. The gyro rotor works in autorotation and the angle of attack distribution tends to make it potentially more efficient than the helicopter rotor in cruise.
Gyros can attain higher cruise speeds without the same concern for retreating blade stall.
The induced drag is high, but adding partial power to the rotor can help.
That allows the gyro rotor to fly at a flatter angle for the same lift.

Add too much power and you need anti-torque compensation and you're adding back in those helicopter losses.
A jump takeoff or hover mechanism can only decrease efficiency.

A streamlined enclosure probably counts for a lot as speed increases, since drag increases as the square of airspeed. An open frame machine will not do well in the efficiency department.

I don't recall the figures for the DeBird (partially powered), but I think it has a decent cruise speed and doesn't use much gas. The sweet spot is something like 15 hp to the rotor.

[Vance]

Yes Al, I agree completely.

I think it would be great fun to design a high-speed power efficient autogiro.

We could call it the “Oxymoron Autogiro” we could christen it just about the time one of those VW powered fixed wing things passed us going 200 miles per hour. Worse still would be one of the Continental powered racing biplanes.

I love autogiros for what they are and I think it is wonderful when someone tries to expand the flight envelope.

Juan De La Cierva presented all the calculations for a 200 mile per hour autogiro without resorting to wings unloading the rotor. I would like to see that. The power required wasn’t that much greater than the airplanes of the era that were capable of 200 mile per hour flight and much less than a 200 mile per hour helicopter of today.

I do not understand the allure of hover. I am hoping someone will help me to understand.

I find rolling out to the runway in an autogiro so much nicer than a hover taxi to the runway in a helicopter with skids.

Thank you, Vance

[dragonflyerthom]

Vance

I am going to the lake now. I will get back to you on the hover concept. I do agree with Al. Have a great weekend. I will be on the lake until the 30th but will be checking back from time to time.



Thom

[Passin' Thru]

Al Hammer sez:

“The gyro rotor works in autorotation and the angle of attack distribution tends to make it potentially more efficient than the helicopter rotor in cruise.
Gyros can attain higher cruise speeds without the same concern for retreating blade stall.
The induced drag is high, but adding partial power to the rotor can help.
That allows the gyro rotor to fly at a flatter angle for the same lift.”

Amazing to me, even a little power added to the rotor helps a lot!

Way back when Dr. Bensen developed and tried marketing a “zip drive” for rotors that used a small 2-stroke motor with an infinitely variable ratio transmission mounted to the rotor head. (Don’t confuse this with the little “put-put” prerotator)
I had the privilege of borrowing one for a couple of weeks to play with, and in spite of some shortcomings, this thing showed tremendous potential! Although it was only 2 -2 1/2 horsepower, it maintained enough torque to the rotor I had to reverse the trim tab on my rudder for the P factor to compensate for the rotor torque. With my open frame gyro, the top speed was maybe 10 – 15 MPH higher, (the drag catches up rather quickly!) but the most noticeable thing was my normal cruise speed of about 60 MPH could be maintained at considerably lower throttle on the “mighty Mac”.

Also of interest was the manner in which the centrifugal “governor” advanced the drive ratio proportional to the rotor speed during pre-rotation and initial spin up. The drive ratio started at its lowest and advanced as the rotor speed increased, maintaining about the same load on the “little screamer” at all times. Once the rotor reached about 120 RPM, which was rather quickly, I do not believe you could flap the rotor. You just brought the stick fully back and smoothly moved to full throttle. The added torque accelerated the rotor very quickly. Almost immediately the machine rocked back. A bit of forward stick and you were flying!

Apparently the little device never caught on in the gyro market. Perhaps in part due to the fickleness of the little screamer. You could never start the thing after starting the Mac. It seems the vibration excited the little pumper carb and invariably flooded it. If you started it first, then you had to hand prop the Mac under a turning rotor. I was always very uncomfortable with that! Although it did wonders for the flight efficiency of the gyro, that constant screaming right over your head became a bit nerve wracking. In spite of the motor problems, I believe the infinitely variable ratio rotor drive is a ripe field for examination. Not to second guess the good man, but I suspect this is the direction Larry Neal is moving with his “Metro Launch System”.

During one of the gasoline crunches Bensen tried to market a variation of the “Zip Drive” as a bicycle drive. It worked well in that application.

[Al_Hammer]

We could call it the “Oxymoron Autogiro” we could christen it just about the time one of those VW powered fixed wing things passed us going 200 miles per hour.
Hey Vance, you floored me with that one! Very funny and it puts the talk of gyro efficiency in proper perspective.

Passin' Thru:

Thanks for that tidbit on Bensen's device. We tend to take for granted all the work that went before.

[Vance]

Thank you Al,

I have been trying to learn humor from you, Jim, Chuck and Ken. I am glad you feel that I am making progress.

It seemed disrespectful to you and Thom, but I thought I would try anyway. I am not sure that Thom got it. Thom, I am truly interested in your attraction to hovering.

I suffer from this very thing. I want to compromise what an autogiro is to make it something it is not and cannot be. It is very easy for me to forget the point and run amuck with big horsepower, slick aerodynamics and cross country capability. Some of this is good, but I always go too far.

My rotor head is just silly and building a rotor test stand to learn things that I already know seems counterproductive. I am getting answers that don’t have questions. It is not hard to improve the numbers, but the value is questionable.

My funding interruption makes things move slowly and my friends feel I have lost my drive. I think it moves me closer to art. I think that my direct drive pusher is getting closer to the essence of gyroplane passion. It is the third major redesign and my first pusher. Its engine compromises it, but I can’t help myself.

Thank you, Vance