gyro weight vs fun?

[13brv3]

Greetings,

In my reading here, I've seen statements such as "lighter is better", and heard heavier gyros called "pigs". The overall point seems to suggest that a lighter gyro will be more fun to fly.

The more I think about this, the more it doesn't completely make sense to me. I can easily see that adding 100 lbs to an existing gyro, without changing the rotor size, and adding more power would make it a pig. However, if you compensate for the weight with the proper size rotor, and additional power, wouldn't it be just as fun to fly? What am I missing?

Here's my specific dilemma. I "want" a gyro, for fun, local area flying. I "need" an aircraft to test a single rotor Mazda engine, which is about 220 lbs installed, and 100+ HP. My goal is to find a gyro that will allow me to use the single rotor engine, but if that's going to make it a pig to fly, then I won't be happy with it.

I'm almost certainly going to end up with a Dominator. If I didn't have the desire to test the single rotor engine, then the choice would be easy- an Ultrawhite, with a 503, or maybe 582. That combination is well known as a safe, fun aircraft to fly.

If I use the heavier, and more powerful single rotor engine, along with Ernie's recommended rotor size, will it still be fun to fly? I have to believe so, but since I'm new to all this, I figured I should ask.

Thanks,
Rusty

[gyroplanes]

I'm not an aeronautical engineer or master of physics, but the same rule applies to cars, motorcycles or boats as well. A loaded Great Lakes ore ship takes 20 minutes to stop. A lightweight Ford Mustang will out accelerate and out brake a Lincoln with the same engine.

[Timchick]

Rusty,
My suggestion since you are new to gyros is to go with the Dominator, fly it for awhile and then decide if you want to do something else that's bigger and has more power. Fly a proven design to get your feet wet.

[scottessex]

With the engine at 220 lbs, that is alot of wieght for a single seat machine,
My engine weighs just a hair over 100lbs and is 65hp.
A 100 hp rotax 912 weighs 138 lbs. unless you weigh about 140, the 220 lb engine is just alot of extra weight to drag around.
More weight requires more HP.

A light weight machine WILL perform better than a heavy one, this has always been true in aviation.

They even try to save weight on airliners, beleive it or not.

[13brv3]

Tom,

Your Mustang vs Lincoln example is like what I said about adding 100 lbs to a gyro without changing anything else. That will certainly be a problem. Now if you gave the heavier Lincoln more power, wider tires, and bigger brakes, it could certainly accelerate and stop as well as the mustang.

Tim,

The thought of starting with an existing, tested Ultrawhite is appealing, but isn't really my first choice. If anything, testing the single rotor engine is a higher priority, so if I can't use a gyro for the engine, then I'll just have to put the gyro off until I'm done with the engine testing.

One of the things that makes me interested in the Dominator is that it has already been flown with the heavier, and more powerful Subaru type engines. In that respect, it is already a proven concept.

Scott,

When I give an "installed" engine weight, I mean for everything related to the engine. I weighed a 912S with it's cooler, oil tank, hoses, mount, etc, and it came to 159 lbs minus oil.

If everything goes as planned on the single rotor engine, I expect it's total installed weight to be well under 200 lbs, perhaps as low as 180. Power can be as high as 160+ HP with a turbo, and it won't even change the weight because the turbo can act as a muffler. Obviously, I won't be turbocharging the Dominator.

I've also always heard that lighter is better, but in the fixed wing world, this meant comparing two similar planes that don't weigh the same. For example, If you compare a light RV-8 (O-360, basic day VFR panel) with one that has a big block V8, and an IFR panel, there might be a couple hundred pounds difference in weight. This will make a noticeable difference in handling, but I suspect that much of that is due to the fact that the wing loading is higher.

Gyros have the ability to easily compensate for the rotor loading, so more weight does not have to mean higher loading. If the rotor loading is kept the same for the higher weight machine, and enough power is added to compensate for the higher weight in climb, why wouldn't the heavier gyro perform as well? I'm not saying it will. I'm just saying that I don't understand why it wouldn't.

Rusty

[Ga6riel]

perhaps this is an answer you can appreciate
While lighter is undoubtably better there are limits to that synopsis.
Perhaps what you are looking at is a variation of scale
where for instance you might compare a single seat machine with a rotor diameter of 23ft, to a dual seat version with a rotor diameter of 27ft. You could...and perhaps should see this variation as a scale factor.

Now it is well known that within the vast kitplane market there are numerous 50% 66% 75% etc scale fighter aircraft. In true scale representation, ie the ailerons and areas are exactly to scale; such aircraft are quite unecessarily touchy too control, far beyond that of the fighter they represent........sound familiar?

What it comes down to is this, while you can scale an aircraft design up or down within practical limits, while dimensionaly an aircraft may be twice that of another, say a rotor of 23ft becomes 46ft, the area is 414 sq ft compared with 1662 sq ft. Now at the same disc loading you can see that things are becoming a tad loose. Where @ .75Lbs sq ft we get 550lbs vs 1246lbs. So while dimensionaly machine B is twice the size it supports 2.25 x the weight at that loading. In reality we would expect and can get better weight performance, it would be to the power of 3.

scale factors
area ^2
volume. mass. force ^3
moments ^4
inertias ^5

These conflicting values provide quite different properties between the machine sizes we can create. And the implications of this collision of factors means the smaller machine is quicker in response and exhibits more lively performance.
I hope that helps...

[Mike Schallmann]

I fly a single seat gyro with an empty weight of 430# and an all up weight of approx 740 # . It is powered by an EA81 putting out an honest 100HP-- I have several friends that have Rotax powered Air Commands with 582's I can literally fly circles around them --on rate of climb they may edge me out slightly but in overall speed I'm a lot faster. They can also fly a little slower than me but I I can turn just as quickly, land just as short -and take off in the same distance and to boot I burn less fuel--at the PRA convention at Waxahachie Tx a few years ago I did pretty good in the speed run --one thing I can do that they cant -- I can fully fuel up and cruise at 75 mph for well over four hours -- realistically the most I have flown is 250 miles as that leaves me with a good reserve of fuel. I suppose a 914 on a similiar gyro would outperform me -but at a cost of $14K its not worth it to me --my Soob complete with redrive ,radiator fluids and prop weighs 205# and it only cost me $3K to build -- my whole gyro cost less than $6K ready to fly --

[Brian Jackson]

Interesting post, Rob.

I remember in my early days as a kid dreaming of the possibility of "scaling up" a balsa wood model to carry a pilot. I think most of us have at least pondered the possibility at a young age. I, on the other hand, actually started doing it until I realized that a doubling in scale involves cubing the volumes (a factor of 8), but then since you can't scale air, things like reynolds numbers throw an added, non-analogous complication into the equation.

After studying this forum and the various resources that get linked to from time to time, I'm starting to understand how even with added power as compensation, you're still dealing with a heavier mass with much greater inertia/kinetic energy, which takes more time to maneuver, even if power was scaled by the cube rule. EDIT: The engine is still only providing forward thrust, not directional control.

Perhaps I'm wrong, but a layman's observation of watching the flight paths of a bumblebee vs. a house fly got me thinking about this subject. It's a poor comparison because I don't know how much energy is exerted by each to fly, but I assume neither expends more than is needed, as conservation of energy is a fundamental criteria of all living things.

But assuming the bumblebee is 8 times heavier than the fly, and expends 8 times the energy in flight, you'd think they would be both equally maneuverable. But in that observation I could see that the fly was able to literally "turn on a dime" and reverse direction almost on a sharp point. The bumblebee needed more time to change direction, flying in a more S-curve path, unlike the fly's almost "Z-curve" path. EDIT: They can both fly about the same speed in straight & level flight.

Like I said, this is a poor analogy/comparison, but it made me wonder if the simple act of changing course at a given velocity requires greater force than simply "scaling up" the static thrust. I'm sure Chuck Beaty (my physics hero:-) could explain this, but nonetheless it's what got me thinking about the topic.

Another thing I noticed while driving to work one morning was braking distance vs. force felt against my seatbelt. I'd always thought that acceleration & deceleration was on a linear scale until I realized that that last few feet of braking from 10 MPH to zero "felt the same" against my chest strap as the initial brake from 60 MPH to around 10 MPH over the same length of time. Then it hit me that, I'll bet either the velocity or the distance is squared.

I'm not sure mathematically how these two observations correlate, but it'd be interesting to hear from Chuck and others. After all, we're all here on this forum to learn. It's a wonderful teaching tool for those willing to pay attention and remain "teachable."

Rusty, I'll be eagerly following this thread. Thanks for posting!

Respectfully,
Brian Jackson

[Harry_S.]

I can't see why a weekend gyro flyer would want a machine that would make 100 mph?!

If you want a single seat machine that is not a speed demon but is probably the *spriteliest*...is that a good word...flyer out there, try a bare bones BENSEN B8 style with a MAC 90 on it. You want fun flyin'...you got it.;)


Cheers :)

[13brv3]

Rob,

All good point along the concept of "scale". Much of this falls into the category of non-obvious (to me anyway) variables. I knew that inertia would factor into it for maneuverability, but just don't have a good feel for what effect it will have.

When looking at this as a matter of scaling up or down, I guess it would be reasonable to say that the closer you stay to the proven size, the more like the original it should behave. If that's true, than I'm probably worrying about nothing, since the Dominator is already known to work well with an EA-81/redrive combo (200+lbs total?), as well as a 914 (guessing 175-180 lbs total).

In thinking about this some more, I'd bet there are folks flying at nearly the same weight when you count pilot + engine. I'm 6'1" and 190 lbs, which is not light, but also not heavy. I'm sure there are folks with 50+ lbs on me that are flying these things. Heck, I need an incintive to lose about 10 lbs too :p


Mike,

Thanks for the comments. I've now realized that I might have been better off asking direct questions about performance that folks were getting with heavier engines. Hopefully, your results are typical.

What size fuel tank do you have in your gyro?

Brian,

I'm glad you find this interesting. I have an almost uncontrollable need to understand how things really work, and sometimes I ask too many questions. Often the result is irritating people, rather than entertaining them :D

Cheers,
Rust (should be working on my RV-8)

[Ga6riel]

Brian
the bumblebee and the fly isnt a good analogy because it has been discovered, after some years of research...that the bee flys via the lift created due to vortex its wing motion creates..prior to this finding this was not properly understood, because by the numbers a bee just couldnt fly. Nature lovers used to taunt both scientists and engineers with that fact with their lack of knowledge over the mysteries of mother nature.....

As for the brakes, the physics of it has the change of motion as an acceleration (yes even when stopping) thought of in this way, the power (if u like HP) of the brakes is more or less the same, hence the acceleration is similar. What does change is the distance required to stop or avoid, and this is by no means a linear scale, just a few miles per hour over the limit will see you braking to a stop in a much greater distance.

[Brian Jackson]

Rob, good point. I knew that was a bad analogy and, on a humorous note, remember how the "Perpetual Motion" advocates taunted science about why the bunblebee couldn't fly. Makes me wonder if Martin Hollmann (http://www.aircraftdesigns.com) didn't have a tongue-in-cheek joke in there with his BumbleBee (http://www.aircraftdesigns.com/gyroplanes.html) design!

Thanks for the braking comment. I knew I wasn't nuts for sensing the same G-force in those last few feet coming to a stop versus that pervious equal-length duration of going from 60 MPH to 10. But now I'm curious... Since the energy is expelled from friction brakes as heat, is more heat energy generated in those last few feet (10 seconds) of braking than the previous 10 seconds of equal force? In other words, does it take the same amount of energy to cut your velocity by half regardless of speed?

I ask because I'm trying to envision the particles of a wheel rotor & brake pad sliding over each other. The higher the speed the less time each has to interact with the other at a given point, which makes sense. But when you add up all these atoms in the shape of a brake pad, the only thing that makes sense is "time under applied force."

I did some research today and found the following formula:
9.8 m/s/s (gravity acceleration is 9.8 meters per second per second). It IS a square!
which makes sense now because of the seat belt observation. Since gravity affects static or moving mass equally, (hence NASA's "slingshot around a planet or moon" approach to conserving energy with space probes making turns,) it would stand to reason there's a point of equilibrium regardless of mass. In this case we're talking about a heavy Gyro. But equilibrium points also exist in space... e.g., geostationary communication satellites. They "hang" at a constant point above Earth because their exact altitude creates equal centrifugal and centripetal forces. It's a balance of gravity pulling them in vs. the force on a string of spinning a weight around.

Sorry for the tangent thougt, but in regards to the friction/heat thing during braking... heat is defined as the "vibration of molecules," which all matter exhibits, expressed as temperature. I can also understnd how friction (motion under force) can vibrate molecules to produce heat that then contact air molecules to distribute this heat. But I don't understand how t...

Oh wait... I think I have a way for everyone reading this to try this out.

OK. Put your hands together in a "praying" position. Now apply a couple of pounds of force between them, like holding a package of bacon (or Tofu, for the new-agers & metrosexuals). Without changing force between your palms rub them back & forth. Now do the same at higher reciprocal speed. Notice a sharp increase in temperature?

So I guess I answered part of my own question... sorry, just kinda thinking out loud. But physics is sort of the study of where energy goes over time, and we're discussing Gyro maneuverability (change of direction over time) it seemed appropriate. I can only surmise that, of a gyro's rotor & tail surfaces are the sole force in maneuverability, (plus the arms & legs of the pilot), when you add the temperature increases all up), the energy is equal for its mass.

Am I crazy then to assume (disregarding max tensile strengths) that a higher weight gyro, all things being equal, would require more muscle strength for the same control ratios?

Ya know... I'm really starting to show my "nerd" tendencies... Let's start a Football thread!

Cheerleaders, (oops, I meant "Cheers")
Brian

[Al_Hammer]

A fly ,as Brian pointed out, does seem to maneuver faster than a bumblebee, and yet they both use their wings to manipulate vortices and both have reynolds numbers in the same range.

I believe this is the same thing that is happening at a larger scale when we compare an utralight gyro with a member of the heavy iron species.

The lighter machine just seems to maneuver faster. Even though you can put a proportionallly larger engine on the big machine, it still isn't as agile.

The reason may have to do with what as known in the model world as k factor and dynamic similitude speed, DSS.
The acceleration of gravity does not change with scale factor.

http://www.scaleaero.com/maneuver_realism_speed2.htm

[WHY]

Hsey Russell

Consider converting a rag and tube hombuilt aircraft frame to a tractor ,this could be a natural ?

Tony

[WHY]

Russell

Don Adamson has a great potential for such a project, it is a Stits Playboy fuselage ready for recover and a engine, company is 92nd West Aviation in Lonoke, Arkansas it is advertised on Barnstormers, for $1500. He is in the aviation salvage business, nice guy, I have done business with him before.

Tony

[13brv3]

Thanks for the comments Tony. I had given some thought to doing something like that, but as a gyro newbie, I think that's a bit out of my league. I'd better stick with a proven design.

I do like the idea of a tractor gyro, but the pickin's are mighty slim. At the moment, all I know of is the Pitbull, and the Little Wing. What little I've heard of the Pitbull wasn't all that positive, and the Little wing would take too long to build unless a pre-welded fuselage was available, and they aren't taking orders for those at the moment.

Of course if my Kolb doesn't sell, I'll be continuing to use it as a single rotor test aircraft, and will have to wait on the gyro. I'll find out the answer to that question in a couple more hours.

Rusty (bid high)

[Mike Schallmann]

I had a 8 gal seat tank and two 3.5 gal saddle tanks for a total of 15 gals --at cruise I burn about 3.25 GPH --so I could get about 4+ hrs . Ive changed to a single 12 gal tank --but I still have the option of adding the saddle tanks for a total of 19 gals -- good cruise lenght --but I dont think my bladder would hold out--

[GyroRon]

Rusty, you can ask and recieve a zillion answers to your questions. Just keep in mind that most gyro people have only flown one or two machines, certainly not alot of different machines to get a idea of how one will fly over the other.

Myself, I have been lucky enough to fly ALOT of different gyros. I have flown alot of pusher gyros and so far none flys better than the Dominator. There are others that fly very good and are close to as good as the Dominator, but for overall blend of everything just working like it should, a Dominator is hard to beat.

Now as far as Dominators, I have flown the following types.

5 different single places with Rotax 532/582 engines and Pods.

1 Single place with Rotax 618 engine and pod.

3 Different single places with Rotax 503 and no pod ( commonly called a UltraWhite )

1 Single place with a AMW 3 cylinder 100 horsepower two stroke and a pod

2 different Single places with Subaru EA-81 engines with reduction drives and pods

1 Single place with a Rotax 912S and a Pod

1 two place with a Sub4 subaru conversion and a pod

And for some but not all of the other makes of gyros I have flown...

1 Pitbull Tractor gyro with Subaru EA-81 with reduction drive

1 Little wing clone with VW with Reduction drive

2 Different gyros based on the " Falcon " design, both with Direct Drive Subaru ea-81's

Single place MadMax with Subaru EJ-22 and reduction drive

highly modified Bensen with Cont 75 horse engine

KB-2 with drive drive VW

Bensen B-8 with Mac engine

RFI-150 tandem two place with Subaru EJ-22 and reduction

Aircommand single place with pod and 582

Aircommand single place without pod and 582

Aircommand single place with pod and Rotax 618

Aircommand single place without pod and Rotax 447

Aircommand Side by Side two place with Subaru EA-81 with reduction

Aircommand Tandem trainer with Hirth 110 horsepower F-30

3 Gyrobees with Rotax 447, 1 Gyrobee with 503 Rotax, 1 Gyrobee with 60 hp MZ-202

Soma single place with Hirth 65 hp 2706

J-2 certified gyro

RAF 2000 - two of them -

Mazda powered Parsons trainer


Anyway, my point is I have flown alot of gyros and have a fair amount of experience. Lighter gyros fly better, alot better, than heavy gyros.

My advise to you is to build the Dominator and keep it as light as possible and personally I would not put the Mazda on it until after you have become a accomplished gyro pilot. The best thing you could do is to buy a Dominator " Ultrawhite " ( there is one posted for sale here by Doug Riley for 9 grand used ) and get gyro lessons and fly it for a few months and once you got the hours, pull the Rotax off and sell it and then redo the engine mount for your Mazda if you are dead set on the Rotary engine.

[WHY]

Rusty

am very interested in the single rotor rotary (Mazda?). how did you come about this engine, build it or buy it. Would someday like to have a rotary on my gyro.

Tony

[WHY]

Rusty

Also what type of re-drive does the engine have or does it have one yet.

Tony

[13brv3]

My advise to you is to build the Dominator and keep it as light as possible and personally I would not put the Mazda on it until after you have become a accomplished gyro pilot. The best thing you could do is to buy a Dominator " Ultrawhite " ( there is one posted for sale here by Doug Riley for 9 grand used ) and get gyro lessons and fly it for a few months and once you got the hours, pull the Rotax off and sell it and then redo the engine mount for your Mazda if you are dead set on the Rotary engine.

Hi Ron,

I do appreciate your reply, particularly considering the gyro experience you seem to have. However, As I mentioned before, the engine is the priority here, and if I can't put it on a gyro, then there will be no gyro in my immediate future.

Buying an Ultrawhite with a two stroke is simply not an option at this point, though I do agree that it would be the best option if the single rotor engine weren't involved. I have a two project rule, and the RV-8 is number one. The single rotor engine is number two.

Cheers,
Rusty

[13brv3]

Rusty

am very interested in the single rotor rotary (Mazda?). how did you come about this engine, build it or buy it. Would someday like to have a rotary on my gyro.

Tony

Tony,

Contact me offline about the engine.

Rusty (13brv3-at-Bellsouth.net)

[WHY]

Rusty

will do

Tony

[Mike Schallmann]

Ron
I have to disagree with you--a lighter gyro DOES NOT fly better than a heavy gyro --it quite simply flys differently. I havent flow the mix of gyros that you have but I have flown Bensons with Macs and Rotaxes, Dominators with Rotax and Hirths, a couple of RAF's and a Parson and several homebuilts. The only gyros that I felt that performed better were the ones that were that had sufficient horsepower for the weight and were stable by design--so IMHO HP and design are a better indicator of handling than weight alone---

[Udi]

...If I use the heavier, and more powerful single rotor engine, along with Ernie's recommended rotor size, will it still be fun to fly? I have to believe so, but since I'm new to all this, I figured I should ask.

Thanks,
Rusty
All gyros are fun to fly. Since you have no experience with a light gyro, a heavy gyro will be a blast for you to fly, providing it has enough power for the weight. If you are asking what the difference between 2 Dominators is - both having the exact same power to weight ratio but one is weighing 100 pounds more than the other, the answer is simple.

A heavier gyro needs a larger rotor. A larger rotor, due to its larger mass, responds slower than a lighter rotor of the same brand. The heavier Dominator will have a rotor that feels heavier and responds more slowly to your commands. Keep in mind, Rusty, any heavy gyro (of the modern types) is much more agile than a Cessna 172, for example.

Having said that, I haven’t flown an aircraft yet that I haven’t enjoyed flying. Every aircraft that takes you up to the sky and brings you back down safely is fun to fly. If your Mazda engine is going to be reliable - use it. You won't know the difference.

Udi

[GyroRon]

Rusty, Mike.... what Udi said in his last post sums it up pretty clearly.

The lighter the gyro is, the less the stick forces are needed to fly the thing.... Especially if your hotdogging. The Dominator ultrawhite is about 75 pounds lighter than my Dominator and just in that 75 pound reduction the lighter UW Dominator flys with significantly less forces needed to toss it around in the sky.

Yes compared to a Cessna 172, even the heaviest gyro we would call a pig, would out manever and feel sportier than the fixed wing.

A Dominator single place with a engine of equal power to the Subaru EA-81 with reduction drive ( 80 to 100 horsepower ) and simular weight ( 200 to 225 pounds ) should still result in a decent flying gyro as like I said I have flown two dominators set up this same way.

Now as for the suggestion I made to possibly buy the used Ultrawhite.... Look at these prices,

Rotorblades = 1700$

Pre rotator = 1200$

Seat tank = 300$

rotorhead = 700$

steel parts kit = 1500$

Dominator Tall tail = 950$

instrument pod with instruments = 500-700$

prop = 500-700$

Airframe = 1500$

total 9250$ and this does not include a engine. Unless you build the dominator completely from plans you will spend at least this much to build your dominator.... and even then you will only save a small amount over this total. My advise is to buy the one Dougs student is selling as it is already put together and flying and for less than you can build a new one for. you can buy it for less than you can build it for, the take your gyro lessons and fly it as is for a few hours to get comfortable with gyros then sell the engine.

you mentioned "two stroke is simply not an option at this point" Well I hope that is not because you think it is a bad engine. A rotax 503 is about the best engine you could find for any light aircraft. At any rate, this Rotax is worth 2500-3500 USED!!! so buy Dougs students machine for less than what is costs in parts to build a new one and SELL THE 2 STOKE... and you have a completed airframe ready for your project engine for several thousand less than you can just buy the parts to build one for. It does not take a very smart person to see this is a good deal.

I advise you to build your rotary engine and run it on a test stand and monkey around with it till you know it is ready to fly and THEN put it on the gyro. At that time you can sell off the Rotax 503 and put a few grand in your pocket.

I am still trying to understand why you want a gyro to begin with. Do you just want a flying machine that takes well to adding any ole kind of engine? Or do you want a gyro because you simply want to fly a gyro?

[Mike Schallmann]

I pulled my reciepts together and here is what my gyro cost to build. Remember I machined most all of the parts myself .About the only major parts I didnt make were the rotorblades ,seat tank and the prop -I literally made everything else myself - from off the shelf parts or from raw stock.Some of the items listed below were bought used and are identified by an (*)- but to me that is part of the fun of this adventure--The price of the engine /redrive includes a ZERO time rebuild---

Rotorblades * $1200
Engine/redrive * $2850
Seat Tank * $125
Rotorhead $150
Steel parts $75
Aluminum Sheet $240
Prop $450
Aluminum for Airframe $125
Misc hardware $375
Instruments $ 300


Total $5890 ready to fly (less paint)

[13brv3]

Mike, Udi, Ron,

Thanks for an excellent round of posts! I'd say I'm satisfied that there's nothing wrong with my plan to use the single rotor engine in a Dominator. Heck, if I don't fly anything but heavy two place gyros while training, even the portly Dominator will seem light an nimble by comparison.

Mike,

I'm impressed at the low cost of your gyro. I might try something similar one day, but since I'm new to gyros, I figure I'd better stick to something fairly standard for now.

Ron,

Nothing wrong with your financial logic regarding the used machine for sale. It is a good deal, and the fact that it's about a zillion miles away is probably all that's kept me from looking into it more. There was also an UW minus engine in Michigan for $6k. Either machine would need substantial changes (engine mount, full pod, larger rotors, different pre-rotator maybe), so I think I'll be better off starting from scratch.

There is certainly some appeal to flying the UW just like it is for a while, just to see if I really want to own a gyro. If I decide to build one with a rotary, or if I just decide I don't care for gyros, then I could sell the UW for close to what I paid for it. Until the Kolb is sold, I don't have space, or money for the UW, and it's likely there will be others for sale closer to home, though maybe not with Doug's personal seal of approval :-)

Cheers,
Rusty

[Screw]

Screw-in

I just saw this thread and briefly thumbed through it. I have stated alot of times that lighter is better, but as has been stated, that is not intirely true.

Me believes that the flying characteristics of a truely fun flying gyro is a combination of serveral things. Because I'm not an engineer, and only have my experiance to rely on, I look at three things in particular.

1. Power to wieght Ratio. Using rough math I just divide available HP into All Up flying wieght. I like it at 10lbs per HP or less. I've seen gyro fly fine with 14lbs per HP. The lighter the airframe and less stuff, the lighter the AUW, therefore more HP per Pound.

2. Disc Loading. I like flying Dragon Wings, and to me, they fly best at 1.3lbs per square ft. Use the formula: A=Pie R Square To determine the Area of a givin set of blades then divide that number into your All Up Flying Wieght.

3. Finally, Thrust Test. As a general Rule, you should always use the largest diameter prop possible, then set your pitch to your desired RPM, Temps, Ect. The Thrust test is what it is. For a 600lbs AUW gyro, I like 320-330 lbs of thrust.

When people go tinkering with one of the three above, chances are they effect the other. I think Ernie at Rotor flight has one of the highest perfoming singles out there. An UltraWhite Airframe with no bells and whistles, matched with a Rotax 582. Very strong, lightwieght machine with incredable performance.

Screw-Out

[13brv3]

Thanks for the observations John. Your answer is just about exactly what I was looking for when I started this thread.

As for disc loading, in the archives, I've seen figures of 1.3-1.6 lb/sq ft for DW rotors. I guess I'm not surprised to hear that you like the lighter loading, since I would think that gives better maneuverability, and slow speed performance. I would likely defer this selection to Ernie.

You also mentioned prop size, wrt thrust. I think the one thing I don't like about the standard single place Dominator is the small (60" I think) prop diameter limit. I know that they used to offer a version that would work with larger props, but if I recall correctly, that has been eliminated. I supposed it could still be done if you were building from plans, or were willing to modify some of the standard parts you receive.

Cheers,
Rusty

[stuart]

Rusty, Have you flown in a gyro yet? Faced with the same situation, i'd want to be sure i liked them before buying one. blue skies, stuart

[13brv3]

Hi Stuart,

I flew about 3 hours of dual with Dofin Fritts in Brewton a few years ago, and thought it was really cool. I haven't lost the urge to build one since then, but just haven't worked it into my project schedule yet.

Rusty

[Screw]

Screw-In

Rusty, Not to sound like a salesman or nothing, but one of the best "Set-Up" single place gyro I've seen in a while is Brent Browns "Peg Leg." It's in the for sale section cheap too.

It is a very lightwieght airframe like a Dominator with an MZ-202 swinging a large 73' Powerfin. I'm not sure but I think he running 23' DW and just added a Pre-Rotator. Brents a big boy and didn't use the pre-rotator....He's hard core that way, but he added it to sell the gyro.

If I could have, I would have bought for a single for myself. Look into it.

Screw-Out

[Rotornut]

Harry Said / try a bare bones BENSEN B8 style with a MAC 90 on it. You want fun flyin'...you got it.

Those were the Good Ole Days Harry.

I know I love to Hear Dave Pratter every morning at BD Day. MJ :)

[13brv3]

Hi John,

That's a pretty amazing tale of woe on the sale of the Peg Leg. I guess resale on gyros is as bad as it is on light fixed wing planes.

Even though I've spent too much on my RV-8, I have promised myself that I'll take the money from the sale of my Kolb, and put it towards a gyro. Unfortunately, I don't anticipate the Kolb selling that easily, or for nearly what it's worth :(

Rusty

[GyroRon]

I could have sold Brents gyro 4 times now in the time he has had it for sale. He does not know how to properly market a gyro and I have tried to offer him advise that he did not want to hear. His machine is a good deal and if he showed some detailed pictures of it and advertised it properly he would have no problem selling it for his asking price.

Gyros do have a weird resale value. They do tend to depreciate unless there is something extremely special and valueable about it - Sparrowhawk kits completed and flying are worth more than what they cost to build for example. You will likely not get anywhere close to what you paid to build a gyro new if you resell it later with most gyros, but this is the same with most ultralight and lightsport airplanes too.

Having a non standard engine can make it hard to resell too. I think most people would not pay much for one with a experimental single rotor engine, so keep that in mind Rusty.

Vans RV airplanes are the hot ticket right now. For what they cost, they are incredible in that they will fly slow, takeoff and land on a short runway, they fly near 200 mph and can do aerobatics. Because of this, there is alot of people who want one, so the resale value on one that is in good shape and with decent equipment will be more, sometimes much more than what it cost to build the plane. Even with a experimental engine such as a mazda or Subaru they still sell for good money simply because it is a RV and people want to go fast....

As for the small prop on the Dominators. Ernie sells the single place machines with everything set up for a 60 inch prop. He sells the two place machines with everything set up for a 68-72 inch prop. He can easily sell you the stuff to build a single place with the two place landing gear and tail and mast so you can use the larger prop..... but of course all this stuff costs more! It will be cheaper to do it in the beginning than to try to refit a used gyro for the larger prop.

I am impressed that Mike can build a gyro for that price, but know that is unrealistic to duplicate today. The Rotorblades cost alot more today, aluminum costs more, seat tanks cost more, hardware costs more, etc.... Heck just a redrive for the Subaru would set you back 2500$ today.

Rusty, if your serious you need to get over to Wauchula and go up with Davey Seace and see what these kinds of gyros fly like, and then go visit Ernie at his shop and see how these are built and so on.

[Aussie_Paul]

Myself, I have been lucky enough to fly ALOT of different gyros. I have flown alot of pusher gyros and so far none flys better than the Dominator. There are others that fly very good and are close to as good as the Dominator, but for overall blend of everything just working like it should, a Dominator is hard to beat.


To true Ron, not many gyro pilots have flown more than a couple of gyros. Your list is comprehensive, and I have have been firtunate to have flown a lot of gyro varioations, BUT obviously, without looking at your list, you have not flown a Magni or my Hybrid. I have flown both sngle and two seat Dominators. Dominators are a damn fine aircraft though.

Aussie Paul.:)

[Screw]

Screw-In

Good Post Ron, I agree.

Screw-out

[13brv3]

Thanks for more good info Ron. I'll keep the large prop version of the Dominator in mind if I do start from scratch.

I also agree with the recommendation to pay a visit to Dominator country. I had hoped to put that off until the RV-8 was able to take me down there, but it might be worth taking a trip sooner than that. Does anyone have Dave Seace's email address, or phone number?

Thanks,
Rusty (wondering how to get the UW shipped from NY)

[Screw]

Screw-in

AH HAAAAAAAAAAAA!

I got it Rusty! Contact Brent Brown, I think he just dropped the price recently to 6k Or that Ultrawhite for 9k. Buy it!

Learn to fly it "As Is." In the meanwhile you can start planning on the motor mounts and everything for the transition since you will have the machine right there to pull any info you need.

Once you make the engine swap, you can sell or hang on to it. Either way, your not losing any money.

Think of it as your buying a completed airframe "Ready To Fly." It just happens to have an engine that came with the gyro.

I think it cost me around 10k for my 2 place Dominator assembled by "The Master" less engine, prop, instruments, and head.

Brents gyro (set up for and comes with a very large Powerfin) is a steel ready to fly at 6k Period! If you eventually sold the motor that came with it, it just lowers your airframe investment. OMG! I'm sure it wouldn't be hard to sell the 65hp MZ.

Screw-Out

[13brv3]

Is this the same "Screw" who started post #33 with "Not to sound like a salesman or nothing" :D

Seriously, I do realized what a bargain both of these gyros represents, but I've decided to follow Ron's suggestion to take a trip down to Wauchula for a visit to Ernie, and Dave Seace. Ater an hour or two with Dave, and a look around the Dominator facility with Ernie, I think I'll be in a much better position to know what I want.

Unfortunately, July is practically ruled out already, due to coworkers vacation time, my on-call weekend, Mentone (I presume either Ernie or Dave will be going), etc. I might be able to get down there before July, but more realistically, it will be after, so I have to believe both of these bargain gyros will be sold.

Thanks again for all the comments on this thread.
Rusty

[Screw]

Screw-in

LOL. Just thinking of you man.:D

Screw-Out

[Aussie_Paul]

My favourite fun toy is my Hybrid with 4 US gallons of fuel. I can throw that thing around have a lot of fun.

With the 30' rotor you have to anticipate manouvres ahead of time. With all that hp and such a low disc loading I can fly it so slow as to turn tighter than most single seaters.

Aussie Paul.:)

[13brv3]

Hi Pau,

I think I'm finally starting to grasp the concept of rotor size vs response time. Still fun, just different fun :D

Rusty

PS- Yes John, I did see that Peg Leg has been reduced to $5000 :p FWIW, I'm set to fly with Dave Seace on the 25th, and will stop in on Ernie the 26th. Hopefully, I'll have a better idea what I want to do after that.

[birdy]

Any gyro can do wot another can do, of equal power to weight.
The only thing that changes is the RATE of any manuver. The heavier machine needs slightly more time/room to change att ect, but will do the same moves as a lighter one.
IOW, i can do the same things in me wasa [ modified RAF]as in the ferel[ purpose built mustering machine], only i need to give the weight and blades more time to respond in the wasa.

[Al_Hammer]

Ok, physics fans, this came as news to me, but here is what I just learned by googling around...

The smaller gyro will be quicker in it's responses because it has a better ratio of thrust to moment of inertia.

Why is this necessarily so?

Well, its a mathematical thing. The moment of inertia, which is a measure of the resistance to accelration in rolls and banks, etc, decreases with size much, much faster than does rotor thrust.. So you inevitably wind up with more control power in the smaller vehicle.

If the gyro is 1/2 scale size compared to another gyro, it will have 4 times the thrust to inertia ratio even if the engine power is kept in proportion to the weight. (1/2 scale means 1/8 the weight, so its an extreme example.)
Following physical scaling rules, as the vehicle size decreases, the moments of inertia decrease with the FIFTH power of the scale factor, while the rotor thrust nominally decreases proportionally to the vehicle mass, i.e., with the THIRD power. Miniature helicopters can
easily have a high thrust-to-weight ratio (it can easily reach values as high as 2 to 3), which tends to accentuate
the scaling effects

[Udi]

...If the gyro is 1/2 scale size compared to another gyro, it will have 4 times the thrust to inertia ratio even if the engine power is kept in proportion to the weight. (1/2 scale means 1/8 the weight, so its an extreme example.)
I think you are confusing several factors, Al. What you are talking about here is a direct scale down of a given gyro, ie. mass AND size. The gyros we are talking about, whoever, are not scaled down like that. Compare a single place Dominator to a Sparrow Hawk, for example, and you see that the scale down is only in mass, not in size. The dimensions of the two are almost identical.

The mathematical expression of MOI is I = itgr{(r^2)dm} which means the MOI is a square function of the size factor and linear function of the mass factor. A gyro that is identical in its size distribution but double the mass density will have a double, not quadruple, MOI.

Tandem gyros, as compared with single place gyros will have a significantly higher MOI in pitch and yaw but the roll MOI will be almost directly proportional to the difference in mass.

I think the sluggshiness we see in heavy gyros is almost completely a function of the higher inertia of the rotor itself, which makes it, not the gyro, respond slowly to control input.

Udi

[Al_Hammer]

Udi,
I think it is fair to say that gyros get bigger as well as heavier as you go up the scale, say from 1 place ultralight to 2 place lead-sled to the multiplace, multi-passenger gyros of days gone by.

Rotor response rate is typically slower as the rotor gets larger, as you said and that only increases the apparent sluggishness of larger machines, it is not the sole reason for it. Rotor thrust is what pulls the mast and actually controls the gyro. The thrust goes up slower than the MOI as you increase linear dimension.

Using your integral definition applied to actual objects, if you look up the moment of inertia of some simple solids you'll see how the MOI does indeed vary as the fifth power of linear dimension.

For a solid sphere, MOI= 2/5 MR² where M is mass and R is the radius of the sphere. This is easily derived from the integration you presented and I linked a website below that steps through it.

If the linear dimension is halved, the mass, which varies with volume, is 1/8 as large. The radius, R is 1/2, so R² is 1/4 as great.
The MOI is 1/32 of the previous value or a factor of 1/2 to the 5th power.

Moment of inertia for continuous bodies:
http://physics.ucsc.edu/~josh/6A/book/rotation/node19.html

see also http://zzyx.ucsc.edu/rcbees/aerodynamics/Wing%20Loading/

[Udi]

Al - I don't think I explained myself well enough. What I was trying to say is that R stays pretty much constant. The distribution of mass in a single place Dominator and in a Sparrow Hawk is almost identical (i.e. the distance from say the CG to say the pilot is the same). The R does not change. What is changing is the m (because there are two people instead of one and the engine is heavier and the rotor is heavier etc.) and so the more correct calculation of the ratios of MOIs is:

I1=2/5 M1 R1², I2=2/5 M2 R2², R1~R2 ->> I2/I1=M2/M1 :)

The same holds true for 2 Dominators, one ultrawhite with a 503 engine, a 150 lbs pilot and a 23 ft rotor, the other with a 300 lbs pilot, a Soob engine and a 27 ft rotor.

Udi

[Al_Hammer]

¥es, Udi I see what you are saying. I still think that a gyro's linear dimensions and mass distribution will tend to scale up as you go to the heavier machine, but I will take your word for it on the sparrow hawk vs Dom.

At least I did learn something interesting about moment of inertia from reading those web sites.

[Ga6riel]

If you look back in this thread you will see I say pretty much the same thing as Al. Im not unhappy about that because I know this to be so.

The easiest, and most accurate way to envisage the problem at hand:
to paraphrase that...as gyros get bigger they respond more slowly, less crisp

To avoid someone saying ahh yes, but brand X has always been a better handling gyro than brand Y The use of a scale be it up from a single place design, or down from a 2 seater eliminates that conundrum....but presents another problem.

While by dimension areas vary by the square, those of force, volumes and mass vary by the cube, moments by the power of 4, and inertias by the power of 5. The innequity in the collision of these factors creates convincing variations in the flying qualities between larger and smaller machines. This is why mother nature didnt leave us with 6ft tall ants, engineering wise it just isnt possible. You should not simply make a machine a larger version of another and expect it to handle the same or even safely

While the same is true to F/W A/C you can at least vary the sizes of ailerons and elevators, fiddle with the aspect ratios to restore the desired behaviour. In a rotary wing machine your pretty much stuck with the same aspect ratio, whatever contol energy your arms can muster, and a tail that will fit somewhere behind the prop. The good thing about this is that it fits with our natural ideas of life, small things are zippy, big things are steady and stable.

While elsewhere you can see the discussion dance around lbs per horsepower and disc loading....that 'idea' of design will start to show some paliative differential from the datum aircraft they were taken when you step so far outside the model that you require more disc area to satisfy a performance attribute.

~ ignore that at your peril

[mceagle]

A good analogy would be the big car V's the little car. The tyres are scaled up on the big car giving it the same weight per squ inch of tyre area but the little car is far more zippy and responsive to drive, wheras the larger car is more at home cruising the longer distances. For those that wish to have more fun around the airport, the lighter gyro is the answer.
There is another interesting factor that dosen't seem add up in this scaleing comparison. Perhaps Chuck or someone may be able to help us out here. I had a 447 machine that weighed 200lbs complete (approx 410 with me and fuel). In it you could do things you could never do in a flying bulldozer, no matter what the rotor diameter. It was capable of climbing at 10 kts, had an MPRS of 15 kts, was still capable of 70 kts and could be thrown on its side and pulled back to a standstill and then comfortably fly back the other direction without losing height. Such things are just not possible with an aerial bulldozer.

[birdy]

Such things are just not possible with an aerial bulldozer.

They are Tim, just not at the same RATE as the lighter ones, of equal power t weight and rotor loading.

[Aussie_Paul]

Such things are just not possible with an aerial bulldozer.

They are Tim, just not at the same RATE as the lighter ones, of equal power t weight and rotor loading.

So actually they are not possible Birdy. I agree Tim. It's just that I like my aerial bulldozers now. It does not matter which end of the gyro spectrum you fly, they can all fly as stable aircraft. It is just a pity that there are still unstable gyros being built, BUT the stability message is getting though, and in a few years time I will look back and be proud, as I am now, of what I have done to increase the awareness of gyroplane stability.

Aussie Paul.:)

[birdy]

So actually they are not possible Birdy.
Hmmmm................ seems i gota spell it out abit simpler for PB.
As i said before in the last page;
The only thing that changes is the RATE of any manuver. The heavier machine needs slightly more time/room to change att ect, but will do the same moves as a lighter one.
IOW, they can do the same things, only slower[the heavier ones].
Even an underpowered one can do wot a powerful one can, its just that it'll have to sacrifice some alt to make up for the lack o power.

But then, i know your only stir'n me again PB, i know you know.

[Adam H]

I know this is a little off topic but mceagle, how did you make a 200 lb gyro?

[Chopper Reid]

If you are flying for fun, then the lighter the gyro the better. My old open framed gyro despite not having the power of my new one, was easier to fly and a lot more fun !

[Aussie_Paul]

If you are flying for fun, then the lighter the gyro the better. My old open framed gyro despite not having the power of my new one, was easier to fly and a lot more fun !

Brian, my fun is going places!!!:D

Aussie Paul.:)

[Passin' Thru]

Brian, my fun is going places!!!:D

Aussie Paul.:)
.
Well sir, no offense intended, but if that be fact, then you really should consider a fixed wing!

[Aussie_Paul]

.
Well sir, no offense intended, but if that be fact, then you really should consider a fixed wing!

Passin' thru.

I will re phrase that. I love going places in my gyroplane. I have done the fixed wing thing many years ago. No fun in that compared to doing it in a gyro.

Aussie Paul.:)

[Ron Iaconis]

If you are flying for fun, then the lighter the gyro the better. My old open framed gyro despite not having the power of my new one, was easier to fly and a lot more fun !
I always fly the openframe light gyros. Once, Lee Bradshaw took me up in his Air & Space 18 A,,,,,It was early mornin at Middletown, Ohio,,,PRA Convention about ahhh????? 1987. Lee carried only minimal fuel, the early air was crisp & cool. Lee said to me he wanted to do a jump take off and with the summer time climate and air density it was necessary to be light in fuel and early in the morning to successfully jump into the air. Well it all worked and off we went. When we got airborn and at an altitude of aproximately 1500 ft AGL, Lee asked me if I wanted to fly the Air & Space, I cautiously accepted, and found that the controls were " heavy" in my comparison to my little toy. Very soon I asked Lee to regain his piloting of the bahemouth, for I was not comfortable. The experience I will never forget,,,,but the heavy and cumbersome flight characteristics of a heavy gyro just did not agree with me. That is why I prefer my little toy at 250 lbs soak in wet.

[13brv3]

I appreciate all the ongoing replies. I'm currently scheduled to fly an hour or two with Dave Seace on Sunday, and then visit Ernie Monday on the way home. With any luck, I'll have a lot more info to work with after this weekend.

Cheers,
Rusty

[mceagle]

I know this is a little off topic but mceagle, how did you make a 200 lb gyro? G'day Adam. The gyro looked something like a bumble bee. I havent got a picture I can post but I worked on the principle that it is hard to save 10 lbs but it is easy to save 1 lb 10 times. Everything was kept as light and simple as possible with the end result that it was very tender if misused on the ground. Free air cooled 447 rotax with "B" box, 2 bld. wooden prop, 3/8" ply tail cable braced, no "tow" boom or instruments, plastic garden seat, 2 gall. plastic fuel tank, plastic wheels, Bensen head, no pre-rotator, no elec. start, and no battery. The very light weight meant that it was stronger than most gyros in the air.
I have built one 20 lbs lighter but the 20 hp Zenoah engine let it down, even though it did fly.

[scottessex]

That is exactly why we are trying to keep the 2 place dominator with the 618 rotax under 400 lbs, so far so good.

[Adam H]

G'day Adam. The gyro looked something like a bumble bee. I havent got a picture I can post but I worked on the principle that it is hard to save 10 lbs but it is easy to save 1 lb 10 times. Everything was kept as light and simple as possible with the end result that it was very tender if misused on the ground. Free air cooled 447 rotax with "B" box, 2 bld. wooden prop, 3/8" ply tail cable braced, no "tow" boom or instruments, plastic garden seat, 2 gall. plastic fuel tank, plastic wheels, Bensen head, no pre-rotator, no elec. start, and no battery. The very light weight meant that it was stronger than most gyros in the air.
I have built one 20 lbs lighter but the 20 hp Zenoah engine let it down, even though it did fly.
Did you still use Bensen type construction? By that I mean standard 2x2 keels and mast?

[mceagle]

Yes, with 3/4" round suspension legs and uprights..