Un-powered Gyrocopter - a Possibility?

[Rotor Rooter]

The airplane has its un-powered relative; the sailplane, which climbs and flies in thermal updrafts.

The question is, has there ever been an un-powered gyrocopter that was specifically built for climbing and hovering in thermal updraft?

If not, then then next questions must be; would the craft be technically feasible and would it create an interest from a recreational (or competitive) perspective?

_____________________

Hafner's Rotachute and the Focke Achgelis Fa-330 are probably too heavy and complex to be considered; but a very light un-powered back-pack gyrocopter might ......


Dave

[gyro]

I think with right diameter rotors you could certainly give it a shot. and the relative wind comming up/off a slop would certainly get them spinning without needing a prerotator.

Birdy demoed somthing very simulair to that here in this video. http://www.youtube.com/watch?v=HLGEPbuM8UE

another one http://www.youtube.com/watch?v=nY8SmllLcIU

The main thing is to establish some form of forward flight so the angle of the rotors dont pull you back. The guys with the parachutes have to hurry up and get them above there heads or else it does the same thing.

[Gestur]

My guess is that any gyro-like contraption would make a very inefficient glider. Thermaling is probably out of the question, given the typical 4:1 glide ratio (or something like that), unless the thermals are exceptional. I guess it would be a bit like trying to thermal a parachute.

Slope soaring might be possible given a strong enough wind and a good slope - though you might want to check twice for spectators getting too close to the rotor blades during take-off... Obviously that's not much of a problem with paragliders or hang-gliders.

Apparently some people have managed to slope-soar stripped down RC helicopters:

http://www.runryder.com/helicopter/t12043p1

Birdy's video is interesting, but I can't tell whether the engine is idling or producing thrust. Maybe I need better speakers.


/Ulrik :^)

[Gyro_Kai]

A glider has a glide ratio (loss of height on distance flown) of 30-60. Our gyros are around 4-5. So there is still some modification necessary. The autorotation is simply not a very efficient way of flying.

Kai.

[WaspAir]

Originally Posted by Gestur

My guess is that any gyro-like contraption would make a very inefficient glider. Thermaling is probably out of the question, given the typical 4:1 glide ratio (or something like that), unless the thermals are exceptional. I guess it would be a bit like trying to thermal a parachute.
/Ulrik :^)

I agree that glide ratio would certainly be poor, but that's only one aspect of glider operation, and not the one that counts for thermaling. For effective soaring flight, one needs to be able to climb well, and that means having a slow minimum vertical sink rate. The slower you sink through the air, the weaker an updraft you need to give you a net upward motion. Thus, glide ratio is largely irrelevant to climb performance, since you're not trying to cover distance as you circle; only the vertical component matters in a climb.

The difference between these two is important. A glide ratio tells you how efficiently you can use your altitude once you get it, while the minimum vertical sink rate indicates how easy it will be to get the altitude in the first place.

I have flown vintage design sailplanes that are spectacular climbers, able to thermal upward in very weak vertical currents, because their minimum sink rate is low, but with low wing loading they are not especially good at converting altitude into a long flat glide (getting ratios in the neighborhood of 17:1). I have also flown modern water ballasted ships that don't climb as well but get outrageous glide ratios (well over 50:1).

For good climb performance, it would be nice to have one spot on the polar where the sink rate was less than say, 200 fpm, to take advantage of weaker thermals.

If one can devise a gyro glider that naturally sinks slowly, there's a chance of climbing with it.

[Gestur]

WaspAir,

You are of course correct: minimum sink is what matters in this case. I can only assume I jumped to the conclusion that any wing (rotating or not) with a 3:1 or 4:1 glide ratio probably won't have a very favorable minimum sink either.

/Ulrik

[Doug Riley]

Bensen's gyroglider manual states the obvious: the Bensen gyroglider was not designed for soaring, but for the most flying fun at the least cost.

Here's one way to think about heavier-than-air aircraft design:

ANY craft that uses the acceleration of air to hold itself up is energy-inefficient: A helium/hydrogen balloon can stay up FOREVER while consuming zero energy. Hell, you can hang your gyro from a tree with a rope and, in a sense, it's being held up in the air without using energy.

To make our lift in a gyro or FW, we perform a primary energy-using act that itself is useless: we stir up air molecules, creating local breezes that end up as heat in the atmosphere. Strictly as a by-product of that process, we get a reaction force that holds us up. It's like burning coal just to get the ashes -- but that is what we do in any heavier-than-air craft.

We'd like to get the most "ashes" (=lift reaction) and the least unusable heat. As it happens, that is best done with extremely low airfoil speeds (minimizing the profile, or pure, drag). It's also best done by speeding up the air molecules as little as possible (heck, zero speed-up would be nice, but it's impossible). To get a given amount of thrust/lift while speeding up the molecules as little as possible requires speeding up a LOT of them just a TINY amount. This means low wing (blade) loading.

Therefore, a soaring gyroglider's rotor should be VERY slow turning and should be huge. As a starting point,the rotor blades of such a thing would be nearly the same area as fixed wings for a man-powered, FW version of the same aircraft: think the Gossamer Condor with its wings spinning a few RPM.

[Rotor Rooter]

Thanks guys,

It sound like it might be possible. Some thoughts are;

• The rotor would have very low disk-loading.
• Large chord slow turning rotors.
• The blades could be made of very light (but strong) composite construction, or fabric covered frame.
• Launch could be by donkey and cable.
• Might be electrically powered for take-off and the batteries dropped by parachute over the takeoff site.
• The weight of the gyro may be only 50-70 pounds.
• The gyro would be very inexpensive.
• Perhaps thermals over dark fields might provide enough lift??
• It would have a gimbaled control.
• It may be very safe to fly.
• It may be very safe to land, due to very slow descent rate, slow rotor speed and relatively strong blades.
• Pilots could have 'hover time' contests, etc.

Any more thoughts, both pros and cons?

Dave

[Doug Riley]

The "strong" part is the catch.

By being huge and light enough to fly, the blades necessarily become fragile. Yet, low wing-loading aircraft are subject to severe G loads precisely because their wings can make far more lift than needed for their weight. All it takes to create these large excess loads is a sudden gust (an uncommanded increase in airspeed).

Two of the very nice things about a rotor are dependent on relatively high RRPM: (1) it's small enough physically so that it can be made very strong, without breaking the bank weightwise, and (2) its high rotational airspeed dilutes any gust-induced changes in airspeed.

You have to give away both these advantages when designing a gyro to run on very little power. Yet that's precisely what soaring is about.

[Rotor Rooter]

Doug,

Your point about strength is well taken. A friend who owned a competition glider many years ago said that it was stressed for -10Gs. Perhaps, the teetering hinge, flexible fiberglass spar, ribs and cloth skin, plus a low inertia "pilot-only" fuselage, might reduce this problem.

Dave

[quadrirotor]

There is a video somewhere!...

[Timchick]

Has anyone ever tried towing a gyro-glider up to altitude behind a glider towing plane and then released it? It may not rise in the thermals and soar but it would be a neat ride.

[gyro]

Tim, I sent you the video.....check your email.

[gyro]

Originally Posted by quadrirotor

There is a video somewhere!...

the video can be found here: http://forums.x-plane.org/index.php?showtopic=26577

Hmmmmm.....dont seem to be working. I sent it to Tim he will most likley Utube it :~)

[Hognose]

Originally Posted by Timchick

Has anyone ever tried towing a gyro-glider up to altitude behind a glider towing plane and then released it? It may not rise in the thermals and soar but it would be a neat ride.

That was how the Germans conducted training on the Focke-Achgelis Fa 330 gyrokite. They'd tow it to altitude behind a liaison or training plane like a Storch or Arado.

cheers

-=K=-