Item 1670

OTHER: Aircraft - Gyro/Heli - Non-powered

Sketch;

 

This is an alternative planform for consideration if the forward flight is relatively slow.

Specifications:

Conclusions from the Material Below on Rotor Calculations:

The Non-powered gyrocopter has a blade loading that is 1/4 that of the Gyrobee.

The gross weight of the Non-powered gyrocopter is 300lb vs. the Gyrobee's gross weight of 500 lbs.

The rotor diameter of Non-powered gyro is only 8 inches greater than that of the Gyrobee.

The blade chord is 9.75 inches greater then that of the Gyrobee.

The larger chord means a large blade thickness, which means a stronger/lighter blade.

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Gyrobee (calculated as a hovering helicopter)

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Smaller Craft: (calculated as a hovering helicopter)

Craft with a reduced gross weight from that of the Gyrobee but with the same disk loading and blade loading as the Gyrobee.

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Non-powered Gyrocopter: (calculated as a hovering helicopter)

Craft with the same gross weight as the above [Smaller Craft], but with 4 times the blade area.

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Performance Calculation of Gyros ~ Jukka Tervamaki

Large Chord & Low Tip Speed

 A reference: The Ultrasport-254 has a disk loading of 1.66 lb/ft2 and it is reported to have a descent rate of 600-700 ft/min = 10-11.7 ft/sec.

More Specifications:

The blades on this craft should perhaps have a slight positive twist.

 

Stability:

Non-powered Gyrocopter - a Possibility? ~ from Rotary Wing Forum

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

The question is, has there ever been an Non-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 Non-powered backpack gyrocopter might ......


Dave

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

Birdy demoed something very similar 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 don't pull you back. The guys with the parachutes have to hurry up and get them above their heads or else it does the same thing.

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 :^)

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.

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.

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

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.

Thanks guys,

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


Any more thoughts, both pros and cons?

Dave

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.

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

From Quadrirotor

http://www.rotaryforum.com/forum/attachment.php?attachmentid=49047&d=1220485179

http://www.rotaryforum.com/forum/attachment.php?attachmentid=49049&d=1220485179

http://www.rotaryforum.com/forum/attachment.php?attachmentid=49048&stc=1&d=1220485179

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=-

For the very same reasons Doug already pointed out I think that making a practicably soarable gyro would be very difficult if not near impossible. It may be possible as a proof-of-concept only.

One other issue is that the speed at which minimum sink is achieved can't be too high or else there's no way to stay in the thermals. Gliders commonly achieve minimum sink at just slightly above stall speed.

-- Chris.

 

>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.

Same story on the other side of the channel with the Halfner Rotachute- final tests into 1943 included "tows by a de Havilland Tiger Moth and Avro Tutor were made up to heights of nearly 4000 feet (1,200 m) and at speeds of up to 93 mph (150 km/h)."

Halfner originally though that a gyro glider would have a similar sink rate to a fixed wing glider capable of carrying the same weight but that turned out to be optimistic.

They would make quite a ride from the fan tail of a cruise ship but all the gyro gliders I ever read about are like soap box cars- they need a hill.

 All of the previously mentioned non-powered gyros appear to be using conventional rotor blades.

From Wikipedia;- Typical aircraft wing loadings range from 20 lb/ft² for general aviation aircraft, to 80 to 120 lb/ft² for high-speed designs like modern fighter aircraft. The critical limit for bird flight is about 5 lb/ft².

From Sailplane Directory;- The average wing loading for a sailplane is 5.2 lb/ft².

This implies that the blades on a Non-powered gyro should be approximately 4 times those found on regular gyros. Obviously, these large blades would also be turning much slower. This supports what Doug has been saying.

The prospect of such a craft is still an intriguing possibility, if the safety issues can be overcome.
~ During flight;- strong rotor blades should minimize the danger of severe G loads.
~ During landing;- the gliders sink rate of approximately 2-3ft/sec, combined with no forward velocity, plus VERY slow turning (low inertia) high strength blades, should minimize any danger to the pilot and the blades.

For launching; What about a recoverable Non-manned hot air balloon?

A question; How would the rotor obtain its prerotation?

Dave

For paragliders and hanggliders you can use a 1000m / 3000ft rope, a winch or car and get almost 500m/1500ft hight - depending on wind of course.
Why this have not been done for a usual gyruglider I don't know or understand.

The glide ratio for a paraglider is 7-8, so 4 for a gyroglider is bad - but not so bad that you won't get any fun out of it - I guees.

Jens

A lightweight rotor can be produced by adopting the so-called Princeton wing, developed at Princeton in the 1970s and forgotten. Use a lightweight long tubular spar (say, carbon fiber). String a cable parallel to the spar at the distance that will be the the blade chord. Join the ends with plates. You get something that looks like hacksaw, only with the cable in the place of the saw blade.

Pull a fabric (lightweight dacron?) sock over the 'hacksaw' so that it is a tight but not too tight a fit.

You get a wing. The tubular spar is the leading edge and the cable is the trailing edge.

Have wind blow at the contraption at a slight angle of attack and the dacron surfaces bend and form a good airfoil profile.

I can easily imagine two such BIG lightweight blades forming a gyro rotor that would have very low wing loading yet be lightweight enought to be carried mounted on backpack-like structure or a minimum trike.

Pre-rotation remains to be solved. If we're talking a trike, why not pedal-powered pre-rotation?

Larry,

Quote:

What is flying a machine with 0.57 lbs/ft loading like in the mountains?

I cannot answer this one.

As a guess; The Disk loading is 0.57 lb/ft2 and the blade loading is 8.17 lb/ft2. Perhaps the blade loading become more important then the disk loading at reduced rotor speeds. In the linked example above the tip speed is about half that of the Gyrobee.

Quote:

If low loading reduces power required (it does) then why isn't anybody building a gyroplane with a cheap 20HP paramotor and a big rotor?

I have searched in books and on the Internet, plus asked on PPRuNe a question similar to yours, in respect to helicopters. The basic question has been; "Why is the value of 0.12 considered to be the upper limit of the solidity ratio for helicopters. There has never been a satisfactory answer. Therefore, I assumed that the reason for high rotor rpm had to do with the use of centrifugal force for effective blade operation. Today's lightweight composite construction is allowing builders to implement much more rigid rotors.

Quote:

What sort of blades did you use to replace the Rotordyne ones in your proposed machine and at 180 RRPM will they still be able to resist flapping the way they do at 450RRPM?

The blades would be a new design. They could be produced where both blades and the connecting 'spar' are done as a single 26 +/- long part. Using composite construction, the central spar could have the strands aligned span-wise. This would provide strength for in-plane and out-of-plane forces but the blades could have their relative pitch changed.

In addition, an 'effective' flapping hinge offset, complete with delta-3, could be built into the root end of both blades. This would pull pitch out of the blades if excessive coning was to take place due to high G-force perturbations.

Also, the above pitch change could be ground adjustable or in-flight controllable; to suit the selected rotorhub.

The hub might be teetering, teetering with adjustable hub springs , or rigid with weight shifting control (as in the previous video).

Just ideas.

Dave

Bruno,

Thanks for your two interesting ideas.

Found this patent of your Princeton wing


Another potential idea for the prerotor: ~ for use when an external device, such as a car or winch, is used to initially pull the gyro.

Consider having a small section at the root end of each blade where the upper and lower airfoil skins can open up like a clamshell. The hinge is at the leading edge of the blades and the opening takes place at their trailing edge.

This clamshell would remain closed at all times when the blade was on the advancing side. This closure would be instigated and maintained by the free airflow over the clamshell doors.

On the retreating side the free airflow would be from the trailing edge to the leading edge of the blades. This would open the clamshell doors and their flat-plate drag would start to rotate the rotor. Eventually the retreating root of the rotor would build up a higher rotation speed then the free airflow and this free airflow would close the clam doors.

Just another idea to provoke; thought, a scathing rebuttal, or other wild ideas.


Dave

Another Means of Launching:

A gas filled balloon with a lifting capacity of >300 lbs. At the nose of the balloon is a horizontal bar, which extends out about 5 feet. This bar is connected to a winch on the ground by a cable.

Under the balloon's CofG is a mechanism that prerotates the gyro's rotor-blades. Light cloth vanes, which are attached to the balloon just above the gyro's rotor, resist the rotation of the balloon. These vanes will operate in the gyro's streamtube and will aerodynamically induce a counter rotational moment on the balloon.

This device could be continuously launching a number of these hover-gyros over a dark field or into the updraft at the side of the ridge, etc. etc.

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

A word of caution about this.
You almost never see balloons and gliders operating from the same airport. They can operate from the same place, but usually not at the same time. The conditions that balloonists want are the opposite of what glider pilots want -- thermals are essential for gliders and dangerous for balloons. The balloon folks are usually out at dawn and land at or before the first signs of developing wind or any thermal activity; the glider pilots (who love wind-driven ridge lift and strong thermals) don't even drive to the airport before the balloonists have packed up and headed home.
Conditions that are good for soaring with the gyro-glider could make control of the balloon launcher one heck of a challenge.

WaspAir

I don't know Dave- it's hard to imagine a 5-10FPS updraft putting as much air through the rotor as the 250-300 pounds of thrust normally used to maintain level flight in a single seat machine.

Doug's original comment about what's effectivly a couple of sail planes flying around each other wing tip to wing tip is what I see when I think of a soaring gyro- of course any rotor fits that model abstractly but in this case it's not so abstract.

Have you figured out how much air you're expecting an updraft to push through your rotor to drive it? Maybe you need depleated uranium tip weights so you can dive into the thermals and use the rotor as a fly wheel to store some "make hay while the sun shines" energy.

Larry Goodhind

Larry,

The link in post #23 has been cleaned up a little. The data on that web page is based on Prouty's calculations for a hovering helicopter. The hovering induced velocity for the Un-powered Gyrocopter at its GW of 300 pound calculates out at 11 ft/sec.

This 11 ft/sec downward induced velocity is, of course, mechanically generated. Perhaps you, or Doug, or someone knows what the upward induced velocity (or conversion value) would be to hover (autorotate) this craft at fixed elevation on an updraft?

________________

This concept "of sail planes flying around each other wing tip to wing tip" is what many of the very early pioneers did. Of course, they only had materials such as wood, steel, fabric and wire to work with. Today we can return towards their concept with light, strong composite materials. We no longer need high rotational inertia to maintain rotor integrity.

Doug has mentioned the potential risk resulting from a gust on a lightly loaded structure. This may be the Achilles's heel of an un-powered gyrocopter. The hope is that; the rotor (pair of wings) can structurally take the abuse, and, that the craft will right itself if the precone is relatively large and the elevation above the ground is high enough.

__________

An undesired slowing of the rotor may be a problem, but perhaps an 'effective' delta3 built into the composite may help.

In addition, it may be possible for the pilot to put negative pitch into both blades. The negative pitch might recover lost RRPM. In fact, it might be used for initial rotation (pre-rotation) if the craft was dropped at elevation.


Dave

The Ultrasport-254 has an induced velocity during hover 17.85 ft/sec. It claims to have an autorotative descent rate of 900 ft/min. = 15 ft/sec.

This might imply that this un-powered gyro would have an autorotative descent rate of (11/17.85) * 15 ft/sec = 9 ft/sec, before flare.

Dave

 

 

 

Will the low center of thrust (in respect to the rotor) be bad or good;

  1. For weigh- shifting?
  2. For teetering rotorhead?

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