flutter-suppression technologies

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berridos

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Wonder how that system works. Overriding servos that move the ailerons against the wing oscilations?
 

Jay Kempf

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Sure looks that way. Great idea to put a lot of servos driving a lot of redundant surfaces. That is the way to making this sort of thing commonplace. A 2x-4x redundant direct drive servo of some sort that was light, reliable and simple would be really interesting. Cut the trailing edge up into 16 segments and mix all functions on one system from gust alleviation to glide path control to low drag trimming and high CL trimming. Wings would be a lot simpler if we could do that. Right now you would never consider doing anything but the flap drive that way. There seems to be a lot of research going into flexible structures these days. Real (enough) time FBW systems are being researched in all sorts of corners of the industry. Raises all boats.
 

bmcj

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I don’t know a lot about vibration, but could you develop some sort of passive self adjusting counterweight to reduce flutter in the same way as some devices can be attached to a rotating shaft to counter rotational vibration?
 

fly2kads

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It will be interesting to see how those technologies trickle down to our little airplanes. Sailplanes and cross-country machines, where efficiency is important, would be good candidates. That would make for interesting trade studies to see the crossover points where complexity vs. weight vs. efficiency vs. cost all makes sense.
 

berridos

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These technologies will arrive much earlier to the hobby fpv drones in banggood for 20$ than to hba.
 

wsimpso1

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That would require some fast powerful actuators and some powerful real time processing to stay ahead of the flutter. Response speed of system from measurement to control surface changing lift must be at least 2x fastest flutter mode being controlled.

Fast powerful actuators continuously pumping the controls use power that must be drawn from the engine, either electrically or hydraulically. This is significantly larger amount of power than current fly-by-wire.

If the airframe saves more fuel than the extra fuel (engine power) needed to flap the controls, then it is a true save. If flapping the controls cost more power than the airframe saves, it is not an improvement.

Then there is the issue of weight of all these control actuators - between redundant power sources, redundant actuators, control system plumbing or wiring, this could add substantial weight.

Last issue is it would need a lot of redundancy - let the wing flutter, and the ship is lost. Hot seats for crew and passengers? Maybe with a plethora of small trailing edge devices, you can afford to lose one here and there and still be OK.

Billski
 

Jay Kempf

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All true. In a very high aspect ratio wing flutter is the limit and normally at pretty low speeds. Thin wings are much harder to route and hide sophisticated controls as well. So small actuators that only control a small surface but lots of them might be a wash weight-wise. Watched the evolution in RC gliders to small metal gear super thin servos. lots of individual surfaces is the norm now with aileron mixed with flaps. The benefit is local lift management. So think of patching a wing for stall spin behavior. You just mix the small surfaces so that the tips never stall. For cruise you optimize the drag bucket at every station along the wing. For gliders they are designing around two points much like power planes. They want a super low drag high speed cruise but they also want a super low drag highest CL condition just above stall and manageable and spin resistant all the way to the edge. You don't want to spiral in on a marginal thermal.

All that is directly applicable to fuel flow required at cruise and safe low speed handling. One thing you can do with a lot of TE tabs is you can mix the aileron function to put the change in lift at the moment arm you want it to be for any reason. So if bending or twisting needs to be tailored it can be.

So take all that and make it work and you can mix gust alleviation in as well. The more small panels (trim tabs) the less torque required per actuator, the more redundancy. It would be possible to have a system where the aileron was direct and mechanical and the servos/trim tabs for gust or flap function was servo driven electric. As long as the primary control can override worst case of secondary failure it is still safe (enough).

Agreed that the servos and system would have to be very fast at acquiring the data and acting. But modern servos are fast and accurate enough. Been noodling how to make a somewhat stock servo redundant when you can't really back drive them easily. So basically the servo would have to be multiple almost direct drive or very small mechanical gear down all on one shaft. Could be done. Have built clutched servos before. Those are a pain in the butt to get right and certainly not fast acting. You could keep the control surfaces very narrow to reduce torque required.
 

Hot Wings

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Agreed that the servos and system would have to be very fast at acquiring the data and acting.
I remember a paper proposing using piezo actuated Gurney flaps for this purpose. We already use stacks of them in fuel injectors that have to pulse several times per power stroke so the technology is getting close?

As for redundancy of servos how about 2 servos tied together with a V-tail type mixer. If one fails the software can tell from the disparity in feedback from each and then increase the stroke of the remaining active servo.
 

Jay Kempf

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Have a new 3D printer that uses something called CoreXY technology. Every move involves two motors opposite belt tension. Tension wouldn't work but one if something like that was moving rigid linkage and one failed the other could just compensate after noticing the output wasn't right. I saw a mechanical autopilot isolator mechanism in a paper a while back, have to find it again. Still I would rather see a bunch of motors on one shaft. Maybe the secret is to put all the redundant motors on one shaft going to a common gear reduction at one end or maybe both ends for anti backlash. Wait, forget I said that. That'll never work and isn't patentable. Carry on.
 

John Halpenny

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Have a new 3D printer that uses something called CoreXY technology. Every move involves two motors opposite belt tension. Tension wouldn't work but one if something like that was moving rigid linkage and one failed the other could just compensate after noticing the output wasn't right. I saw a mechanical autopilot isolator mechanism in a paper a while back, have to find it again. Still I would rather see a bunch of motors on one shaft. Maybe the secret is to put all the redundant motors on one shaft going to a common gear reduction at one end or maybe both ends for anti backlash. Wait, forget I said that. That'll never work and isn't patentable. Carry on.
One of the first fly by wire aircraft was the Concorde supersonic airliner. Each control surface was divided into three separate panels, and each panel had its own control and actuator. The idea was that if any one of them failed, the other two could overpower it and keep the plane flying. It also meant that at high speeds, when it needed very small but precise control movements, they could use only one panel instead of all three.

John
 

Map

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If a control surface is actuated by a servo (irreversible control), conventional (control surface) flutter would not be possible. But other flutter modes would still be a factor.
I'm not sure what the benefit would be of designing an airplane that had flutter modes that would need to be suppressed actively and what about what if that system fails? I expect it would involve software and I'm not interested in flying a small airplane that requires software to fly safely.
 

Aesquire

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I'm a bit of a Luddite about fly by wire, but looking at the latest sailplanes, the wing is very cramped for aileron and flap control runs, and getting the systems to work as the wing flexes is a serious challenge. Dozens of servos and a wire? Both airliners and gliders would benefit from the efficiency of a variable airfoil with no discontinuity to cause drag.
 

berridos

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To achieve washout (variable) on a wing, would you move up the wingtip aileron section with overriding servos and move down the inner aileron section with overriding servos? Would such an adjustment achieve the same effect than buildin washout?
 

Riggerrob

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I'm a bit of a Luddite about fly by wire, but looking at the latest sailplanes, the wing is very cramped for aileron and flap control runs, and getting the systems to work as the wing flexes is a serious challenge. Dozens of servos and a wire? Both airliners and gliders would benefit from the efficiency of a variable airfoil with no discontinuity to cause drag.
Yes,
NASA is starting to experiment with continuous, flexible trailing edges. Their stated goal is to reduce noise from the tip vortex at the outboard end of landing flaps. A continuous trailing edge would eliminate that vortex. More importantly, it could incorporate a dozen small servo motors driving a dozen different shafts to gradually change trailing edge deflection with maximum lift inboard, but tips reflexed so far that they provide downward force. One suggestion was a series of asymmetric "carrots" that rotate bout the fore-and-aft axis. When they rotate, they change deflection in only a small portion of the trailing edge. That downward force will stabilize the flying wing in pitch. All the great flying wing designers (Horten, Prandtl, etc.) tried to optimize twist.
 

peter hudson

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Paulo Iscold did fly by wire controls in his unlimited class sailplane project.
 

Jay Kempf

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Exactly! Wonder what servos he used? Paulo is a pretty talented and resourceful guy it seems. Didn't know he had landed at Cal Poly.
 

sming

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If its the same project as in his talk hosted by the amazing experimental soaring association :
I remember pausing the video and googling them with success ;)

Cheers to ESA from europe, thanks for the hard work of publishing these talks, I've watched them all!
 
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