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Raptor Composite Aircraft

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pictsidhe

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Huh, I just saw a flock of raptors flying SW, towards Cherokee county. Six black vultures.
I'd bet that aileron is plenty stiff in torsion - one of the side effects of a significantly overbuilt structure. As a contrast, the Hiperbipe has full span flaperons of very narrow chord, folded aluminum skins with no ribs, and a counterweight only at the tip.

With Raptor, I'd now be looking at point loads at the spade/aileron interface. I can see that getting nasty with all that weight on a long arm.
Some parts of the Raptor are massively overbuilt. Other parts are underbuilt. I don't know which the ailerons are. Their weight suggests overbuilt. But they could have a poor choice of laminations, making them heavy and soft...
 

pictsidhe

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That works, thanks.
Scary video. I heard something about 18" deflection and cracks.
I wonder if the Raptor was getting aerodynamic aileron flutter on his wild ride run instead of runway bumps starting it. That would be a first, I think.
The Raptor had flutter. Bumps can help show something that is nearly unstable, such as his previous milder rodeos.
 

TFF

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Balancing the controls like that is very early 1930’s. Adding it to the spade when it should not need spades is really double dog strange.
 

Marc Zeitlin

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Perhaps the reason for the outboard bias for added counterweight is that the flexural displacement/oscillation is goi t to occur at the tips and not at the root of the (springboard) canard?
Very good. That jogged my memory, and IIRC that's what Jon told me. Makes sense.

On ailerons, where the root isn't at the root of the wing and the tip isn't at the tip of the wing, and there's little if any flexure over the length, the position of the mass balance probably isn't as critical IF the aileron is very torsionally stiff.

But I'm guessing - I'm NOT an aerodynamicist or a flutter guy.
 

Marc Zeitlin

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Scary video. I heard something about 18" deflection and cracks.
Yeah, 18" - 24" of deflection total at the tips. Scary as hell. And yet, apparently there was no damage - they took the canard off, examined everything, declared it good, reinstalled it and sent the guy home TO BALANCE HIS ELEVATORS CORRECTLY PER THE PLANS, staying well below Vne for the trip.

And yet, about 1/3 of the EZ's that I inspect have unbalanced elevators and/or ailerons when we remove the control surfaces and check them. Few are FAR out, but out of spec is out of spec. Now, AFAIK, there has never been an instance of aileron flutter on an EZ type aircraft, but there have been a few canard flutter instances, this movie being the most well known.

I wonder if the Raptor was getting aerodynamic aileron flutter on his wild ride run instead of runway bumps starting it. That would be a first, I think.
All oscillation is not flutter. It's very hard to imagine that a stiff (relatively) composite wing and aileron would couple aerodynamic and structural modes at such a low frequency. More likely, in my mind, is that unbalanced ailerons with substantial play in the system from the stick aft (and between the ailerons) would get out of phase with the rocking of the structure and drive purely aero loads, increasing the rocking. No structural bending or twisting would be occurring at very low G's and very low speeds, so no coupling between aero and structural modes.

Again, IMO.
 

BBerson

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All oscillation is not flutter.
Lots of weird stuff can happen. Multi bladed helicopters can get "ground resonance" when a skid touches the ground. Can destroy the helicopter if not stopped by flying off or quick landing. So I don't know if the Raptors wobbling would have stopped if it went airborne. Or get worse.
 

Rod Schneider

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The “rough” runway has been mentioned several times as a possible factor in starting the oscillation. This is my home airport (KCNI), and I’ve arrived and departed countless times in several different airplanes (RV-6, AT-6, A36 Bonanza, and others) and have watched other planes landing and taking off. None of them have ever shown any signs of the side to side rocking or the “bouncy” ailerons that the Raptor exhibits............ This runway is as smooth as the majority of any other airports I’ve ever been in or out of.
 

Malish

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The “rough” runway has been mentioned several times as a possible factor in starting the oscillation. This is my home airport (KCNI), and I’ve arrived and departed countless times in several different airplanes (RV-6, AT-6, A36 Bonanza, and others) and have watched other planes landing and taking off. None of them have ever shown any signs of the side to side rocking or the “bouncy” ailerons that the Raptor exhibits............ This runway is as smooth as the majority of any other airports I’ve ever been in or out of.
This is right, I did fly to this airfield many times and NEVER noticed shaking ailerons or rocking movements on aircraft.
Remember, I lived in Atlanta for 25 years and learn my wings at PDK.
https://en.wikipedia.org/wiki/DeKalb–Peachtree_Airport
 
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Jay Kempf

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Just watched the last video. At least now people on YouTube are commenting other than gushingly positive now. That will at least bring some scrutiny if that is the only place where deposit holders are watching. Can't tell from the video if the hand on the stick was helping or adding to the amplitude and frequency of the oscillations. The windshield view was showing some pretty big rocking. Roll PIO?

Question I have is if this didn't happen up until now with similar runs and similar speeds all else being held equal, what changed. Has something in the composite structure having to do with the wing torsional rigidity or the aileron mounts become looser in the few runs that have been done? What I did notice on the last couple videos is he is holding full down elevator through the run. That is putting more pressure on the nose gear which might be manifesting somewhere else in the structure...? Who knows. Hard to separate variables and analyze at this point.
 

Doggzilla

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The entire aircraft seems far too flexible. I don’t recall ever seeing a composite aircraft this bendy.

Maybe it set at the wrong temperature or humidity. The temperature composites set at can affect their rigidity because it changes the internal pressure during thermal expansion . It can make the resin “loose” around the fibers and very flexible.

Resin can be very picky. I recently saw a piece which literally peeled off
 

Turd Ferguson

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Question I have is if this didn't happen up until now with similar runs and similar speeds all else being held equal, what changed.
The ailerons were flopping up and down more than the normal amount of flopping (which Peter blames on removing the weights). At the time it started rocking one aileron appeared to be flopping to full travel with corresponding roll.
 

Doggzilla

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I think we can all agree that the aileron flapping is bad.

But it wouldn’t be happening if the wing was not flapping either. But why is the wing flapping? (Check the video where he manually flaps the wing to check the ailerons)

The wing is clearly flexing at the root when he shakes it. Meaning the fuselage is not rigid enough.

We know the fuselage is already flexing because the gear well wall flexed enough for the bearing to pop out.

The fuselage is not rigid enough.
 

flyboy2160

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..It's very hard to imagine that a stiff (relatively) composite wing and aileron would couple aerodynamic and structural modes at such a low frequency...
I agree.

But the flutter expert who helped with the analysis of my plane claimed that there could be aerodynamic flutter coupling between control surfaces, especially if they were unbalanced, and the rigid body modes of vibration of the entire plane. These rigid body modes - 3 translations and 3 rotations - are very low frequency, even less than 1hz.

So even if the high speed taxi isn't technically free-free, it might be semi-free since he's getting close to his rotation-nose liftoff speed. Didn't somebody here or on Youtube swag the rolling oscillation at ~1 hz?

Peter the Great apparently hasn't done the flutter analysis he promised after Len's bail. If so, he might have seen this Wild Ride coming, especially if he modelled his soft, unbalanced ailerons.
 

Doggzilla

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You know how the B-52 and airliners hang their engines off the front and below the wing to use it as a anti flutter weight? Same thing, but for the control surfaces.

Its just called a spade because it looks like a little garden spade instead of an engine.

Peter's video on the balancing is actually really good, it clearly shows what causes it and how the weights fix it. If you learn anything from his videos, thats probably it.

I actually highly recommend any new members check it out because it really clearly shows the dangers of unbalanced controls, and he does a good job of actually cancelling it out during his demonstration.
 

cheapracer

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Spades make my head spin.

As I think Deuelly meant above, there is only one static balance position, as soon as the ailerons are raised or lowered, that balance is gone, doubly so because of 2 aileron weights wanting to return to static position, and then there's aileron differential to add to the equation somewhere.

... that's before aero comes into it.

Nah, too much of a headache for me, and I think for well versed aero experts only, indicated by the higher level craft that you usually see them on.

This explanation sounds simple enough, but note that he clearly says that they are "Very difficult to balance"

 

BJC

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Static balancing is done to have an opposing torque at the hinge line when the hinge is accelerated. That can be accomplished with the weight not in the plane of the hinge and the aileron C.G.

Consider a free body diagram, with a pivot point, a point mass behind it, and a point mass forward at a distance that produces a torque on the hinge equal to the torque from the aileron mass. That condition is statically balanced.

Now accelerate the hinge upward at, for example, 2g. The aileron point mass will generate an inertial force that will try to rotate the aileron to deflect down, (mass X 2g X arm = torque). The balance weight will also be accelerated upward at 2g, and it’s inertial force will produce a torque equal to the aileron’s, but in the opposite direction.


BJC
 

cheapracer

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Maybe, like a car tyre, it requires pressurization to achieve maximum structural stability...?
That's how a modern airliner works apparently.

Though i think the Raptor project is just thick skinned, in more ways than one ...
 
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