Raptor Composite Aircraft

[Andy_RR]

This is very interesting. I presume and increased radius was employed? Perhaps something to do with tripped flow at small aileron deflections?

Probably more likely something to do with vortex shedding exciting a troubling natural frequency at some airspeed. Given that vortex shedding frequency is a function of TAS (that's how vortex flow meters work), you really don't want to wave bluff bodies around in the air more than you can help it as they are in effect variable frequency generators and the frequency will likely arrive at a resonance somewhere along the speed curve.

 

[pictsidhe]

I must have ben reading the wrong books...

 

[Toobuilder]

Looks like another 10 pounds added in the last video.

Looking at the construction and hardware choices of the landing gear only, it's not hard to see why this project is so massively overweight.

 

[pictsidhe]

This is very interesting. I presume and increased radius was employed? Perhaps something to do with tripped flow at small aileron deflections?

The nose radius of Frise ailerons often needs tweaking. Too small can cause seperation, and in bad cases, flutter.

 

[wsimpso1]

Control surfaces are mass balanced to make the control surfaces vibrate with the structures they are hung from. That prevents the control surface from pumping the natural bending and torsion modes of the wing or stabilizer it is attached to. Yes, this is pretty much easy science.

Vortex shedding can still excite fundamental frequencies of the wing, stabilizers, and control surfaces. This is shoved out to "high enough" true airspeed by combinations of structural stiffness, control system stiffness, and managing vortex shedding, and other items that may have quite a bit of art added to science.

 

[pictsidhe]

Peter 'perfectly' balanced one aileron, with two big clamps temporarily holding it together. He then said he overbalanced the other side, but thought that wouldn't matter once everything was connected up. Was he not paying attention in his lesson in how well that can work?

 

[Deuelly]

His static balance not being in the same plane as the mass of his ailerons is going to reek havoc with his dynamic balance.

Brandon

 

[pictsidhe]

With the ailerons balanced by the spades, the cg of the assembly will be several inches below the hinge. Is this likely to be an issue?

 

[wsimpso1]

His static balance not being in the same plane as the mass of his ailerons is going to reek havoc with his dynamic balance.

Brandon

Please elaborate for the benefit of the group.

 

[BBerson]

Looks like another 10 pounds added in the last video.

Yes, and aft of the CG. Also makes the center of mass of the wing/aileron further aft which may not help.
The Cirrus has metal ailerons. Wonder why?
The DC-3 has fabric covered ailerons.
Lighter ailerons should be on the next design, maybe not full span.

 

[Deuelly]

Please elaborate for the benefit of the group.

Sorry, should have said ailerons and hinge line plane.

Brandon

 

[BBerson]

His static balance not being in the same plane as the mass of his ailerons is going to reek havoc with his dynamic balance.

Brandon

I think putting only one balance weight (instead of distributed like Cessna) might cause a dynamic torsion issue in the long aileron. I didn't see any floppy twist in the video, but could happen.

 

[Marc Zeitlin]

I think putting only one balance weight (instead of distributed like Cessna) might cause a dynamic torsion issue in the long aileron.

The EZ type aircraft have a steel rod for mass balance in the LE of the aileron, so the weight is constant from tip to root. However, the elevator on the canard has an outboard mass balance and an inboard mass balance that are point masses (effectively). So both types are used. There are apparently many ways to skin the flutter cat... I assume that Burt picked the "point mass" system for the elevator since the canard/elevator combination on these canards is effectively a slotted flap, and there would be no way to shape the slot and LE of the "flap" (elevator) if the mass balance was distributed. Since the ailerons are NOT slotted flaps, a distributed mass could be used.

Both the elevator and aileron are slightly OVER balanced - meaning that when hung from the hingeline, the LE is slightly below the TE. The plans specify how much. Interestingly, if extra weight is needed to balance the elevators, the plans specify to only add it to the outboard position (although I see MANY planes in which it was added inboard - it's almost like folks can't read). Jon Karkow, late of Icon Aircraft and a longtime senior engineer at Scaled, told me that his understanding was that the inboard mass balance weight didn't actually accomplish anything and he didn't know why Burt had put it there - his understanding of flutter theory indicated that all the weight (if not distributed) should have been outboard. He gave me a good explanation for why, but I don't remember it (being old and senile).

So. Is only one balance weight bad? Sometimes not, apparently, since the only elevator flutter instances in EZ type aircraft occurred when the elevator wasn't balanced correctly, but who knows in this case.

You can download a video of canard flutter on a Varieze here:

http://cozybuilders.org/Accident_Investigations/index.htm​

it's pretty amazing .

 

[Toobuilder]

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.

 

[BBerson]

You can download a video of canard flutter on a Varieze here:

Getting "Safari can't download that video".
Is that available on YouTube?

 

[Marc Zeitlin]

Getting "Safari can't download that video".

Probably due to being a WMV file...

Is that available on YouTube?

It is now . See:

The interesting part starts at about the 2:20 mark, but it's not like the whole thing is very long. A short version, that only has the flutter portion, is here:

 

[bmcj]

Perhaps the reason for the outboard bias for added counterweight is that the flexural displacement/oscillation is going to occur at the tips and not at the root of the (springboard) canard?

 

[mcrae0104]

With the ailerons balanced by the spades, the cg of the assembly will be several inches below the hinge. Is this likely to be an issue?

I would have expected this to be a problem but similar bob-weight style counterweights have been successfully used on other aircraft like the Emeraude and Navion (see illustrations here) so perhaps it it not an issue, at least at the relatively low speed of those two types.

 

[Deuelly]

With the ailerons balanced by the spades, the cg of the assembly will be several inches below the hinge. Is this likely to be an issue?

That's the issue I see. It's not the single point of balance but the fact that the CG is away from the hinge point.

Well that and if his spades are attached as poorly as some other things are they may depart under G load. When that happens, he's going for a ride.

Brandon

 

[BBerson]

It is now . See

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.