# Raptor Composite Aircraft

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#### BBerson

##### Light Plane Philosopher
HBA Supporter
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
What about accelerations in yaw? The balance weight below the hinge line will see more effect from a cyclical yaw from nose wheel shimmy or something.

#### flyboy2160

##### Well-Known Member
What about accelerations in yaw? The balance weight below the hinge line will see more effect from a cyclical yaw from nose wheel shimmy or something.
The aileron isn't free to rotate in yaw or in roll - it only rotates in pitch. Per FAR 23, the counterbalance support must be good for 24G vertical, 12G side to side and aft, and have a fundamental frequency 50% greater than the control surface.

#### Deuelly

##### Well-Known Member
Log Member
The aileron isn't free to rotate in yaw or in roll - it only rotates in pitch. Per FAR 23, the counterbalance support must be good for 24G vertical, 12G side to side and aft, and have a fundamental frequency 50% greater than the control surface.
It's not free to rotate, but having the center of mass below the hinge line will cause movement with yaw and longitudinal acceleration and deceleration. How much and its effect is unknown. I do know having slop in the control system won't help negate its effect.

Brandon

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#### RJW

##### Well-Known Member
What about accelerations in yaw? The balance weight below the hinge line will see more effect from a cyclical yaw from nose wheel shimmy or something.
Wasn't it fore and aft flutter that ripped off the wings of early Grumman Avengers? I think it was due to the ailerons not being balanced vertically. It took them a long time to figure it out because nobody thought the wings could oscillate fore and aft. There is a video somewhere of it happening in a wind tunnel. I just can't find it now.

Rob

#### wsimpso1

##### Super Moderator
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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.
I looked and could not find anything on that except one sales brochure that mentioned modulus drop from too low cure temperatures for epoxy resin, but gave no numbers on acceptable cure temperatures or on how much the modulus changes. Please supply links to data or literature covering this.

Billski

#### BBerson

##### Light Plane Philosopher
HBA Supporter
Wasn't it fore and aft flutter that ripped off the wings of early Grumman Avengers? I
I haven't heard that. But anytime something new is tried, get ready for surprises.

#### Doggzilla

##### Well-Known Member
HBA Supporter
I looked and could not find anything on that except one sales brochure that mentioned modulus drop from too low cure temperatures for epoxy resin, but gave no numbers on acceptable cure temperatures or on how much the modulus changes. Please supply links to data or literature covering this.

Billski
I’ve seen large castings “flop” open before like they were an omelet. The fibers and resin were very loose, as if the glass was in compression instead of tension.

But now that I think of it, it’s far more likely he just used a flexible resin. This is common in boats and windmills. It’s actually intentional.

https://www.epoxyworks.com/index.php/understanding-flexible-properties/

Anyone know what resin he used?

#### Kyle Boatright

##### Well-Known Member
HBA Supporter
Here's a picture I made this evening of the Cherokee County Airport, where Peter is doing his test runs and where the aircraft will (presumably) make its test flights.

This is what it looks like for miles in every direction. The only modestly suitable emergency landing site is the highway which runs parallel to the runway. Note the drop-offs on each end, and the rolling, wooded terrain.

Just a bad place for first flights of a high performance aircraft.

#### Doggzilla

##### Well-Known Member
HBA Supporter
You know what? If he attached the wings the same way he attached the landing gear, that would explain the extremely floppy wings.

That’s what killed our friend flying the kasperwing.

What do the mounts look like?

#### cheapracer

##### Well-Known Member
Log Member
What do the mounts look like?
I might be mistaken, but I seem to remember Autoreply being unimpressed with the wing mounts.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Maybe, like a car tyre, it requires pressurization to achieve maximum structural stability...?
Seriously doubt it. Fuselage pressurization is typically for an 8000 foot cabin when high. At each airport, the air outlets are wide open - no delta between atmosphere and cabin. Pressure difference is ramped up as the airplane climbs and never has less than about 22" Hg in the cabin. Recall that the atmosphere is about 15" Hg at 18000 feet, so that is about 7" Hg or about 3.5 psi.

In order for fuselage pressurization to matter, you would have to be depending upon 3.5 psi at 18,000 feet to make things stiffer. And down at the surface, where the landings and takeoffs and manuevering and so on occur, you would have much less pressure.

To fill in the rest of the understanding, when airliners were not pressurized, they had one level of fuselage structure and some of those airplanes have demonstrated essentially unlimited airframe life - DC-3/C-47 as an example. When the first pressurized airlines came along (Boeing 307), they had to beef up the fuselage to stand the pressurization and load cycling that goes with it. Perhaps you have heard of jetliners with fuselage fatigue issues, including one that turned into a convertible in flight...

No, pressurization does not help the structure, it makes the job tougher.

Billski

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Talking about the wing and fuselage flexibility got me to go in and look at the latest video. Normally, I do not. Something about not supporting those that you think are dangerous...

A close review of the segments where Peter is shaking the wingtips will show that he supports the airplane near the nose gear and main gear, and that both wing tips are moving when he shakes one. The left wing tip is easy to see, being on the order of a foot from the camera, but the right tip sail 34 feet away is just barely visibly jiggling too. Looks like both wingtips could be moving about the same amount too. The fuselage area appears to be not moving. If there is some flexibility in the support near the landing gear, the fuselage could rotate about its roll axis a tiny bit. If the fuselage is rolling back and forth slightly to the point where the outer ends are moving about a half inch, at the fuselage, rigid body rotation would produce a total vertical movement around 0.07" - that is too small to see on this GoPro from 15 feet away. So, from this video is no proof that the wing root is mostly flexing on the fuselage.

Is the fuselage too soft? Maybe, but the 11/19 video does not prove anything of the sort. What it does prove is that his unbalanced ailerons do interact with his wing movement, which are likely to pump wing flutter if not corrected and that the new level of balance will reduce likelihood of having that flutter mode. All the rest are yet to be shown.

Billski

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#### wsimpso1

##### Super Moderator
Staff member
Log Member
On to the 11/22 video. Spherical and other self-aligning bearings are supposed to be used in places where part and airframe deflections under load are large enough that significant angular movements between parts will happen. These sorts of bearings tend to have rather modest capacity to resist loads in the axis of the shaft running through them. While these arms are supposed to primarily support loads only pushing down on the main gear, there must have been something wrong here as axial loads were large enough to overcome the adhesive holding the bearing in place. That both bearings were pushed out in opposite directions is telling too. Sounds like unintended loads resulted from the landing gear geometry and perhaps from a lack of gear leg constraint...

How did the bearings come loose:
The adhesive was overloaded and failed - not terribly likely, there are several square inches per bearing times adhesive strength in the thousands of pounds per square inch, which would require a LOT of force;
The bearing/ring/bore were not adequately prepared, bearing adhesive never really had a grip, then the bearings were pushed free during that interesting rolling diversion;
One bearing was pushed out, then the large swing by the arm pushed the other bearing free.

Peter's fix of putting washers on the shaft to bear on the airframe may work in the short term, but I am concerned that if they do have axial loads in the arm and its pivots, the washers will just rub their way into the laminate of the structure. A proper analysis of the total load picture on this joint under the range of landing and ground operation is in order. I suspect that a substantial Garolite bushing bonded into the airframe on each side and the bearing correctly attached with adhesive should work. I also suspect that an Oilite bronze shoulder bushing on each end in a Garolite bushing should do the job. The analysis of the system will show if either bearing type needs shoulders to support axial loads or not.

Billski

#### Marc Zeitlin

##### Exalted Grand Poobah
... What it does prove is that his unbalanced ailerons do interact with his wing movement, which would pump wing flutter if not corrected and that the new level of balance will prevent that flutter mode...
The only thing I would modify about your post is to change the two "would" and "will" to "may"'s in this sentence.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
The Piper Super Cub aluminum late model aileron isn't 100% balanced. Looking at the manual last night, I noticed the aileron balance procedure requires a temporary 7.2 lb nose weight to test for correct balance.

#### Doggzilla

##### Well-Known Member
HBA Supporter
From post #3069

HenryK will remember. The member was his friend and they named an airport after him.

The aircraft had folding wings and the joints pulled out of the composite due to a bounce on takeoff.

They were designed for aluminum wings with a spar, not composites.

If Peters mounts are anything similar, I would highly recommend reinforcement plates to spread out the stress concentration.

#### Volzalum

##### Active Member
If Peters mounts are anything similar, I would highly recommend reinforcement plates to spread out the stress concentration.
I believe that Peters wings have a 3 piece spar: 1 piece in each wing and one piece that extends through the fuselage and extends a bit outside for the the wings connect to.

#### Doggzilla

##### Well-Known Member
HBA Supporter
Any pictures of how they connect to one another?

#### Deuelly

##### Well-Known Member
Log Member
The Piper Super Cub aluminum late model aileron isn't 100% balanced. Looking at the manual last night, I noticed the aileron balance procedure requires a temporary 7.2 lb nose weight to test for correct balance.
You don't need 100% balance. Even the Curtiss P-40 with a VNE of 480 mph didn't have 100% balance elevators. What ever balance you calculate has to put flutter above your VNE.

Brandon

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