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Date: Sat, 17 Mar 2007 20:17:56 -0400
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Subject: Re: [LML] Aileron Flutter 
From: "bob mackey" <n103md@yahoo.com>
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Randy Stuart wrote about his LNC2:

> I'm flying around today and I looked out the cockpit and I
> noticed my right aileron fluttering. Looked at my left
> aileron and it's doing the same thing. I turn left and
> right, the ailerons are working fine but still fluttering.
> I got to my desination, bought some fuel and went flying
> some more. This time I didn't see much flutter, if any, at all.

A few things changed when you added fuel to the wing*:
1) The mass of the wing increased, decreasing the resonant frequencies
for the flapping and twisting vibrational modes.
2) The fuel also damps the motion of the wing, reducing the "Q" or
resonant efficiency.
3) You may have been flying a little slower (TAS) with the heavier load.
4) The temperature of the wing structure may have changed, altering
its stiffness a little teeny bit.
5) You demonstrated that you are without a doubt a test pilot
when you intentionally flew an aircraft with a known aileron flutter.

The fact that the ailerons flutter at any fuel state indicates that
something isn't quite right. It may seem to fly OK for now, but
rate of wear on the aileron hinges is probably MUCH higher when
fluttering. As the hinges wear, the problem will probably get worse
until something fails. I would strongly suggest figuring out why
there is flutter and fixing it permanently before it gets worse.

Here are some things to check:
- aileron mass balance
- aileron hinge slop
- slop anywhere in the aileron control system
- proper rigging
- are the ailerons in the right place? the leading edge should
  be slightly proud (0.040" ?) of the faired airfoil surface.
- aileron stiffness: any delamination inside the aileron?
  Built to the plans?
- wing stiffness: is there any reason why the wing's torsional
  or flapping rigidity might be less than designed?
  e.g. delamination, experimental design alterations, etc.

When you find the problem and fix it, please let us know what it was.

-bob mackey


* If you only added fuel to the nose and still saw the flutter
go away, then only item #5 applies.