3. Additional fuel tanks
I have installed additional fuel tanks behind the spar and have
a total capacity of 110 imperial gallons. Because PFA were concerned about
lower skin adhesion to the ribs they made me put double flanges on

each rib

to reduce the risk of peel forces. I had to test the torsional

stiffness of

the wing by bolting it to a steel spar on the workshop wall and

twisting it.

From the formula provided by PFA a Vcf (critical flutter) of 630

knots was

calculated - that will be sufficient for me.

Does anyone have this equation handy?  I've been looking for it with no
luck.

Thanks.

--
Chris
microcosman.com

Vance might. Vance?

Paul Lamar

Bill Freeman wrote:

Typically a flutter survey involves exciting the primary surfaces to their
natural frequency on the ground and then calculating what airspeed would
match this freq.   Just a rough idea, I've never done it.

Bill

I have sent a request to Ray Clegg for a copy of this equation. As Bill stated above,
a
vigorous flutter analysis requires a vibration survey, provided by driving the suspect
surfaces to resonance with various sources. Any resonances that demonstrate
potential coupling should be modified. Some relation to flight speed can be
roughly computed using such things as vortex shedding predictions. High
torsional stiffness, as is common with composite construction is a definate plus,
and the noted designer Irv Culver suggested - keeping torsional frequencies higher
than "flapping" frequencies is good. 

Composites, and wood structures, generally
have pretty good damping, and the riveted joints in sheet metal are also
damping. (The "spin" welding proposed for the Eclipse jet looks like a recipe
for disaster to me, with both lack of damping and built in crack starters -
fortunately, I predict they will never be delivered to customers for other reasons)
I do not claim to be and expert in flutter, and am strongly suspicious of those
that do. Vance

 
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