On 15 Jan 2007 19:48:55 -0800, "DonMorrisey"
wrote:

A friend's homebuilt recently went down with an 8000 hour pilot at the
controls. No one was hurt and the plane was landed in a field. The
pilot reported hearing/feeling an extremely loud vibration from the
wing, he immediately killed power and landed. One of the wings was
visibly buckled. The airplane is all aluminum with a 36 ' wing span.
The NTSB showed up and after getting the plane to a hangar, the wing
was dismantled. The rear spar had failed and was twisted and buckled,
although the wing had held together. The NTSB guys said the very solid
structural design and construction of the wing was what saved the plane
from coming apart in the air, as well as the pilot's quick response.
The conclusion by the NTSB was aileron flutter, they found several
bolts in the aileron hinge bracket assemblies (which hold the aileron
to the rear spar) that were supposed to have been drilled 10 MM from
the top and bottom edge of the spar flange and these had been drilled
at 25 MM or so. That was it and they walked away. There was no
visible damage to the aileron, the aileron spar or the hinge bracket
assemblies. The pliot reported no vibration in the stick. My friend
is convinced it had something to do with the washout of the wing. The
wing is a NACA 4413 Airfoil, modified in that it has no undercamber on
the bottom, the bottom is flat. The washout, which is built into the
wing during construction, is a couple of degrees. The plane I am
building uses the same wing/washout. I have done research but can't
find anything specific linking washout to flutter.

Any thoughts on this??

Thanks. Don...

flutter can be prevented by....

having the cg of the aerofoil section in front of the spar.

the aileron can be treated as an aerofoil section in the same way but
the entire overall wing cross section needs to follow the rule as
well.

the rear spar needs to be more flexible than the front or main spar.

the ailerons must not have the ability to move without the control
moving them.

the corollary is that if you get any or all of these in the opposite
sense then you can aid in the occurrence of flutter.

washout in itself cant cause flutter.

Stealth Pilot