structural question about a twisted wing

[robbie]

question one: what type of reinforcements will make a built up rib style balsa wing stronger in terms of twisting?

question two: how important is a non-twisting wing in terms of the forces acting upon the wing in flight?

reason for asking: most recent wing i built ended up with a bad twist in it after tissue covering that rendered it unusable but it seemed real strong on the x axis and the y axis, just flexy when i tried to twist it.

[Marion]

A lot of diagional parts (ribs, etc) will make it more resistant to twisting. The covering will help a lot too.

[Weisse Luft]

D-box from LE to main spar does the most for the forward section of the wing. Look at the way the covering wrinkles when you twist it. The wrinkles run with the direction of the principle tensile strain (resultant of stress) and are orthogonal to the compressive strains.

Running thin sheet balsa reinforcements with the grain parallel to these wrinkles will stiffen against torsion but are much less effective for compressive strains.

The reason for the low torsional stiffness is the relative low tensile modulus of the covering. In fabric coverings, some weaves have different tensile moduli depending on direction with the weave always lower than the warp(not to be confused with distortion but the long elements on the loom)

[Ollie]

Monocoat is probably the stiffest of the film type coverings and will add torsional rigidity to a rib and spar open bay type of wing construction. By holding the wing in a given twisted or untwisted position while shrinking the Monocoat, you can lock in the twist shape.

[robbie]

thanks for the answers!