Unbalanced layup
Unbalanced layup
(OP)
Is composite wing mainly of quasi layup construction? and is it only for the only skins or the stiffeners like spars, ribs and stringers. I came across a presentation mentioning using unbalanced layup on the wing design to overcome the twisting, is this just simply add on extra plies on a quasi layup skins??





RE: Unbalanced layup
RE: Unbalanced layup
Well in fact any unequal number of off-axis plies (except 90s of course). You get unbalanced layups with unequal numbers of +30, -30 plies for example.
RE: Unbalanced layup
Spar webs need lots of 45 degree plies. Ribs need a good mix, with (usually) quite a few fibres in the vertical direction to resist Brazier crushing loads and tension due to over-fuel pressures and crash pressures.
Before the aerodynamic effects of gross structural coupling between incidence and torsion were understood some terribly dangerous monoplanes were designed. In WWI quite a few German pilots were killed by such effects.
Deliberate material-based bend-twist coupling was probably most famously used on the X29 with its forward swept wing.
While you can achieve such coupling with uneven numbers of + and - angle plies, it can also be done by using the distribution through the thickness and to keep the same number in each direction. (This is probably more practical for a more monolithic structure than a box.) Just put all the +angle plies nearer the centerline of the beam than the -ones (or vice versa, depending on what you're trying to do). Under bending, the +plies above the neutral axis try to shear one way and those below it shear the other (giving twist). The same goes for the -plies, giving twist in the opposite direction. However, the plies furthest away from the neutral axis are more effective, giving a nett twist in their direction.