What is the nature and magnitude of the forces acting on wing spars in the horizontal plane?
One would imagine that front spars are in (horizontal) tension and rear spars in compression due to the force of frontal drag tending to push -or rotate- the wing back horizontally from its attachment at the root. If this is the case, how big are these horizontal forces compared to the vertical lift force they have to bear? Is it a matter of multiples or an order of magnitude difference?
Also, can flutter act in the horizontal plane as it does in the vertical?