There was then no flight experience with wings of this amount of sweepback. Many modern helicopters use some form of simple sweepback on the blade tip. Too much dihedral or sweepback generally causes Dutch roll. It had three-bay wings without sweepback, dihedral or stagger, partly to facilitate wing folding. The wings were heavily staggered and had pronounced sweepback, both features intended to improve stability. The wings of both the monoplane and biplane versions featured prominent sweepback. Analysis by Boeing engineer Vic Ganzer suggested an optimum sweepback angle of about 35 degrees. The leading edge sweepback angle was held at 50 degrees by a rigid spreader bar.