The Effect of Folding Wings

Folding wings as a device for fitting very large airplanes into airport ramps, taxiways, and maintenance areas would have stability and control consequences. While fairly long wing sections could fairly readily be folded up, shortening fuselages by fold­ing hardly seems practical. This means that tail length in terms of wing spans would be reduced.

Longitudinal stability and control would be adversely affected by the shorter relative tail length of folding wing designs. Higher downwash and larger trim drag would result. There would be increased yawing moment due to rolling. An extended-span transport airplane would have some of the flight behavior of a high-performance sailplane, with strong demands on rudder power to coordinate rolls. However, the most adverse effect and most difficult to correct would be reduced rudder power for low-speed control with an engine out.

Even without folding wings, the current Airbus A3 80 layout has 10- to 20-percent reduced tail length in terms of wing span than current designs, such as the Boeing 747-400. The same adverse trends in stability and control as for the folding wing case, noted above, might be expected.