A VTOL aircraft which is in a state of hovering flight possesses no inherent stability of its own, consequently it may be found necessary to introduce some artificial form of control of the aircraft in both rolling and pitching motion. Such a control device may consist of an auto-stabiliser which enables the pilot to maintain the aircraft in a state of stationary hover, or to perform some manoeuvre by rolling or pitching the aircraft. This paper investigates the wing vibration problems associated with the roll attitude control of a transport aircraft in which the jet-lift engines are mounted in pods situated on the wings. Fig. 1 illustrates diagrammatically a typical transport aircraft configuration in which there are sixteen jet-lift engines mounted in two pods, one on either wing, each pod containing eight lift-engines.