The directional stability and control of an airplane during the landing roll

Abstract

This thesis considers the problem of the directional instability, as exhibited by aircraft with tricycle landing gear, during the landing roll after touchdown. The approximate equations of motion are solved on an analog computer to describe the motion of an aircraft as it moves along the runway after it has landed.

It is shown that during the landing roll the tricycle landing gear arrangement with a locked nosewheel is basically an unstable configuration. The principle cause of this instability is the nosewheel itself, since it contributes a large destabilizing component to the aircraft’s overall directional stability. This undesirable influence can be reduced by using the elevator, or the horizontal tail, to keep the nosewheel lightly loaded during the landing roll.

Because of the inherent instability of a tricycle landing gear, some type of control is needed to keep the aircraft on the runway during the landing roll. Both the rudder and the nosewheel were examined to determine their effectiveness as steering controls. It was found that the airplane is more easily controlled if either the elevator or the horizontal tail is used to reduce the load on the nosewheel.