Aircraft landing gear ground loads when spinning-up the wheels at touch-down

Abstract

The investigation covers all combinations of landing speed, coefficient of friction between the tyre and the ground, and harshness of landing, for any type of pneumatic tyre and wheel unit. Particular attention has been given to landing speeds between 50 and 150 m.p.h., coefficients of friction from 0 to 2.0, and landings giving vertical wheel accelerations of lg, 2g, 3g, 4g. It was found that for any landing, the vertical reaction at any wheel which has just finished spinning-up increases with increase in the moment of inertia of the wheel and tyre unit, and the landing speed, and decreases with increase in the free tyre radius, the aircraft weight, the time to reach the maximum vertical wheel reaction, and the coefficient of friction between the tyre and the ground. It should be noted, of course, that there is a relation between the moment of inertia, the free tyre radius and the aircraft weight, - in general the free tyre radius and the moment of inertia will increase with aircraft weight. For any wheel and tyre unit it is shown that there are various combinations of landing speed and coefficient of friction which will cause the wheel spinning up to iust cease at the same instant as the maximum vertical wheel reaction is reached, and except for very gentle landings, the maximum value of μ required is usually much less than 1.0. Figs. 1 to 7, together with the notation given in Section 8, are self-explanatory and expand the above observations.