An analysis of falling leaf suppression strategies for the F/A-18D

A large-angle simulation model for the F-18C/D has been recently validated and reported. Utilizing this model, various methods of suppressing falling leaf motions were evaluated. The results indicated that falling leaf motions were highly susceptible to damping applied to the wind roll axis. The difficulty of implementing such a scheme is that the required states are not always measured, or measured accurately. Another suppression strategy, which performed at nearly the same level, involved applying a damping moment directly against the instantaneous angular momentum vector of the aircraft. The advantage of this system is that it requires information which is available and accurately measured on most fighter aircraft. In general, the method performed consistently on all types of falling leaf motions and would likely be effective in oscillatory and flat spins. Comparisons between these two motion suppression schemes as well as others are presented. (Author)