DYNAMIC INSTABILITY OF FINNED MISSILES CAUSED BY UNEQUAL EFFECTIVENESS OF WINDWARD AND LEEWARD FINS

A dynamic instability is described for rolling, finned missiles with canted fins. The instability occurs as an undamping of the angle of attack and is caused by differential lift from unequal effectiveness of the windward and leeward fins. The instability is similar to a Magnus instability in that a yawing moment occurs that causes damping of negative precession and undamping of positive precession motions. The equivalence of the Magnus coefficient and the differential fin lift forces is derived, and the instability is demonstrated with computer simulations of the equations of motion for the angle-of-attack convergence of a reentry vehicle. The computer results are compared with a closed-form solution for the angle-of-attack convergence envelope.