From Sioux City to the X-33

Abstract

The history of the “Propulsion Controlled Aircraft (PCA)” problem is reviewed. While there had been repeated warnings that life-threatening hydraulic failure in a modern airliner can occur despite an estimated probability of 10 −9, only after the Sioux City accident was the possibility of using some automatic fly-by-throttle back-up control system for crippled airplane seriously considered. Several different schemes to help pilots fly hydraulically depleted aircraft by using collective and differential thrust of the engines will be reviewed. Special attention will be devoted to the system theoretic “model matching” methodology, in which the propulsion controlled aircraft is compensated so as to respond as if it were under normal aerodynamic control. Applications of these concepts to Unhabited Air Vehicles (UAV's) will also be considered. Finally, it will be shown how the propulsion control concepts can be extrapolated to the X-33, the reduced scale demonstration vehicle of the new space shuttle, the engines of which cannot be gimballed so that differential thrust instead of thrust vectoring has to be used. The latter application is more in the spirit of “reconfigurable control” and is based on the novel methodology of Linear Set Valued Dynamically Varying (LSVDV) control.