Mechanics and Control : Proceedings of the 4th Workshop on Control Mechanics January 21 23 1991 University of Southern California USA The workshop on Control Mechanics originated in 1988 beca me an annual event and gained considerable recognition in advancing control of nonlinear and uncertain mechanical sy tems and promoting application of advanced mechanics in con trol. The fourth meeting continues the tradition with 17 papers containing original and recent work of the partici pants developed in 3 basic directions: feed back control of uncertain systems flexible mechanical structures and flight control