At the Draper Laboratory (1968-73), he was principal designer of the Apollo Project Lunar Module manual control logic used for all moon landings, and he created a preliminary design for the Space Shuttle atmospheric flight control system. There, he also initiated a project to develop a Bedside Biomedical Computer for the analysis of cardiovascular data, a precursor to today's computer-based EKG machines. His work at TASC (1973-77) included modeling of pilot/aircraft interactions, fuel-optimal flight of jet transports, digital control of high-performance aircraft and helicopters, submarine dynamics and control, and statistical assessment of the effects of electric powerplant waste water on biologically indigenous populations. While serving as an Air Force lieutenant (1960-63), he was a Range Safety Officer at NASA's Wallops Flight Facility.
From 1994 to 1997, he served as the Engineering School's Associate Dean for Academic Affairs. During that time, he initiated new programs of graduate study and undergraduate computer education, and he developed an innovative approach to teaching engineering freshman seminars. In 1998, the founded Princeton's Certificate Program in Robotics and Intelligent Systems. During his 20 years as director of the program, over 350 students were awarded the certificate at graduation. As Director of Princeton's Flight Research Laboratory from 1977 to 1983, Stengel, his students, and staff conducted pioneering experimental research on digital flight control systems, flight computer networking via fiber-optics, aircraft flying qualities, and aerodynamic system identification. This research used Princeton's two fly-by-wire, variable-stability aircraft and a specially instrumented sailplane.