Laboratory Tests of an Air Cushion Recovery System for the Jindivik Aircraft.

Full-scale static tests and vertical drop tests were made with an air cushion recovery system (ACRS) installed on the Australian Jindivik drone. The actual aircraft fuselage and wing were used, while the jet engine and other equipment were simulated with inert weights. These laboratory tests were exploratory and results were used to determine a final design. The air supply system components were varied to determine their effect on hover conditions, brake drag, three static and dynamic spring coefficients, three damping ratios and frequencies, and the vertical energy absorption. Twelve configurations were tested using combinations of these components; ejector, tip turbine fan, trunk pressure relief valve, and wing tip roll thrusters. The roll stiffness decreased from 70 down to 36 ft-lb/degree as cushion flow was added. The dynamic heave stiffness was 40% higher than the static heave stiffness. The damping ratio was 0.25 in heave, 0.065 in roll, and only 0.046 in pitch. The trunk coefficient of friction decreased from 0.6 (no air flow) to 0.4 (1 lb m/sec) and then to 0.15 (6 lb m/sec) due to an air lubricity effect. The recovery system had a 50% stroke efficiency. The ACRS trunk assembly weighed 55 lbs. A complete ACRS would weigh an estimated 87 lbs or 2.4% of the takeoff gross weight. (Author)