PARAMETRIC INVESTIGATION OF VTOL HOT GAS INGESTION AND INDUCED JET EFFECTS IN GROUND PROXIMITY

A large-scale VTOL test bed designed around the Ames Lift Engine Pod was used for ground-proximity tests at the Ames Research Center VTOL test facility, under sponsorship of the Naval Air Systems Command. Objectives were to obtain parametric data on gas ingestion and jet effects experienced by jet-powered VTOL configurations. Results showed that ingestion and induced-lift effects are configuration- and time-dependent; for many configurations the degree of ingestion experienced cannot be tolerated in operational aircraft. This contrasts with results of recent small-scale tests. Wing geometry, size, location; engine arrangement, lift/cruise engine location and pitch attitude have strong influences on ingestion tendencies and jet-induced effects. Near-field temperature environment appears to be influenced by engine arrangement and number of operating engines. Rapid inlet temperature rise with a high temperature distortion at the compressor face sometimes resulted in engine stall. Hot gases expelled from the engine subsequent to stall occasionally caused stalling of adjacent engines. Large induced force levels and moments resulted from near-ground operation of many configurations. Positive- and negative-induced lift were measured. Aerodynamic suckdown results with a single jet-fundamental geometry configuration are in agreement with empirical correlation of small-scale tests. Results showed that transient measurements with rapid-response thermocouple and recording equipment are needed for realistic assessment of VTOL environment and inlet temperature rise caused by ingestion. (Author)