Reingestion characteristics and inlet flow distortion of V/STOL lift-engine fighter configurations

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National Aeronautics and Space Administration, 1970 - Jet engines - 41 pages
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Reingestion of exhaust gas into engine inlets during hover, and inlet flow distortion with the associated loss in total-pressure recovery during transition were studied using a largescale generalized lift-engine fighter model powered by 5-85 engines. Exhaust gas reingestion during hover was studied on a static test facility, and inlet flow distortion and total-pressure recovery loss were studied in the 40- by 80-foot wind tunnel. Two lift-engine arrangements were studied, the swiveling, retractable and the internally fixed. Both arrangements were subject to excessive thrust loss and compressor stalls due to reingestion when the engine exhaust was vectored nearly vertical. Vectoring the exhaust approximately 20' from vertical essentially eliminated reingestion problems. Vectoring the lift-engine exhaust forward and the lift-cruise engine exhaust aft tcr balance the aircraft and minimize reingestion appears to be a feasible means of allowing VTOL operation. Inlet flow distortion and total-pressure recovery were within acceptable limits for the swiveling, retractable lift-engine configuration. With the inlet guide vane installed to help turn the flow into the engine, the vertically mounted lift engines of the internally fixed configuration with an inlet radius to diameter ratio of 0.19 produced acceptable inlet flow distortion and totalpressure recovery results. Without the guide vane the nominal acceptable distortion level of 10 percent was exceeded at the higher velocity ratios.--P. i.

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