A Throat-Bypass Stability-Bleed System Using Relief Valves to Increase the Transient Stability of a Mixed-Compression Inlet.

Abstract : This report presents the transient performance of a stability-bleed system installed in a YF-12 flight inlet that was subjected to internal and external airflow disturbances in the NASA Lewis 10- by 10-Foot Supersonic Wind Tunnel. This stability-bleed system could actually be flown on the YF-12 aircraft, because it was designed to fit withstand the YF-12 flight environment. The purpose of the system is to allow higher inlet performance while maintaining a substantial tolerance (without unstart) to internal and external disturbances. At Mach numbers of 2.47 and 2. 76, the stability-bleed system increased the inlet tolerance to decreases in diffuser-exit corrected airflow by approximately 10 percent of the operating-point airflow. The stability-bleed system complemented the terminal-shock-control system of the inlet and did not show interaction problems. For disturbances which caused a combined decrease in Mach number and increase in angle of attack, the stability-bleed system with valves operative kept the inlet started 4 to 28 times longer than with the valves inoperative. Hence, the stability system provides additional time for the inlet control system to react and prevent unstart. This was observed for initial Mach numbers of 2.55 and 2.68. For slow increases in angle of attack at Mach 2. 47 and 2. 76, the stability-bleed system kept the inlet started beyond the steady-state unstart angle. However, the maximum transient angles of attack without unstart could not be determined because wind-tunnel mechanical-stop limits for angle of attack were reached.