This paper describes the operating principle of a rotating stall control system and the results of testing a prototype control on a low-speed research compressor and on a J-85-5 turbojet engine. The control is an electrical feed-back control system which uses unsteady pressure signals produced by sensors within the compressor to detect the presence of stall and provide a correction signal when stall occurs. In the prototype system, the correction signal is used to drive a hydraulic actuator which provides a mechanical operation on some variable geometry feature of the compressor being controlled. On the low-speed research compressor the variable geometry was the stagger angle of the stator rows. On the J-85 engine, the control was installed to override the normal operating schedule of the compressor bleed doors and flaps on the inlet guide vanes. Both series of tests were successful in that the control rapidly eliminated rotating stall when it occurred and in some cases did not allow rotating stall to occur at all.

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