Tests of an Improved Rotating Stall Control System on a J-85 Turbojet Engine

Abstract

An improved version of a rotating stall control system has been tested successfully on a J-85-B turbojet engine. Past tests had pointed out the desirability of increasing the response speed of the control. In this study, the installation of the stall control on the J-85 was modified so as to decrease the response time of the control by a factor of ten over that attained in the past tests. The modified control was tested to see if the decreased response time improved the ability to clear rotating stall once it has started, and also to see if rotating stall could be anticipated and prevented by proper selection of the variables in the stall control detection system. The performance of the stall control was tested by closing the bleed doors on the engine until rotating stall occurred or until the control anticipated stall and held the bleed doors open. The tests showed that the control is capable of anticipating stall before it occurs and keeping the engine completely clear of stall at speeds up to 80 percent of design speed. No tests were performed above 80 percent of design speed because opening the bleed doors at such speeds might aggravate the stall rather than clear it.