Abstract: To enhance stall margin without degrading engine performance the case of the fan of a fan-jet engine is treated by incorporating a passageway to remove flow from the main flow stream. The location and amount of the low momentum flow relative to the rotor being removed is critical. The flow is removed at a judicious location downstream of the leading edge of the rotor blade and returned at a judicious location upstream of the point of removal. The amount of removed flow must be no greater than 8% of the total flow in the fan rotor. Anti-swirl vanes in the passageway and discreetly sized inlet and outlet passages of the passageway return the flow to the main stream at an increased velocity. The intake is so designed that it selectively removes only the weak low momentum flow relative to the rotor and encourages the strong mainstream flow to remain in the main gas stream.

Abstract: The outer shroud of an axial flow compressor is treated to remove the low momentum flow adjacent the tips of the compressor blades in a judiciously located and sized passageway that removes the low momentum flow relative to the rotor blades at a location downstream of the blades' leading edge and returned at a location upstream of the point of removal. It being critical that no more than 12% of the total flow in the compressor rotor is removed for treatment. Anti-swirl vanes in the passageway serve to remove or reverse the swirl component from the removed low momentum flow. The intake is so designed that it selectively removes only the weak low momentum flow relative to the rotor and encourages the strong mainstream flow to remain in the main gas stream.

Abstract: A surge prevention system for a fan jet engine of an aircraft serves to manifest a signal whenever pressure distortions at the engine's inlet is calculated by judiciously located total pressure probes mounted downstream of the fan on the fan struts in the fan discharge duct. The engine's bleed valve is automatically opened to prevent surge and the fuel control's speed sensor is automatically reset to compensate for any loss of thrust. Safety switches are included to render the system inoperative whenever the aircraft is in the margin of stall and the reset feature is rendered inoperative for normal bleed open operating conditions.