| Abstract | According to field reports, a number of T2 Sensor Heater Control Valves of J85-CAN-15 main fuel controls have been found “failed-open”. A limited analytical assessment and experimental investigation into the effects of such a failure on engine performance has been carried out. The analyses predicted only minor changes in engine fuel flowrate but more significant changes in Inlet Guide Vane and compressor Bleed Valve schedules. Experimental tests, conducted on engine S/N 8930, in which the T2 sensor air temperature was raised artificially by 20 to 30°C, confirmed the small changes in fuel flowrate, but showed the influence on IGV/BV schedules to be considerably less than predicted analytically. The overall effect on both steady state and transient operation was similar to downtrimming the main fuel control of the engine. It is concluded that, under the above test conditions (CIT = -15°C, T2 = +5°C), a “failed-open” T2 heater valve would not seriously jeopardize safe engine operation.
However, analytically it is predicted that at low inlet air temperatures, encountered at higher altitudes all year round, the T2 speed cutback initiation would be significantly delayed, resulting in considerable aerodynamic overspeeding and, consequently, decreased compressor stall margin. It is recommended that this predicted effect on compressor stall propensity be investigated in a flight test program. |
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