Abstract: Corrected fan speed (N1C2) and engine pressure ratio (EPR) are controlled, by controlling exhaust nozzle area (EA) according to a schedule or map so that as altitude increases (P2 decreases) the axial forces on the low rotor are sufficient to minimize low rotor vibrations. The altitude band (critical load region) is determined that produces loading levels in which vibrations appear. As this band is approached, conventional control of N1C2 and EPR is automatically over-ridden. N1C2 is decreased with altitude and exhaust area is reduced, thereby increasing the axial force (load) on the low rotor. When the upper limit of the band is reached, conventional control of N1C2 and EPR is automatically resumed, resulting in crossing the critical load region rapidly over a narrow altitude band.

Abstract: A control system for controlling the margin of temperature between the turbine's operating temperature and temperature limit throughout the engine operating range is manifested by utilizing a trim logic schedule that provides a constant margin value for each operating condition of the gas turbine engine. The system allows the engine to achieve the requisite performance while maintaining durability requirements.