Originally Posted by
Turbine D
I'm not sure about the turbine temperature control architecture used on F135 engines, but in some other military engines like the F101 or F110, EGT isn't used to control turbine temperature upper limits. In military engines, there is less turbine temperature margins when operating on a normal fan speed schedule. To protect the high pressure turbine from excessive over temperature the control system incorporates a turbine blade temperature limiting function known as T4B. A dedicated optical infrared pyrometer is used to measure the temperature of the HPT turbine blade. This signal is fed to the electronic control which reduces core fuel flow to limit the turbine temperature. T4B anticipation logic is built in to prevent excessive overshoots during power bursts.
GE tried to use that pyrometer trick on the GE90-94B - didn't work as well in the commercial environment as it did on the military and they went back to a thermocouple based system on the GE90-115B (and GEnx). However my point remains, pulling back thrust to protect turbine temps caused us big problems in commercial (it didn't help that Pratt had a POS wire harness that would short and indicate very high EGT causing the control to pull back thrust during takeoff). So we did away with EGT limiting except during autostart - counting on the pilot to pull back power if there was an exceedance and it wasn't an emergency.