
hkultala wrote:Only about 22-23 klbs of that 28k is thrust from the core, and works at supersonic speeds. The rest 5-6 klbs comes from bypass air, which is only adding drag, not thrust, at supersonic speeds without afterburner. (because the air has to be slowed down to subsonic speed at the inlets, but the fan cannot accelerate it back to supersonic speed).
EJ200 engines of EF Typhoon has lower bypass ratio, giving them together about equal core thrust, and less drag from the bypass air. But EF Typhoon is a smaller plane, with less drag on clean configuration.
With an engine with core thrust of something like 25 klbs, F-35 would have no trouble of supercruising.
That is not really how modern mixed flow afterburning turbofan engines work. The bypass flow and core exit flow are mixed at roughly equal pressures and exit through the exhaust nozzle together to make thrust. The fan pressure ratio essentially sets the engine pressure ratio, and you can’t say the bypass air is not making thrust during supersonic flight.
An engine pressure ratio of 2 gets you sonic flow from the exhaust. A F100-220 and the F110-100 have an EPR of approximately 3, which gets you a supersonic exhaust, so you can make some Mil thrust above M1, but not enough to maintain above the transonic range. You have to push the fan / engine pressure ratio significantly higher than that to get supercruise thrust at Mil power.
To supply the extra power to drive the fan at the higher pressure ratio take more core power. You can run the core harder and hotter, or you can make it bigger (I.e. lower bypass ratio).
The other issue with supercruise as traditionally defined as 1.5M, 40K has a 100F inlet temp on a standard day. Most engines make their maximum thrust at 60F -70F inlet temp. They run into turbine speed and temperature limits as the inlet temp increases, and the thrust declines as the inlet get hotter. So to maintain that supercruise thrust, the engine has to be designed with enough rotor speed and temperature margin to produce full thrust under that 100F inlet condition.
P&W FSR (retired) - TF30 / F100 /F119 /F135