You want a high mass flow rate, aided by a high exhaust velocity. (High dry thrust rating)… Lower bypass ratios and higher pressure ratios assist this greatly. Higher pressure ratios come with additional heat. Having a higher bypass helps alleviate some of this heat but comes at the detriment of higher parasitic drag around the core that is not aiding mass flow rate or the overall pressure ratio much if at all. Any air that can escape around the core after some point… will.
Yes it is not a directly comparable engine which is why I tried to compare mostly to the RM12 and the M88. The static numbers for T/W on the F119 are worse but it is almost guaranteed that the dynamic thrust numbers especially dry are considerably more than the EJ200. The Eurofighter has an advantage when it comes to wave drag but is mitigated heavily when ordnance is carried compared to the F-22.
Still, the F-22 is said to accelerate faster dry than the F-15 does wet beyond the sound barrier and it was stated that the Raptor actually had more issues slowing itself down to the target cruising speed of 1.5M than it did getting there in the first place. They would accidentally pass the target speed often and needed to cut power to stay in the efficient range. Here is the original quote;
“Sustaining the target Mach was not difficult for the Raptor,” said Col. C.D. Moore, Combined Test Force commander, at Edwards Air Force Base, Calif. “The difficulty was keeping the Raptor from going faster than the target speed. Yesterday the airplane demonstrated that it can achieve awesome speed, flying above 1.5 Mach at a low power setting, for a sustained period of time. No other fighter in the world can do that.”
Moore flew yesterday’s mission, piloting the first flight-test F-22 off the assembly line. He was pushed by Raptor 01’s two powerful Pratt & Whitney F119-PW-100 engines to speeds greater than Mach 1.5 during a two hour flight over Edwards.
“The F-22 is designed to dominate future air combat by integrating supercruise with advanced avionics and stealth,” said Brig. Gen. Michael Mushala, Aeronautical Systems Center’s F-22 program director, commenting about the significant milestone.
Jet engines typically will produce better fuel efficiency if they can sit at a given velocity with an exhaust velocity similar to the free-stream inlet velocity. Since this is not possible for a low bypass turbojet which requires an exhaust velocity much greater than the inlet’s - there must be a compromise. High bypass turbojets are most efficient in this regard because the exhaust velocity can be much closer to the cruising speed of the aircraft, but this is not the case when discussing turbofans for fighter jets.
Fighter jets cannot utilize high bypass turbojets because they require much higher excess thrust. To accomplish this while maintaining some of the benefits of the bypass primarily for cooling or afterburner performance (but also to some degree of efficiency), they utilize a low bypass turbofan.
So, a compromise must be made. The exhaust velocity must be high enough to produce the necessary dry thrust to propel the fighter beyond the sound barrier and up to the efficient speed range but not high enough that it is not efficiently cruising at such an airspeed. The F-22 clearly found a compromise, and actually is over-built for the purpose as it tends to run past the efficiency range and accelerates too much in certain conditions beyond the target of 1.5M as stated in the quote above. Still, it can be very efficient as it is stated that they conducted a 2 hour flight where at one point they were supercruising up to 1.5 mach.
