Asoka
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OK! Let's make things simple :
- The total mass of the airflow times the difference between exhaust speed and flight speed equals thrust.
- The high bypass of a turbofan allows better fuel economy at cruising speed and those engines are less noisy.
- The response time of a low bypass is better because it moves less air : "it shifts faster" ( combat essential ).
- Since no big fan to move slow air, less cross-section, vital for drag reduction to go faster easier ( & stealthier ).
- Lower bypass ratio produce less total thrust but more of it per kg of engine A.K.A better thrust to weight ratio.
- Lower bypass ratios perform best at higher speeds; high bypass ratios are optimized for high subsonic cruise.
- To hike thrust, fighters use afterburners ( higher nozzle speed ) and airliners maximize flow with high bypass.
Cores are, as some mates mentioned, often similar since as we showed the difference lies elsewhere.
I.E. GE F-110 to CFM-56 . . .
View attachment 415912
Have a great day all, Tay.
"- To hike thrust, fighters use afterburners ( higher nozzle speed ) and airliners maximize flow with high bypass."
Good summary!
While it is true having a large cross section is not good for speed, it is also true that at high altitude, when the air is much thinner, this problem is not as severe. With much less air resistance at high altitude, this is much better for high speed cruising.
Most planes achieve their maximum speed at high altitude > 30,000ft, rather than at sea level.
However, at high altitude, you need a bigger air intake to scoop up the thin air. The Mig-25 is famous for having a huge air intake, for this high speed, high altitude cruising.
While we don't know for sure, I got a feeling J-20 that, with its large air instakes and adjustable DSI inlets, it could also cruise at very high altitude and very high speed for a very long time, because of its advanced aeroframe and powerful engines.
It is notable that although F-22's top speed is listed as Mach 2.2, its Max. Speed is actually classified. Some people speculated it is, at least, Mach 2.5+, which is F-15's top speed.
F-22 is much more aerodynamic than F-15, and has 40% more thrust.
Think about it, F-22 is a speed demon.
When J-20 first appeared, a lot of people believe its a high speed interceptor like the Mig-25, and/or long range striker like the F-111, because of its size.
Now, we know J-20 has excellent subsonic and supersonic maneuverability, but will it has high altitude, high speed capability, as well?
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