F-22 Speed = Mach 2.84 Calculations!!, page 1

Originally posted by sminkeypinkey
Sorry and all, interesting little exercise in maths etc but this has no relation to the reality.

Firstly you can't just ignore drag as it's the next biggest germane factor after outright power.

Secondly you have completely ignored the F22's construction materials.

One of the things that made Concorde such a big deal of an achievement was it being a fully certified scheduled airliner capable of sustaining mach 2.2 for thousands of miles.

The sustained speed ability was a feat few other aircraft could match (never mind the rest of it) because Concorde had 'heat soak' capabilities way beyond the requirements a brief supersonic dash places on a run of the mill supersonic aircraft (yes, I know about supercruise - but that is only claimed at speeds of under mach 2)....North American did it with the XB70 and Lockheed achieved similar with the SR71/A12 aircrafdt but at mach 3+.

Few others have come anywhere near such an ability, ever.

Concorde was 'limited' to mach 2.2 because of the materials she was constructed from, not due to power or drag limitations. As an aluminium alloy skin was settled upon for Concorde that in itself demanded that mach 2.2 be the 'top speed' when in fact, given the power and aerodynamics of the plane, it need not have been.

Therefore to know the max speed of the F22 one muct know the heat soak abilities of the airframe and any limitations the unavoidable kinetic heating at high speeds impose on the construction.

This isn't a field for a quick calculation on the back of an envelope, those days are long long gone. Keep up the math though!

[edit on 8-8-2004 by sminkeypinkey]

Very good post.

As quoted by USAF sources, the Raptor is a Mach 2 class aircraft, speeds seen through the 60's to 90's for the F-4 and F-15 are peak dash speeds, with no weapons, not a very good indicator of its performance in a combat situation. Such speeds are largely irrelevant now. Mach 2.2 or therabouts seems to be the max the F/A-22 will do. It is not power limited, it is airframe limited. Do some research and you'll see the aircraft has a built in speed warning, it is VERY easy to overspeed the aircraft. The original requirements were for a Mach 1.5 supercruise but its since been released it will do Mach 1.72 without using afterburner. If you look at specific fuel consumption figures you'll see exactly why using afterburner isn't a good idea at all.

Guestimations for the F119 engine is that it produces almost 39000 lbs of thrust giving based on engines of a similar bypass ratio a dry trust of around 26000 lbs.

SFC of a typical bleed bypass turbojet (calling it a turbofan is really a misnomer as its bypass ratio is about 0.2 to 1 versus 0.6 to 1 for the F100) is around 0.85 lbs of fuel/ lb thrust per hour giving a fuel flow of approx 22100 lbs of fuel per hour at mil thrust, multiply that by 2 and you can give a broadly accurate guage of how long it'll take the 18300 lbs of internal fuel the Raptor has to run out....approx 50 mins. USAF sources have said in a 1 hour mission the Raptor will supercruise for half that time, leaving the rest of the time for climbout, ingress to the high risk area, and egress after the supercruise portion of its mission and landing.

SFC in afterburning is really horrendous, again given a general rule of thumb, a typical bleed bypass turbojet has an augmented SFC of 1.8, 2 x 39000 is 140400 lbs of fuel per hour fuel flow. Every second they're not using afterburner is life to a fighter pilot. Top speeds consequenty have become largely irrelevant in light of this. The whole Raptor philosophy is speed with a reasonable amount of economy.

Other SFC figures

F100-PW-220 (14590 dry/ 23770 afterburning) bypass ratio 0.6:1

0.68 dry: at mil power 9921 lbs fuel/hour
2.55 at max afterburner: 60613 lbs fuel/hour

F100-PW-229 (17800 dry / 29000 afterburning) bypass ratio ~0.3:1

0.74 dry: at mill power 13172 lbs fuel/hour
2.05 at max afterburner: 59450 lbs per hour

You can see the trend as bypass ratio goes down, non afterburning SFC goes up and Afterburning SFC goes down generally. In the higher bypass engine the core is smaller, burns less fuel, and the exhaust is oxygen rich compared to the lower bypass ratio engines so proportionally its afterburning to dry thrust ratio is higher. More free oxygen, more afterburning potential.

The F119 is a very low bypass engine, almost a straight turbojet, the bypass air is only used to cool the afterburner liner more or less, as it runs much hotter than any engine in the F-15. By several hundred degrees.

Adding such heat in a VERY high supersonic dash like the F-15 did would stress an already highly burdened propulsion system to the limit. The Raptors max allowable speed is well below Mach 2.5. It just isn't needed in any combat situation, both tactically and for fuel state.

[edit on 8-8-2004 by MPJay]