F-22 Speed = Mach 2.84 Calculations!!

I have seen numerous topics regarding the actual speed of the F-22, generally it is quoted at around mach 1.8-2.0. I wanted to do some basic quick rudimentary calculations ignoring air resistance to calculate a rough actual speed. What I did was take some data from two planes. The Mig-29 Fulcrum(Thrust: 2 x 19180 lbf, Max Takeoff wt:49,383 lb, max speed:1491 mph) and the Su-33 Flanker(Thrust: 2 x 28219 lbf, Max Takeoff wt:72,751 lb, max speed). What I then did was a thrust to weight ratio calculation for both the planes and came up with a value of 0.776. I assumed that this ratio was proportional to the velocity. Taking the F-22 data (Thrust:2 x 39,000 lbf, Max Takeoff wt:80,000 lb) and its thrust to weight ratio of 0.975 I calculated the velocity of the F-22 by solving:


1491 X
------ = -------
0.776 0.975

This gave me a velocity of 1873 mph. Taking the speed of sound to be 659 mph, this gives a speed of mach 2.84. Is this an overestimate of the speed? It sounds pretty fast. I was gonna go all out actually trying to solve the differential equations and calculate the drag on the airframe, but that would have me involved in learing the Navier Stokes equations, reynolds numbers etc.....too much. Any feedback would be appreciated.



[edit on 7-8-2004 by TACHYON]

Actually I believe that the speed of sound is 760 mph. But at sea level I thinks it 670 mph.

Which changes the mach number to mach 2.46. Which sounds more resonable.

[edit on 7-8-2004 by Murcielago]

I believe the Air Force is not releasing the actual top speed of the Raptor they only officially say Mach 1.8+. Note the raptor produces more thrust than any other US fighter, and it can go Mach 1.5 without afterburners yet it can only go 1.8 with afterburner something aint right here. That means that the raptor only gets a .03 mach boost from its afterburner. Other US jets get at least another mach or more as boost from their afterburner. I think the raptor can go beyond mach 2.






[edit on 7-8-2004 by WestPoint23]

Westpoint, lol I already said that. What do u think of an estimate of mach 2.84? It is one mach beyond 1.8 like you said? This is definetly up in the Mig-25 Foxbat range.



[edit on 7-8-2004 by TACHYON]

Originally posted by Murcielago
Actually I believe that the speed of sound is 760 mph. But at sea level I thinks it 670 mph.

The quoted speeds of the Russian aircraft were mach 2.26 and mach 2.17 respectively so i assummed that they are correct. Im sure then that they took the measurements at ground level. LOL

[edit on 7-8-2004 by TACHYON]

You know the SR-71 had slightly less thrust (32,000lbs each engine) and weighed more (100k pounds or something) yet was able to reach mach 3.2.
The reason for this had more to do with the intakes than the actual engine
If the F-22 does indeed have variable intakes, i would say its mach 3 capable, if it doesnt.. mach 2 is more likely

Good work TACHYON on the speed estimate for the Raptor. I could see mach 2.8 as a very real possibility. I fear it might be a long time before we know for sure. I mean the SR-71 ceiling was 85,000ft for how long and now its reported as 100,000+ the planes retired and with still dont have exact numbers

2.84 Pfftt My Nova can do 3.00

Originally posted by NickS1004
You know the SR-71 had slightly less thrust (32,000lbs each engine) and weighed more (100k pounds or something) yet was able to reach mach 3.2.
The reason for this had more to do with the intakes than the actual engine
If the F-22 does indeed have variable intakes, i would say its mach 3 capable, if it doesnt.. mach 2 is more likely

Also the engines were different and it was more aerodynamic.The Sr-71's engines were i believe turbojets and funcitoned better at higher speeds, but fighter engines are turbofans. Thank You ShadowXIX. I read in one of my books, and they gave a chart saying that the speed was limited by the airframe, because of the temperatures it might reach. Although im not a materials expert im not sure if that is the case. I wish I could scan in the images of the charts.

[edit on 7-8-2004 by TACHYON]

Originally posted by SpockO_o
2.84 Pfftt My Nova can do 3.00

It is pretty good for the raptor, considering the fastest enemy SAM's are the Russian S-400 capable of generally 4-5 Km/s(not sure on exact figures). By the time the raptor sees it launch it will try to accelerate away, and the missle may not be able to catch it. Hopefully not too many SAM's becuase this is a top speed only on afterburners.

[edit on 7-8-2004 by TACHYON]

Actually, you can't take subsonic calculations and extrapolate them to supersonic calculations and get an accurate air velocity result.

Basically, two sets of equations.

EDIT: Plus, thrust over weight won't get you an accurate calculation. You're going to have to take into account drag.

[edit on 8-7-2004 by Valhall]

Originally posted by Valhall
Actually, you can't take subsonic calculations and extrapolate them to supersonic calculations and get an accurate air velocity result.

Basically, two sets of equations.

EDIT: Plus, thrust over weight won't get you an accurate calculation. You're going to have to take into account drag.

[edit on 8-7-2004 by Valhall]

The Mig is supersonic. I said it was a basic calculation, and I did say I ignored drag. LOL, did you read my post.I would take those factors into account but I simply do not have the time yet to devote to such research.

[edit on 8-8-2004 by TACHYON]

The Raptor has to have less drag than the F-15 cuz it carries all of its weapons inside the F-15 doesn't yet it is still able to do Mach 2.35 with less powerful engines than the raptor.

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]

this is really cool, if the F-22 can go that fast, but i wish i could find a webstie besides this one that confirms this.

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]

Bill Sweetman has said that "the F-15 can attain its top speed only iwth a minimal weapons load and no external fuel, and most pilots never see 2.5 on the machmeter. The F-22 has plenty of thrust for Mach 2.5, but providing that performance would have demanded variable inlets and higher-temperature materials throughout the aircraft."

I definetely belive the speed is airframe limited because of the high temperatures involved. Maybe we can turn this into a info. hunt topic something like gathering info on the skin materials and such and making predictions of the speed. What I believe is that 2.84 is the maximum upper limit without ariframe considerations. The top speed in actuality may be well below this.



[edit on 8-8-2004 by TACHYON]

Originally posted by WestPoint23
The Raptor has to have less drag than the F-15 cuz it carries all of its weapons inside the F-15 doesn't yet it is still able to do Mach 2.35 with less powerful engines than the raptor.

Thats pretty fast, I thought it was Mach 2.5 tops. Anyway is the F-15 skin alumunimum or something and what about the raptors.

Originally posted by TACHYON
Thats pretty fast, I thought it was Mach 2.5 tops. Anyway is the F-15 skin alumunimum or something and what about the raptors.

Titanium 64 (Ti-64) 36%
Thermoset Composites 24%
Aluminum (Al) 16%
Other Materials* 15%
Steel 6%
Titanium 62222 (Ti-62222) 3%
Thermoplastic Composites >1%
www.globalsecurity.org...

A top speed of an aircraft is not necessarily as important as a tactically useful speed. The Raptor is optimised around its supercruise design point of Mach 1.5, dash speeds are rare and only consume fuel. You have to remember that it has an advantage of stealth, it does not by design need to dash in (or out) of the FEBA at Mach 2 plus to accomplish its mission. Therefore the Mach 2.5 speeds of previous generations of fighters is just a byline in history.