F-22 combat radius requirement

Bill Sweetman wrote in his book F-22 Raptor that the Air Force, when drafting the requirements for the ATF, demanded that the new fighter have a combat radius of 700 nm and fly the portion of that 700 nm over hostile territory at supersonic speeds (about 300 miles in and out). The official F-22 website states an airforce requirement of 260+100 nm. Has the service degraded actually its aircraft specification by nearly 50%?

Does it matter? From what I understand, in terms of range, speed, agility, and overall combat effectiveness, the F-22A took the USAF specs, shat all over them, and said "hahaha, I can do better than that!"

http://www.afa.org/magazine/Nov2005/1105paths.asp

The F/A-22’s ability to cruise supersonically is an essential feature. If you didn’t buy it for stealth, you’d buy it for speed, Lewis said. He noted that F/A-22s at Langley can get to Washington, D.C., in just seven minutes and be able to loiter in the area for 41 minutes before going home.

PS: The distance between Langley and Washington, D.C. is around 130 miles/209 km.

mil_hobbyist wrote:Bill Sweetman wrote in his book F-22 Raptor that the Air Force, when drafting the requirements for the ATF, demanded that the new fighter have a combat radius of 700 nm and fly the portion of that 700 nm over hostile territory at supersonic speeds (about 300 miles in and out). The official F-22 website states an airforce requirement of 260+100 nm. Has the service degraded actually its aircraft specification by nearly 50%?

These numbers make no sense. With a supercruise speed approaching 1,000 mph, the Raptor would travel 200 NM (100 NM in, 100 NM out) in hostile territory in about 12 minutes. That's not cruise, that's a dash. A very conservative estimate for supercruise would be at least 30 min, which would translate into 250 miles in, 250 miles out. The combat radius of the Raptor should be about 1,000 NM or thereabouts.

toan wrote:http://www.afa.org/magazine/Nov2005/1105paths.asp

The F/A-22’s ability to cruise supersonically is an essential feature. If you didn’t buy it for stealth, you’d buy it for speed, Lewis said. He noted that F/A-22s at Langley can get to Washington, D.C., in just seven minutes and be able to loiter in the area for 41 minutes before going home.

PS: The distance between Langley and Washington, D.C. is around 130 miles/209 km.

Loiter for the Raptor means supercruise. At 1,000 mph, 40 minutes gives you about 670 miles, or 335 in, 335 out. Add to that 130 miles, 465 miles radius. Still doesn't add up. Remember: Raptors cruise at 60,000 ft., where air is thin and fuel consumption low. You have well over 20,000 lbs. of fuel on board, with engines that boast a low sfc. When all is said and done, I stand by my 1,000 NM assessment, which is obviously unclassified!

Of course, you can carry four external 600 gal tanks you can drop upon entering enemy territory, ensuring stealth isn't compromised. In which case range goes up significantly (each tank carrying 4,000 lbs of fuel, for a total of 16,000 lbs additional fuel). Factoring in the additional drag, you increase your range by at least 50%.

idesof wrote:Loiter for the Raptor means supercruise

I'm not sure I agree with that. It's a broken record I know, but thrust ain't free. It has to come from somewhere.

Guysmiley wrote:

idesof wrote:Loiter for the Raptor means supercruise

I'm not sure I agree with that. It's a broken record I know, but thrust ain't free. It has to come from somewhere.

Umh, that's why it's called superCRUISE! Raptor's engines produce as much dry thrust as an Eagle's do in afterburner, and that for a clean aircraft only slightly heavier than the Eagle but with a hell of a lot less drag, especially supersonic. Raptor should have easily at least twice the range of an Eagle with external tanks.

Here's the thing. It was reported in Code One that even though an Eagle had to be in AB to keep up with a Raptor at full-mil power, their fuel consumption rates were "comparable". What exactly is comparable? We'll probably know in 10 years.

Supercruise does not mean cruise. The terms mean different thing. Follow me here, drag is proportional to velocity squared, now going from M 0.8 to M 1.72 you're more than quadrupling drag to say nothing of shock losses. If you really want to cut your fuel use, set one engine down to idle and one at a cruising thrust (This technique suggested by Gums in the A-37). Commercial airliners do the same thing sometimes with 3 engines. Supercruise is simply defined as being able to go and reach supersonic without the use of afterburners. That says nothing about efficiency. Remember SFC is rate in thrust/hr/lb of fuel. So the more thrusties the more you're burning. Thrust ain't free. Even at an SFC of .3 (english units as defined before, that number is a wet dream, most high bypass turbofans don't get that) you're still burning a LOT to get that much.

According to AW&ST, June 12, 2006:

For the anti-cruise missile mission, F-22A can cruise 41 minutes with the speed of around 1.5 Mach, while the traditional fighters like F-15 and F-16 can just cruise 7 minutes with that speed.

Fuel consumption is greater at supercruise than at regular cruise. But not by much.

I think this has been posted here before.


Based on ~35,100lbs of gas (full internal, two CFTs, and 3 610 gallon tanks) the F-15C has a ferry range of 3,100nm according to the USAF officially. That translates to a SR of roughly 0.088 nm/lb. I assume thats at a nominal cruise mach of about 0.80 or so. The SR for the F-22 according to Stevenson's slide is ~0.076 nm/lb at M0.9 at 40,000'. There is one data point on his graph for M0.8 at 30Kft which is about 0.005 nm/lb better than the 0.90/30Kft. Assuming that holds true for 40Kft that translates to 0.080 nm/lb. Thus with the normal load out for the F-22 and F-15C we have the following max ranges (still air, run 'em dry)

F-15C

1,549nm

F-22 (20,650lbs/18,400lbs)

M 0.80 @ 40 Kft (estimated)- 1,652/1472nm

M 0.90 @ 40 Kft - 1,569/1,398nm

M 1.00 @ 50 Kft - 1,239/1,104nm

M 1.5 @ 45 Kft - 826/736nm

M 1.5 @ 50 Kft (estimated) - 939/836nm

The F-100 is probably around 890lbs/minute thus the F-15 is probably at roughly 1780lbs a minute total. To cruise at the same speed it'd have to use some burner (which is time limited so it really can't but we'll ignore that for now) so a crude guess of the FF at 45Kft is 760lbs/min at M0.9. I would wager that this is probably close for M1.5 at the min burner or what ever it would require to sustain M1.5. With a total FF of roughly 1,520lbs/min that would mean it would take about 11.5 minutes to drain the tanks in which time the F-15 should cover about 190nm. So the F-15C should have a estimated SR at M1.5 at 45Kft of about 0.011 nm/lb or about 1/4th the F-22s.


It has been confirmed that the Raptor holds around 20,650lb of gas so take the first numbers into your calculations. The F119's fuel effiency is still around the same as the F100's because of it's higher thrust engines but the greater internal capacity and lower drag of the F-22 helps tremendously at supersonic speeds.

Guysmiley wrote:Here's the thing. It was reported in Code One that even though an Eagle had to be in AB to keep up with a Raptor at full-mil power, their fuel consumption rates were "comparable". What exactly is comparable? We'll probably know in 10 years.

That makes no sense whatsoever. How can a fighter producing an equivalent amount of thrust dry to another in afterburner have a "comparable" fuel consumption rate? If that were the case, screw the new engine and just use the old one, right? See what I'm getting at? Either Code One got it wrong, or you misunderstood.

LordOfBunnies wrote:Supercruise does not mean cruise. The terms mean different thing. Follow me here, drag is proportional to velocity squared, now going from M 0.8 to M 1.72 you're more than quadrupling drag to say nothing of shock losses. If you really want to cut your fuel use, set one engine down to idle and one at a cruising thrust (This technique suggested by Gums in the A-37). Commercial airliners do the same thing sometimes with 3 engines. Supercruise is simply defined as being able to go and reach supersonic without the use of afterburners. That says nothing about efficiency. Remember SFC is rate in thrust/hr/lb of fuel. So the more thrusties the more you're burning. Thrust ain't free. Even at an SFC of .3 (english units as defined before, that number is a wet dream, most high bypass turbofans don't get that) you're still burning a LOT to get that much.

Sure you're burning fuel, but you're not burning it at the rate you would if you were using AB. AB is the most fuel inefficient way to get thrust out of an engine. You're basically dumping fuel straight into the consumption chamber, as opposed to getting thrust from the fan and compressor. As for drag, remember: drag at sea level, or even at 30,000 ft., is not what it is at 60,000 ft., the height at which the Raptor cruises. Very thin atmosphere = comparatively low drag. So, your velocity squared formula has to take into account air density as well. Drag through water, for instance, is higher than drag through air. And air density at 30,000 ft. is much higher than at 60,000 ft. The Raptor simply slices through the air at that height at about Mach 1.7 very much CRUISING without AB.

toan wrote:According to AW&ST, June 12, 2006:

For the anti-cruise missile mission, F-22A can cruise 41 minutes with the speed of around 1.5 Mach, while the traditional fighters like F-15 and F-16 can just cruise 7 minutes with that speed.

1. According to the previous report, Raptor could make 1.5 Mach supercruise with 80% military thrust at medium to high altitude.

2. Mach 1 is about 295 m/sec at the height of 30,000~40,000fts. Therefore, cruising 41 minutes with the speed of around 1.5 Mach should roughly equal to the distance of 295/1000*3600*1.5*41/60 = 1,089 km / 677 miles / 588 nms.

3. Suppose that around 80% of the internal fuel of Rapator is used for this cruise (20,650 Ib * 0.8 = 16,520 Ib), then the SR for F-22 in this condition should be around 0.0356 nm/lb.