Some interesting claims about the F-22 on Wikipedia

Anything goes, as long as it is about the Lockheed Martin F-22 Raptor
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sferrin

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Unread post01 Sep 2006, 20:36

Raptor_One wrote:I don't know how much airflow is necessary to keep the combustion process going at those altitudes, but you'd likely have to be going pretty fast. Then again, you have to be going pretty fast at those altitudes just to keep from stalling. Not only that, but you have to have enough airflow over the control surfaces to maintain stability. I have no idea whether you'd starve the engine of oxygen before stalling or losing stability. It's likely aircraft dependent.


It really does depend on the engine. U-2s cruised at at least 72,000ft witha J75 and they weren't even going very fast as far as jet aircraft are concerned. Now they use a varient of the F118 (which is a varient of the F110). Where the F-22 is going faster and the engine has a much higher compression ratio (than the J75) well. . . something to think about.
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Raptor_One

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Unread post01 Sep 2006, 22:12

Oh... I wasn't talking about altitudes in the 70K range. I was talking more like 90-100K range. And by pretty fast, I don't mean SR-71 fast. :) Like someone said in earlier in this thread (I think), if the engine is properly trimmed for high altitude flight (or can trim itself automatically for any condition encountered), high altitude operation might not be a problem. Another thing to consider is that while the engine might not cut out at extremely high altitudes, the amount of thrust output could be next to nothing. Also, what's the stall speed for an F-16 at 90,000 ft? Dare I say supersonic? LOL! If not, it's high subsonic. The F-16's wing is extremely small compared to the F-22's or even the F-15's. How high did the Streak Eagle go, by the way?
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Unread post01 Sep 2006, 23:27

This quote from the USAF museum website.

"The single-seat F15A on display,
"I may not agree with what you say....but I will defend to the death your right to say it".
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sferrin

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Unread post02 Sep 2006, 00:05

Raptor_One wrote:Oh... I wasn't talking about altitudes in the 70K range. I was talking more like 90-100K range. And by pretty fast, I don't mean SR-71 fast. :) Like someone said in earlier in this thread (I think), if the engine is properly trimmed for high altitude flight (or can trim itself automatically for any condition encountered), high altitude operation might not be a problem. Another thing to consider is that while the engine might not cut out at extremely high altitudes, the amount of thrust output could be next to nothing. Also, what's the stall speed for an F-16 at 90,000 ft? Dare I say supersonic? LOL! If not, it's high subsonic. The F-16's wing is extremely small compared to the F-22's or even the F-15's. How high did the Streak Eagle go, by the way?


BTW does anybody here know the details of how in the hell a Mig-29 snagged the sustained altitude record at nearly 95,000 feet?
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Unread post02 Sep 2006, 01:44

Where did you read that a MiG-29 sustained level flight at 95K ft? That sounds... impossible. Who knows though... maybe its lifting body design allows it to continue generating lots of lift at high altitude. It doesn't sound quite right though. I actually have a MiG-29 manual that has CL vs. AoA curves and the reference area used for those coefficients. I could (but doubt I will... hehehe) calculate its absolute ceiling for a given weight and airspeed. And something tells me it won't come out to 95,000 ft under any circumstances. That's outrageous though... what is the MiG-31's absolute ceiling at Mach 2.8? Don't tell me it's not higher than the MiG-29's!!! hahaha....
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sferrin

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Unread post02 Sep 2006, 04:05

Raptor_One wrote:Where did you read that a MiG-29 sustained level flight at 95K ft? That sounds... impossible. Who knows though... maybe its lifting body design allows it to continue generating lots of lift at high altitude. It doesn't sound quite right though. I actually have a MiG-29 manual that has CL vs. AoA curves and the reference area used for those coefficients. I could (but doubt I will... hehehe) calculate its absolute ceiling for a given weight and airspeed. And something tells me it won't come out to 95,000 ft under any circumstances. That's outrageous though... what is the MiG-31's absolute ceiling at Mach 2.8? Don't tell me it's not higher than the MiG-29's!!! hahaha....


It's real. Why do you think I'm going "WTF?" just like you? :shock: I'd read about it a long time ago (it happened long enough ago that when they brough the Blackbird back OUT of retirement briefly they considered taking the record back but nothing ever came of it). Some solar-powered all-wing NASA job holds the record now at 96,000 something feet but the Mig-29 held it for quite a while.
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Unread post02 Sep 2006, 06:26

Well... it must be the lifting body design. The thing was probably flying along at high Mach and some strangely high AoA for sustained supersonic flight. The lifting body design must perform very well at high altitudes. Also, the MiG-29 is extremely light. I doubt an F-14 our Su-27 could accomplish the same type of feat simply because they're too damn heavy. The MiG-29 is for sure the smallest high-performance aircraft that acts as one big lifting surface. I wonder how fast it was going up there and how it actually climbed to that altitude. You might not be able to get to such an altitude and sustain flight there without some crazy climb profile.
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habu2

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Unread post02 Sep 2006, 22:02

Considering the altitude density at 95Kft I doubt a lifting body design is much of a factor....
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Unread post02 Sep 2006, 23:35

habu2 wrote:Considering the altitude density at 95Kft I doubt a lifting body design is much of a factor....


The more lifting area you have at those altitudes, the better. Using most of the aircraft as a lifting surface is more efficient than only using the wings. The main fuselage will generate some lift at an angle of attack regardless of shape, but the lift to drag ratio of the fuselage alone could be terrible. However, if the fuselage is purposefuly shaped to generate a good lift/drag ratio, you're making optimum use of space (in an aerodynamic sense). That's the idea behind the B-2, isn't it?
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Unread post03 Sep 2006, 09:43

Raptor_One is right about that part. Wings are less and less useful the higher up you go. Unless you have a very high aspect ratio wing (U-2/TR-1) or a very lowly loaded wing (NASA Helios) in order to stay aloft at high altitudes while remaining subsonic. Even if your airspeed is down to 100 knots, you may well be supersonic so using flaps and other high lift devices becomes less attractive.
The lifting body design does away with the wing and its associated intereference and form drag. In addition, they are by design of very low aspect ratio. If you can still find NACA Technical Note #539 and Report #431, you'll find that between an aspect ratio of approx. 0.75 to 1.50 there is a "marked delay in the breakdown of the longitudinal flow as the angle of attack of the airfoil is increased." Pretty much they're defining vortex lift, something that airplanes from the Draken to the Concorde to the Viper utilize in their designs.
The point (if I can bring it all together) is that the Mig-29 is shaped like a guitar pick and has a lot of hidden lifting area not counted in its wing area. Low wing loading + a lifting body design + powerful engines and a minimal fuel load = high sustained altitude. Could the Raptor do it? Of course. Will we ever see it? Who knows, but its fun to imagine.

Whew. Reading all those books finally paid off :)
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Unread post03 Sep 2006, 10:40

It's not just maximum G that's important, but the rate of onset of Gs. A pilot can black out going from 2 to 4 Gs if the rate is high enough, while going up to 8 Gs at a slower rate wouldn't.

Jeff
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Unread post03 Sep 2006, 10:42

Raptor_One wrote:...but if you calculate the possible Mach numbers that 16000 MPH equates to ...



I assume that's in afterburner? :D

Jeff
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Unread post03 Sep 2006, 14:34

Did I say 16,000 MPH? :D Yes... that would be in afterburner alright. More specifically, afterburner stage "ludicrous".... for "ludicrous speed".
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Unread post10 Sep 2006, 15:08

but only at Dark Helmet's command.... :applause:
holy s@*t, there's two of 'em!
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