F-22 Raptor speed

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

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Unread post12 Jan 2009, 21:31

Big difference is the inlets. The SR-71 inlet has very complex variable geometry to allow the engine to keep producing thrust at M3.5, while the F-22 inlet is a simple fixed geometry device which is not designed to work at M3+.
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Unread post13 Jan 2009, 03:46

LordOfBunnies wrote:Not necessarily man. Drag and how things interact at speed affect things a lot. When people quote a Cd for an aircraft they're usually quoting the Cd at a given Reynolds Number or a range where it plateaus. Get the Raptor going fast enough and I'm pretty sure you'll get some gnarly shock-shock interaction. God forbid the thing hit some type 3 or typer for S-S because that'll burn a hole right through it. If you start having shocks intersect things that they're not supposed to you could start damaging the airframe and the drag would skyrocket. The most likely occurance of this would be the nose shock hitting the wingtips.


See the X-15's ventral when they had the scramjet model attached for a good idea of what happens. Granted that was at Mach 6+ but you get the idea. :shock:
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skyhigh

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Unread post27 Feb 2009, 11:05

Why not take the Raptor on a 90 degree nosedive from 65000 feet to see how fast it can go? (I guess Mach 2.42 in afterburner, Mach 1.82 supercruise, level flight)
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Unread post27 Feb 2009, 21:52

They won't do that because that is not a operationally representative limitation. They know probably within one or two one-hundreths of a mach number how fast the jet will go in practical terms (material/structural limitaions) and probably could figure out how fast it'd go theoretically just by simulation.
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Unread post28 Feb 2009, 00:30

skyhigh wrote:Why not take the Raptor on a 90 degree nosedive from 65000 feet to see how fast it can go? (I guess Mach 2.42 in afterburner, Mach 1.82 supercruise, level flight)


Well, basically because it's going to melt. Either the canopy or the composites around the airframe are probably going to fail, and that's either going to destroy the airplane or make it ridiculously hard to repair (Do they have a Class AA yet?).
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Unread post28 Feb 2009, 05:37

Prinz_Eugn wrote:
skyhigh wrote:Why not take the Raptor on a 90 degree nosedive from 65000 feet to see how fast it can go? (I guess Mach 2.42 in afterburner, Mach 1.82 supercruise, level flight)


Well, basically because it's going to melt. Either the canopy or the composites around the airframe are probably going to fail, and that's either going to destroy the airplane or make it ridiculously hard to repair (Do they have a Class AA yet?).


There are pictures floating around the web of Raptors with paint and presumably RAM sandblasted off the nose when the pilot exceeded the recommended speed limit.
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Unread post28 Feb 2009, 09:15

What about the P&W F119-PW-100 turbofans? Can they withstand the extreme airflow until the fan blades, compressors and combustion chamber blow up like a popping balloon? I doubt it.
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Unread post28 Feb 2009, 20:57

We already know the canopy is the limiting factor here.
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That_Engine_Guy

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Unread post28 Feb 2009, 21:40

skyhigh wrote:What about the P&W F119-PW-100 turbofans? Can they withstand the extreme airflow until the fan blades, compressors and combustion chamber blow up like a popping balloon? I doubt it.


The engine's control system 'most likely' monitors that. In the F100 series control system, things like inlet pressure, compressor discharge, and burner pressure are monitored and controlled. If at high-speed/low-altitude where the air is dense, the N2 RPM will be limited as a function of compressor discharge pressure so that the diffuser case does not rupture.

So yes, as the pressure in the F119 built up to a critical level (burst point) the engine would effectively reduce compression and/or RPM to keep from damaging it's self. The F119 is more 'operator error resistant' than the new F100's, so there is little a pilot could do, either by intent, or neglect, to hurt it.

Both engines are full-authority-computer-controlled under normal conditions, but in SECondary mode the F100 looses many of it's safety limiting features/controls as authority is passed back to the pilot. One is much more likely to 'hurt' an F100 when running in SEC.

I'm sure the performance limits on the F119 are greater than the F100 or the F110, but eventually everything will reach a fail point.

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Unread post28 Feb 2009, 21:51

Yeah, the F119's in the Raptor both have dual FADEC systems and would not allow damage to occure. Hell if the engine doesn't like something during the demo's, you can see the FADEC system 'refuse' to put the engine into afterburner momentarily. Seen it plenty during demo's where one will light and the other either won't light or lights late.
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Unread post01 Mar 2009, 03:11

That_Engine_Guy wrote:
skyhigh wrote:What about the P&W F119-PW-100 turbofans? Can they withstand the extreme airflow until the fan blades, compressors and combustion chamber blow up like a popping balloon? I doubt it.


The engine's control system 'most likely' monitors that. In the F100 series control system, things like inlet pressure, compressor discharge, and burner pressure are monitored and controlled. If at high-speed/low-altitude where the air is dense, the N2 RPM will be limited as a function of compressor discharge pressure so that the diffuser case does not rupture.

So yes, as the pressure in the F119 built up to a critical level (burst point) the engine would effectively reduce compression and/or RPM to keep from damaging it's self. The F119 is more 'operator error resistant' than the new F100's, so there is little a pilot could do, either by intent, or neglect, to hurt it.

Both engines are full-authority-computer-controlled under normal conditions, but in SECondary mode the F100 looses many of it's safety limiting features/controls as authority is passed back to the pilot. One is much more likely to 'hurt' an F100 when running in SEC.

I'm sure the performance limits on the F119 are greater than the F100 or the F110, but eventually everything will reach a fail point.

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So a FADEC equipped F119-PW-100 turbofan can minimize the abusive amount of airflow to protect the components from melting or even blowing out, e.g. the F119 cannot handle airflow speeds above Mach 1.82 without self-destruction, right?
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Unread post01 Mar 2009, 04:22

skyhigh wrote:So a FADEC equipped F119-PW-100 turbofan can minimize the abusive amount of airflow to protect the components from melting or even blowing out, e.g. the F119 cannot handle airflow speeds above Mach 1.82 without self-destruction, right?


Well yes to the first part, and no on the second.

Yes, the 'FADEC' on the F119 will keep the engine running at 'optimal' power for a requested throttle setting based on current conditions. It optimizes engine operation constantly and will not allow the pilot to 'request' something that will hurt the engine.

Example - If said pilot requests MAX power down low and the aircraft reaches a critical point where inlet pressures make the compressor discharge pressure too high, the FADEC on the engines will essentially 'throttle back' on their own to prevent damage. This is what 'full-authority' means; if the pilot asks for something the engine will say NO if appropriate for motor-self preservation.

The flight envelope for the F119 is still classified, so nobody can truthfully say what the engine's top speed is. After all the true top speed is dependent more on the airframe. (The F100 in an F-15 has ALWAYS had a higher top speed than an F100 in a Viper due to the Eagle's variable inlet system and a more rigid canopy design.) At high-Mach the inlets are very important in keeping airflow steady and subsonic, if they don't the disruption in airflow will choke the compressor of air at which point engine power drops and the aircraft begins to slow. I'm sure the Raptor's inlets work to whatever speed she is cleared for.

So NO; the F119 is capable of handling any speed or flight condition a Raptor pilot asks of it, so long as that request is within the programmed flight envelope for the airframe/engines. The F-22/F119s are integrated to function as a single unit, so one won't hurt the other.

I'll add my :2c: here and say the F119 should be much more capable of producing speed than the Raptor's airframe could ever handle. In the F-15 and F-16 the engines are cleared to the airframe's maximum speed, and in both installations the engine could go fast enough to damage/destroy the aircraft before the engine(s) would fail. So whenever you see someone official release the true top speed for the Raptor, remember the engines could go faster...

(Ever see the movie "Blackbird" produced by Lochkeed in the early 1990s? It shows the pilot RETARD the throttles when they reach MACH 3.2 :shock: I may add he pulls them back pretty far too! The J58s would run faster than the Blackbird could :wink: )


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Unread post02 Mar 2009, 13:34

And thats why at Mach 3.2 the response to a missile launch was to throttle up.
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Unread post02 Mar 2009, 17:54

skyhigh wrote:
So a FADEC equipped F119-PW-100 turbofan can minimize the abusive amount of airflow to protect the components from melting or even blowing out, e.g. the F119 cannot handle airflow speeds above Mach 1.82 without self-destruction, right?


Where did you get this notion? The F-119 is designed for sustained high speeds, and the F-22 is quite capable of safely exceeding M1.82.
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Unread post02 Mar 2009, 21:38

Ah, so on the MiG-25, the engines would fail before the airframe would, but the opposite is likely true of the F-22? Those F119s are hot stuff...
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