F-22 Raptor speed

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

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Unread post01 Oct 2006, 12:21

I normally just watch these discussions, but I have to jump in here. It sounds like many (or most) of you are looking at this quote from a technical or engineering point of view, not from the world view of a fighter pilot. Let me throw out another thought.

There is a general rule in a fighter squadron about stories - it's called the 10% rule. It means that a minimum of 10% of what you say has to be true. Here is another general rule for fighter pilots: "Never do math in public" Now while they may have "done the math" - it doesn't mean it's right.

What's my point? While fighter pilots don't lie, don't expect them to tell the whole truth. Story telling is part of the culture - the security part fits in with it. I have done static displays at airshows, media events, DV visits, etc. As a rule, when asked about information that I know I can't tell you about (max range of AMRAAM is a favorite) - I will be either a little "exagerative" and/or a little vague/evasive. In a fighter pilot's mind, 25-30 minutes could mean 25-30 minutes once I was level or 25-30 minutes when I finally put my final destination in the computer (not including climb & descent - which we don't really put in our math). It could also mean 40-50 minutes with a couple minutes conveniently forgotten about. The possibilities are endless - to most fighter pilots that type of discussion is not mathmatical science - it's time for embellishment.

I hope that makes sense to you guys - don't try to do the engineering off what a fighter pilot tells you in an article, a bar, or a casual conversation. He may know the technical info, but we don't talk that way on a daily basis.
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Raptor_One

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Unread post01 Oct 2006, 17:03

No way! You mean to tell me that those F-22 pilots didn't have their calculators and -1 manuals out for an exact calculation? NO WAY... I DO NOT BELIEVE IT! :D
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sferrin

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Unread post01 Oct 2006, 19:20

Raptor_One wrote:I'm not arguing with you on this one. It's obvious that your intent is not intelligent debate. You and some others have some strange desire to prove the F-22 is faster and faster and faster. If it's not speed, it's probably something else. The only problem with this is your use of silly "evidence". If you want to have a debate about variable geometry vs. fixed geometry inlets, that's fine. Just make sure you actually understand the basic science behind oblique shockwaves, normal shock waves, and so on. Look up stagnation pressure loss. Find out how it is reduced through the use of multiple oblique shocks. It's rather hard to get really good supersonic performance without the use of variable geometry intakes. Why do you think Concord used them? Why do you think the F-15 uses them? Why do you think any aircraft that has them uses them? Do you think it was just some fad? It's not as important as stealth these days, and there are more powerful engines now too.

By the way... what kind of shock system developed in the XFU-8-3 intake at Mach 2+? I somehow doubt it was a normal shock. And as for boundary layer diverters, this is nothing new either. I don't know why you think the F-22 is special because it has them. So does the F-16 and F-18 (fixed inlet fighters). What of it? It's also a bit amusing when you talk about how the normal shock is trapped in the F-22's intake. You act as though this is a special feature of the F-22. Any aircraft with a conventional jet engine needs to pass the airflow through a normal shock at supersonic speeds before it hits the engine face. Jet engines don't like supersonic airflow. You pass air through a set of oblique shocks at high Mach to slow the air down efficiently before passing it through a final normal shock to get the flow subsonic. That's just how things work. The faster you pass the air through a normal shock, the higher the stagnation pressure losses. That's why oblique shock systems are used via variable geometry intakes.

Another thing I find funny is how you coo over the dumping of excess airflow. Again, this is nothing new. The F-15 does this along with a bunch of other aircraft. Bleed air doors... wow... amazaing! Been around for a long time, dude! I don't think you actually understand what stagnation pressure losses are, which is why you probably think variable geometry inlets are useless. An inlet's job is to slow the airflow down to subsonic speeds. You can do this in a variety of ways. Some are more efficient than others. The measure of this efficiency is the stagnation pressure ratio of the inlet for any given Mach number. Air comes in at supersonic speeds and gets decelerated to subsonic speeds through one or more shockwaves. This is just what happens. All this other stuff you're talking about does not negate the stagnation pressure losses that occur when passing through one or more shockwaves. If the F-22 has a single oblique shock followed by a normal shock, that's not very good for Mach 2+. It's better than a single normal shock, but not optimal. The F-15 uses 3 normal shocks at Mach 2+ before the normal shock. That is optimal for those speeds. This is just fact, okay? Textbook stuff. All this other stuff you're on about is fluff.

Did I say I wasn't going to argue with you? Damn, I lied.


Wasn't my arguement it was djcross's but then I wouldn't expect you to clue in to something as basic as who said what. BTW I'd take his opinion over your's any day (and likely so would everybody else here). As for the XF8U-3 who cares? It was capable of well over Mach 2 with a fixed intake and that's really the only point I was trying to make- that a fixed intake doesn't automatically limit you to Mach 2 or less.
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FireFox137

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Unread post01 Oct 2006, 19:34

With all of the variables of pressure, temperature, fuel load, weapons load... wind speed and wind direction... How are you measuring speed? Relative to the ground? Or to the wind direction? Is top speed equal to dash speed that is only to be allowed in time of war? ...and for how long? The F-22 ain't no SR-71 that can fly above Mach 2 for extended periods of time. The F-22 is an aircraft with a convential design and using "conevential" materials. Sure it may hit 2.5 Mach with more ease than an F-15 but how much does dash speed play into a2a combat? Sure I know speed is sexy, but it's not that importatant if the aircraft can be tracked and targeted with missiles that ARE much faster than any fighter today. Look, with the right weather conditions, the F-22 may very well be able to cruise at Mach 2 relative to some groud reference system... But, whats the difference? Really?
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idesof

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Unread post01 Oct 2006, 20:05

FireFox137 wrote:With all of the variables of pressure, temperature, fuel load, weapons load... wind speed and wind direction... How are you measuring speed? Relative to the ground? Or to the wind direction? Is top speed equal to dash speed that is only to be allowed in time of war? ...and for how long? The F-22 ain't no SR-71 that can fly above Mach 2 for extended periods of time. The F-22 is an aircraft with a convential design and using "conevential" materials. Sure it may hit 2.5 Mach with more ease than an F-15 but how much does dash speed play into a2a combat? Sure I know speed is sexy, but it's not that importatant if the aircraft can be tracked and targeted with missiles that ARE much faster than any fighter today. Look, with the right weather conditions, the F-22 may very well be able to cruise at Mach 2 relative to some groud reference system... But, whats the difference? Really?


The difference can be huge. Have you ever heard of the F-14 lobbing several Phoenix missiles at Mig-25s and not a single one hitting? Why? Because the Mig-25 simply outran the missiles. At long range, an aircraft's top speed as a means of evading a missile is actually quite effective. Moreover, with stealth, by the time it is detected by a double-digit SAM, it is already past the threat with supercruise, and it wold be exceedingly difficult for that SAM to down a Raptor in a tail chase, especially since it would be out of radar range by that time. Also, you have the kinetic energy imparted on your own missiles. Top speed, I agree, is immaterial if you can only achieve it for a matter of seconds or a few minutes at the most. However, if you are able to sustain it for, say, 30 minutes or more, that does give you a huge advantage in combat. It allows you to dictate the terms of engagement and/or disengagement at will. Even if the Raptor's top supercruise speed is "only" Mach 1.7 or Mach 1.8, that is an enormous advantage, far more than supermaneuverability, which everyone and their grandmother can achieve nowadays.

Finally, how in the world is the F-22 a "conventional" design? Since when is it using "conventional" materials? Also, anyone on this board who thinks they know how the Raptor's intake system works is in for a big surprise when the cat is finally out of the bag.
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idesof

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Unread post01 Oct 2006, 20:22

Speaking of reporters' uninformed quotes, here's one for you:

"Those feats range from dropping weapons at supersonic speeds from 50,000 feet, to testing new bombs that can hit 400 percent more targets than they were previously capable of reaching, to flying and fighting in joint exercises with capabilities never before seen by aircraft of any kind."

No doubt referring to the SDB, which has yet to be tested on the Raptor. Of course, it increases the number of ground targets a Raptor can strike by 400% (technically, the increase is 300%, the number is 400% the prior amount). Anyhow, that is very different than "new bombs that can hit 400 percent more targets than they were previously capable of reaching." :roll:
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Unread post01 Oct 2006, 21:43

Actually idesof, the inlet design of the 22 is basic, but the devil's in the details, always has been. It's called an external compression inlet because the initial shock runs away from the fuselage. The F-35 has an internal compression inlet because the initial shock runs towards the body. What all supersonic inlets do is use mutliple shocks to slow the air so the losses across the normal shock are minimal. Variable geometry means you are at design condition more often, but if you use a static inlet then you can make it a robust design. The 22 obviously has a very robust inlet or it wouldn't be able to do all the cool things it does. You can look at these things and get the basic engineering principle from them, but it takes close analysis to know the details where it really matters. For a couple years now I've wanted to crawl inside an inlet and look at the design and measure things, but yeah classified so no... never. It's wish that will never come true.
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Unread post01 Oct 2006, 21:43

Fixed intakes for supersonic M2+ flight are not unusual.

On subsonic aircraft the A7 had an excellent one, except for its reputation as a people eater.

The E.E. Lightning designed to the British Air Ministry's 1947 specification F23/49, two years after WW2 ended had a fixed elliptical intake with a fixed bullet. Now I will admit it was a dog on gas with a 900 mile range at least until the F6 and the F53 came along with the large ventral and overwing tanks.

The official ceiling was a secret and usually stated 60,000+ ft (18,000 m), Brian Carroll, one of the top examiners reported taking a F-53 Lightning up to 87,300 feet (26,600 m), for flights planned to go above 70K you had to wear full pressure suits. In 1984, a U-2 was intercepted at a height which they had previously considered safe from interception, over 88,000 ft (26,800 m).

In time-to-height and acceleration trials against F-104 Starfighters at Aalborg the Lightnings won, with the exception of the low level supersonic acceleration, which was a dead-heat.

Intake design, like gas turbine combustion and Microsoft Windows, is a black art full of mystery and frustration. What works on models and in theory often does not work in the real world.

The outboard engines on service Concords would surge if started with over a 5 knot crosswind which would fine the pitch of the LP Compressor blades, to fix this they started them during taxi.

In about 20 years some of the answers to the comments in this thread about the Lightning 2 will be answered, until then all is speculation.
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TC

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Unread post01 Oct 2006, 22:09

idesof wrote:The difference can be huge. Have you ever heard of the F-14 lobbing several Phoenix missiles at Mig-25s and not a single one hitting? Why? Because the Mig-25 simply outran the missiles.


Outrunning the missile would be impossible for the MiG-25. It doesn't fly that fast. The Phoenix was a Mach 4 missile.

The Foxbat can only sustain Mach 2.8 to 3 for about a minute, otherwise you start tearing the engine up. Viktor Belenko reported this after his defection, and fmr. Iraqi Foxbat pilots have later confirmed this.

Seems more like poor tactics in the engagement, bad missiles, or a combination thereof. In Vietnam, the Sparrow was notorious for going stupid after launch. Perhaps Snake, our resident Vietnam MiG killer, will see this one and hop in.

idesof wrote:anyone on this board who thinks they know how the Raptor's intake system works is in for a big surprise when the cat is finally out of the bag.


Don't go there. That "cat" should stay bagged, unless it is declassified many years down the road, or some stupid @$$ leaks that info. :nono: Hate to be blunt, but that was classified when I was around the program. Yes, it still is, and no, I didn't have access to that information, because I was not an engine troop. That the thing that many don't realize. Even with a TS clearance, they still don't tell you things that you don't need to know.

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Unread post01 Oct 2006, 23:18

TC wrote:
idesof wrote:The difference can be huge. Have you ever heard of the F-14 lobbing several Phoenix missiles at Mig-25s and not a single one hitting? Why? Because the Mig-25 simply outran the missiles.


Outrunning the missile would be impossible for the MiG-25. It doesn't fly that fast. The Phoenix was a Mach 4 missile.

The Foxbat can only sustain Mach 2.8 to 3 for about a minute, otherwise you start tearing the engine up. Viktor Belenko reported this after his defection, and fmr. Iraqi Foxbat pilots have later confirmed this.

Seems more like poor tactics in the engagement, bad missiles, or a combination thereof. In Vietnam, the Sparrow was notorious for going stupid after launch. Perhaps Snake, our resident Vietnam MiG killer, will see this one and hop in.

idesof wrote:anyone on this board who thinks they know how the Raptor's intake system works is in for a big surprise when the cat is finally out of the bag.


Don't go there. That "cat" should stay bagged, unless it is declassified many years down the road, or some stupid @$$ leaks that info. :nono: Hate to be blunt, but that was classified when I was around the program. Yes, it still is, and no, I didn't have access to that information, because I was not an engine troop. That the thing that many don't realize. Even with a TS clearance, they still don't tell you things that you don't need to know.

Curiosity killed the cat. Satisfaction?...got him fed to a Rottweiler.


Correct me if I'm wrong, but if you are talking about a long range shot, and the target establishes lateral distance (not taking off in the opposite direction), and not necessarily going Mach 3 but, say, Mach 2.5, even the Phoenix, by the time it gets close enough to the target to acquire it via its own active radar, it should have already burned out its motor long before and will hence be coasting, at which point it should not be difficult to outmaneuver. The Phoenix was never optimized for fighter-sized targets but for Soviet bombers and large cruise missiles which did not vary their heading, and which were heading straight toward a carrier. The Phoenix range, while stated as being 125 miles or so, was really more like 80 miles in actual flight distance, not the range at which it could be fired from the target, which relates to the former figure for a head-on engagement. In that sense, there was a reason the Navy retired the F-14 and the Phoenix: as a pair, they were never really designed as an air-superiority system, but as a long-range intercept system against bombers and cruise missiles. Once that latter threat was no longer an issue, the F-14, especially without Amraam capabitlity, did become obsolete.
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Unread post02 Oct 2006, 00:03

After over 3 years of simply reading the posts on this forum, I was finally compelled enough to register to make a comment.

I sit here reading this thread in absolute amazement. There have been some pretty laughable discussions on this forum among a lot of very zealous military aviation enthusiasts, but this one absolutely takes the cake.

A big "SHACK" to VprWzl on the 10% rule. And to most of the rest of you... no offense, but why does this issue matter so much to you? Take what the pilot said with a grain of salt. The top speed of the F-22 does not affect your daily life in any way, shape or form....other than to give you something to discuss on this forum.

I didn't say this to offend anyone. I just think it is ridiculous to pick apart something that was (quite clearly) not meant to be taken so seriously.

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Unread post02 Oct 2006, 00:14

sferrin wrote:Wasn't my arguement it was djcross's but then I wouldn't expect you to clue in to something as basic as who said what. BTW I'd take his opinion over your's any day (and likely so would everybody else here). As for the XF8U-3 who cares? It was capable of well over Mach 2 with a fixed intake and that's really the only point I was trying to make- that a fixed intake doesn't automatically limit you to Mach 2 or less.


Nice comeback, dude! Sorry, but you obviously are lacking knowledge of the basics, making intelligent debate on these issues impossible. If you don't understand how an intake even works, why are you debating the merits of fixed vs. variable geometry intake design? If I were you, I'd stick to calculating the F-22's max supercruise speeds based on casual comments pilots make to the press.
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sferrin

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Unread post02 Oct 2006, 00:52

Raptor_One wrote:
sferrin wrote:Wasn't my arguement it was djcross's but then I wouldn't expect you to clue in to something as basic as who said what. BTW I'd take his opinion over your's any day (and likely so would everybody else here). As for the XF8U-3 who cares? It was capable of well over Mach 2 with a fixed intake and that's really the only point I was trying to make- that a fixed intake doesn't automatically limit you to Mach 2 or less.


Nice comeback, dude! Sorry, but you obviously are lacking knowledge of the basics, making intelligent debate on these issues impossible. If you don't understand how an intake even works, why are you debating the merits of fixed vs. variable geometry intake design? If I were you, I'd stick to calculating the F-22's max supercruise speeds based on casual comments pilots make to the press.


While you on the other hand dodge the issue completely other than to attempt to toss off insults. Grow up.
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Unread post02 Oct 2006, 01:00

sferrin wrote:While you on the other hand dodge the issue completely other than to attempt to toss off insults. Grow up.


Dodge what issue? It's funny how actual pilots have come in here and told you you're being silly, yet you want to tell me I'm dodging some issue. This is rich.
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Unread post02 Oct 2006, 01:13

It can go fast, but how about fuel flow rate? Can't kick A$$ without Tanker gas. Anybody see where now the AF is serious about a new tanker and a new bomber and a transport smaller than a C-130? Wonder what projects will have their funding cut? I just wonder.
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