F-15 max speed

bazdriver · by **bazdriver** » 14 Jan 2010, 20:34

SEP: you know. At 50000ft, it's(SEP) so low that acceleration will be so slow and you will use use as much fuel to get here.

Now: -fuel flow I give : Flight Manual
- time to accelerate from Mach 1.0 to Mach 2.3, 40000ft, clean, PW100- 100 at 102% trim, starting weight 38000lbs : 175 sec !

- Flight test data : 1 0ctober 1985 : F-15 Flight Manual

Top Mach 2.5 speed limited by airframe structure, engine/inlet limitation, stability concerns(inertia coupling, you know?). Trying to stay at Mach 2.5 would lead to major structural failure shortly followed by destruction. Get faster: same result. Achieving the USAF requirement was already a big goal. All wind tunnel , flutter, stability, structural test conducted lead to the same conclusion. Flying above Mach 2.3 is already eroding the safety limit factor. In those Cold War days the USAF would have been most pleased to show its new superfighter at Mach 2.6 or more if they have been able to do it. Enginneer determined the limit even before the aircraft flies. Trying to do more is suicidal.

So is my suggestion. When the F-15 would be finally retired, ask the AF to buy a QF-15 remotely piloted. They will remove the stick, throttle and ejection seat handle! And let's go!! So at this time, you will became the highest speed man in a F-15 ever. The most stupid too. But hopefully this will not last for long!!! Engineers are designing aircrafts, not pilots(though you can be both), and when they put a limit, respect it!!. That's what smart test pilots do!

mustang65 · by **mustang65** » 15 Jan 2010, 02:09

What is wrong with the inlet on the F-15, I am sure they could make a better one if the one on the jet cant deal with the stress of high speed? At 45000 feet that altitude is perfect for a speed run, you will have less fuel burning. I am also sure that the F-15 is not burning 2100lbs/hr of fuel that high, and if it takes the F-15 that amount of time to get to that speed then there is plenty of time to maintain top speed for five minutes. If you have tanks that will get you to about mach 1.8 maybe more then drop them get up to top speed and you should have more then 7,000 pounds of fuel remaining. With a new inlet that could handle the stress of that speed. The VMAX is rated to one hour so that is more than enough time to maintain top speed for five minutes. They could make the F-15 in the 65000lbs class that would be enough for five minutes at top speed but that is never going to happen. It would be sweet to see an enlarged F-15 though.

psychmike · by **psychmike** » 15 Jan 2010, 10:45

duplicate

psychmike · by **psychmike** » 15 Jan 2010, 10:46

mustang65 wrote:What is wrong with the inlet on the F-15, I am sure they could make a better one if the one on the jet cant deal with the stress of high speed? At 45000 feet that altitude is perfect for a speed run, you will have less fuel burning. I am also sure that the F-15 is not burning 2100lbs/hr of fuel that high, and if it takes the F-15 that amount of time to get to that speed then there is plenty of time to maintain top speed for five minutes. If you have tanks that will get you to about mach 1.8 maybe more then drop them get up to top speed and you should have more then 7,000 pounds of fuel remaining. With a new inlet that could handle the stress of that speed. The VMAX is rated to one hour so that is more than enough time to maintain top speed for five minutes. They could make the F-15 in the 65000lbs class that would be enough for five minutes at top speed but that is never going to happen. It would be sweet to see an enlarged F-15 though.

Oh Lordy, if Mustang65 wants to say that developing new turbojet engines, new drop tanks, new inlets, and now a larger airframe would allow the F-15 to hit Mach 99 for a few days, I'm willing to concede the point.

Clearly, he's not interested in learning from TEG, Bazdriver, or others in-the-know. He's refuting these experts, the technical manual, and anything else he doesn't want to hear and fixating on things that fit his view. It's a sad case of confirmatory bias: "I know that I'm right and I will disregard anything to the contrary."

Clearly, there are people who don't see that very high performance aircraft are built to tolerances and balance complex, competing, and dynamic forces. Between Mustang and Skyhigh, we'd have wings of F-35s with GAU-8s crammed in where the lift fan would go and fleets of aircraft carriers with vertical launch missile tubes where the flight deck would be. Creativity is one thing, fantasy is another.

A - "I'd like to put bigger wheels on my car."
B - "They won't fit inside the wheel well."
A - "Let's make the wheel wells bigger."
B - "The engine won't fit."
A - "Let's move the engine."
B - "It'll change the balance of the car."
A - "Let's change the suspension."
B - "Why? What you're suggesting has no practical purpose."
A - "Because it'd be sweet to see."

mustang65 · by **mustang65** » 16 Jan 2010, 06:48

It seems really silly that it is only limited to a minute above Mach 2.3 when it was designed for Mach 2.5.

shep1978 · by **shep1978** » 16 Jan 2010, 09:37

mustang65 wrote: It seems really silly that it is only limited to a minute above Mach 2.3 when it was designed for Mach 2.5

That's still bloody impressive though really! Especially considering its age and considering whilst there might be faster jets out there like the Foxbat the likes of the Foxbat can't turn like a 15 can and isn't half as versatile in that the 15 can still dogfight with the best of them when flown right. Its combat record speaks for itself (obviously) too.
I would listen to the guys on here though when they tell you its (F-15's) limits as some of them do know exactly what they're talking about and thats a real privalige to be able to get answers like that in this day an age of the internet when so many clowns spout so much crap on so many other forums. Try asking the same questions on other forums and I bet you won't get the same level of technical insiight you do here.

That_Engine_Guy · by **That_Engine_Guy** » 16 Jan 2010, 18:14

mustang65 wrote:It seems really silly that it is only limited to a minute above Mach 2.3 when it was designed for Mach 2.5

It was done to fill a contractual obligation. Plain and simple.

Part of the USAF contract said, the FX (Now F-15) WILL achieve MACH 2.5

The contract didn't say how long, or by what means.

During testing (With V-MAX) engaged the YF-15s with their YF100 engines did reach MACH 2.5; which enabled McD to get the contract but....

When USAF test pilots started to 'test' the EAGLE at MACH 2.5, and maintenance was performed after MACH 2.5 runs were 'tested' it was found to be really REALLY bad for the airframe/engines.

When you find bad things during testing, IE engine damage, melted parts, cracked parts, sheet-metal begin pulled from rivets, missing hardware, etc... you impose limits. That is what testing is for.

Example; my car has an engine that is capable of pushing it well over 100MPH, the speedometer says so, and so does Car & Driver Magazine. I know it, the OEM knows it, and C&D has reported it, but; The owners manual (IE - flight manual) specifically states, operating the car beyond legal limits may be dangerous, and that racing the car on a track is hard on the engine/drivetrain and voids the warranty. I've even driven it at 100MPH but only for a few seconds. (In a straight, well secluded stretch of back-road.) I can tell everyone I have a 100MPH car. Sure I can make it go faster/longer if I put more $$ into it with a turbo, new computer, tires, brakes, cool steering wheel, etc... but why? It's already a 100MPH car. It's not feasible or needed for every day use as my daily driver.

What you're talking about with MACH 2.5 and the F-15, is like the upper/right .1% of the flight envelope that will only be used .00001% of any Eagle's usable life-span on average. It was only put there to make a point. "We have a super-fighter that can, if we want it too, fly at MACH 2.5"

Keep 'em flyin' :thumb:

TEG

mustang65 · by **mustang65** » 18 Jan 2010, 04:37

Aren't the new aluminum alloys like the ones on the F-22 able to take the stress of high speed? If it were a combat situation and you were chasing a mig and you were just out side the rang of your missiles you were at mach 2.3 already for a minute and this mig had just got vital reconisance that would compromise the lives of American troops would you go top speed for five minutes in an attempt to catch the mig and shoot it down. And you were right by your base coasting with tanks before the notification.

That_Engine_Guy · by **That_Engine_Guy** » 18 Jan 2010, 05:42

mustang65 wrote:...this mig had just got vital reconisance that would compromise the lives of American troops...

That is why we have Patriot and Standard Missile systems.

When we were in Kuwait (before the last little party to oust a particular dictatorship) there were Patriots stationed at our facility to keep any 'stray' MiGs from getting the drop on our base. We were only a matter of minutes from the border by way of a super-sonic fighter, and there was no way to scramble and intercept an aircraft in that short of time.

What missiles are perfect for... point defense!

Your said MiG would never have gotten photos to begin with; if the MiG did make it into the area, it would never make it back out!

Besides, there weren't even F-15s in the area... :roll:

I slept very secure at night there, knowing our Army brothers and sisters were at the scopes of that Patriot battery.
:cheers:

Keep 'em flyin' :thumb:

TEG

Enough with the Eagle high MACH what if's... It would all boil down to what a pilot thought he could live through and the situation at hand. We've already discussed the limits, why they are there, and how much money it would cost to improve the situation. There isn't the need, it was only a design point, it is almost never used, almost never would be used, that's why we have SAMs like Patriot and Standard. If they can blast a satellite or ballistic missile they'd make short work of any MACH 3 recce jet.

fiskerwad · by **fiskerwad** » 18 Jan 2010, 14:05

That_Engine_Guy wrote:
Enough with the Eagle high MACH what if's...

http://www.youtube.com/watch?v=KR28cdU7fpQ

Perhaps water injection would help with thrust, TEG?

:wink:

fisk

psychmike · by **psychmike** » 19 Jan 2010, 03:17

TEG:

In addition to valuable experience and knowledge that really elevates the caliber of discussion on these forums, you have the patience of a saint!

Have a good one!

Mike

That_Engine_Guy · by **That_Engine_Guy** » 19 Jan 2010, 19:22

psychmike wrote:TEG: In addition to valuable experience and knowledge that really elevates the caliber of discussion on these forums, you have the patience of a saint! Mike

Thanks Mike.

Maybe it is due to my work with the kids ?(My own or the young engine guys/gals)

TEG

wrightwing · by **wrightwing** » 26 Feb 2010, 12:33

mustang65 wrote:Five minutes isn't that long it can maintain top speed for five minutes. I am not talking about twenty minutes or ten just five that is definitely possible.

One more time for our edification, what is the point of this exercise? There is no tactical usefulness of running your jet out of gas. You have to allow for enough gas to land your plane, or at least to make it to a tanker, before it runs out, which will limit the length of time you can fly at top speed, aside from the structural issues that have been brought up. This means that the practical limit is much lower than the theoretical limit.

mustang65 · by **mustang65** » 11 Mar 2010, 21:54

The F-15 would not run out of gas though, you should be able to get to a new base or a tanker. As for the tactical use fullness that would never happen in combat. Five minutes at 1875 mph is possible as TEG said probably due to the safety concern which probably is the canopy. What is the safety concern that prohibits the F-15 to go that fast?

mustang65 · by **mustang65** » 15 Mar 2010, 01:38

It takes the Eagle about 175 seconds to reach mach two and probably another minute to get to top speed. That should give the Eagle plenty of time to do the speed run. As for the point there isn't one it will probably never happen, but if it did the Eagle would be able to maintain top speed for five minutes.