The F-15 Eagle - Maximum Speed?

Cold war, Korea, Vietnam, and Desert Storm - up to and including for example the A-10, F-15, Mirage 200, MiG-29, and F-18.
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Kryptid

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Unread post04 Oct 2008, 20:20

Has the F-15's absolute maximum speed been released to the public?

Is its top speed drag-limited (based on thrust-to-drag ratio), airframe-limited (its airframe cannot endure the heat and stress generated by the speed that its engines could potentially push it to), or engine-limited (the engines can push the aircraft to speeds that are harmful to the engines themselves)?

I've seen the F-15 stated as having a speed of 1,650+ miles per hour, but how much faster can it go? I've even seen it stated that the Eagle can reach 1,875 miles per hour, but that seems a bit high.

Any answers?
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TC

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Unread post04 Oct 2008, 22:20

Mach 2.5, but that's more theoretical than anything. A two-bagger with a combat load will not go Mach 2.5. I'm not sure whether the Streak Eagle was used to determine the max speed, as it had everything non-essential removed, thus saving added weight.
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outlaw162

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Unread post05 Oct 2008, 00:33

1875 miles per hour is 1630 knots.

At some altitude where 1630 knots True Airspeed can be achieved (40,000+) and considering a good approximation of Mach 1 is 10 nm per minute, then 1630 knots TAS equates to:

2.7 True Mach number which is probably right around 2.5 Indicated Mach.

You're both right.


:D

regards, OL

(clean F-4D in the high 40's could get 2.02 TMN on a good day, so I 'spect a clean stock Eagle might get close to 2.5. Other than ISR and speed records, not a whole lot to be accomplished up there at those speeds. Things change though.)
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TC

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Unread post05 Oct 2008, 02:16

If I were going for the highest speed attainable by an Eagle, it'd have to be in the A model. The As were the lightest out of the Eagle fleet. An A model with the MSIP II upgraded engines, would be a no Sierra rocket ship! 8)

Other factors to consider when going for better speed and performance are temperature, humidity, and altitude above sea level.

BTW Outlaw, I LOVE your signature line! Mad Max rules!
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Kryptid

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Unread post05 Oct 2008, 05:46

Based on what I know, weight doesn't affect an aircraft's top speed. It <i>will</i> affect acceleration, but not top speed. A heavy aircraft with low thrust could still get to a high speed if the aircraft has low enough drag and a sufficient fuel supply; but it might take a while.
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TC

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Unread post05 Oct 2008, 06:13

Added weight does affect your plane's ability to ACHEIVE your top speed, however.
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parrothead

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Unread post05 Oct 2008, 07:28

IIRC added weight requires added lift which will generate added parasitic drag. How much this will affect your top speed I don't have a clue :wink:
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ATC

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Unread post05 Oct 2008, 22:00

Kryptid wrote:Based on what I know, weight doesn't affect an aircraft's top speed. It <i>will</i> affect acceleration, but not top speed. A heavy aircraft with low thrust could still get to a high speed if the aircraft has low enough drag and a sufficient fuel supply; but it might take a while.


OK, but what about F=MA You can't get to a speed without accellerating to it.
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Roscoe

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Unread post06 Oct 2008, 06:54

If max speed is limited by the canopy or stability or something other than thrust=drag, then the following doesn't apply.

That said, max speed occurs when max thrust equals drag, i.e. no net force so no more acceleration. Drag can be simplified as parasite drag (aerodynamic friction) and induced drag (drag due to lift).

Weight affects induced drag so lets amplify this one a bit. Generating lift isn't free. Vortices and downwash are byproducts of lift; both require energy transfer from the aircraft. That energy transfer (loss) manifests itself as drag. The more the airplane weighs, the more lift must be generated (in level un-accelerated flight, weight=lift). More lift, more drag. More drag, then the engines can't push it as fast.
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parrothead

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Unread post06 Oct 2008, 07:02

Thanks for the clarification and correction there, Roscoe! I knew increased lift created increased drag but I had the term wrong.
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Raptor_One

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Unread post06 Oct 2008, 22:13

F-15C in a clean configuration w/F100-PW-220 engines can do Mach 2.45 at altitude for standard day conditions. For colder than standard day conditions, it is Mach limited to Mach 2.5 at altitude. In other words, it can go faster than Mach 2.5 in a clean config at altitude when it's colder than standard conditions, but it's not designed to do so safely.
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That_Engine_Guy

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Unread post07 Oct 2008, 00:44

Even the F100-PW-100s could exceed the airframe's limits. The engines would be junk after a dash above 2.5, but if needed the extra power/speed is there. :cool:

Most sources will say the Eagle's top speed is "MACH 2.5+" and I'll add that the "plus" does indeed mean something. (Even if it does break the aircraft and engines.) :doh:

Like posted before the "rated maximum speed" is quite often the accepted "safe maximum speed" for the machine as a whole. So yes an Eagle can fly around, fuel load/configuration/altitude permitting, at MACH 2.5 without a problem. When you get into the "2.5+" category, many hours of maintenance will be required after flight, and 2 new engines will most likely be needed.

Hey VarkVet, didn't the Vark get above it's "MAX Speed" back when... Without giving numbers, I've heard stories about it's dash performance too. Impressive for the TF-30s! :cheers:

Keep 'em flyin' :thumb:
TEG

Oh; remember the Raptor's Max Speed is only "MACH 2 Class" :lmao:
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kamov

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Unread post21 Oct 2008, 14:27

Top speed in the 15 is FTIT limited.... yeah you can hit V-Max and dash to around 1800, but your engines will be toast. Lots of other varables also come into play, but FTIT is the first wall the Eagle will hit when reaching top speed.
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johnwill

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Unread post21 Oct 2008, 17:21

TEG,
The Vark has been to at least 2.7 Mach in GD flight test. At low altitude it has been to 890 KCAS, again in GD flight test.
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Kryptid

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Unread post22 Oct 2008, 16:24

Unfortunately, Mach is a relative term since it is based on the speed of sound. It varies with altitude and temperature. I prefer using miles per hour because it is always the same regardless of environmental conditions. Can anyone give me some solid mph data on the Eagle's speed?

Alternatively, can anyone give me an equation showing the relationship between the speed of Mach 1 (in mph or km/h) and altitude?
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