How long does it take an F-15 to reach mach 1?

[lenbrazil]

I ask here because it has to do with the response time of the fighters from Otis AFB to NYC on 9/11.

[jaydeehess]

lenbrazil said:

I ask here because it has to do with the response time of the fighters from Otis AFB to NYC on 9/11.

The wikipedia page en.wikipedia.org/wiki/F-15_Eagle
states the max afterburner thrust is 129 kN(kilo-newtons each engine) so that is 258 kN total.
The max takeoff mass is 30,845 Kg
Mach 1 is 1200 KPH or 334 meters/sec

F=ma
258000=30845(a)
a=8.36m/s^2 (0.85 g)

v=at
334=8.36(t)
t=40 seconds

BUT!!! that simplifies things too much. This would be what happens only if the plane never had to rise above the ground higher than the wheels have it before it starts to actually fly. So 40 seconds is an absolute minimum.

Also max speed for an F15 is only 1.2 mach at low altitude. It can manage mach 2.5 at high altitudes but that then requires it obtain that high altitude first.

Also an F15 at full thrust(ie full afterburner) has only minutes worth of fuel. Going great guns to get to a location is useless if it requires that you land immediatly upon arrival at that location.

[Jason]

A better question would be "what is the average time between an alert and getting fighters off the ground in modern US airbases?"

[Obviousman]

It also depends what you mean by "low". At 30,000ft I think the F-15 can reach about Mach 1.9 or so.

In any case, I'd say that it would be about 60-80 seconds for them to accelerate using afterburners. Once in A/B, you are chewing up the go juice fast.

[scooter]

There are a lot of variables in the scenario that day...

What was the configuration of the fighters that morning? Fuel tanks, missiles...weight and drag.
Also, going Mach involves afterburner, afterburner=large gas consumption. Very unlikely they would be above mach for any period of time. Also, all aircraft are more efficient at higher altitude, and the climb to altitude takes time, and is subsonic.

There are a lot of "Hollywood" based theories out there that don't reflect the reality of alert air defense fighters.As an air defense guy during my AF career, the response that awful morning was about what I would expect...confusion, miscommunication, and re-writing the book as the events unfolded. They did their best...
EDIT...also, if the fighters were on 5 minute alert, barring any unusual conditions (long taxi, weather, ets) they should be airborne within 5 minutes. The "Battle Stations" status is in the cockpit with all checklists done up to, but not including, engine start. Once the scramble order comes through (with a "canned" departure routing) its a quick move to start engines and begin taxi. I'm not certain what the alert status of the various NORAD alert fighters were that day.

Dave

[PhantomWolf]

You have to remember that even after the first attacks they were still following standard protocol in which they weren't allowed to fly over Mach 1 anyways. I think when I worked it out, assuming they travelled there is a striagth line, which I'm not sure they did, they flew there at an average of mach 0.5-0.6

[lenbrazil]

jason said:

A better question would be "what is the average time between an alert and getting fighters off the ground in modern US airbases?"

below is an excerpt from a post I made on another forum

According to John’s source “…a pair of F-16 "Fighting Falcons" on 15-minute strip alert was airborne from Andrews just 11 minutes after being notified by the North American Aerospace Defense (sic) Command (NORAD) of a Cessna straying towards the White House. [AP Nov11/03; CNN June20/02]…”.

So even AFTER 9/11 it took 11 minutes from the time NORAD give the order just for fighters to take off to intercept a plane flying towards the White House and that the allotted time was 15 minutes and John claims that intercepts “normally took 3 – 8 minutes”. One would expect scrambles to have taken longer before the terrorist attacks but on 9/11 fighters took off at 8:52, that was:

6 minutes after getting the official order (8:46) ,
12 minutes after getting an unofficial order(8:40) and
15 minutes from the time NORAD was notified (8:37).

The scramble time is not the issue, (though it was when I posted the message above) the issue is why it took 19 minutes to cover 194 miles in plane that can do mach 2.

[lenbrazil]

phantomwolf said:

You have to remember that even after the first attacks they were still following standard protocol in which they weren't allowed to fly over Mach 1 anyways. I think when I worked it out, assuming they travelled there is a striagth line, which I'm not sure they did, they flew there at an average of mach 0.5-0.6

I'll have to find the quote but some NORAD guy saiid something along the lines of "our fighters routinely fly supersonic in appropriate situations. Both pilots said they flew supersonic (see post below)

[lenbrazil]

I obviously wrote the first message on this thread rather quickly.

I posted the text below on a couple other forums:

How long does it take F-15’s to reach mach 1 or mach 1.5 ?

There are conflicting reports on how fast the fighters from Otis AFB that took off at 8:52 or 8:53 AM on 9/11 to intercept flights 11 (which they didn’t know had crashed) and 175 flew. The reported speeds vary between 500 and 1200 mph [ www.cooperativeresearch.org/context.jsp?item=a852otisscramble ]

CTers (I’m NOT one) claim the fighters flew suspiciously slowly but the pilots said they flew supersonic. The question is why did they only reach Manhattan (coincidentally) at 9:11? 18 or 19 minutes to cover the approximately 194 miles = 613 – 647 mph average speed well below mach 1.

I think it could be due to two factors.

1) It takes time to accelerate to break the sound barrier and cruising altitude and then time to slow and come down.

Can any of you tell me about how long it would take to reach mach 1 or mach 1.2 or 1100 – 1200 mph (about mach 1.5)? About how far would they have traveled at that point?

Also I imagine conversely it would take time decelerate and a fighter would only want to be slightly faster (if at all) that the aircraft it was intercepting.

I imagine they also would have lost time/distance reaching cruise altitude and then descending again.

So one has to differentiate between top speed flown and average horizontal speed for the trip.

I know there is a 250 Kt speed limit below 10,000 feet but I saw on a USAF site that military planes have a waiver. I also know that supersonic flights are normally prohibited but some one from the air force said interceptors routinely fly supersonic ‘in appropriate situations’ (not an exact quote).

2) The fighters might not have flown the shortest distance from Otis to NYC (which basically would have had them flying over Long Island) but rather taken a slightly longer route over the Atlantic. A USAF general testified before Congress that the fighters scrambled from Langley AFB (which is NOT in Langley, VA but about 130 miles south of DC) did do so as not to fly in the busy East Coast corridor. I imagine this also might be done to avoid creating sonic booms over populated areas (would this be an issues at the altitudes they would have been flying) and possibly to reduce the risks to people on the ground if they crashed. These factors maybe related to the subsonic rule mentioned above. One site estimated such a route to be about 225 miles.
www.911myths.com/html/fighter_speeds.html

I am interested to here the opinion of anyone with expertise but what I would find especially valuable are links to reputable sources.

Len

PS F-15’s are said to have top speeds of about 1850 mph but it’s my understanding this is only for new jets in perfect conditions and that 1500 mph is really the upper limit.

[lenbrazil]

obviousman said:

It also depends what you mean by "low". At 30,000ft I think the F-15 can reach about Mach 1.9 or so.

In any case, I'd say that it would be about 60-80 seconds for them to accelerate using afterburners. Once in A/B, you are chewing up the go juice fast.

Just for clarification is that 60 - 80 seconds from take off? If so that seems to contadict this passage from a USAF F-16 pilot

The clock was ticking. At these fuel burn rates, the jet had only about 5 minutes to accelerate from 500mph-or about 0.9 Mach-to more than 1,200mph, before I hit bingo fuel.

[…]

Today, the jet seemed to be accelerating a little slowly. I wondered whether it would make the Mach 2.0 cutoff to pass the test. This jet had a history of engine problems; would they persist? It continued to accelerate through Mach 1.5, and I thought it might have a chance. As the voice warning of "Bingo fuel, bingo fuel" began to sound off in my headset, I passed Mach 1.95. I decided to give it a few more seconds to make it over the hump.

It sounds to me like it took him 5 minutes to acelerate from 500 - 1200 mph.

He seems to be saying the speed of sound is around 600 mph, he said he was at 40,000 feet over Germany. In the US that would mean temps of -50 to -60 F which would make the speed of sound about 675 mph at ground level barometric pressure. Would the lower pressure at that alltitude explain the difference?

hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html

The above raise a 2nd question, how much of the F-15 higher mach speed is due to the speed of sound being lower and how much is due to the plane being able to fly faster?

[Al Johnston]

lenbrazil said:

The scramble time is not the issue, (though it was when I posted the message above) the issue is why it took 19 minutes to cover 194 miles in plane that can do mach 2.

That's a shade over ten miles a minute, or 600mph, about 0.8+ mach (depending on altitude). As an average speed from a standing start, that's pretty smoky.

The speed of sound decreases as the air density decreases in the troposhere. Once in the stratosphere, it remains fairly constant at a bit over 600mph.

[golfhobo]

Hi, Len:

I'm not sure just why you are asking this. It really is not the issue. I can't give you either expertise in fighter speeds, nor good links. Just maybe some common sense.

The 911 myths source you cited is pretty self explanatory, with one exception. The generals and pilots testifying stated that SOP dictates that, due to a perceived threat from east of our shores, the SOP for scrambling interceptors would send them out to sea BEFORE they even had time to receive vector coordinates, target info, or confirmation of orders. So, the distance to NYC is immaterial, and therefore all computations of speed are irrelevant.

The exception is that, what was "testified" to is most likely a coverup, or "canned response" to any question of their efficiency. They're not going to clearly state that they were unprepared for a threat from within our borders. The truth is most likely that they went WAY out of their way before being vectored toward the targets. This explains the 19 minute response time, and allows for the truth of the pilots that they were going "as fast as they could" within the constraints of fuel economy.

The truth of the matter is that NEADS and NORAD grossly miscalculated the events of the day, when a tough decision had to be made... some guy was "out of the room," and the weekend warriors manning the alert stations at the airbases were probably immobilized by shock and lack of experience.

I'm not blaming the pilots one bit. I'm sure they performed their duties expertly. The problem lies with our country's preparedness level at the time of the attacks. You, of all people, should be confident that there was no conspiracy to fly slowly or in any way ALLOW these attacks. It was just a failure of the system.

Heads should have rolled at the FAA, NORAD, NEADS and whatever fighter wings were involved. Sadly, I doubt any of this has happened. Maybe, we ALL deserve a second chance. I hope we are better prepared next time.

Hobo

[Halcyon Dayz, FCD]

But next time they won't be using aeroplanes though.

[jaydeehess]

halcyondayz said:

But next time they won't be using aeroplanes though.

BINGO

The number of ways to kill and maim relatively large numbers of people is limited only by the imagination of humans, and so far homo sapiens (including those supposedly backward Arabs) have been pretty imaginative.