WaltBJ wrote:

SNIP:
Ed Rasimus wrote:
Now, let's put to bed this idea of accelerating through the mach
straight up.
A couple reminders:
1) with a thrust to weight atio of 1.6:1 the Streak Eagle is
distinctly higher powered than anything any of us flew in the service.
2) It's shedding weight in full afterburner during the takeoff and
climb. I don't know what the fuel consumption of an F15 full-out is
but it's certainly over a ton a minute, so the T/W is increasing.
3) The only comparision I have experience with is the F104B on an AB
go-around at the end of a mission but with 1500 pounds of fuel reaming
a B model with 2 AIM9s weight about 16300. With 18000 pounds of thrust
it was very sprightly indeed. Thing was, that 18000 pounds of thrust
is measured in static condions. I have seen the fuel flow gauge on
both the F104s and the F4s rise from about 8500pph (per engine) on
pre-takeoff run up to 12000pph at 600 KIAS on level acceleration after
takeoff, obviously due to ram effect. Since jet thrust has a linear
relation of fuel burn - the thrust to weight ratio in flight cannot be
determined from thrust developed while sitting still on the ground.
Note that I do not know what is happening in the afterburner; the only
correlation I ever heard of was the AB fuel flow was about 4 times
that of the fuel flow to the engine itself. Also, the J79 manual
figure in AB for takeoff was 750 pounds per minute - per engine. FWIW
the engine fuel flow is determined by the necessity of keeping the
total air flow/fuel flow ratio right around 55 to 1. ( Lots more air
than stoichiometric needs to keep the engine from melting.)
4) So what I'm saying is that there is no doubt in my mind that a
lightened F15 with a minimum mission required fuel load could and did
exceed Mach 1 climbing vertically.
5) BTW with Jeff Ethell's flying experience and the highly visible
attitude direction indicator in an F15 why question his statement that
they were indeed vertical? Checking a vertical climb on the gyro is no
big deal - and one also looks out at the horizon.

Walt BJ

I can't compete with all you knowledgeable guys with the maths or actual
flying experince, but I thought I'd just contribute this..........

The Sukhoi P-42 - a modified Su-27 Flanker which took all the time-to-climb
records from the Streak Eagle - was similarly modified with tweaked engines
and lightened airframe.

It had thrust-to-weight ratio was almost 2:1 at takeoff.

The following is an extract from Andrei Fomin's book on the Su-27 :-

"The fighters engines were augmented, with the thrust of each engine
increasing by more than 1,000 kgf (in FAI reports a thrust of 2x13,600 kgf
was mentioned and the engines were presented under the designation of
R-32). The steps taken gave the P-42 a unique thrust-to-weight ratio
equalling almost 2 at takeoff. As a result, the P-42 was able to gather
speed and break through the sonic barrier when climbing".

It doesn't actually say 'climbing vertically' - but it does say supersonic
whilst climbing.

My page on the P-42 is at :- http://www.duffeyk.fsnet.co.uk/p-42.htm and
the list of some of the P-42's 27 world records is at :-
http://www.duffeyk.fsnet.co.uk/p42_records.htm

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Ken Duffey - Flanker Freak & Russian Aviation Enthusiast
Flankers Website - http://www.flankers.co.uk/
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