View Full Version : high altiude jet engine performance ?

October 19th, 2010, 09:00
Seems that I'm stuck. The jet I'm developing the FDEs for performs correct at S.L. With and without AB the correct top speed etc...
As soon as I get up to e.g. 10000ft the engine lacks considerable thrust with and without AB.
Even in the high subsonic range without AB.
Any idea how I can get increased engine performance at high altitude?

Best regards


Milton Shupe
October 19th, 2010, 16:07
I sent you a few things by email.

October 22nd, 2010, 01:11
Hi Milton, thanx a lot for your help :)



November 1st, 2010, 10:09

Hope all is going well. Sometimes the difference in SL and altitude performance may be drag rather than thrust linked. I have had good luck tuning some of these issues (at least in prop planes) by making subtile adjustments to the Mach drag curve.

Keep up all the good work! Tom

November 2nd, 2010, 10:40
>Sometimes the difference in SL and altitude performance may be drag rather than thrust linked

Confirmed, and that's exactly what I like in FDE design! The subtle changes one needs to do to make e.g. a T-38 slip just through Mach1 or to adjust the Vimd.
It's the fine balance one needs to find for a good flight model.
Found out that FSX doesn't really like planes that are supposed to be subsonic at S.L. but supersonic at high altitude and everybody tells you that this isn't going to work in a realistic way.
In the end I found a way to 'flat rate' the engine to get the neccessary thrust at high alt.
There's a terrific competent guy here who can compute all real world thrustlevels for all engines and altitudes and he confirmed that it's FSX which is off concering jet engines at high alt.

Thanx for your kind words, and it looks like the T-38 will be as realistic as the 310 as we have now to ex T-38 pilots in the team.
Hope you don't miss the testing for this great plane!

Best regards


November 3rd, 2010, 10:36
Looking forward to flying the t-bird. Haven't flown her myself as I graduated from being a bush pilot, but I fly with probably a hundred guys that flew or instructed in it, so a good ground for questions.

Did a FD for the F-86 at one time, which was barely capable of going M1.0 in a dive. I always visulize a tugboat pushing a wall of water. A somewhat similar phenomenon, except the waves and speed are influenced by the hull length rather than the speed of sound.

Cheers: T