Ok. So iv'e been having this problem with FSX ever since I got it like 3 years ago. Whenever I fly jets, no matter which one, I can't get it to fly or accelerate at high altitudes nearly as fast as it does at low altitudes. I know it should be the opposite because the air is thinner at high altitudes. I am not a noob so I am not talking about KIAS, I am talking about KTAS. For instance, if I try flying my Superbug at FL300 I have to use full burners to keep a reasonable cruising speed but at FL050 I accelerate about 10 time faster and can fly much faster. Am I not understanding something? Is something wrong? Is FSX just unrealistic like that? I've done a lot of research and found nothing about my issue. I need answers!!!
I found and copied this.
I hope it helps you.
Most supersonic fighters in fsx fly way too fast at low altitude, and way too slow at high altitude. This is due to errors in fsx, resulting in incorrect thrust. Some designers have tried to include mach drag, but not many. Combined with inaccurate induced drag, most fighters in fsx fly more like UFOs than turbojet aircraft.
7. How can it be fixed?
This is tricky, and involves tables 1502-1507 in the .air file. Basically the engine needs to run higher rpm at higher altitude to produce more thrust. Some 160% N1 and 130% N2 may be required at 36000ft. Aircraft can be given very accurate flight envelopes, but those values will be messed up.
Getting the aircraft to turn properly is another story, and equally complicated.