Hi “molnibalage”,
Indeed, in reality there can be two charts for which the thrust slopes as a function of Mach and altitude could not be the same for 2 different engines, even if they’re of the same type or class (ex: turbojet, turbofan with x number of bypasses, etc.) and this has mainly to do with the inlet and inlet duct designs and partially with the flow characteristics through the rest of the engine until it meets the outlet and there’s a clear example here as the TF-404GE’s FULL AB thrust curves (that “l3crusader” has provided on page 5) differ quite much as slopes and peak values from the AL-31’s FULL AB thrust that you’ve linked, so it’s hard to find an overall function that can satisfy all situations in a global manner, which I tried…! There might be software which can simulate (with a given accuracy) some results according to an engine design with a given amount of detail, yet I haven’t used any kind of software to estimate engine performance at all. All I did was to take a crude F-16 Block 50 GE engine’s data, make a picture of how the thrust curves look like as a function of Mach and alt and only tried to adapt these curves for the engines of the aircraft which I’ve worked on to provide better aero data, so I must admit that I didn’t work very hard on the engines data individually and only used a multiplier for all functions, taking care to match the max. thrust given by wikipedia at the same Mach number for which the F-16’s GE thrust value is shown by wikipedia, thus not altering the function’s shape. At least, this was my idea of transferring these functions to all other aircraft knowing that the F-16’s GE has the real measured data and I can trust it. It might’ve been non-recommended doing this, because as seen in this case (and I don’t doubt that in the earlier cases this wouldn’t repeat), the slopes don’t match and are quite far from each-other. Also keep in mind, that in the charts that you linked the thrust is in KN (or at least that’s what it seems), while the charts I’ve updated are in pounds of force. This difference between slopes is indeed a serious problem because it alters the real X axis acceleration of the aircraft and compromises a realistic dogfight experience even if the aero data would be perfectly real, but I didn’t know where to find real experimental data of the engines which I can manually insert (with some passion and patience) and re-check, then save it into the file and fly…! I wasn’t badly intended and I must say again that I’m not specialized in jet engines, all I know is only theoretical and up to a point, I didn’t learn any serious methods to estimate engine thrust yet…, maybe I’ll take the time to enhance this area, but now I’m only concerned to give better aero data mostly.
If the default engine data might be more accurate (I didn’t check), then that should be used instead, meanwhile I can guarantee that the aero data is better, at least up to where the shock stall occurs, and overall good even beyond the shock stall’s Mach number.
If someone can have the patience to provide me any accurate (which is corrected) experimental data (both aero and engine data when possible), I’d start putting that data exactly as it is and stop bothering with mathematical estimations and I think I’ll start doing so for the Lyulka AL-31 for Su-27 and for the F-404 GE of the F-18 as I have them now!
Best wishes!