Hello Istvan, I gave the SE5 a go, sadly I gave up.
I extracted the FM by Kant and tried to alter some of the entries, however, not being a FM Guru this was merely tinkering and not very well at that.
Usually when you open up a FM you get the plane fmd file and also the emd file for the engine, here this was not the case just the fmd and two numbered files I cannot open.
These do not seem to be class files but I am assuming they contain the engine data, anyway I could not open them to see. ???
I tried using the entries from various fmd files using the Kant engine entry in the fmd file but even though the aircraft loaded there was no improvement.
My trial then moved to actually using complete FM files from other aircraft by adding them to the java of the SE5 which I opened, the best was the Fokker VII I think which seemed to move crab like along the ground slowly and almost began to turn. Once the AI reved the engine it did correct itself and take off though.
The next best was from a Spad sadly this started promisingly and then nosed over.
Others gave little or no improvement so I gave up on it.
Hopefully someone with the knowledge to exactly what goes on with FMs will come along and answer your prayers, alas, not me.
Wishing you all the very best, Pete.