This is turning into a stimulating conversation, on an old post - nice to see some life in it again. The porpoising in First Eagles 2 usually happens when aircraft flown by AI are being chased or are chasing another plane - fast oscillation, up and down, of the elevators. I'll see if some of the tips here help with that. Peter01 posted some tips on this a few yrs. ago in the FE2 discussion list but none of those tips seem to get rid of the porpoising. I've got the cruise speed set on aircraft to 90% of top speed in FE2 - maybe this is the problem...will report back if I find something that works.
Happy flying,
Von S