Hello,
I think (I'm not the only one) that the current P51D (p51d_20141227.zip from the main repository, same as from SVN) is too difficult at takeoff and landing. A clean landing with no roll departure is almost impossible.
After observation, my conclusion is that, at these steps (when grazing the ground), the "spin and stall" feature is triggered too brutally, at a too low angle of attack (10 - 11°). Moreover, it remains active when the aircraft touches and is rolling on the ground (with the nose upward).
I propose a more progressive spin departure, starting at a slightly higher AoA. Also, it is totally cancelled when touching the ground, where it has no justification.
I have been as much careful as I could, aiming at not degrading the behaviour in altitude. I absolutely want not to betray the fabulous work done by sadly missed Hal Van Engel.
I have also changed the spiralling propwash effect. This contributes to the aircraft pulling leftwards at acceleration before takeoff. It was initially obtained (if I understand well) by an angular shift of the engine (6° disorientation leftwards) , which is a bit artificial IMOH. Moreover, if it were to counteract the propwash effect, this disorientation should be rightwards. I could not find any mention of it on the real aircraft (??).
I changed it for a propwash action on the vertical tail, which is closer to the real effect.
The aircraft is now much easier at takeoff and landing, we can even get a 3-point landing. I feel that the main general behavior in stall and spin is still present enough, not degraded. I feel that it has not lost its strong, very interesting character. I hope not being wrong.
Less important, I have also exchanged the VSI and Acceleration instruments location, more logic and in accordance with what is seen on many pictures of the dashboard.
I have also included the p51d-autostart patch proposed by efel in this message (Thanks, effel. I hope you don't mind, please tell me otherwise). Without it the engine does not start, even manually.
P51D-dany-20151215 (unzip and just copy the p51d folder which is inside, letting aside the archive title)
Dany