I'm working with ODE and everything works fine. I have an biplane which flies, lands, takes off, etc. But there is a problem when it flies towards the earth (perpendicularly). Here is my code:

where m2 is force applied (thrust), which increases with time.... g is gravity = -386.... adn f is lift force f = 8879, since the mass of the plane is 23. When I fly horizontally wverything is ok, but when i fly towards the ground the plane flies backwards away from the ground if "w" is pressed, instead of flying faster since also gravity force acts on it.
I tried to write addvellocal instead of addforcelocal, but now the plane flies forward if "w" is pressed, but does not fall on the ground (when directed towards it) if "w" is not pressed, though there is gravity acting on t.....
Does anyone know what can be the problem?? and why it behaves so weirdly?

after 2 hours I solved this problem on my own. I just put the fps_max and ph_fps_max_lock equal to 50, now almost everything works fine. Yet I have a new question. Every plane has its center of mass where its engine is set, since engine is the heaviest part. But in my plane, the center of mass is just at the center of the plane, so it does not properly fall down, not lke normal planes. I have PH_BOX, so it behaves as if it is a box, how to make the engine understand that the plane's tale is lighter than its engine part? I cannot make it PH_POLY, since it is a moving object.

you can add the gravity using VECTOR* vPos but it will give also angular speed

Can you make two PH_BOXs (one for the front and one for the back of the plane) attached with a constraint with one being heavier than the other? Don't make the visible plane in two separate parts though

yorisimo's response seems ok, i guess you can also use:

phent_addforcelocal (ENTITY* entity,VECTOR* vForce,VECTOR* vPos );

where vPos is the location on the plane you want to add a specific force, may be able to use it to push the front down a bit.. but really why do you need this? if you want the front to appear heavy, cant you just keep tilting it down a bit and increase speed based on the tilt angle?