Got it after 7:00 hour of work !
the gear fall and dissapear !
i have rename my r-gear_top (whit tire attached on it), r_wheelwell
then make a small box (.001m x .001m) erase hall poligon so ivisible ! 8)
name it r_gear_top put the pivot of the box ender the plane at 11 metre of distance time of the fall 1.5 sec (Distance pivot = .5*Gravity*Time^2) make the whellwell (the gear) the parent of the r-gear_top and export the thing
thank alot for the help guys i apreciate