Chaps
Just to tidy up what happens off a ski-jump:
You can run a car up one and it will stay airborne (thanks to Mr Newton) for a length of time that depends on both the exit speed and the ramp angle.
You can run a MiG29/Su27 (or any other conventional non thrust vectoring jet) up one and it will fly for longer than the car because it has SOME wing lift. Clearly the extra time benefit will depend on the actual L/W ratio at exit. All you have to do after exit in this case is to be accelerating at enough kt/sec such that at the end of the number of seconds the ramp provides you have reached normal flying speed for your weight This is the ‘runway in the sky’ notion. (on an airfield the undercarriage holds you clear of the ground and allows you the number of seconds needed to accelerate to flying speed).
BUT- and it is a big but - the pilot must be able to control the attitude after exit while the aircraft accelerates to flying speed. This is what the MiG29/Su27 could do because they have aerodynamic flying controls that are effective well below normal flying speed. Without such controls you are going to have to enhance the V squared stuff with some sort of reaction control system.