Turn Spitfire to Bird:
Test fly the spitfire in the museum. Drop both bombs and use all ammo except nine rounds. Turn off the engine by pressing [Ctrl] + A + E and it will turn to a bird

3D Dynamics Editor:
Ctrl + Alt + Y = 3d Dynamics Editor (place planes, flak, etc.)

Unlimited Weapons:
Open the ww2.ini file and find the line that says Unlimited Weapons. Change it from no to yes.

Change Planes:
While flying hold Alt and "P", you will be able to pilot your allies plane.