Press SHIFT + E and release it very fast, then press 2, 3, 4 and secondary exits and cargo hatches will open and close. Depending on the aircraft, you may also press SHIFT + D or SHIFT + C for special effects.
Instead of setting a low framerate to save resources, set it to unlimited. Your computer will display as many frames per second as it can, while allowing you to increase the graphics somewhat considerably. This is most noticeable on slower computers.