Lift

Lift is essential for flight. Without it we'd be rather stuck here on the ground. Lift itself is not a force, but the result of other forces.

Air flows over a wing (or aerofoil) and is separated at the leading edge. It goes above and below the wing, eventually meeting at the end (trailing edge). The wing is shaped so that the air flowing over it is accelerated and goes faster towards the trailing edge than the air below the wing (along the chord line). This means there is less pressure above the wing than below it, so the wing is 'pushed up' (lift) and takes the aircraft with it.

This diagram shows how a wing generates lift.

In the case of a rotary-winged aircraft such as a helicopter or Osprey (those things are bloody awesome) the aircraft has its wings on an axle that rotates very quickly. Sort of like a giant fan. The lift is then generated to pull it up and hover, rather than having the aircraft to need to be moving forward in order to push air over the wings and generate the lift to take off.

A bloody awesome Osprey.

As I stated in a previous post, ROBLOX is a vacuum-like environment, and not all aspects of physics are accounted for. Therefore, moving an aircraft forward or rotating its wings very quickly won't generate lift on its own, and scripting it to do so can be very tricky. The aforementioned BodyMovers will probably come into play in the case of Air: Force, with some sort of thrust in the Y axis being provided based on speed. In which case, the physics will be simulated and won't precisely imitate the real world, but it should look and feel like pretty much the same thing.