im thinking that these might be good controls:
jump button: helicopter goes up
Crouch button: helicopter goes down
forward=forward
back=back
left=turn left
right=turn right
primary fire button: a machine gun type of weapon
secondary fire button: missiles
(u could also switch the 2 weapons around. The missiles should have a few seconds to reload so that people dont spam them. The explosion for the missile shouldnt be too big though, or else it ould be a little bit cheap)