I know it's a game about planes but helicopters are still aircrafts. It's currently really hard to make a good-looking helicopter that flies well. The main reason is that we have to use some plane props and a vtol engine to simulate a real helicopter prop.
That's why I think it would be really great to add an helicopter engine that allows use to pitch/roll on its own just like a real one, and a stabilizing small prop for trimming and yaw.
What other helicopters parts would you like to see added ?