Press and hold R3 as you climb straight up towards the sky. Press the brake all the way down and blip the throttle one single time before the engine shuts down (repeat as necessary). Keep the plane centred. It takes practice to learn how to see when the plane is really straight and beginning to fall. Let the plane fall and pick up a little speed (takes about one second) and then release R3. Now let go of the brake and balance the plane with your rudders and control stick. Try to keep it sideways.
Releasing R3 forces the camera to become fixed on your plane so you can see without needing to move the camera. To pick up speed in reverse, hold the brake all the way down and blip the throttle one time before the engine shuts off. Learn to balance the angles to prolong your reverse flight as long as possible. It is difficult to learn, but everybody can learn!