there are two parts of the engines poth parts are the same speed having them both on at the same time is how you reach top speed, but what I do is use 1 and 2 together to lift off and then turn off one of them for less speed and better control in the air.

1 and 2 activate engines, b is auto pilot (not that stable but pretty good), 1 on num pad is drop bomb, 2 on num pad releases clusters of bomb, arrow keys for controls and y for extra thrust and smoke trail.