Force Help

Hello, I am working on a game with a quad copter and I have 4 forces added to 4 empties that are positioned in the center of each rotor. To move forward, I have the back forces increase. I need to have the craft "reset" and stop itself after I release the button. I tried using GetKeyUp and decreasing the back force, but I do not know how to calculate the opposite forces that are needed to stop the craft because the amount of time changes each maneuver. Thanks ahead of time!

btw, I am currently using code that limits Transform.rotation to prevent spinning out of control when moving forward. I am not sure if I should just use torque for everything movement related.