Your setvelocity script stop the helicopter's movement mid flight. Lets say I was flying 100 MPH, I hit space bar and it stop me to 0 MPH. To fix this, change the part where it says Setvelocity and change it to Addvelocity. This will make it so you will go up, while maintaing your current velocity. I also suggest reducing the Z value (Where is says 0 0 1) and make it lower if you are using addvelocity.