Airplane Controls - Lift

Hi, I’m trying to make my plane lift off and ascend, but instead it descends. Can anyone help me? Thank you.

var liftSpeed = 20.0;

function FixedUpdate(){

if(Input.GetButton("Lift")) 

{

    transform.position += transform.forward * liftSpeed * Time.deltaTime;

}

}

If you just want it to ascend vertically, use:

  transform.Translate(Vector3.up * liftSpeed * Time.deltaTime);

It will go up like a Sea Harrier.