Rigidbody AddForce Problem ?

Hello everyone, i have a Camera attached to cube. And we can fly, i want my cube to shake a bit when hit a building. So i put this code to the buildings ;

 var Cube : GameObject; // I made this GameObject because i also want cube to animate  but i didn't add this in here
 var distance = 1000;
 var a : int = 0; // this value is for making the action once
 
 
 function Update()
 {
 if(a==0){
  if (Vector3.Distance(transform.position,Cube.transform.position)<distance) // didn't use collider because if i do the plane is falling down and loosing the control.
 {
 a=1;
 Cube.rigidbody.AddForce(Vector3(0,0,-50)*1000); // if i use this it adds force backwards and i can't take my plane control back, what should i use?
 }
 }
 else{
 
 }
 }

And I ALSO tried using this but didn't work,any ideas ?

 Cube.transform.Translate(Vector3.forward * -100 * Time.deltaTime);

What should i use, i'm using SAC plane control here it's ;

 var YawSpeed = 30.0;
 var TurnSpeed = 30.0;
 var ElevateSpeed = 16;
 var Acceleration = 200;
 var MaxSpeed = 800;
 private var Speed = 0.0;
 
 
 
 function Update(){
 
 if(Speed >= MaxSpeed){Speed=MaxSpeed;}
 
 if(Speed  50 )
 {
 
 }
 else {
 
 
 }
 }