Flight Sim help

 using UnityEngine;
 using System.Collections;
 
 
 public class FlightControls : MonoBehaviour {
 
     public KeyCode
         accelerate = KeyCode.LeftShift,     //  Key used to accelerate
         decelerate = KeyCode.LeftControl;   //  Key used to decelerate
 
     public float
         maxSpeed = 1000000, //  Maximum speed
         minSpeed = 0;       //  Minimum speed
 
     public Camera 
         playerView;     //  The main camera
 
     GameObject cameraTarget;    //  The point that the camera looks at (just above the plane)
 
     float
         currentSpeed = 0;   //  The current speed
     
     void Start()
     {
         cameraTarget = new GameObject();    //  Creates a new pivot point
         playerView = Camera.main;   //  Sets the current camera
         Cursor.visible = false; //  Hides the cursor
 
         if(GetComponent<Rigidbody>() == null)   //  If there is no rigidbody
         {
             gameObject.AddComponent<Rigidbody>();   //  Create a rigidbody
             GetComponent<Rigidbody>().useGravity = false;   //  Don't use gravity
         }
 
         cameraTarget.transform.parent = transform;  //  Sets the pivot point as a child to the plane
     }
 
     void Update()
     {
         Controls();
         CameraControls();
     }
 
     void Controls()
     {
         if(Input.GetKey(accelerate) && currentSpeed < maxSpeed) //  If the accelerate key is pressed and the plane can accelerate
         {
             currentSpeed++; //  Accelerate
         }
 
         if (Input.GetKey(decelerate) && currentSpeed > minSpeed)    //  If the decelerate key is pressed and the plane can decelerate
         {
             currentSpeed--; //  Decelerate
         }
 
         transform.Rotate(new Vector3(Input.GetAxis("Mouse Y"), Input.GetAxis("Horizontal"), -Input.GetAxis("Mouse X")));
         /*
          * Rotation breakdown:
          *  - X rotation is the pitch   (up/down)
          *  - Y rotation is the yaw     (left/right)
          *  - Z rotation is the roll    (tilt left/right)
          */
 
         GetComponent<Rigidbody>().velocity = transform.forward * currentSpeed; //   Moves the plane forward at the current speed
     }
 
     void CameraControls()
     {
         playerView.transform.LookAt(cameraTarget.transform);    //  Looks at the pivot point
         cameraTarget.transform.position = transform.position + (transform.up * 2);  //  Sets the pivot point 2 units above the plane
         playerView.transform.position = transform.position - (transform.forward * 10) + (transform.up * 2); //  Sets the camera 10 units behind and 2 units above the plane
     }
 }

Attach this script to a cube of size (3, 0.3, 3) and you have yourself a primitive flying object