How can I rotate an object without moving it up or down?

This is my code there, i have an aircraft, it has a rigidbody component with no gravity(i have some constraints) the movement is good but when i try to rotate it left or right, it's rotating and increasing/decreasing its height. What can I do?

 public class Movement : MonoBehaviour
 {
 
     
 
     private Rigidbody rg;
 
 
     // Start is called before the first frame update
     void Start()
     {
         rg = GetComponent<Rigidbody>();
     }
 
     // Update is called once per frame
     void Update()
     {
 
         
         rg.transform.Translate(Input.acceleration.x, 0, -Input.acceleration.z);
         rg.transform.Rotate(Vector3.back * Input.acceleration.x * 2f);
     }
 }