Rotate an object back to its old rotation

Questions & Answers
1

Hello all.May be the title is not so clear,so I would like to explain it.I am currently making an aircraft game.The controls are simple,press arrow buttons and rotate it around z axis.I managed to do this.The problem is that,I want the aircraft to return its idle position smoothly if no arrow keys are pressed.I tried some code but it didn’t work.I really appreciate any help.Thank you!

Here my code to turn it:

using UnityEngine;
using System.Collections;

public class CarController : MonoBehaviour {

	private float sensitivity = 70;
	private float speed = 40;
	public float zRotate;
	public float backReturn;
	private bool rightArrowUp = false;

	void Update () {

        // change position by arrow keys    
		transform.position += new Vector3(Input.GetAxis("Horizontal")*speed*Time.deltaTime,0,0);

        // change rotation by arrow keys	
		zRotate -= Input.GetAxis("Horizontal")*sensitivity*Time.deltaTime;	
		zRotate = Mathf.Clamp(zRotate, -5, 5);
		transform.rotation = Quaternion.Euler(0, 0, zRotate);

       //rotate back its idle position(0 degrees)
       // how????
    
	}
      
}
2

just wrote this.

Lerp is what you need though, great if you can work this out for yourself, so consider this code a spoiler that you dont have to look at

using UnityEngine;
using System.Collections;

public class rotateThis : MonoBehaviour {

	// Use this for initialization
	Quaternion originalRotation;
	float rotateSpeed = 0.1f;
	bool restoreRotation = false;

	void Start () {
		originalRotation = transform.rotation;
	}
	
	// Update is called once per frame
	void Update () {
	

		if(Input.GetKeyDown(KeyCode.A)&& !restoreRotation)
		{
			restoreRotation = true;
		}

		if(restoreRotation)
		{
			transform.rotation = Quaternion.Lerp(transform.rotation,originalRotation,Time.time * rotateSpeed);
			if(transform.rotation == originalRotation)
			{
				restoreRotation = false;
			}
		}
	}
}