DroneController.cs

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class DroneController : MonoBehaviour {
    Rigidbody rigidbody;
    AudioSource audio;
    bool thrustAudio = false;
    bool thrustAudioOn = false;

	// Use this for initialization
	void Start () {
        rigidbody = GetComponent<Rigidbody>();
        audio = GetComponent<AudioSource>();
	}
	
	// Update is called once per frame
	void Update () {
        ProcessInput();
        ProcessAudio();
	}

    private void ProcessInput()
    {
        var key_w = Input.GetKey(KeyCode.W);
        var key_a = Input.GetKey(KeyCode.A);
        var key_d = Input.GetKey(KeyCode.D);
        var key_ua = Input.GetKey(KeyCode.UpArrow);
        var key_la = Input.GetKey(KeyCode.LeftArrow);
        var key_ra = Input.GetKey(KeyCode.RightArrow);

        if (key_w || key_a || key_d || key_ua || key_la || key_ra) thrustAudio = true;
        else thrustAudio = false;

        if (key_w || key_ua) Thrust(0); // Main thrust
        if (key_a || key_la) { Thrust(-1); return; } // Port thrust
        else if (key_d || key_ra) { Thrust(1); return; } // Starboard thrust

        return;
    }

    private void ProcessAudio()
    {
        if (!thrustAudioOn && thrustAudio)
        {
            audio.Play();
            thrustAudioOn = true;
        }
        else if (thrustAudioOn && !thrustAudio)
        {
            audio.Stop();
            thrustAudioOn = false;
        }
    }

    private void Thrust(int v)
    {
        switch(v)
        {
            case -1: // Port
                Debug.Log("Port thrust " + Time.time);
                transform.Rotate(Vector3.back);
                break;
            case 0: // Main
                Debug.Log("Main thrust " + Time.time);
                rigidbody.AddRelativeForce(Vector3.up);
                break;
            case 1: // Starboard
                Debug.Log("Starboard thrust " + Time.time);
                transform.Rotate(Vector3.forward);
                break;
            default:
                throw new NotImplementedException();
        }
    }
}