Unity 2d C# бензин для самолетика

Добрый день, Есть скрипт C#

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

[RequireComponent(typeof(Rigidbody2D))]
[RequireComponent(typeof(CapsuleCollider2D))]

public class CharacterController2D : MonoBehaviour
{
// Move player in 2D space
public float maxSpeed = 3.4f;
public float jumpHeight = 6.5f;
public float gravityScale = 1.5f;
public Camera mainCamera;

bool facingRight = true;
float moveDirection = 0;
bool isGrounded = false;
Vector3 cameraPos;
Rigidbody2D r2d;
Collider2D mainCollider;
// Check every collider except Player and Ignore Raycast
LayerMask layerMask = ~(1 << 2 | 1 << 8);
Transform t;

// Use this for initialization
void Start()
{
t = transform;
r2d = GetComponent();
mainCollider = GetComponent();
r2d.freezeRotation = true;
r2d.collisionDetectionMode = CollisionDetectionMode2D.Continuous;
r2d.gravityScale = gravityScale;
facingRight = t.localScale.x > 0;
gameObject.layer = 8;

if(mainCamera)
cameraPos = mainCamera.transform.position;

}

// Update is called once per frame
void Update()
{
moveDirection = 1;

// Change facing direction
if (moveDirection != 0)
{
if (moveDirection > 0 && !facingRight)
{
facingRight = true;
t.localScale = new Vector3(Mathf.Abs(t.localScale.x), t.localScale.y, transform.localScale.z);
}

}

// Jumping
if (Input.GetKey("space"))
{
r2d.velocity = new Vector2(r2d.velocity.x, jumpHeight);
}

// Camera follow
if(mainCamera)
mainCamera.transform.position = new Vector3(t.position.x, cameraPos.y, cameraPos.z);
}

void FixedUpdate()
{
Bounds colliderBounds = mainCollider.bounds;
Vector3 groundCheckPos = colliderBounds.min + new Vector3(colliderBounds.size.x * 0.5f, 0.1f, 0);
// Check if player is grounded
isGrounded = Physics2D.OverlapCircle(groundCheckPos, 0.23f, layerMask);

// Apply movement velocity
r2d.velocity = new Vector2((moveDirection) * maxSpeed, r2d.velocity.y);

// Simple debug
Debug.DrawLine(groundCheckPos, groundCheckPos - new Vector3(0, 0.23f, 0), isGrounded? Color.green : Color.red);
}
}

Когда цепляю его к самолетику, он летит вправо, на пробез набирается высота, так вот, хотелось бы сделать систему, чтобы когда закончилось топливо, он больше не могу набирать высоту (тоесть пробел отключен) Как это можно реализовать?

P.S я чайник)