Can a Jet Plane Take Off on a Treadmill?

[Brad Jensen]

To reduce this problem to its simplest terms, imagine that the velocity of the airplane and the velocity of the treadmill are equal, at zero. What happens?

The answer without all the nitpicking is no, the plane will not take off unless it is moving relative to the air it is in. If it is on a treadmill moving backwards at the same rate the plane is moving forward, it will not lift into the air. Unless it is a Harrier jump jet., or AV8, with thrust vectoring. Or an Osprey. They can take off with thrust vectoring in still air.

 

[jbriggs444]

If it is on a treadmill moving backwards at the same rate the plane is moving forward

That's the ambiguous condition this thread started with. Is the plane moving forward relative to the ground or relative to the treadmill?

 

[berkeman]

This again, really... all over, again... ?

Yeah, thread closed temporarily for Moderation...

 

[Nugatory]

If it is on a treadmill moving backwards at the same rate the plane is moving forward, it will not lift into the air.

The best way to visualize this problem is to imagine that you've taken your model airplane (with properly rotating wheels) into a grocery store, set it down on the conveyor belt, and are pushing it. Can you push it against the direction of the belt? Yes, whether the belt is moving or not. What do the wheels do when you push it against the direction of the belt? They turn. If the belt is moving while you're pushing they turn faster, but that's all.

The thrust from the engines is no different than the force of your hand pushing the toy airplane: the thrust is pushing the airplane forward relative to the air. Is there any force acting on the airplane in the opposite direction to resist the engine thrust? There is if the airplane is tethered to the treadmill or if the wheel brakes are locked so that the wheels cannot turn. In this case the airplane remains at rest relative to the treadmill and its wheels do not turn. There is if the airplane is tethered to the ground; in this case the airplane remains at rest relative to the ground while the treadmill moves and the wheels turn.

However, if the airplane is not tethered and the wheels are free to spin, then there is nothing to oppose the thrust of the engines so the plane accelerates forwards relative to the air, the ground, and the treadmill. The wheels turn faster because the airplane is moving relative to the belt, that exerts no force on the airplane.

 

[russ_watters]

I think we've beaten this to death. We'll keep it locked.