Can a Jet Plane Take Off on a Treadmill?

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  • Thread starter Thread starter Dalton Peters
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    Airplanes Lift
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Discussion Overview

The discussion revolves around the hypothetical scenario of a jet plane attempting to take off from a treadmill that moves backward at the same speed as the plane moves forward. Participants explore the conditions necessary for the plane to achieve lift, the definitions of motion and speed, and the implications of the treadmill's movement on the plane's ability to take off.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants argue that for a plane to take off, it must be moving forward relative to the air to generate lift, suggesting that the treadmill's backward movement would prevent this.
  • Others point out that the question is poorly defined, emphasizing the need to clarify the reference frame for measuring speed.
  • A few participants highlight that if the plane is stationary relative to the ground, it cannot achieve lift, regardless of the treadmill's speed.
  • There are discussions about the role of wind and whether the plane could take off in a wind tunnel scenario, where airspeed could be sufficient for lift despite ground speed being zero.
  • Some participants express confusion over the forces at play, questioning how the treadmill's movement affects the plane's ability to take off.
  • Concerns are raised about the terminology used, with some arguing that the plane's velocity must be considered relative to the air, not just the ground or treadmill.
  • Participants discuss the implications of the plane's thrust and the forces acting on it, questioning how these forces interact with the treadmill's motion.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as multiple competing views remain regarding the conditions under which a plane could take off from a treadmill. The discussion reflects significant disagreement and confusion over the definitions and implications of motion in this scenario.

Contextual Notes

The discussion reveals limitations in the clarity of the original question, particularly regarding the definitions of motion and the reference frames involved. There are also unresolved questions about the forces acting on the plane and how they interact with the treadmill's movement.

  • #31
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.
 
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  • #32
Brad Jensen said:
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?
 
  • #33
OCR said:
This again, really... all over, again... ?
Yeah, thread closed temporarily for Moderation...
 
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  • #34
Brad Jensen said:
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.
 
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  • #35
I think we've beaten this to death. We'll keep it locked.
 
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