re: Myth Busters/Can a plane take off on a conveyor belt

Ok, this is totally not what I had in mind when this question was asked (guess I need to read more). My understanding is that you had a plane moving 100 mph (hypothetical, b/c I don't know how fast it needs to go to fly) and it's sitting on a treadmill going 100 mph in the reverse direction. Therefore the plane is not moving. But if the plane is moving, then sure, it'll fly.

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My understanding is that you had a plane moving 100 mph (hypothetical, b/c I don't know how fast it needs to go to fly) and it's sitting on a treadmill going 100 mph in the reverse direction.

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That is the case, but the catch is that the 100 mph for the plane is its airspeed, not wheel speed, because it uses jet engines pulling against the air as propulsion as opposed to the wheels.

I dunno how simple this can get. Without wind propulsion the plane isnt going to fly. Sounds good on paper but the physics doesnt allow it. If a plane is on a treadmill going 168 knots(which was said that was the speed to achieve flight) and the plane was going that speed, wouldnt it be motionless?

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I dunno how simple this can get. Without wind propulsion the plane isnt going to fly. Sounds good on paper but the physics doesnt allow it. If a plane is on a treadmill going 168 knots(which was said that was the speed to achieve flight) and the plane was going that speed, wouldnt it be motionless?

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Nope

If the plane is going 168 knots it wouldn't matter what the conveyor was doing because the plane is going to be flying right off the end of it. The conveyor could be doing a thousand knots and it would be the same. The plane is flying. The conveyor is just there to confuse you.

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I was thinking it was like a person on a treadmill. Your feet are moving but you're not going anywhere.

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True... but you're missing one of the variables in that case. Say you're standing on a treadmill wearing rollerskates (plane wheels) and holding on to the rails. You stand still, of course, the skates just move with the treadmill. Now... if there were an external force such as pulling on a rope that is securely attached somewhere in front of you (like, jet engines pushing against air) then you will of course move along the rope. The speed of the treadmill can increase to the max, if you can pull yourself forward with the rope, you'll still move forward.

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I think the point of the test is that the plane is not moving relative to the air around it. If this is the case, if the plane does not move forward relative to the air around it, like a person does on a treadmill, then it won't take off. If the plane moves forward on the treadmill, what is the point? I stand by my opinion/fact.

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it's not like a treadmill. a person on a treadmill is propelling themselves forward by pushing off of the ground.

think of it like this.
there's a long treadmill. there are hand rails on either side of it. you stand in the center of the conveyor belt on roller skates. you take your hands far out and front of you and pull Yourself forward. the treadmill goes in the opposite direction at that same amount of force.

You would still move forward. Your arms pulled you forward (with relation to your initial position) and are in facting holding you at your new postion on the treadmill. your wheels would still be spinning underneath you but your arms are keeping you in your place.

Your arms and the rails= the jets and the air.

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i think you'll find that they do it with a small plane and a cesna.

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LINK

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The episode, which airs in December, finds Savage and Hyneman tackling a question baffling everyone from bloggers to pilots: If a plane is traveling at takeoff speed on a conveyor belt, and that conveyor belt is matching the speed in reverse, can the plane take off?

``We put the plane on a quarter-mile conveyor belt and tested it out,'' says Savage about the experiment using a pilot and his Ultralight plane. ``I won't tell you what the outcome was, but the pilot and his entire flight club got it wrong.

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So, judging by the initial reactions of the pilots on here... the plane probably took off.

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if there were an external force such as pulling on a rope that is securely attached somewhere in front of you

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That's 2 external forces in the skating example. The handrail and the rope.
In the plane example, the only external force is the engine and it is being reversed by the treadmill.

BOOM!!!

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Think about it like this, you're on a treadmill with skates on.

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:lightbulb:

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That's 2 external forces in the skating example. The handrail and the rope.
In the plane example, the only external force is the engine and it is being reversed by the treadmill.

BOOM!!!

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This is true... in the plane's case, if the engines weren't on, the plane would move backwards, as opposed to stay in place. (Like, if you were standing on a treadmill with skates on, and not holding anything, you'd move backwards too.) Or, if it were using its wheels to taxi at the opposite speed of the treadmill, it would stay in place. (Like if you were holding a rail or walking on a treadmill) But the wheels aren't used to take off, only taxi.