Mythbusters to take on - PLANE ON A TREADMILL!!!

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Lets say airplane has a Vmu of 50kts. It is moving at 50kts the minimum unstick speed and you crank the tread mill up to 50kts to counter act this. The airplanes wheels are moving at 100kts, but the airplane still achieves 50kts of airspeed so it flies.

Unless say the brakes are set etc. :p
 
USMC and taseal, you're not thinking about the physics correctly. Remember that an airplane's wheels can rotate freely (unless someone holds the brakes). The airplane moves by pulling/pushing the air, not by turning its wheels against the ground like an automobile.

When the plane starts moving forward (because the prop or jet is moving air), the wheels just rotate freely underneath it. If the ground underneath the airplane where to suddenly move in the opposite direction, the only effect would be to spin the wheels faster. It won't slow the plane down at all (disregarding the small amount of friction in the wheel bearings).

If you would like to picture it differently, instead of the airplane using its engine to move the plane, imagine that there is a rope tied to the front of the plane, and a bunch of people standing out in front of the treadmill start pulling on the rope. If the treadmill starts to run the opposite direction, no matter how fast it moves, it cannot stop the group of people from pulling the plane forward. The wheels spin freely, and the motion of the treadmill has no affect on the movement of the plane. The people's ability to move the plane is independent of any influence from the treadmill. The same is true if we allow the aircraft engine to do the work. It is pulling/pushing the air, thus its ability to move the aircraft is also independent of the treadmill. Don't confuse the way that an aircraft propels itself with the way that an automobile does.

All right, one more example. Similar to the last. This time it is you that is standing on the treadmill. You start walking forward, the treadmill starts turning the opposite direction, and you are cancelled out. You don't move in relation to the air around you, correct? Now, tie a rope to a tree located out in front of you, and put on some roller skates. Start pulling on the rope to move yourself forward, and imagine what happens when the treadmill starts to run. Glory be, you can still pull yourself forward (in relation to the air around you) and the only affect that the treadmill has is to make your roller skate wheels spin faster and faster. It can't stop you from moving forward though, can it?

Are we there yet?

:D
 
I give up on this thing

I swore (other forum) that I will never ever click on a treadmill topic again....

what am I doing here. :(

but yeah, I see where you are coming from Steve... the wheels should move freely under it, and not effect anything...

its just such a stupid thing that my mind doesn't want to comprehend what is going on lol
 
Yeah yeah yeah, blah blah blah.... science science science.

But what about a cat on a treadmill?

[yt]peLD2vlxRM0[/yt]
 
I <8 cats.

Though the real cat-like thing that kitty could have done would be to find the power source to the treadmill, rip the plug out of the wall, walk up to the ball on the now-stopped treadmill, sit on top of it and fall asleep until the next feeding. :p
 
still dont get it...I understand aerodynamics but I am just sitting here picturing an airplane at full throttle on a treadmill with zero forward motion. If those wheels are going a thousand miles per hour it makes no difference providing there is no relative airflow over the wings to make the plane fly.

I do understand how the wheels work and that they are just free on bearings and not mechanically driven. I should probably stop posting because I think what I am envisioning is not what we are talking about here and I am making myself look stupid
 
USMC-SGT said:
I am just sitting here picturing an airplane at full throttle on a treadmill with zero forward motion.
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That's the problem. An airplane at full throttle on a treadmill would have forward motion, since the treadmill is powerless to stop it.
 
Not at all USMC, you are interpreting the question in a different way, which I would say is equally correct. The airplane cannot accelerate to flight speed while stationary on the treadmill, no matter how fast the treadmill moves, and so the airplane cannot take off!

BUT,

If instead we consider a very long treadmill, on which the airplane is allowed to move forward to take off, then this is what happens, irregardless of how the treadmill moves.
 
USMC-SGT said:
still dont get it...I understand aerodynamics but I am just sitting here picturing an airplane at full throttle on a treadmill with zero forward motion.
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Like Berkut said, this is where you're missing the boat. The treadmill cannot stop the airplane from moving forward, no matter how fast it (the treadmill) runs. The airplane will have forward motion, there will be airflow across the wings, and it will fly.


crazy_pilot.gif
 
SteveC said:
Like Berkut said, this is where you're missing the boat. The treadmill cannot stop the airplane from moving forward, no matter how fast it runs.
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Not true. If the treadmill matched the speed of the TIRES, the airplane would not go forward. If it matches the speed of the aircraft itself (which is the assumption that most people use), the airplane will go forward.
 
Chris_Ford said:
Not true. If the treadmill matched the speed of the TIRES, the airplane would not go forward. If it matches the speed of the aircraft itself (which is the assumption that most people use), the airplane will go forward.
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I don't understand the distinction. Aren't the tires attached to the airplane, thus have to go the same speed?
 
SteveC said:
I don't understand the distinction. Aren't the tires attached to the airplane, thus have to go the same speed?
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No. I'm talking about the rotational speed of the tires.

Normally, they are the same, however, in certain situations they are not. On ice, for one example, and on our hypothetical treadmill on another.
 
See, what I want to know is how they're going to get a treadmill to do this. I'm not talking about size, I'm talking about speed. Lets assume they can find a treadmill big enough to do this. And I want to make sure that I've got this right, the myth is that the treadmill moves at the same speed as the tires rotate, correct? Not the same speed that the plane is going?

Lets assume it's the former. The plane adds power and starts moving. It gets to 1 kt...so the treadmill starts to move at one knot. Now, if the aircraft was on solid ground, the tire is rotating at the speed it would be for 1 kt. With the treadmill, it's now moving at the speed it would be for 2 kts. If the treadmill has to keep up with the speed of the tire, it therefore has to speed up to 2 kts. Which then means the tire is now spinning at the speed it would be for 4 kts. So the treadmill has to speed up to 4 kts. Which then means the tire is now spinning at the speed it would be for 8 kts. So the treadmill has to speed up to 8 kts. Which then means the tire is now spinning at the speed it would be for 16 kts. So the treadmill...

See where I'm going with this? If that's the actual myth, won't the treadmill HAVE to instantly start moving at an infinitely fast speed as soon as the tires start rolling?
 
If that's the actual myth.

Most people seem to assume the treadmill matches the airplane's speed and so would only need the 60mph or so it takes the ultralight to T/O.
 
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