Plane on a Treadmill

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cmoneyr

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Which is exactly why the plane in youtube accelerated so fast, (in comparison to treadmill) yet never left the ground.
The point of the youtube video wasn't to have it take off, it was to prove that a plane would move forward when placed on a treadmill moving in the opposite direction. From there it's easy to infer that because all that needs to happen for a plane to take off is for air to pass over the wings at an acceptable rate that it would be possible for one to take off.
 

jbhtexas

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Which is exactly why the plane in youtube accelerated so fast, (in comparison to treadmill) yet never left the ground.

Dude, the reason why the plane in the YouTube video never left the ground was because the treadmill was too short! The plane never had a chance reach sufficient velocity before it smashed into the end of the treadmill.

The acceleration of the plane relative to the treadmill belt isn't what lifts the plane off the ground, the velocity of the wings relative to the air through which the wings are moving is what lifts the plane off the ground. When the wings are traveling fast enough through the air, the plane will lift.

Are you drunk???
 
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singsing

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I'm just glad my earlier remarks are buried three pages deep now. THE PLANE WILL TAKE OFF. The only thing the thrust of the engines will have to overcome is the weight of the plane itself. Tire speed is the only real difference being on the treadmill.
 

herbicide

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As we're all internet forum addicts... I'm sure we've heard of the "Plane on a Treadmill" puzzle.
And just to summarize - the question is, if a plane is on an infinitely long treadmill that is capable of accelerating to match the speed of the plane, will the plane take off?

There's no official answer, and you can find die hard supporters of both answers.

Well, Mythbusters is taking it on. They actually originally planned to air it a month or so ago, but delayed it. If I'm correct, it's airing this upcoming Wednesday - the 30th.

Perhaps everyone would be interested in placing bets for takes off vs. doesn't take off. Moderators would have to be in control of what wins, theoretically the Mythbuster result. But they've had controversial results in the past, and could end up with a "possible" or "unknown" result, etc. So we'd have to let our moderators choose winner or tie/no result.

Anyone remember if this (plane on a treadmill) has been discussed here before?


OK, I have been basing all of my arguments on the above bolded statements, the original debate, no relative air speed to the wings of the plane. If I misunderstood something, let me know.

jbhtexas said:
The acceleration of the plane relative to the treadmill belt isn't what lifts the plane off the ground, the velocity of the wings relative to the air through which the wings are moving is what lifts the plane off the ground. When the wings are traveling fast enough through the air, the plane will lift.

As I said before I did not read the entire 400,000 post thread, so if I missed something, I apologize, as I agree with the above statement.

I still hold my challenge to my bet with the bolded text above* Fixed wing only, and no puller propeller aircraft, VTOL. STOL, allowed.
 
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jbhtexas

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Calculate the wheel bearing friction as well and you are getting close...

Then read up again on the principles of an airfoil (wing) and I will see you all tomorrow.

The max takeoff weight for a big Boeing 747 is about 970,000 lbf. The Cf for tires on ordinary concrete is about .01. The rolling friction resistance would then be about 9700 lbf.

The four engines on a 747 can develop about 60,000 lbf thrust each. It would seem that the engines can sufficiently deal with the rolling resistance. I'd also guess that there is plenty of thrust to deal with wheel bearing friction.

I know all about airfoils...
 
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MrGreg

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I've read two versions of this riddle. The first version said the treadmill matched its speed to the plane's speed. The second version said the treadmill matched its speed to the plane's wheel speed.

Correct me if I'm wrong, but those are two very different situations, with two different answers...
 

herbicide

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I've read two versions of this riddle. The first version said the treadmill matched its speed to the plane's speed. The second version said the treadmill matched its speed to the plane's wheel speed.

Correct me if I'm wrong, but those are two very different situations, with two different answers...

In my feeble, insulted mind, you are correct. I have been arguing the "plane speed" scenario to others who seem to be arguing the "wheel speed" version.
 

MrGreg

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In my feeble, insulted mind, you are correct. I have been arguing the "plane speed" scenario to others who seem to be arguing the "wheel speed" version.

Hehe, I didn't read through all 16 pages, but the discussions didn't seem to match up. The original post said the treadmill speed matched the wheel speed, so it seems logical that the plane would go nowhere. The real question is what would happen if the treadmill speed matched the plane speed, which you guys (and girls) have covered in lots of detail

Edit: What the heck am I still doing up??
 
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herbicide

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I read the original as plane speed = treadmill speed.

In my feeble mind if the treadmill speed = plane speed, the plane never advances on the treadmill, therefore no relative air or ground speed, therefore is no airspeed observed on the wings, therefore no lift.

As we're all internet forum addicts... I'm sure we've heard of the "Plane on a Treadmill" puzzle.
And just to summarize - the question is, if a plane is on an infinitely long treadmill that is capable of accelerating to match the speed of the plane, will the plane take off?

There's no official answer, and you can find die hard supporters of both answers.

Well, Mythbusters is taking it on. They actually originally planned to air it a month or so ago, but delayed it. If I'm correct, it's airing this upcoming Wednesday - the 30th.

Perhaps everyone would be interested in placing bets for takes off vs. doesn't take off. Moderators would have to be in control of what wins, theoretically the Mythbuster result. But they've had controversial results in the past, and could end up with a "possible" or "unknown" result, etc. So we'd have to let our moderators choose winner or tie/no result.

Anyone remember if this (plane on a treadmill) has been discussed here before?

I said I was going to bed an hour ago.
 

ISUAlum2002

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Apr 11, 2006
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Re: CyBookie - Plane on a Treadmill

Me too. All in. I will even throw all my worldly assets into this for real $$$

Please oh please make an event for this. In fact, I will put all my real life assets on the line as well as long as I am the beneficiary of all of herbicide's real life assets.
 

CloneFan65

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Apr 11, 2006
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Just as soon as you prove it true.

:biglaugh:

If 1 doesn't equal 0.9999999... then there exist a number x>0 s.t. 0.9999999... + x = 1. Then x > 10^-n for some positive integer n, but 1 - 0.9999...9 (with n+1 9's) = 10^-n-1, so...

x = 1 - 0.99999... < 1 - 0.9999...9 (with n+1 9's) < 10^-n < x, therefore x < x

so by contradiction, 1 = 0.9999999...

QED
 

Warder60

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I haven't thrown in my opinion yet, so here goes. First my credentials -- electrical engineer (takin physics...), and ~45 hrs as private pilot.

Lets establish that the wheels are "free". Unlike your car, there's nothing driving the wheels, or preventing them from rotating. Except brakes, in fact mainly use brakes to taxi around.
As stated earlier, you apply high throttle to start rolling, and then back it off to control your taxi.
If you've taken physics, you'll remember there's 2 kinds of friction. One you use to start motion, the other is used once motion is started. Once you overcome the first one, the 2nd is much less, hence why you throttle up to start taxiing, then back off so you don't take off on the taxiway.
Then think about a plane landing. There are lots of factors here, ground level altitude, heat, humidity, wind. Planes always touch down at different speeds. Mainly due to wind. Compared to the airbody, it'll be approximately the same, in relative to the ground, maybe not. Easiest way I can think to explain is if the wind is blowing strong against the wing, you don't have to be going as fast to get enough airflow over the wings to generate lift. (and you always land in to the wind because of this, every runway has 2 directions to land, and most airports will have multiple runways going different directions to better support this)
So with all that in mind, the wheel is free rolling. And has to be. If it was on any kind of gear or something, it'd flip itself, or destroy the gears as soon as it touched down.

Now. Planes have either a prop or jet, and both of them push air back to make the plane go forward. So they're pushing the body of the plane against the air. Once it overcomes air resistance and wheel's friction, it'll start moving forward.

The treadmill matches the plane going forward, and moves the opposite direction. This force is applied to a free-spinning wheel.

I drew a little picture as I understand it (attached). The end result is the wheel is going to spin really fast. But the treadmill is NOT opposing the jet or prop, therefore plane moves forward, generates lift, etc.
In the non-perfect world we live in. Yes, there's some frictional resistance on the wheel and bearings, etc, but it's minimal, and the prop or jet will still overcome it.

Therefore, I think the plane takes off :cool:
 
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MrGreg

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Oct 18, 2006
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Never mind, you're right herbicide. The original post said treadmill speed = plane speed. It's the second post that I read as treadmill speed = wheel speed, but that was more of an interpretation rather than the actual question.
 

Warder60

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Whether the treadmill matches the speed of the plane or the speed of the wheels is irrelevant I think.
Matching the speed of the plane it'll take off easy, with the wheel rotating around twice as fast as normal.
Matching the speed of the wheel, I believe will lead one to infer the speeds will approach infinity. An interesting concept, and likely imply mechanical failure on multiple levels, but assuming a perfect world, the plane doesn't care the wheels are rotating at infinity and moves forward in the air and takes off.
 

aeroclone08

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Here's my very artistic free-body diagram. Notice the only force opposing the thrust is drag (which occurs treadmill or not treadmill) and wheel drag (which also occurs treadmill or no treadmill). There are no other forces acting on the aircraft.
 

isutrevman

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Airplane's need to be moving to fly. Air needs to be "pushing" up on the wings. Its the wind that makes them take flight. Think of videos of tornadoes blowing roofs off houses. The roofs go air born because of the wind getting under them and lifting them off the house. A plane on a treadmill has no wind to lift it and there is NO WAY it can fly. I honestly don;t understand why someone would think an airplane could fly on a treadmill, the wheels don't make an airplane fly, the wings do, and the wings need wind to make the airplane fly. With a treadmill, there is no wind.
 

herbicide

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Whether the treadmill matches the speed of the plane or the speed of the wheels is irrelevant I think.
Matching the speed of the plane it'll take off easy, with the wheel rotating around twice as fast as normal.
Matching the speed of the wheel, I believe will lead one to infer the speeds will approach infinity. An interesting concept, and likely imply mechanical failure on multiple levels, but assuming a perfect world, the plane doesn't care the wheels are rotating at infinity and moves forward in the air and takes off.

But isn't then the treadmill is no longer keeping up with the plane, if the plane is moving forward?

I would think the only way to test this would be to have a treadmill that could go really fast, as well as landing gear on a plane that could handle super high ridiculous speeeds
 

CyinCo

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I haven't read the pages and pages of this thread. But I would bet anything the plane doesn't take off (if I understand the scenario correctly). In the end the, plan isn't moving relative the air. The wheel speed means nothing. It is all about air moving over the wing that causes lift. If the plane isn't moving relative to the air, it doesn't matter. It might as well be parked. The life won't be generated.
 
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