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turner112

Airplane on a treadmill

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I didn't see this posted already so I thought I'd go ahead and post it.http://pogue.blogs.nytimes.com/2006/12/11/...mill-conundrum/"Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"I was surprised there is so much debate on this. Unless I'm missing something, the plane would easily take off. Airplanes produce thrust not torque so the wheels are completely irrelevant in this problem. It wouldn't be any different than a plane accelerating on ice or in mid-air. I think people are also becoming confused because they think the question is suggesting the plane would being to hover while appearing stationary. The plane would consume the same length of runway whether it was on the treadmill or concrete. Is this correct?John

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>I didn't see this posted already so I thought I'd go ahead>and post it.>>>http://pogue.blogs.nytimes.com/2006/12/11/...mill-conundrum/>>"Imagine a plane is sitting on a massive conveyor belt, as>wide and as long as a runway. The conveyor belt is designed to>exactly match the speed of the wheels, moving in the opposite>direction. Can the plane take off?"Yes it was already posted a while ago. :)Basically the answer is that the situation described is physically impossible. As soon as the engine imparts a minumum speed to the aircraft, the treadmill and the wheels reach infinite velocity. And any sorts of thing happen when we introduce the infinity.Marco

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>>Yes it was already posted a while ago. :)>>Basically the answer is that the situation described is>physically impossible. As soon as the engine imparts a minumum>speed to the aircraft, the treadmill and the wheels reach>infinite velocity. And any sorts of thing happen when we>introduce the infinity.>>Marco>>Actually, the rotational speed of the wheels would not reach infinite velocity. The rotational value would be the sum of the treadmill speed and the aircraft forward velocity. They would however reach a terminal rotational velocity and destroy themselves before the aircraft reached takeoff speed.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpgwww.SSTSIM.com

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>>"Imagine a plane is sitting on a massive conveyor belt, as>wide and as long as a runway. The conveyor belt is designed to>exactly match the speed of the wheels, moving in the opposite>direction. Can the plane take off?">>I was surprised there is so much debate on this. Unless I'm>missing something, the plane would easily take off. Airplanes>produce thrust not torque so the wheels are completely>irrelevant in this problem. It wouldn't be any different than>a plane accelerating on ice or in mid-air. >>I think people are also becoming confused because they think>the question is suggesting the plane would being to hover>while appearing stationary. The plane would consume the same>length of runway whether it was on the treadmill or concrete.>>>Is this correct?>>JohnThe reason it generated so much debate is the sentence "The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction." Some people read this sentence to mean that there can be no forward movement of the aircraft allowed. Other people don't put any weight in that sentence and say that it will of course takeoff. On an actual real life treadmill, like one of those used by OK-Go in their video of "Here it goes again"

the second group of people are right since the speed of the treadmill is fixed. But that is not the kind of treadmill hypothetically proposed in the question, since the wheel of the airplane will have to be greater than that of the treadmill in order to achieve forward movement along the treadmill surface, which is disallowed in the question. That is why it was such a long thread. This is just another one of those impossible answer questions.

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Who you going to call?MYTH BUSTERS!Sounds like a good project for them.

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Yes it can take off, provided the wheels can handle the extra friction from having to spin much, much faster (I think we agreed about double normal speed)If you don't believe me, read through all 172 posts in the last threadhttp://forums.avsim.net/dcboard.php?az=sho...ing_type=searchFor those who still don't get it, think of this:-Grab your sneakers and go to your local gym and hop on a treadmill. Turn it on and start running. What happens? Of course, you stay in one spot. -Now, change the sneakers for roller skates (or roller blades for you younger folks). Now, skate on the treadmill. What happens? Well, if you keep the right speed, you still stay in one spot. -Finally, get someone to stand directly behind the treadmill. Get back on with your skates, but instead of skating, have the person put their hands on your back to keep you from moving backwards. Now, you are staying in one spot coasting on your skates. - Now have that person push you as hard as they possibly can. What happens? You will move forward, assuming the wheels of the skates can handle the extra friction. This is the answer. The wheels of the plane freely spin. Put a car on a treadmill, and it will stay in one spot, because the engine makes the wheels spin. However, the engine of an airplane does not spin the wheels to make the plane takeoff. The engine(s) act on the air around the plane, not the treadmill. All the treadmill does is spin the wheels on the landing gears. The engine of the airplane is just like the person pushing you from behind the treadmill. Get it? (I got it wrong the first time too.) :)

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>Yes it can take off, provided the wheels can handle the extra>friction from having to spin much, much faster (I think we>agreed about double normal speed)>>If you don't believe me, read through all 172 posts in the>last thread>http://forums.avsim.net/dcboard.php?az=sho...ing_type=search>>For those who still don't get it, think of this:>>-Grab your sneakers and go to your local gym and hop on a>treadmill. Turn it on and start running. What happens? Of>course, you stay in one spot. >>-Now, change the sneakers for roller skates (or roller blades>for you younger folks). Now, skate on the treadmill. What>happens? Well, if you keep the right speed, you still stay in>one spot. >>-Finally, get someone to stand directly behind the treadmill. >Get back on with your skates, but instead of skating, have the>person put their hands on your back to keep you from moving>backwards. Now, you are staying in one spot coasting on your>skates. - Now have that person push you as hard as they>possibly can. >>What happens? You will move forward, assuming the wheels of>the skates can handle the extra friction. >>This is the answer. The wheels of the plane freely spin. Put>a car on a treadmill, and it will stay in one spot, because>the engine makes the wheels spin. However, the engine of an>airplane does not spin the wheels to make the plane takeoff. >The engine(s) act on the air around the plane, not the>treadmill. All the treadmill does is spin the wheels on the>landing gears. The engine of the airplane is just like the>person pushing you from behind the treadmill. >>Get it? >>(I got it wrong the first time too.) :)However, the aircraft wheels would be rolling at a higher rpm than the treadmill if the plane is moving across the treadmill....

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This is easy-The speed of the wheels is completely irrelevant.The problem arises due to rotational and mechanical friction from the wheels on the landing struts. Even still, an airplane recieves it's thrust (like stated previously) not from the wheels but from the the propellor. If the forward thrust is greater than the friction on the struts, then yes it could probably take off. It is possible anyway.

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>This is easy->>The speed of the wheels is completely irrelevant.>>The problem arises due to rotational and mechanical friction>from the wheels on the landing struts. Even still, an>airplane recieves it's thrust (like stated previously) not>from the wheels but from the the propellor. If the forward>thrust is greater than the friction on the struts, then yes it>could probably take off. It is possible anyway.Except that the question postulates that the aircraft wheels' and the treadmill wheels' rotation have to match. You are absolutely right with regard to a real world treadmill though. But you need to read the question a little more carefully. Arguing this question is like arguing whether the chicken or egg came first. Like that question, this one actually has no answer. If you think that the plane should takeoff, then you violate the requirement for the wheels to rotate at the exact same velocity, and if you think that the plane should not takeoff, then you violate the fact that the airplane wheels are free rolling and that the thrust of movement come from engine thrust not connected to the treadmill surface. There is no answer to this question. To argue either side means you've been duped.

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>This is easy->>The speed of the wheels is completely irrelevant.>>The problem arises due to rotational and mechanical friction>from the wheels on the landing struts. Even still, an>airplane recieves it's thrust (like stated previously) not>from the wheels but from the the propellor. If the forward>thrust is greater than the friction on the struts, then yes it>could probably take off. It is possible anyway.It's obvious you have no experience in aircraft wheels and tires as the speed of the wheels IS the limiting factor ;-) . The wheels, bearings and landing gear will more than likely hold up to the rotational stresses but the tire will fail before taking off. As an example, the speed restriction on the 727 tires is 225 MPH. An avarage loaded 727-200 lift-off speed is around 150 MPH. Assuming the treadmill is going at 150MPH in the opposite direction, the wheel speed will be 300 MPH at lift-off. That's 75 MPH over the tire limit giving a high probability of failure.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpgwww.SSTSIM.com

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I don't get it? I keep reading about wheel speed. Wheel sheep does provide lift.I can see a plane setting still in a stong wind take off with a proper flow of wind.So if on a thread mill turning at a proper speed only provide speed of zero, because thrust becomes irrelevant since the speed of the wheels turning reduce the effective thrust forward or backward and gravity which pulls down becomes the force of dominance.Pretty interesting.

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"Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"This is so imprecise that no answer is possible without making further assumptions. What is meant by wheel speed - linear (if so relative to what?) or angular velocity? What is meant by "match" - equal to the wheel speed or equal and opposite to the speed?Don't let's waste more time on this - see the original thread

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I heard this one on the Neal Boortz radio show. Boortz holds a PPL and owns a Mooney, but even he seemed to be stumped by the question. I don't get it. The conveyor can move faster than the space shuttle, but it won't get you off the ground, unless you are facing into the wind and the wind is faster than V2. You need lift under the wings to get airborne, not speed in the wheels. The answer is "no".~EwingKATLMSI K8N Neo2 PlatinumAMD Athlon 64 3200+ 2.0 GHz2GB Corsair PC-3200 512x4 Dual Channel CL2.5 DDR DIMM eVGA nVIDIA GeForce 6800 GT 256MB DDR3Sound Blaster Audigy LSOCZ Powerstream 420WWinXPPro (SP1)

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