Once and for f*cking all....

[einstein57]

who cares, just watch them land in crosswinds


COOL!

remnds me of my trip to portland maine. Super small prop plane with a mojor cross wind. That pilot had some skills.

I think two j's is just f ing with us to keep the thread going. That the only rational reason he is arguing about it. Anyone who does not agree the plane will take of as long as there is no parts failure should trade in their car keys for a bus pass. An e30 will just be far to dangerous in your hands. Your mind will not be able to handle going more than 50 mph. (Thats what people thought before the invention of the internal combustion engine)

[sticksdaman]

last i heard the treadmill (conveyor belt) had a mechanism in it to match the the speed of the plane instantaneously. This would keep the plane stationary on the runway.




oh and im gunna go ahead and say it wont take off based on this information

[einstein57]

that's it give me your car keys. remember the airhog probably has a maximum speed of 6 knots and they set the treadmill at 10mph in the video.

[Justin B]

I'm sorry guy, but you're wrong once again. Your argument is false. You say the plane will be moving forward at speed x. You say the "thrust" does not come from the wheels, so how does it attain this speed x? Oh, that's right it's from the thrust of engines. This thrust moves teh plane forward and the conveyor belt matches the speed but in teh opposite direction. Therefore the speed of the plane relative to the ground is zero and the god damn plane stays on teh ground.

Simple matter of fact is that all of you people don't understand simple classical physics. It's quite funny really.

You sir, need to go back to school, or if you're still IN school, stop being such a goddamn stupid stoner. You obviously didn't read my post thoroughly. The conveyor belt is moving at the same speed backwards as the plane is going forward, the engines push the plane forward. What do the wheels do?

Think about it for a second.

Got an answer yet?

Ok.

They FREE WHEEL. They'll spin as fast as they need to go, they dont slow down the airplane from ground underneath it going backwards.

The wheels do NOT provide enough friction to keep the plane static. And I addressed that ANYWAY in my post. If the plane is not going forward OR back, or net speed, the conveyor belt shouldnt be moving at all.

If there was no thrust coming from the engines, and the plane was sitting static the conveyor belt, sure, it would move back since the wheels DO provide enough friction to keep the plane on solid ground. As far as the plane knows, its not going anywhere since there isnt any thrust but will go backwards just because it's sitting in the same spot. Read the problem agian, and read my post about 100, and draw little stick figure diagrams if it'll help you comprehend reality.

Oh, and watch the YouTube Video, troll.

Simply physics people, get your head out of your ass.

[Justin B]

Oh, if you havent figured it out by the posts ive made, I'm not saying the plane will take off without any ground speed relative to the ground outside of the treadmill. It certainly DOES get ground speed, it just so happens that the treadmill pulls back on the plane too just increasing the friction at the wheels, but not enough to make any difference in its acceleration relative to the ground outside of the treadmill....which is in imagination land, as long as it needs to be to let the plane accelerate and take off.

Wheels spin twice as fast, create more drag, but DO NOT keep the plane from accelerating forward and taking off.

Simple matter of fact is that all of you people don't understand simple classical physics. It's quite funny really.

Look who's talking.

[Justin B]

last i heard the treadmill (conveyor belt) had a mechanism in it to match the the speed of the plane instantaneously. This would keep the plane stationary on the runway.




oh and im gunna go ahead and say it wont take off based on this information

Um. Read the problem dude. It instataneously matches the speed of the plane. So, if the plane is stationary, now... is the treadmill moving at all?









NO!



You people kill me. You contradict yourself in your own damn post. Think a little harder. The reason it instataneously matches the planes speed, is so that when the plane starts moving forward at .000000001mph, the treadmill starts doing it backwards, but accounting for the drag at such a low speed, the plane is only going a bit slower than that, so the treadmill does that, then as it continues to accelerate, the treadmill is always going at exactly the same speed the plane is going forward


The first bump is the plane, 2nd is position on the treadmill, call it a seam.
-----^--------------------*-----
----------^----------*----------
---------------^*---------------
----------*----------^----------
-----*--------------------^-----

Wheels under ^ are just moving twice as fast. If you cant see that, I dont know how you passed school.

[TwoJ's]

Oh, if you havent figured it out by the posts ive made, I'm not saying the plane will take off without any ground speed relative to the ground outside of the treadmill.

You're quick to pass judgement about my intelligence, and the fact that I didn't read, but you're missing one thing: My argument isn't contradicted by yours. All I am saying is that IF the speed relative to the ground is zero, then the plane will not take off. Do you disagree?

And trust me, I've got quite a grasp of physics.


Oh, and stoner? WTF are you talking about?

[sticksdaman]

ok....

i read it as the purpose of the tradmill was to counteract any attempt by the plane to gain forward movement (relative to the ground around it). and no forward movement would mean no wind over or under the wings no lift, no take off, no movement at all...

[TwoJ's]

I think two j's is just f ing with us to keep the thread going. That the only rational reason he is arguing about it.

You're somewhat right. I chose to argue because people were throwing out really bad reasons for why it would or wouldn't take off. I had to shut them down and fuel the fire, right?

If you read my shit carefully, you'll see that I'm not denying that it will take off in a real world experiment. The only thing I actually said is that if the plane is not moving relative to the ground, that it won't have any lift. That tool's argument about the wind tunnel and shit like that just made me keep going. Regardless, the debate will go on until Jamie and what's his name do the experiment. I don't know where they'll get such a large conveyor belt though. Maybe a scale model?

Now I really quit.

[Justin B]

Okay, lets see here. I was just a little frustrated. None of it was personal, it's just what came to mind to say while posting. Seriously, look at the problem and tell me that I'm wrong again. Apparently there are a couple ways to look at it, except in reality, there's only one that actually would happen. I understand where you're coming from and it's entirely true. If the plane stays stationary, it will not take off, heck, it won't even create an ounce of lift. but really. The problem specifically states that the treadmill must match the planes speed. Do we agree on that? I certainly hope so. What speed is it talking about? Wheel speed? That's what you're going by. However, the airplanes speed is zero. As it is not moving forward at all. The treadmill and wheel speed if the plane is held down or somehow kept from rolling forward or back a single inch on the treadmill will always be the same, so maybe that's where some of you are thinking that. However, like I just said, the plane is not moving anywhere itself. If the plane is truly attempting to take off though, it will most certainly start to lurch forward, and that's where the instantaneous treadmill speed kicks in, it instantaneously starts rolling backwards at the same speed the plane is being pushed forward by whatever propulsion device is on it, like a jet, etc. The plane will move forward, but the wheels will accelerate twice as fast as the change in acceleration speed. Get something that rolls and a piece of paper, the thing that rolls is your plane, and the piece of paper is the treadmill. Now assume in lala land, that this piece of paper is infinitely long. It's obviously not, but bear with me. Put whatever you have that rolls on it. Now push that thing forward, while at the same time pulling the paper back at the same speed, and faster as you go. That's the same principle. Your finger pushing whatever it is along the paper are the engines. The engines, or you finger pushing the object forward had absolutely no problems moving the object/plane through the air and in relation to the surrounding static ground. Moving it forward was not effected in any way that's worth mentioning by the ground underneath moving backwards.

I agree with your point, as the plane wont take off if it doesn't move along relative to the outside ground and usually, thereabouts the same as air speed-ish which actually is more important but that for this problem doesn't matter and we're assuming there is 0 wind. However, if the engines are attempting to move the plane forward, they will with absolute ease. Please think about it for a while, and if you need, try that little experiment. It's really simple, just as simple as your point but it's just not what the problem was asking.

I'm just absolutely amazed that we just went through this a few months ago and somehow we brought it back to life after I thought we reached a general conclusion that it would indeed take flight.

[Justin B]

Oh yah, I'm done too unless one of you actually quote me.

[VacMan]

Maybe this will help our friend Two J's. In the boldfaced section replace "rope" with "thrust from jet engine" and you have your answer. Your problem is you're assuming that the wheels of a plane somehow affect it's speed and that the plane will remain stationary. It will not. The conveyor belt could go 1000mph and as long as the plane's wheels can handle spinning at 2000mph, the plane will take off. Just like the wheels on your rollerblades will handle the necessary speed increase as you pull yourself forward and off the treadmill.

Dear Cecil: Please, please, please settle this question. The discussion has been going on for ages, and any time someone mentions the words "airplane" or "conveyor belt" everyone starts right back up. Here's the original problem essentially as it was posed to us: "A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

There are some difficulties with the wording of the problem, specifically regarding how we define speed, but the spirit of the situation is clear. The solution is also clear to me (and many others), but a staunch group of unbelievers won't accept it. My conclusion is that the plane does take off. Planes, whether jet or propeller, work by pulling themselves through the air. The rotation of their tires results from this forward movement, and has no bearing on the behavior of a plane during takeoff. I claim the only difference between a regular plane and one on a conveyor belt is that the conveyor belt plane's wheels will spin twice as fast during takeoff. Please, Cecil, show us that it's not only theoretically possible (with frictionless wheels) but it's actually possible too. --Berj A. Doudian, via e-mail


Cecil replies:


Excuse me--did I hear somebody say Monty Hall?


On first encounter this question, which has been showing up all over the Net, seems inane because the answer seems so obvious. However, as with the infamous Monty-Hall-three-doors-and-one-prize-problem (see The Straight Dope: "On Let's Make a Deal" you pick Door #1, 02-Nov-1990), the obvious answer is wrong, and you, Berj, are right--the plane takes off normally, with no need to specify frictionless wheels or any other such foolishness. You're also right that the question is often worded badly, leading to confusion, arguments, etc. In short, we've got a topic screaming for the Straight Dope.


First the obvious-but-wrong answer. The unwary tend to reason by analogy to a car on a conveyor belt--if the conveyor moves backward at the same rate that the car's wheels rotate forward, the net result is that the car remains stationary. An aircraft in the same situation, they figure, would stay planted on the ground, since there'd be no air rushing over the wings to give it lift. But of course cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly.


A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.


As you point out, one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH.



Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off.


--CECIL ADAMS

BTW, where can I pick up my keys to your car?

[delatlanta1281]

This is awesome!

[BimmerToad]

LMAO, some of you guys just don't get it, but you're so positive you do. Airflow over a wing = lift. Treadmills don't move air.

Give me a large enough fan and I could make a plane fly without a runway, or a super special airplane treadmill.

LOL, you guys are retarded. This topic should be used to thread jack future threads :D

[Erik]

Actually no one is looking at the original question... It asks if the treadmill is moving the same speed of the wheels if the plane will take off. Which, it will not. However, according to the youtube experiment (which is inaccurate) the plane would take off, due to the fact that the wheels are spinning much faster than the treadmill is moving. So really according to the ORIGINAL question, the answer is NO, it will not take off.


/thread