Airplane on Conveyor Belt Mythbusters 12/12

[SouthernCruizer]

[SIZE=12pt]As an aside:[/SIZE]
This has been an interesting discussion. Surely something to keep our brains exercised during the Winter "lay-off". But, Gentlemen:

There is no freakin' reason for childish name calling!

If you are going to call each other names, it is best to use the Admin approved names like:

******, 'Tard, Dickless Wonder, ********, and Weasel-**** as used here.

********************************

:hyper: :hyper: :jerry: DUDE!! you are KILLING me here!! LMFAO

Jay

'04 FJR 1300

 

[madmike2]

[SIZE=12pt]As an aside:[/SIZE]
This has been an interesting discussion. Surely something to keep our brains exercised during the Winter "lay-off". But, Gentlemen:

There is no freakin' reason for childish name calling!

If you are going to call each other names, it is best to use the Admin approved names like:

******, 'Tard, Dickless Wonder, ********, and Weasel-**** as used here.

That doesn't mean WE have to visit that mode, especially directed at a particular individual rather than a "type" of individual.

YMMV

 

[exskibum]

Either way, "wheel velocity" is pointless. I'd love to meet the idiots who espouse that theory and sell them a few bridges...

Except for one TINY problem -- the problem was defined in such a way that wheel velocity and treadmill velocity are the same magnitude but in opposite directions, which is the trick in the problem that has been ignored for pages. (See pages 10 and 11 on this.) Definitionally, the airplane must be standing still to have those two parameters be the same, but 180 degrees opposed. That doesn't mean that a prop or jet engine cannot overcome the treadmill, just that it is not allowed to in the problem definition.

Wanna reconsider "*****" after rereading the problem a bit more critically?

 

[artistic rider]

I think this show will fall under the category of "most watched". Which is a good thing for everyone to see that it won't fly.

 

[Toecutter]

The Physics Forum, where this one has been beaten up for 2-1/2 years, to the tune of 584 pages. Why don't you rocket surgeons take it over there and teach those brain scientists a thing or two?

 

[Scythian]

Either way, "wheel velocity" is pointless. I'd love to meet the idiots who espouse that theory and sell them a few bridges...

Except for one TINY problem -- the problem was defined in such a way that wheel velocity and treadmill velocity are the same magnitude but in opposite directions, which is the trick in the problem that has been ignored for pages. (See pages 10 and 11 on this.) Definitionally, the airplane must be standing still to have those two parameters be the same, but 180 degrees opposed. That doesn't mean that a prop or jet engine cannot overcome the treadmill, just that it is not allowed to in the problem definition.

Wanna reconsider "*****" after rereading the problem a bit more critically?

Definitionally, the airplane must be standing still to have those two parameters be the same

No, it just means that as the plane speeds forward the treadmill speeds up to match.

You're getting there: it's a false constraint. The fact that the treadmill speads up with the wheels doesn't apply a force counter to the thrust....

If the system were created for real, the plane zooms down the treadmill and takes off. The treadmill can spin the wheels faster and faster, but the plane still goes forward as usual until it lifts off....

 

[Scythian]

Reason I asked the simple question up front and have watched this free for all since is exactly what Southern Cruizer pointed out in the problem: the treadmill is MATCHING the speed of the airplane wheels.
There IS friction in the bearings of the wheel, and because of that, the treadmill exerts a backwards force on the plane. The question seems to be whether the forward vector of the plane created by the thrust of the prop or jet is equaled by the reverse vector of the plane created by the treadmill (given the friction of the wheel bearings transmitting some of the force of the treadmill to the plane).

Seems to me this question is answered in the affirmative by the problem, though, since the wheels and treadmill are defined to be moving at the same speed. If the airplane is moving forward (generating airspeed and lift via differential air pressure over and under the wings), then the wheels MUST BE spinning faster than the treadmill. To stay within the parameters of the problem, the treadmill needs to speed up to match the wheel speed, until the friction of the wheel bearings is sufficient to overcome the thrust of the plane and keep it at a standstill with no airspeed. No airspeed = no fly.

Looking forward to the namecalling to follow here.

*****************

That is the logical conclusion...so there are those that will HAHAHAHA it for sure

Jay

'04 FJR 1300

Yep. 'Cuz it's wrong. Do you really think an F-22, for example doesn't have enough thrust to overcome the wheel bearing friction no matter how fast the wheels were spinning?

I'll bet you could put the F-22 on its belly on a treadmill spinning the opposite direction to match, um, its bellyspeed or something--and it would still take off.

Oh, BTW: HAHAHAHA! :lol:

I love it. I love arguing this weird theoretical ****, especially on aircraft--it's what the Air Force pays me to do. If I can be right an hurt people's feelings, that's the best of all!

Still looking forward to my apology!

 

[exskibum]

Definitionally, the airplane must be standing still to have those two parameters be the same
No, it just means that as the plane speeds forward the treadmill speeds up to match.

Please explain how the bolded statement is possible where the speed of the wheels and treadmill are equal but in the opposite direction (as required by the problem's definition).

If the plane is moving forward, then the wheels are moving faster in the forward direction than the treadmill is in the opposite direction (covering more distance in the same time).

 

[ponyfool]

Definitionally, the airplane must be standing still to have those two parameters be the same
No, it just means that as the plane speeds forward the treadmill speeds up to match.

Please explain how the bolded statement is possible where the speed of the wheels and treadmill are equal but in the opposite direction (as required by the problem's definition).

If the plane is moving forward, then the wheels are moving faster in the forward direction than the treadmill is in the opposite direction (covering more distance in the same time).

Refer back to my post as if the plane were on skids. Assuming the treadmill is capable of matching the wheel's speed in the opposite direction, the treadmill still can't prevent the plane from moving and taking off.

 

[Scythian]

Logic tells me the plane will take off without a problem. The plane pushes itself forward off of the density of the air, not off of it's traction/friction between the wheel and the ground.

Ding, Ding... we have a winner... the prop is grabbing air as it cork screws through the "fluid" (yes air is considered a fluid). If I was riding a skate board on a treadmill and had something like a rope (or propeller with engine instead of rope strapped to my back) to pull myself forward, I would be able to pull myself off the front of the treadmill. Forward motion would be achieved completely independent of what the skate board or treadmill was doing.

****************

So, how could you pull yoursef forward off the front if the treadmill matches your foward motion? You pull harder, the treadmill simply spins faster to match your motion, net speed = 0

Now I'm pointing and laughing :lol: AHAHAHAHAHA!

If you think about it for oh, a nanosecond, you'd realize that you're arguing that the treadmill creates some kind of 'gravity' that opposes my pull. The treadmill can't oppose the pulling, it just spins the wheels faster.

Now can I have my apology?

 

[exskibum]

Yep. 'Cuz it's wrong. Do you really think an F-22, for example doesn't have enough thrust to overcome the wheel bearing friction no matter how fast the wheels were spinning?

Nobody said that. Read the problem again. Of course the jet engine COULD overcome the force of the treadmill, but the constraints fo the problem don't allow that. Throttle back -- you MUST keep the wheel speed and treadmill speed the same, because the problem requires it and the only way that happens is with the plane not moving forward or backward.

So, being ABLE to overcome the treadmill isn't in question; the trick in the problem is that you aren't allowed to do that by virtue of the fact that if the engine does overcome the treadmill, then the plane is moving forward and its wheels are moving faster than the treadmill is in the opposite direction.

 

[exskibum]

Definitionally, the airplane must be standing still to have those two parameters be the same
No, it just means that as the plane speeds forward the treadmill speeds up to match.

Please explain how the bolded statement is possible where the speed of the wheels and treadmill are equal but in the opposite direction (as required by the problem's definition).

If the plane is moving forward, then the wheels are moving faster in the forward direction than the treadmill is in the opposite direction (covering more distance in the same time).

Refer back to my post as if the plane were on skids. Assuming the treadmill is capable of matching the wheel's speed in the opposite direction, the treadmill still can't prevent the plane from moving and taking off.

You're changing the problem -- this one said that the wheels are moving the same speed as the treadmill -- an artificial constraint, YES, but a constraint in the problem designed to generate exactly this kind of red herring discussion.

 

[twowheelnut]

Wait a minute... Now the engineers have a lawyer involved?! Holy ******' Schnikies! We're done for! Hide the wizmminz and chillrens! Run for the hills! Aaaaaaaaaaaaaaagggggggggggggggghhhhhhhhhhhhhhhhhhhhhh!

:grin:

 

[JimLor]

I run on a treadmill. I set it at 10mph and I match its speed. To me, I'm running like mad, to the guy standing on the gym floor next to me I'm running in place - relative to the earth I have 0 groundspeed and 0 airspeed. From a dead stop, an aircraft's thrust propels it forward, on its wheels. On a treadmill where the treadmill matches the wheels speed, the a/c, relative to the earth, is going 0mph - regardless of how fast the wheels are going. Assuming as is stated that the treadmill will match the wheel speed in the opposite direction, and in all due respect to the youtube video, the a/c will not move relative to the earth.

That's my third and final answer, but I have enjoyed this mental exercise and I thank you all! Great ride home tonight, 45 degrees and clear!

 

[Scythian]

Definitionally, the airplane must be standing still to have those two parameters be the same
No, it just means that as the plane speeds forward the treadmill speeds up to match.

Please explain how the bolded statement is possible where the speed of the wheels and treadmill are equal but in the opposite direction (as required by the problem's definition).

If the plane is moving forward, then the wheels are moving faster in the forward direction than the treadmill is in the opposite direction (covering more distance in the same time).

That's the false constraint: the treadmill cannot prevent the wheels from moving faster in the forward direction as the plane zooms down the treadmill--the planes wheels just spin faster and faster as the treadmil speeds up--and faster still as the thrust powers it down the madly spinning treadmill.

The plan takes off--the treadmill cannot prevent it.

 

[Scythian]

I run on a treadmill. I set it at 10mph and I match its speed. To me, I'm running like mad, to the guy standing on the gym floor next to me I'm running in place - relative to the earth I have 0 groundspeed and 0 airspeed. From a dead stop, an aircraft's thrust propels it forward, on its wheels. On a treadmill where the treadmill matches the wheels speed, the a/c, relative to the earth, is going 0mph - regardless of how fast the wheels are going. Assuming as is stated that the treadmill will match the wheel speed in the opposite direction, and in all due respect to the youtube video, the a/c will not move relative to the earth.
That's my third and final answer, but I have enjoyed this mental exercise and I thank you all! Great ride home tonight, 45 degrees and clear!

That's the wrong analogy: unlike you, the airplane doesn't use the things in contact with the treadmill (feet, or wheels) to gain velocity. The treadmill does not affect the propulsion of the airplane.

 

[Fred W]

You're changing the problem -- this one said that the wheels are moving the same speed as the treadmill -- an artificial constraint, YES, but a constraint in the problem designed to generate exactly this kind of red herring discussion.

Envision it this way. Instead of a treadmill, imagine that the conveyor belt, instead of being oval, is another wheel under the plane's wheel. In other words the plane is balancing on a wheel that is the identical diameter to the one on the landing gear. The only way for the two wheels to be running the "same speed" is if the plane is stationary. If the plane moves forward at all, the plane's wheel will be turning imperceptibly faster than the "conveyor belt's" wheel.

It would have been a lot clearer if they just had said outright that the plane does not move forward, but remains in-place over the moving treadmill.

Oh, and one more thing...

 

[Scythian]

Definitionally, the airplane must be standing still to have those two parameters be the same
No, it just means that as the plane speeds forward the treadmill speeds up to match.

Please explain how the bolded statement is possible where the speed of the wheels and treadmill are equal but in the opposite direction (as required by the problem's definition).

If the plane is moving forward, then the wheels are moving faster in the forward direction than the treadmill is in the opposite direction (covering more distance in the same time).

Refer back to my post as if the plane were on skids. Assuming the treadmill is capable of matching the wheel's speed in the opposite direction, the treadmill still can't prevent the plane from moving and taking off.

You're changing the problem -- this one said that the wheels are moving the same speed as the treadmill -- an artificial constraint, YES, but a constraint in the problem designed to generate exactly this kind of red herring discussion.

Exactly--it's a false constraint--the airplane rolls down the treadmill, if long enough, and takes off....

 

[exskibum]

That's the false constraint: the treadmill cannot prevent the wheels from moving faster in the forward direction as the plane zooms down the treadmill--the planes wheels just spin faster and faster as the treadmil speeds up--and faster still as the thrust powers it down the madly spinning treadmill.
The plan takes off--the treadmill cannot prevent it.

Of course it's a false constraint if you throttle up the plane's engine, but that doesn't change the fact that it's a constraint in the problem. Are you gonna solve the problem as posed, or write a different one and then solve that?

Where does the treadmill preventing the plane from taking off come up in this? IT's the parameters of the problem that prevents it taking off -- in order to keep the plane's wheels and the treadmill going the same speed in opposite directions, the airplane must be stationary, whether the wheels and treadmill are going 1 mph in opposite directions or 200mph.

I still think we should lynch Randy, who started this but has been conspicuously absent -- probably grinning at all the flying fur and insults.

 

[ponyfool]

Wait a second, IMO, you are the one trying to change the conditions of the test by now instituting an artificial restraint.

This question, IMO, is derived from the childhood notion of "why can't a plane take off and land on a conveyor belt" but taken a step further with the "matching speed" issue.

There is no magical treadmill that can intuitively match the speed, but if there was, I'd still win my argument, because if the wheels stayed locked up, but there was enough thrust to overcome the drag, the wheels would be stationary, the treadmill would be stationary, and the plane would still take off! Just like if it was on skids.