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The plane would still take off. (I think the engineers designed the plane to have more than enough thrust to overcome any realistic amount of friction from the wheels with more than enough margin to take off. Even with the belt moving as fast in the opposite direction as the plane.)
 
The only way it can possibly work is if the treadmill is set up like this.

treadmill-bike.jpg

EDIT: Hey. Why did my gif load as a jpeg?
 
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It's sort of like this:
3dadce121dbbb51ca81111108010fda0.jpg
 
BuiltFromTrash said:
The plane would still take off. (I think the engineers designed the plane to have more than enough thrust to overcome any realistic amount of friction from the wheels with more than enough margin to take off. Even with the belt moving as fast in the opposite direction as the plane.)
Click to expand...

The belt would move faster, because it accelerates at the rate that the plane is moving. The Boeing 747 takes ~3500 meters to take off, using my first method the conveyer should be moving backwards at 35,000 m/s - almost Mach 10. Using the second it would be infinity.
 
Ok further clarification.

The conveyor belt has extremely low friction bearings and is made of an ultra low mass material but the surface has friction.

As soon as the plane applies thrust, it can only "move forward" by rolling as rolling friction is greater than sliding friction. As the wheels start to turn so does the conveyor..........

Once moving, the conveyor moves at the same speed as the wheels, which are driven the the engine thrust. The conveyor and wheels are matched in speed..............the airplane does not move forward.....

No forward motion, no lift, no fly.........

Bernoulli is correct..........again.......


Ok, actually the way the original question is phrased, "the conveyor moves at the same speed as the wheels", I agree the plane would fly, but if the movement of the plane creates the motive force for the conveyor, no forward motion, no lift, no fly...

In other words I'm convinced either answer is correct depending on how you define the motive force of the conveyor!
 
With 40+ years flying experience in over 30 different types of aircraft I have flown ONE and only ONE aircraft where traction with the ground had any effect at all*. NONE of the other aircraft had any "driving wheel". Skis. pontoons and wheels don't care what the surface is doing. Newton's Third gets you moving, Bernoulli's gets you flying. Drag and Gravity makes it expensive.




*Foot launched hang glider.
 
If the motive force of the conveyor is provided by what it carries, it is by definition, not a conveyor. It is more like a turbine - it is driven.

If you drive a conveyor fast enough that the negligible rolling resistance of the wheels becomes significant enough to balance the thrust force of the engines - you have one heck of a motor driving the conveyor - a conveyor large enough to carry a 747. So why bother with the airplane at all?

Turn the conveyor around, input some ballistic incline, drop the passengers/cargo of the plane onto the conveyor and let it's friction accelerate them towards the destination city, install some means to catch them at the destination city, and forego the plane altogether.
 
Lowpuller said:
Ok further clarification.

The conveyor belt has extremely low friction bearings and is made of an ultra low mass material but the surface has friction.

As soon as the plane applies thrust, it can only "move forward" by rolling as rolling friction is greater than sliding friction. As the wheels start to turn so does the conveyor..........

Once moving, the conveyor moves at the same speed as the wheels, which are driven the the engine thrust. The conveyor and wheels are matched in speed..............the airplane does not move forward.....

No forward motion, no lift, no fly.........

Bernoulli is correct..........again.......


Ok, actually the way the original question is phrased, "the conveyor moves at the same speed as the wheels", I agree the plane would fly, but if the movement of the plane creates the motive force for the conveyor, no forward motion, no lift, no fly...

In other words I'm convinced either answer is correct depending on how you define the motive force of the conveyor!
Click to expand...

You're making the mistake that the wheels are driven by the engine thrust, and a second mistake that the plane creates the motive force for the conveyor.

The engine's thrust moves the plane, not the wheels or the conveyor. The wheels are not connected to the plane's motor and do not push against the ground to drive the plane forward the way a car drives. The wheels only turn because they are in contact with the surface below the moving plane, whether that surface is the runway for a normal flight, or the surface is the conveyor belt for the problem.

In the case of the problem, the conveyor moves at the same speed as the wheels, in the opposite direction, so the conveyor must have its own internal source of power to move backwards. The conveyor is not being dragged along by friction with the wheels (otherwise it would actually be moving forward with the wheels), and it's also not being pushed backwards by the wheels trying to drive the plane forward (because the wheels do not push backward) --- it's turning on its own power to match the speed of the wheels in the reverse direction.
 
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Think about this way,

3 men check into a hotel room (don't ask why). The room cost $30 per night, each man pays $10. Soon the clerk realizes he has made a mistake, the room should have been $25 dollars.

The clerk gives the bellhop the $5 to return to the men. When he arrives at the room the men decide $5 is to difficult to split three ways so they each keep a dollar and tip the bellhop $2.

Each man paid $10, each man got $1 back, so they each paid $9.

$9x3 = $27 + $2 Tip equals $29, where did the missing dollar go?



And what does this have to do with frictionless conveyors and supersonic wing profiles that don't generate lift (that should start another fire).
 
Lowpuller said:
Think about this way,

3 men check into a hotel room (don't ask why). The room cost $30 per night, each man pays $10. Soon the clerk realizes he has made a mistake, the room should have been $25 dollars.

The clerk gives the bellhop the $5 to return to the men. When he arrives at the room the men decide $5 is to difficult to split three ways so they each keep a dollar and tip the bellhop $2.

Each man paid $10, each man got $1 back, so they each paid $9.

$9x3 = $27 + $2 Tip equals $29, where did the missing dollar go?



And what does this have to do with frictionless conveyors and supersonic wing profiles that don't generate lift (that should start another fire).
Click to expand...

LOL! I know this one...
 
So it appears the true riddle is if someone who doesn't understand physics can design something misnamed a conveyor belt, but which is actually a dynamometer, and then convert a gas generating turbine into a rotary machine to drive the wheels on something that used to be a perfectly good airplane and thereby prevent flight.
Yes. It's possible.
 
Look up Schrodinger's Cat or the old philosophical talking point: "if a tree falls in the woods and only Thirsty hears it" or something like that. Problem with those questions is there is no answer....well...Thirsty might have one... but that's the exception. Theoretically I think the first motion would start a chain of events where the belt and tires would attempt to hit light speed in seconds, kind of how one rock can start rolling down a slope, hit more rocks, the multiplication means you have a landslide.

I think incongruent is on the right track with his hypothesis. But then again I suck at Math ;)
 
Another way to look at this problem is to imagine the 747 in a microgravity environment (not without mass, but a situation where the landing gear has zero friction with an imaginary treadmill). Would the 747 move?

Greg
 
GregGleason said:
Another way to look at this problem is to imagine the 747 in a microgravity environment (not without mass, but a situation where the landing gear has zero friction with an imaginary treadmill). Would the 747 move?

Greg
Click to expand...

No. There's no air for the jet engine or wings to function and if there were rockets, there's still no air for them to push against!
 
Steve Shannon said:
So it appears the true riddle is if someone who doesn't understand physics can design something misnamed a conveyor belt, but which is actually a dynamometer, and then convert a gas generating turbine into a rotary machine to drive the wheels on something that used to be a perfectly good airplane and thereby prevent flight.
Yes. It's possible.
Click to expand...

It's conveyer belt controlled by a device that measures rotation, not power output from the jet engine.
 
I would think that a 747 in a micro gravity environment would want to roll about its' long axis (unless the engines are counter rotating) due to torque.
Rex
 
This is how I imagine it:

Plane is sitting on treadmill, nothing is moving.
Plane applies a teensy bit of thrust. Wheels try to roll forward ,

So, at this point, if the wheels start roll; to move forward, the whole plane is then trying / starting to move forward. The wheels are then a visual clue that the plane is 'in motion'

but magical treadmill instantly speeds up to match their speed.

so the treadmill this then also moving in the same direction, albeit rather slowly, and at the same speed as the plane.

At this point the plane is not moving forward

Why not? The plane applied power and started to move. the treadmill is also moving to negate the rotation of the wheels. the plane itself is still moving... (if the treadmill speeds up, and the wheels rotate in the opposite direction, is the plane then going backwards?)

and friction in the hubs are equal to the small amount of thrust.

Plane increases thrust, and the speed of wheels increases, quickly leaving the realm of real world velocity.

For the plane to be moving forward its wheel speed needs to be greater than the belt's speed.

Why? If the plane is moving, the plane is moving regardless of how fast it's wheels are moving..

If they are exactly equal the plane isn't moving, assuming the treadmill itself is stationary.

Then the plane isn't moving, if the treadmill is stationary..

Pretty silly, but fun to argue about!
 
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dr wogz said:
This is how I imagine it:

Plane is sitting on treadmill, nothing is moving.
Plane applies a teensy bit of thrust. Wheels try to roll forward ,

So, at this point, if the wheels start roll; to move forward, the whole plane is then trying / starting to move forward. The wheels are then a visual clue that the plane is 'in motion'

but magical treadmill instantly speeds up to match their speed.

so the treadmill this then also moving in the same direction, albeit rather slowly, and at the same speed as the plane.

At this point the plane is not moving forward

Why not? The plane applied power and started to move. the treadmill is also moving to negate the rotation of the wheels. the plane itself is still moving... (if the treadmill speeds up, and the wheels rotate in the opposite direction, is the plane then going backwards?)

and friction in the hubs are equal to the small amount of thrust.

Plane increases thrust, and the speed of wheels increases, quickly leaving the realm of real world velocity.

For the plane to be moving forward its wheel speed needs to be greater than the belt's speed.

Why? If the plane is moving, the plane is moving regardless of how fast it's wheels are moving..

If they are exactly equal the plane isn't moving, assuming the treadmill itself is stationary.

Then the plane isn't moving, if the treadmill is stationary..

Pretty silly, but fun to argue about!
Click to expand...

The treadmill rolls backwards, it makes the wheels spin faster than on a normal runway. The issue is whether the furiously spinning wheels and the effect of rolling over something that is going at (maybe, if my thoughts are correct) Mach 10. The X-15 found that hypersonic air is turbulent (not laminar as previously believed), and that was at really high altitudes. At ground level, the air would rip off the wheels and probably do in the plane as well.
 
Steve Shannon said:
He said microgravity, not airless.
Click to expand...

The air is held down by gravity, as is the plane. Now if the microgravity was at ground level, the effects of zooming through the atmosphere fast enough to allow for microgravity can't be ignored either.
 
OverTheTop said:
Finally the truth emerges. This is a gem. Not many people realise this!

I can't believe this thread is still going.
Click to expand...

First of all, yes, lift results much more from the deflection of air downwards. Unfortunately this is still not taught (that being said, I learned the equal transit "theory" years ago and many people (at least now) know better.)

The thread is still going because the question is unanswered. It'll go even longer if you mention the "believe" more, especially with different context.
 
Steve,

Thank you for the correct and concise summary!!! albeit many replies back...
 
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