plane on a conveyor belt?

[lukster]

Originally posted by 2bighorn
For Christ's sake Eskimo, you're a teacher. Try to include some deductive reasoning in here. For once try to understand that there's a linkage between the wheels and plane which can transfer only limited amount of force.
No matter the force applied to the wheel, there's a limited amount transfered to the plane and that amount can not be greater then force of rolling resistance. In our case rolling resistance of ball bearings. Ball bearings are your force transfer bridge and it can transfer finite amount of force only. This amount can be easily calculated.

In your wheel movie you're transferring force from the sander to the wheel but everything else is missing. If you want your experiment to be valid, you need to TWO force bridges. One between belt and wheel and one between wheel and the airframe.

Are you intentionally ignoring a belt that might actually approach light speed assuming enough force can be applied? Before it reaches an insurmountable speed a tremendous force will be exerted upon that wheel.

[Kuhn]

There are too many variables added to the question at this point. If we keep adding "what ifs" or "and this too" the question can never be answered correctly. If we stick with the original question my answer still applies.  

[Terror]

Originally posted by Golfer
Exactly how do you plan on getting a spinning wheel on a spinning treadmill to counteract 6,800lbs of thrust for something like a Citation Encore?

Accelerate the wheels at 1000000ft/sec/sec in the opposite direction.  The counter forces from that kind of acceleration on the wheels would be enormous.

Terror

[Kuhn]

Originally posted by APDrone
Explain how chocks work, then.

And brakes too, while you're there.

That was not part of the question asked. So they do not apply.

[2bighorn]

Originally posted by lukster
Are you intentionally ignoring a belt that might actually approach light speed assuming enough force can be applied? Before it reaches an insurmountable speed a tremendous force will be exerted upon that wheel.

Firstly, where did you guys get an idea that it'll reach speed of light? Even if the speed of conveyor is matched to that of the wheel at relatively low frequency it should never exceed speed that twice of the plane at take off. Mathematically, if I would sync the belt every few seconds only, the speed differential would never be as such that the short term acceleration would significantly change the transfer of force.

It's true that faster the wheel spins the bigger the wheel angular momentum is. Angular momentum will keep wheels spinning for a while after they get retracted into wheel wells. If the angular momentum is large enough it may cause gyroscopic effect similar to that of flywheel and it will resist the directional changes due to the stored energy, however it will not stop plane gaining the speed nor the resistance to directional change would be sufficient to prevent pitching the nose high for take off.

While you guys are always hanging on the wheel momentum, do not forget that the plane inertia itself will resist to any change of its forward movement.

If you glue the tires to the belt and slam the brakes, then yeah, something weird might happen.

[eskimo2]

Originally posted by 2bighorn
For Christ's sake Eskimo, you're a teacher. Try to include some deductive reasoning in here. For once try to understand that there's a linkage between the wheels and plane which can transfer only limited amount of force.
No matter the force applied to the wheel, there's a limited amount transfered to the plane and that amount can not be greater then force of rolling resistance. In our case rolling resistance of ball bearings. Ball bearings are your force transfer bridge and it can transfer finite amount of force only. This amount can be easily calculated.

In your wheel movie you're transferring force from the sander to the wheel but everything else is missing. If you want your experiment to be valid, you need to TWO force bridges. One between belt and wheel and one between wheel and the airframe.

Tell me if you can imagine this:
The plane on the treadmill has big electric generators driven by the wheels.  When the treadmill spins the airplanes’ wheels they spin the generators which make as much energy as the output of the planes engines.  In that situation the plane sits still, even though the plane’s engines are on full power.

[eskimo2]

Originally posted by 2bighorn
Firstly, where did you guys get an idea that it'll reach speed of light? Even if the speed of conveyor is matched to that of the wheel at relatively low frequency it should never exceed speed that twice of the plane at take off. Mathematically, if I would sync the belt every few seconds only, the speed differential would never be as such that the short term acceleration would significantly change the transfer of force.

It's true that faster the wheel spins the bigger the wheel angular momentum is. Angular momentum will keep wheels spinning for a while after they get retracted into wheel wells. If the angular momentum is large enough it may cause gyroscopic effect similar to that of flywheel and it will resist the directional changes due to the stored energy, however it will not stop plane gaining the speed nor the resistance to directional change would be sufficient to prevent pitching the nose high for take off.

While you guys are always hanging on the wheel momentum, do not forget that the plane inertia itself will resist to any change of its forward movement.

If you glue the tires to the belt and slam the brakes, then yeah, something weird might happen.

The plane has no inertia, it does not move.

[eskimo2]

Here’s a story that illustrates my idea:  (Note that the term wheels in this story refers to wheels and tires)

Identical triplets Al, Bob and Chuck buy three identical bush planes.  Since they live in Alaska, all three brothers buy and install large balloon “tundra tires” and wheels.  The wheels, planes and brothers are identical.  All three planes will take off from a normal runway in exactly 100 feet and at exactly 50 mph.  The brothers fly their planes to an air show in Wisconsin.  At the air show Bob finds and buys a set of fantastic wheels.  These wheels are exactly like the wheels he has on his plane in every way except they have half the mass.  Their mass is distributed in the same proportion as the wheels that he plans on replacing.  Al thinks Bob is silly and is content with his old wheels.  Bob thinks that Al will eventually want a set, so he buys a second set to give to Al on their birthday.

Bob finds a buyer for his old heavy wheels and installs a set of his new lightweight ones.  He loads the second set into his plane so that it is balanced just as it was before.  Bob’s plane now weighs exactly the same as Al’s and Chuck’s, but its wheels have half the mass.

Meanwhile, Chuck runs into a magician who sells him a set of magic wheels.  These wheels are exactly like the wheels he has on his plane in every way except they have no mass.  Chuck installs his magic wheels.  He loads the second set into his plane so that it is balanced just as it was before.  Chuck’s plane now weighs exactly the same as Al’s and Bob’s, but its wheels have no mass.

When the brothers leave the air show they request a formation take off.  They line up wing tip to wing tip and apply power at exactly the same time.  All three planes weigh exactly the same and must hit 50 mph to lift off.  When Chuck’s plane lifts off his wheels stop spinning instantly since they have no mass.  Since they have no mass, they also have no rotational inertia.  When Al’s plane lifts off his heavy wheels are spinning at 50 mph and have considerable rotational inertia.  When Bob’s plane lifts off his half-weight wheels are spinning at 50 mph and have exactly half the rotational inertia as Al’s wheels.  

Where did the rotational inertia and energy in Bob’s and Al’s wheels come from?
How did the rotational inertia and energy now stored in Bob’s and Al’s wheels affect the take off distance of their planes?
We know that Al’s plane will still take off in exactly 100 feet; where will Bob’s and Chuck’s planes take off?

[SteveBailey]

What speed wiil match the speed of the wheels?

Answer the question.  The question is, when did the conveyer go from matching the speed of the wheels to acceratign them?  I can't find anywhere in the original post where it says the conveyer acelerates the wheels.

[lukster]

Bighorn, let's not be intentionally contentious. There must be some positive value in a friction coefficient to which we can apply a force. You seem to be representing that at some point this coefficient can be so small that any force applied to it is irrelevant compared to it's opposition. At least you understand the principle involved even if we can't agree on the larger force. Assuming this as I will, consider then the masses involved as velocities approach the absurd, namely light speed. Any jet or rocket engine currently in existence is inconsequential in comparison.

[2bighorn]

Originally posted by eskimo2
The plane has no inertia, it does not move.

Simplified definition: inertia is amount of resistance to change in velocity which is determined by mass.

Originally posted by eskimo2
The plane on the treadmill has big electric generators driven by the wheels. When the treadmill spins the airplanes’ wheels they spin the generators which make as much energy as the output of the planes engines. In that situation the plane sits still, even though the plane’s engines are on full power.

That, honestly doesn't make any sense. As long as the energy created by generators isn't used for braking force, plane will still move.

Now, can you imagine this:
Build a bicycle, replace chain with smooth metal band and replace sprockets with smooth metallic wheels.
Would you have to apply more force to pedaling (either with increase pressure or frequency) as on normal bicycle?

[eskimo2]

Originally posted by SteveBailey
Answer the question.  The question is, when did the conveyer go from matching the speed of the wheels to acceratign them?  I can't find anywhere in the original post where it says the conveyer acelerates the wheels.

It has to, because it’s the only thing that works.  Should the conveyor speed up to only 10 mph?  Should it not even try?  Should it be happy at 90%?  99%?

Imagine that you are the control system.  

You see the plane’s wheel roll forward a foot so you turn on the speed control for the conveyor; it moves a foot.  But, when the conveyor moved back a foot, the wheel also moved a foot.  So the wheel has moved two feet, but your conveyor has only moved one foot.  The only way that they will ever be equal is if the plane’s wheel moves back a foot.  So, you turn the conveyor acceleration control like mad.  Now the wheel is accelerating at the rate of 100,000 rpm per second.  That increase in acceleration moves the wheel back a foot so you adjust the rpm acceleration rate to 99,000 rpm per second and the plane is still, at full throttle.

If the riddle stated that the plane had mass less wheels, we could only assume that the conveyor and wheels would instantly spin at an infinite speed while trying to do its job.  It would clearly fail and the airplane would take off.

[2bighorn]

Originally posted by lukster
Assuming this as I will, consider then the masses involved as velocities approach the absurd, namely light speed. Any jet or rocket engine currently in existence is inconsequential in comparison.

Lets assume the same is with destructibility of conveyor and wheels.
If your conveyor is able to reach the speed of light, let my plane be able to do the same.

It is unfair to ignore or bend laws of physics for the parts of equation needed to prove your hypothesis, at the same time apply them rigorously to the rest.

[2bighorn]

double post

[SteveBailey]

Originally posted by eskimo2
It has to, because it’s the only thing that works.  Should the conveyor speed up to only 10 mph?  Should it not even try?  Should it be happy at 90%?  99%?

Imagine that you are the control system.  

You see the plane’s wheel roll forward a foot so you turn on the speed control for the conveyor; it moves a foot.  But, when the conveyor moved back a foot, the wheel also moved a foot.  So the wheel has moved two feet, but your conveyor has only moved one foot.  The only way that they will ever be equal is if the plane’s wheel moves back a foot.  So, you turn the conveyor acceleration control like mad.  Now the wheel is accelerating at the rate of 100,000 rpm per second.  That increase in acceleration moves the wheel back a foot so you adjust the rpm acceleration rate to 99,000 rpm per second and the plane is still, at full throttle.

If the riddle stated that the plane had mass less wheels, we could only assume that the conveyor and wheels would instantly spin at an infinite speed while trying to do its job.  It would clearly fail and the airplane would take off.

Now you are talking distance(feet). The original scenario talks of speed.  You have already admitted the plane will move forward, regardless.  Plane moves, wheels spin, plane takes off.


Again you are allowing for the conveyer to accelerate the wheel... it only paces the wheel.  You cannot change the rules.

Also, why are you ignoring the fact that rolling resistance is constant?