would a plane take off if..

[eagl]

then the wheels will simply drag. There is no way the treadmill + wheel bit would be enough to overcome the thrust of an aircraft.

And by the way, if you allow this, the wheels would drag across the treadmill at... you guessed it, takeoff speed.  When was the last time you saw a plane capable of taking off with the wheel brakes locked?  Not many planes in the world can accelerate to takeoff speed with the brakes locked.

X = Y + Z.  Very simple equation. Wheel speed = treadmill speed + takeoff airspeed (no wind).  It does not add up any other way.  No matter what numbers you plug in, Z must equal zero (the plane doesn't move) if the wheel speed equals the treadmill speed and there is no skidding.  If you allow skidding, then no matter how fast the treadmill is going, the wheels would skid across the treadmill at takeoff speed, which would be this equation:  wheel speed = treadmill speed + takeoff airspeed - skidding speed.  Skidding speed would equal takeoff speed, no matter how fast the treadmill was going, even if it was stopped.

Again, when was the last time you saw a plane that could take off with the wheel brakes locked?  I've never flown one that could do it, and I flew large-motor F-15Es.  The plane would come apart long before takeoff speed was reached due to to tire/wheel/strut failure.  Heck, at idle thrust, the tires will blow and destroy the wheels if the wheels are locked as low as 30 kts.  At max thrust the wheels would probably grind down to nothing before you got to 100 kts, and then you'd be dragging the struts across the runway...

[SlapShot]

Again, when was the last time you saw a plane that could take off with the wheel brakes locked?  I've never flown one that could do it, and I flew large-motor F-15Es.  The plane would come apart long before takeoff speed was reached due to to tire/wheel/strut failure.  Heck, at idle thrust, the tires will blow and destroy the wheels if the wheels are locked as low as 30 kts.  At max thrust the wheels would probably grind down to nothing before you got to 100 kts, and then you'd be dragging the struts across the runway...

That only would prove that the failure was due to other factors ... and not that the aircraft would not take off if tire/wheel/struts didn't fail.

[Jayhawk]

Everyone needs to read the OP slowly and carefully.  I think there is an argument over different concepts here.

[SlapShot]

Eagl ...

Go find an inclined treadmill and set it to it's highest angle and set it to it's fastest speed.

Get a pair of roller skates ... strattle the treadmill facing downwards at midpoint in the treadmill ... hold on to the bars and get on the treadmill ... get your balance, let the wheels get up to speed, and then let go of the bars ... do you stay there ... do you go up ... or do you go down ?

With you logic ... you should go stay right there in the middle of the treadmill because your wheels speed is exactly matched to the treadmill speed.

Please film this because I would bet the ranch ... that you go down.

[eagl]

Sombra's quote is "truth" except for the last sentence.  The test condition is "impossible" to set up.  But if it WAS possible (and it would be with a small enough plane), the plane wouldn't move an inch.

Slapshot, you're going to have to define "free wheeling", since no such thing exists in this universe.  Anything that moves will take energy to keep it moving since we have no frictionless bearings and no perpetual motion devices.  You still haven't explained away how you think it is acceptable to violate the test condition that the wheels rotate at the same speed as the treadmill.  If the plane moves forward, the wheel has to be moving faster than the treadmill.

100mph treadmill, plus the plane moves at 100mph, means the wheels are moving at 200mph, which violates the test condition so you *fail*.  This is why the mythbusters test was meaningless.

And I didn't "invent" an equation.  If you don't understand that, then you lack the basic grasp of newtonian physics required to hold any sort of valid opinion on this whole subject and you might as well invoke witchcraft to explain how the plane moves.

Still, I will humor you.  Let's say we have a plane that takes off at 10 mph (it is very light) and it takes 100 ft to get to that speed, and it can accelerate to that speed in 6 seconds.  We have a treadmill that moves at 10 mph.  That means in 1 hour, 10 miles of treadmill moves under the plane.  Using simple math, that means the treadmill moves 1 mile in 6 minutes, 1/6 of a mile in 1 minute (60 seconds), and 1/60th of a mile in 6 seconds.  A nautical mile is really close to 6000 ft, so let's call 10 mph approx 100 ft in 6 seconds.  If the plane is stationary, the wheel must also travel 10 miles in that 1 hour, which means that the wheel rotates 100 ft every 6 seconds.  But by your idea, the plane must accelerate to 10 mph in 100 ft and in 6 seconds, which means that the wheel must rotate a total of 200 ft in that same 6 seconds.  Therefore a plane on a 10 mph treadmill with a 10 mph takeoff speed must have a wheel speed of 20 mph. 

That violates the test condition, which specifically states that the treadmill will accelerate to match the wheel speed.

You can make the equation as complicated or as simple as you like, but it will still add up to the same - the test is worded in such a way that it requires an impossibility to occur - that the treadmill be capable of going at an infinite speed.  I say that due to rolling resistance the treadmill speed will be somewhat under infinity, yet it will still be so fast as to exceed the strength of any material we might possible use to make the treadmill, wheels, tires, bearings, etc.

I am still wondering what you mean by "free wheeling", since it sounds like you are assuming a frictionless bearing or some other sort of perpetual motion machine that takes no energy to keep moving.  No such thing exists - everything that moves takes power to start or stop the movement by pure newtonian physics, and keeping anything moving in the real world requires you to overcome friction or bearing drag (or both).  And that drag increases by the square of the velocity.  Even if you melt the bearing and are now looking at a fluid bearing with a different friction coefficient, the drag still increases by the square of the velocity.

That's how real math and physics work.  You're trying to prove witchcraft

[eagl]

Eagl ...

Go find an inclined treadmill and set it to it's highest angle and set it to it's fastest speed.

Get a pair of roller skates ... strattle the treadmill facing downwards at midpoint in the treadmill ... hold on to the bars and get on the treadmill ... get your balance, let the wheels get up to speed, and then let go of the bars ... do you stay there ... do you go up ... or do you go down ?

With you logic ... you should go stay right there in the middle of the treadmill because your wheels speed is exactly matched to the treadmill speed.

Please film this because I would bet the ranch ... that you go down.

You're arguing witchcraft (a common-sense approach to problem solving that completely ignores real physics).  If the treadmill was going fast enough to create enough rolling resistance to counteract the gravity force vector, you bet your bellybutton you'd go up.  And by the way, you set up the experiment backwards.  The treadmill would have to be negatively inclined or the treadmill would have to be running backwards.  Since you made that simple error, you clearly can't visualize the forces involved.

Test it yourself.  Tilt a board at a slight angle, place a towel on top of it, and put a ball on the towel.  Adjust the angle of the board until the ball slowly rolls down the board.  Now repeat the test, while pulling the towel up the board.  The ball will still roll in the "down" direction, but will climb up the board. That's the simplest junior high experiment in the world...  And if you pull the towel at the same speed as the ball rotates, the ball *gasp* stays in the same spot.  Amazing.

6 years of focused education in physics, math, engineering mechanics, and aerodynamic, aerospace, and mechanical engineering are backing up my arguments...  Where I went to school, 7th graders did these sorts of experiments and I paid close attention.

Your arguments assume that you zero out some forces, and that leads to divide-by-zero conditions resulting in an invalid "infinite" solution for the treadmill speed.

We've come up with only 2 ways to make this work...  Either the treadmill itself creates enough wind for the plane to fly (would only happen at very very very high treadmill speeds), or the wheels skids along the treadmill surface at exactly takeoff speed and it doesn't matter what speed the treadmill is turning at (the wheel is essentially locked relative to the treadmill surface).  Those are the only two cheats I've heard to get around the "impossible" test condition.

[Saxman]

[bagrat]

ok think of it this way, consider the roller skates on a treadmill idea(u remain motionless), but thrust is a completely different force relative to pulling the air (think of it as holding a rope atatched to a truck). So if your on a treadmill with skates it does not matter how fast the wheels or treadmill are rolling, because the truck(thrust) will pull u foward anyways..... and the rope is invisible. hopefully this will paint a helpfull picture  

also a helicopter does not need wheels at all pure thrust pulls it up, think of a plane as a horizontal helicopter pulling it foward.------------->

[SlapShot]

I vote Skuzzy just lock this thing now, because it's only going to get nasty from here.

It doesn't matter HOW much proof you give people this myth is a crock. They're not going to accept anything but their own narrow view of the mechanics involved.

You were right.

[Jayhawk]

OK, so this hurts my brain, but let me try to wrap my head around it.

The OP states the wheels would be going the same speed as the treadmill, but this (as someone else put it) would be a paradox.  This means the treadmill would move relative to the speed of the wheels.  However the wheels move relative to the ground they are rolling over, because the wheels move independently of the engine.  They usually move relative to the engine but that's because the ground usually isn't a variable, because it doesn't move.

So once you add power to the engine, it is impossible to keep the speed of the wheel and the speed of the treadmill equal.  You can keep speeding up the treadmill but because of the power provided by the engine, the wheel will just increase at the same rate.

Right?

[Seraphim]

This is so funny!
The 2nd time this argument has been brought up, and people still argue till blue in the faces.

Saying a conveyor belt that only turns the wheels, is saying the wheels generate lift. So when the plane is supposedly in the air after the wheels reach takeoff speed, the wheels (from what I've seen on any aircraft) stop rolling eventually, right? Does the plane crash? Don't most modern aircraft have retractable wheels that don't turn while in the air?

This is really still an argument?

 

[CAP1]

No. No Airlift, if your going 70mph but no were, there is no air moving on the wings, thus not able to lift.

you want somethng fun to try dude?

take a regular sport plane up on a windy day.........40 size. if you get everythign right, you can fly in place, and even backwards. 

[TracerX]

This discussion has crossed the line into irrationality.  Once you have to accept that the speed of the belt become so large that the friction of the wheels can keep the plane stationary, this discussion looses all sense of plausibility and testability.  It is impractical to consider that the original premise considered this in the first place, and discussions down this line are not worth discussing.  You are bending the argument to support your preconceived notion of what would happen.  Try to limit your discussions to that which is at least close to the realm of possibility and reality.

There is an error in the original construction of the argument.  Accelerating the belt to nearly infinite speed in fractions of a second is not what was anticipated in the original conception of the argument.  This is the great discovery, not whether the plane will fly.  The plane will always fly, you should be delighted to know that it would take an impossible feat to prevent the plane from flying.  Don't miss the beauty of the argument because you are so set on a different conclusion.

[AKHog]

1. If you believe myth busters pseudoscience on this experiment or any other then you need to have your head examined. Its obvious they didn't even have the means to attempt to simulate the proposed situation.*

2. Everyone knows lift is generated by the wings and not the wheels, to point this out in this argument is pointless.

3. Everyone that thinks the plane can take off ALSO assumes the belt can not accelerate to infinity, nor can it accelerate as quickly as the wheels. This was simply not restricted in the original question. This is a theoretical question, and to limit the answer based on what man can currently construct is pointless in regards to the original question.

There are different answers to the question depending on how exactly it is worded. The OP in this topic said, "The conveyer belt is designed to exactly match the speed of the wheels at any given time". If this is true then the plane simply does not move forward. The wheels and the conveyor both simultaneously quickly accelerate to infinity. The drag created by the tire on runway, bearings, etc also increases to infinity. Thrust is thrust, weather it comes from wheels or props, and no amount of increasing thrust can overcome drag simultaneously increasing to infinity.


If you word the question differently you can come out with different outcomes.


*They assume rotation speed is 60mph, so the wheels are moving 60mph, and the belt should move 60mph in the opposite direction. The wheels are now moving 120mph, but the belt is still only going 60. Completely flawed logic in regard to the original question.

The bottom line is there is just no way to disprove this in an experiment becuase we can't simulate the proposed parameters. As long as it can't be disproven in a real world experiment, people will insist its possible. You've just got to remember this is a theoretical question that doesn't limit itself to our inability to actually build the proposed conveyor belt.

[rabbidrabbit]

Good God, I'm evil!