Aircraft on a conveyor

[megawatt]

A scouser calling anyone else "The dirtiest thievingest low life scum on the planet" is absolutely priceless

Actually your memory isn't great, too much crack ... Joe challenged me to the live YouTube guitar thing which he then posted and I declined, not that it really makes much difference.

It would be nice for Joe to think that this was the reason that I dropped off the site for a while though ... So be it, doesn't matter to me.

MW

 

[imamartian]

lets get back to business....

the engines are pushing against the air..... causing it to move forwards? and yet as it does, the conveyor matches the wheel speed, therefore stopping it moving forwards....

 

[sooey]

A scouser calling anyone else "The dirtiest thievingest low life scum on the planet" is absolutely priceless

Actually your memory isn't great, too much crack ... Joe challenged me to the live YouTube guitar thing which he then posted and I declined, not that it really makes much difference.

It would be nice for Joe to think that this was the reason that I dropped off the site for a while though ... So be it, doesn't matter to me.

MW

He's not the only one who thinks that.
What made me laugh though was that character who turned up a while after you'd vanished. He was an old poster can't remember his name, but anyway he said he was your bro in law I think. Thern he started posting silly videos of some old fart performing, saying they were you and he just happened to have them. It's a good job you were on the other side of the world, you'd have died of embarrasment. The guy was such a stiff. I don't suppose you know who I'm talking about do you?

 

[matt1e]

lets get back to business....

the engines are pushing against the air..... causing it to move forwards? and yet as it does, the conveyor matches the wheel speed, therefore stopping it moving forwards....

Only flaw there is that the plane is still moving forward as the most the conveyer could possibly do is stop the wheel from spining on its axis

Matt

 

[croydoncorgi]

FFS!

WTF does the RPM of the wheels of an airplane have to do with its airspeed (which determines whether it takes off or not)? The limits on acceleration with the engine at full throttle are (I guess) 95% to do with aerodynamic drag and hardly anything to do with rolling resistance of the wheels.

I just can't see the point of debating the question here (or Mythbusters busting it). It's soooooo OBVIOUS!

 

[Deleted member 63160]

lets get back to business....

the engines are pushing against the air..... causing it to move forwards? and yet as it does, the conveyor matches the wheel speed, therefore stopping it moving forwards....

Only flaw there is that the plane is still moving forward as the most the conveyer could possibly do is stop the wheel from spining on its axis

Matt

 

[matt1e]

lets get back to business....

the engines are pushing against the air..... causing it to move forwards? and yet as it does, the conveyor matches the wheel speed, therefore stopping it moving forwards....

Only flaw there is that the plane is still moving forward as the most the conveyer could possibly do is stop the wheel from spining on its axis

Matt

Your point?

 

[Deleted member 63160]

lets get back to business....

the engines are pushing against the air..... causing it to move forwards? and yet as it does, the conveyor matches the wheel speed, therefore stopping it moving forwards....

Only flaw there is that the plane is still moving forward as the most the conveyer could possibly do is stop the wheel from spining on its axis

Matt

Your point?

 

[MoodyMick]

ffs der brains,the wheels are free wheeling!same effect for any vehicle on a treadmill.A car or motorbike would stay in the same position if being driven in gear,make them free wheel and you could pull them forward with a rope

 

[big-all]

the friction off the wheels on the runway turning at say 150 knots would use up say 3 to 5% off the engines power
if the conveyor is turning against the planes direction off travel the maximum effect it can have on the equation will be a similar
so assuming the plane is traveling backwards at 150 knots[impossible as wind resistance will be greater than the rolling resistance] the plane would simply take around 40% longer to take off as it in the initial instance would be using the thrust as a brake with wind resistance helping

 

[imamartian]

ffs der brains,the wheels are free wheeling!same effect for any vehicle on a treadmill.A car or motorbike would stay in the same position if being driven in gear,make them free wheel and you could pull them forward with a rope

calm down mick... the idea of the conveyor in the scenario is to suggest that any forward motion potential is negated... because the 'ground' moves back as quick as the plane moves forward....

I love this puzzle... the person that thought it up is a genius !!!!

 

[doitall]

and finally tested and resolved with a real aircraft and conveyor in Mythbusters on Sky recently.

not true Mega... that rolling sheet runway thing they used didn't actually work.... it went at a similar speed to the plane wheels but never actually matched it - which is crucial to this puzzle.... in the puzzle, the equally rotating wheels would keep the plane in the same spot, therefore affording no lift !!!

Any pilot would know that.

You need air speed for lift off, the wheels turning at 500 miles an hour on a conveyor belt do 500miles an hour the opposite direction will as said mean the plane is stationary.

The wheels were touching the ground in the test they did, had the plane been supported solely on the conveyor it would still be there now.

To prove the point stick the plane on a rolling road the same as found in a garage for testing cars.



For the plane to move forward on the conveyor belt it would have to be going faster than, end of.

 

[Alarm]

For the plane to move forward on the conveyor belt it would have to be going faster than, end of. icon_twisted.gif

At last, someone who understands this.

 

[big-all]

To prove the point stick the plane on a rolling road the same as found in a garage for testing cars.

not the same as a rolling road would remain stationary as no tractive force is sent through the wheels

the only sums you need to do is thrust verses air resistance with rolling resistance bearing friction added on

 

[Space cat]

I remember the original problem and it was badly posed, allowing two possible interpretations. The one in which the plane does NOT take off requires the conveyor to move at whatever speed is necessary to keep the plane stationary. Can it do this.

Actually it can, though we have to disregard such trivial details as the tensile strength of tyre cords. Here's how --

The conveyor moves so as to increase the angular velocity of the wheels and, in the process, it exerts a backward force on the tyres. Since the axles do not move, the wheel bearings must be exerting an equal and opposite force (ie forwards) on the axles. But, by Newton's third law, the axles must also exert that same force BACKWARDS on the bearings. It is this force that counteracts the thrust from the engine and stops the plane from moving.

I said we had to overlook some trivial details. If you take the thrust from a typical aeroplane engine and apply it tangentially to a freely rotating wheel, you don't need to do the maths to realize that the wheel will soon be turning very fast indeed - and that is also how fast the conveyor would have to move. This is why you will never be able to perform the experiment with a real plane.