conveyor belt and plane answered at last ??

[crank39]

Hi 39 & MrW

I believe that if you started the belt with the plane's engines off, the plane would remain stationary. The wheels would move, but not the plane, thus leaving the plane free to propel itself along the belt and take off.

To explain: my point is that the planes engines act on the air, not the wheels.

If we then agree that the moving belt acts on the wheels, not the plane and the plane would remain stationary if the belt was moving, then it would be free to move forwards and take off simply by applying thrust.

Correct in every way, but you forgot to mention as a consequence of the plane moving forward then the wheels would turn forward more than they are doing already, at which point they aren't in sync if you like with the belt speed

 

[doitall]

Wrong crank you didn't read the question.

If the plane is just sat on the conveyor with no power it will move with the belt and the wheels will not be turning.

You need an opposite force to stop the plane moving.

 

[crank39]

Wrong crank you didn't read the question.

If the plane is just sat on the conveyor with no power it will move with the belt and the wheels will not be turning.

You need an opposite force to stop the plane moving.

Agreed........if the brakes where on but I thought we all accepted (to simplify thing's) that the bearings were frictionless and would spin freely for ever and ever, in which case the plane would stay stationary but the wheels would spin

 

[libby lou lou]

Depending on the speed the wind

Depending on the speed of the belt

The opposite force needed to stop a plane moving would be the natural atmosphere pressure, until an unnatural event occured/...

I wonder why she is in bed early again

 

[doitall]

Nope if the engine is off the plane will go with the belt and the wheels will not turn.

For the plane to stay in the same place it needs an opposite force or it needs to be held by something.

 

[securespark]

If you have a young kid it will be less embarrassing.

PMSL!!

 

[securespark]

Hey! Read this!

I think it will enlighten the believers and the non-believers alike!

http://www.airplaneonatreadmill.com/

 

[doitall]

So many holes in that securespark it's a joke, it's also a different question to the one in the original DIYnot thread..

And mythbuster is a complete joke, the planes on a dust sheet not a conveyor.

 

[securespark]

Can you go through the holes with me?

 

[joe-90]

This is the correctly worded question.

Let Doitall answer it please.

"A plane is standing on a large treadmill or conveyor belt. The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?"

Come on Doitall - will it take off?

 

[pred]

In desperation, I have turned to t'interwebby to try and help explain the pro-takeoff POV.

See here: http://www.straightdope.com/columns/read/2642/a-plane-is-standing-on-a-runway-no-its-not-heres-why

In particular this quote,

In principle it's possible to accelerate the treadmill at a rate that will exactly counteract any forward force you care to apply. (This is a departure from the original question, which said the conveyor belt compensated for the plane's speed, not its force.)

And here,

one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way.

Well this post sums it up quite nice "Basic Realization" you've either got it or your thick as two very short planks

However i think those that can't see the wood for the forest will never be able to comprehend this, its probably the same sort of ignorance that Michael Angello had to put up with when he stated the planet Earth was round and for Mr doitall, i'm only joking, of course the Earth is flat, what ever will they think of next, dont tell me, a box with pictures in it or an oven that heats food then you open the door and the oven is cold!! HA! how absurd!!

 

[doitall]

This is the correctly worded question.

Let Doitall answer it please.

"A plane is standing on a large treadmill or conveyor belt. The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?"

Come on Doitall - will it take off?

Wrong joe. That is one variation of the correctly worded post.

The original question apparently was intended as a thought game, therefore any variation would have the same intention with a different answer. which if you read securesparks link will tell you just that.

In Joes example above the plane will take off, because at when it reaches an air speed of 85knots the wheels will leave the ground.

Notice no treadmill spinning at infinite speed.

In the correct version originally posted on DIYnot, if you abide by the rules in the question, the plane or conveyor belt cannot move. the plane cannot take off.

It was fun stringing you lot along though

And as for pred He still doesn't know what day it is, never mind pred

 

[securespark]

In one of your earliest posts, you stated the question was not about jet engines but props? I can't see this myself.

To take a quote from the other thread:

How many more times, the plane does not move forward..relative to it's surroundings, because the conveyor belt ( the runway) is moving in the opposite direction, matching the speed of the aircraft.
There will be no airflow over the wings so Bernouli's effect will not take place, there will be no lift.

Wotan

Not the speed of the aircraft surely, but its wheels.

Again, from the other thread, I think this explains it well. If you disagree, please qualify why:

The plane starts stationary. The wheels aren't turning, and so neither is the conveyor. The engines apply thrust to the AIR which starts to move the plane forwards.

The conveyor control systems senses this and turns the conveyor at the same speed in the opposite direction - but that only affects the FREE-SPINNING wheels, THIS DOES NOT PREVENT THE AIRCRAFT AS A WHOLE FROM MOVING FORWARDS!!! The plane continues to accelerate through the air as more thrust is applied and lift starts to be generated by the airflow over the wings.

At any particular point in time the conveyor is moving backwards at the same speed the plane is moving forwards - so the FREE-SPINNING wheels are rotating at twice the aircrafts speed.

The rolling friction of the wheels spinning at that speed is going to be very small compared to the engines ability to accelerate the aircraft forwards - so the aircraft continues to accelerate.

In the scenario quoted, the plane will take off at it's normal take-off airspeed, at a fractionally higher thrust setting than normal, with its wheels spinning at twice that speed.

Anyhow, DIA, in that thread, you appeared to be pro take-off. Had a change of heart?

 

[doitall]

Securespart, as you probably know by now there is a number of different wordings to the same topic, and depending on the wording depends on whether the plane will take off or not.

According to your link it started off as a thought game, so I see no reason why you can't change the words to make it more interesting so to speak.

This thread and we could probably kept it going till Christmas says.

An aircraft is standing on a very long runway that can move (a conveyor belt). The aircraft moves in one direction, while the conveyor belt moves in the opposite direction. This conveyor belt has a control system that tracks the aircraft's wheels speed and tunes the speed of the conveyor belt to be exactly the same as the wheels, but in the opposite direction. There is no wind. The pilot begins to add thrust to the engines...

Now all you really need to read is wheels, belt speed, the same.

In one of your links you say the belt is going 100mph in one direction and the plane is going at 100mph in the other, so the wheels are turning at 200mph.

I've repeatedly said for the plane to make ground on the conveyor the wheels would have to go faster than. in your case 100/200.

As you also know from the post the wheel speed and the belt speed are matched, which is impossible unless plane and belt are stationary.

If the plane is stationary it can't take off.

Nothing else is relevant it could be anything with wheels stood on the belt.

 

[UriBentMySpoon]

If the forward momentum of the plane is matched entirely by the reverse momentum of the conveyor belt then the plane will remain stationary relative to the Earth. With no movement of air over the wings there is no lift generated. The plane stays where it is.