Airplane Puzzle Question

[GG-Xtreme]

(This question doesn't require any major physics education or advanced math)
A flat conveyor belt is built on top of an airport runway suitable for large aircraft to take off. The length of the conveyor belt is equal to the length of the runway, and it is able to take the weight of a fully loaded Boeing 737. Situated on this conveyor belt is a Boeing 737 aircraft, fully loaded. The airplane is cleaned, the wheel bearings of the plane are lubricated with a special, frictionless lubricant, and the tires are replaced with ones that give increased grip. The conveyor belt is designed to move in the opposite direction of the plane at the exact speed the plane is trying to move forward.

Please don't look up the answer (you probably will not be able to find the correct one anyway). Answer the poll above and post your explanation below (you may use any of your knowledge of physics or math if you can support it).

 

[galaxyAbstractor]

Well, I think they tested this on mythbusters and they succeded. But I don't know any explanation.

 

[mujtaba91]

Yes of course!
The plane will surely take off!
and in half the time usually taken by it
am i right?

 

[sampuu]

Yes of course!
The plane will surely take off!
and in half the time usually taken by it
am i right?

No because the conveyor is going the other way.


Yes, the plane will take off because the movement is not powered by the wheels. In a car, the vehicle moves forward BECAUSE the wheels are moving on the ground. On a plane, however, the power comes from the air being sucked along by the propeller. The wheels are simply there to reduce friction caused by the asphalt on the runway (or the conveyor in this case). What the ground is doing is largely irrelevant.

 

[galaxyAbstractor]

No because the conveyor is going the other way.


Yes, the plane will take off because the movement is not powered by the wheels. In a car, the vehicle moves forward BECAUSE the wheels are moving on the ground. On a plane, however, the power comes from the air being sucked along by the propeller. The wheels are simply there to reduce friction caused by the asphalt on the runway (or the conveyor in this case). What the ground is doing is largely irrelevant.

But that is weird when I think further on it. Say the plane travels 100 km/h forward and the ground 100 km/h backwards, wouldn't the plane stand still in one position then?

 

[sampuu]

But that is weird when I think further on it. Say the plane travels 100 km/h forward and the ground 100 km/h backwards, wouldn't the plane stand still in one position then?

No (or at least, I don't think so ), because its to do with the air rushing past the wings. Sure it really wouldn't be very smooth and you'd have to be a hell of a good pilot but the plane would leave the ground.
The wheels are just bits of rubber on spinning axles so if the plane had no power but the conveyor was moving then sure the plane would go backwards. But as the wheels dont actually do anything other than spin then it would take off because the only reason they are there is to stop the plane scraping the runway. :nuts: eh?

 

[galaxyAbstractor]

No (or at least, I don't think so ), because its to do with the air rushing past the wings. Sure it really wouldn't be very smooth and you'd have to be a hell of a good pilot but the plane would leave the ground.
The wheels are just bits of rubber on spinning axles so if the plane had no power but the conveyor was moving then sure the plane would go backwards. But as the wheels dont actually do anything other than spin then it would take off because the only reason they are there is to stop the plane scraping the runway. :nuts: eh?

But if the plane stands in one position, where comes the air from?

 

[sampuu]

Thats what the propellers and the engines are for.

 

[galaxyAbstractor]

Thats what the propellers and the engines are for.

Then why does the airplane has engines in the wheels on take-off to make it go forward that fast, why not just take off in a still position?

 

[Nathan H]

This was tested on mythbusters. Because of how planes work, the conveyor belt will have no effect. the engines unlike a car push the BODY not the wheels. The wheels themselves will be moveing twice as fast as they would otherwise, but there would be no effect on the takeoff speed.
Basically in a step by step
In a car, The engine turns the crankshaft, the crankshaft turns the wheels which pull the body along
In a plane, the engines push air backwards, pushing the engines forward, taking the plane with it. The wheels are basically like castors, only there to allow ease of takeoff and landing

Edit: the air is sucked in by a compressor, as the engine runs it creates a vaccum, pulling in air burning it and pushing it out the back

 

[GG-Xtreme]

Then why does the airplane has engines in the wheels on take-off to make it go forward that fast, why not just take off in a still position?

It doesn't have engines in the wheels, the wheels are free-spinning. And I didn't know this had been on Mythbusters...

 

[sampuu]

Then why does the airplane has engines in the wheels on take-off to make it go forward that fast, why not just take off in a still position?

Without sounding cheeky, if you'd read my post then you'd see what these people have pointed out - the wheels are on free spinning axles and don't do anything other than turn. :happysad:

 

[GG-Xtreme]

But if the plane stands in one position, where comes the air from?

Thats what the propellers and the engines are for.

This brings up another interesting point.

New sub-question: Does the plane move forward on the conveyor belt, and if it does, does it do so at the speed it normally would?

 

[galaxyAbstractor]

This brings up another interesting point.

New sub-question: Does the plane move forward on the conveyor belt, and if it does, does it do so at the speed it normally would?

I would think if the conveyor belt and the plane went in the same speed in different directions it would stand in one place until the plane takes off from the belt

 

[sampuu]

I would say... yes, probably.

As for the speed, well that's an interesting one.
My immediate reaction was "of course it would be slower, the belt is going the other way". But think of what we've just being saying: the wheels on the ground are only there to let the plane move on the ground (eg roll, not scrape). Does this then mean that they would simply go round and round and round?

If the increased speed (I think we established they would spin at twice the speed they normally would) caused the tires to heat up and blow-out or even come detached then the plane would presumably be moved by the conveyor.

Only one way to find out I suppose...
sampuu calls up his buddies in the air force

 

[GG-Xtreme]

And for those people bringing up Mythbusters, don't always rely on that, because they said you couldn't get electrocuted by urinating on an electrified rail.

 

[galaxyAbstractor]

And for those people bringing up Mythbusters, don't always rely on that, because they said you couldn't get electrocuted by urinating on an electrified rail.

You can't because the flow is in drops with air between them, and electricity doesen't go trough air in such a low voltage.

Back ontopic now. Anyone good at phsycics in here? Then maybe he/she could answer

 

[GG-Xtreme]

You can't because the flow is in drops with air between them, and electricity doesen't go trough air in such a low voltage.

Back ontopic now. Anyone good at phsycics in here? Then maybe he/she could answer

I'm pretty good at physics, but I'm not going to answer my own question just yet. Also, there have been 2 people on the news who died from taking a whiz on train-tracks and live wires.

 

[Nathan H]

People seemed to have missed my post about the spinning wheels. the wheels themselves would be spinning twice as fast because they are on free axels, the plane will go at the same speed because it doesnt need the wheels to take of, it only uses them to stop the undercarriage from being torn off by friction.

 

[galaxyAbstractor]

People seemed to have missed my post about the spinning wheels. the wheels themselves would be spinning twice as fast because they are on free axels, the plane will go at the same speed because it doesnt need the wheels to take of, it only uses them to stop the undercarriage from being torn off by friction.

oooh thats smart. Didn't realize that. You are pretty smart lol