A plane on a conveyor belt

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I've just had an "aaaaaaaaaaaaah!" moment. (no not the messy kind :p)

I hate this kind of puzzle, with that one sneaky little fact that makes you feel so stupid once you spot it!

PK!
 
dude the plane is technically at a standstill even though it's engines are up to speed therefore there would be the same amount of wind rushing past as it would standing still with the engines off now is it possible for a plane to take off vertically?(unless it's a harrier)
 
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The conveyor belt would slow down the movement but essentially as soon as the engines get to full propulsion would just act as rough ground and the plane would take off. If the conveyor was moving the exact same speed against the forward motion of the plane I imagine at leastoe of the engines would suffer some sort of stress before the plane possibly lifted off.
 
Correct me if I am wrong, but a plane gets lift from the fact that the air passing over the top of the wing, has further to travel than the air beneath the wing. This means that the air above the wing, is of a lower pressure, than that below. This imbalance, creates the upward force on the wings, enabling it to fly.

If the plane, has zero speed relative to the air it is in then this imbalance would not occur, and there would be no upward force.

The OP stated that the 'conveyor' would compensate for the increase in speed of the plane, by increasing its own 'counter' speed.
 
semi-pro waster said:
You are arguing with a guy (Blinkz), who is actually a pilot, I'd be highly surprised and more than a little bit concerned if he wasn't aware of what a plane requires to take off and under what conditions.
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Well I'll be first admit that taking off on a moving conveyor belt isn't the standard operating procedure for the 737, and I'm pretty sure that boeing didn't include it as part of their testing schedule :D so I cannot be certain on what would happen lol

but yes I'd like to think that I have a working knowledge of how planes fly......
 
Its an interesting point as your first response is no, then you realise that the plane will move along the conveyor belt at the same speed regardless of how fast the belt turns and go "ahhhhhh"...
 
Key point anyone saying it won't take off is missing - the wheels on a plane spin freely unless under braking.

If the plane moves forward and the belt moves backward the plane still moves forward - just the wheels spin twice as fast.

*IF* you could stop the plane moving forward then yes it couldn't possibly take off no matter how much thrust was created, but the belt won't do that.
 
Capn' $qu!ff said:
dude the plane is technically at a standstill even though it's engines are up to speed therefore there would be the same amount of wind rushing past as it would standing still with the engines off now is it possible for a plane to take off vertically?(unless it's a harrier)
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You have the right idea about how lift is generated, but your focusing on the wrong thing. Think about HOW the engines on an aircraft work, and HOW the aircraft is accelerated. It has NOTHING to do with the wheels. Remember you have have flying boats!! they don't have any wheels or any type of water propulsion, they just sit on the water!
 
Blinkz said:
You have the right idea about how lift is generated, but your focusing on the wrong thing. Think about HOW the engines on an aircraft work, and HOW the aircraft is accelerated. It has NOTHING to do with the wheels. Remember you have have flying boats!! they don't have any wheels or any time of water propulsion, they just sit on the water!
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Yeah but the water isn't generating motive force in the opposite direction to the plane therefore it glides forward over the top of the water and is not at a standstill I know technically the plane is moving forward however it's covering no distance therefore the wind pressure moving past the plane is not changing and so it won't be able to create the lift required!
 
iBot said:
J...This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction)...
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I think this is the aspect that has people confused. A conveyor belt that allegedly performs as such is impossible when the plane is under thrust. The conveyor belt could never equal the speed of the plane because as it speeds up to counteract the wheel speed the wheel speed would in turn increase causing the conveyor belt to speed up etc etc.

Hope my explanation isn't too crap.
 
Capn' $qu!ff said:
Yeah but the water isn't generating motive force in the opposite direction to the plane therefore it glides forward over the top of the water and is not at a standstill I know technically rthe plae is moving forward however it's covering no distance therefore the wind pressure moving past the plane is not changing and so it won't be able to create the lift required!
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The plane will move forward though. The engins thrust against the air, not against the ground (like a car on a rolling road) and therefore the plane will move whilst the belt will only make the wheels spin faster than they would normally.
 
Capn' $qu!ff said:
Yeah but the water isn't generating motive force in the opposite direction to the plane therefore it glides forward over the top of the water and is not at a standstill I know technically the plane is moving forward however it's covering no distance therefore the wind pressure moving past the plane is not changing and so it won't be able to create the lift required!
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I've got a stationary plane, with it's engines at full power, on a conveyor belt that isn't moving.

You're saying that with a huge amount of thrust pushing the wings of that plane forward, it still isn't going anywhere? Where is the force pushing the plane backwards coming from?
 
Capn' $qu!ff said:
Yeah but the water isn't generating motive force in the opposite direction to the plane therefore it glides forward over the top of the water and is not at a standstill I know technically the plane is moving forward however it's covering no distance therefore the wind pressure moving past the plane is not changing and so it won't be able to create the lift required!
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no no, just think HOW does the plane move over the water. The plane would still move even if the water was going the other direction, its the same problem! Go look up exactly how jet engines work and newtons 3rd law (think its the 3rd lol)

The whole conveyor belt moving makes you think that its important but it actually has no effect on the situation apart from actually changing the speed the wheels are moving at rotation.
 
Call me an idiot, I believe you lot when you say it will take off

I just can't get my head round how when you say its moving even though it isnt? I mean surely even if the tyres are going at silly speeds and the engines are on, if the conveyor belt is keeping it still, there isnt any air moving over the wings. Or is it that because the conveyor belt will always be playing catch up with the plane, the plane is theoretically moving, even though physically it hasnt moved an inch?

This post isnt trying to say you're wrong, I just want to try and understand but can't :(
 
Capn' $qu!ff said:
dude the plane is technically at a standstill even though it's engines are up to speed therefore there would be the same amount of wind rushing past as it would standing still with the engines off now is it possible for a plane to take off vertically?(unless it's a harrier)
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The thing you're missing (and the thing I missed at first, the first time round), is that the wheels have no effect on the speed of the plane. They're just spinning freely. So once you get that in your head, you can basically take the treadmill, the wheels, everything out of the equation.

Literally this simple - stuff comes out of the engines

that stuff pushes the plane forward

That the wheels will be spinning twice as fast is irrelevant - because the treadmill can only act on the plane's wheels, and the wheels do not affect the plane's speed

The points in bold is what just refused to sink in with me last time, once it went in I got it.
 
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Capn' $qu!ff said:
Yeah but the water isn't generating motive force in the opposite direction to the plane therefore it glides forward over the top of the water and is not at a standstill I know technically the plane is moving forward however it's covering no distance therefore the wind pressure moving past the plane is not changing and so it won't be able to create the lift required!
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The aircraft engines provide thrust against the air mass. The aircraft moves relative to the airmass - not the water/conveyor belt.

The aircraft will move. Fact. You cannot argue that.

If the aircraft didn't move relative to the air mass then it would not take off but the fact is that it will move relative to the air mass because the conveyor belt, no matter how it turns or at what speed, will have no input as all it will be doing is spinning the aircraft wheels which provide no drive. All they do is freewheel.

Think of it like this. You are standing beside a treadmill and your bicycle is on the treadmill. The treadmill is moving at 10mph. You can easily push your bike backwards and forwards or hold it perfectly still as the wheels will just be freewheeling. The principle is exactly the same.

Some more facts. Blinkz is a 737 rated commercial pilot with a considerable amount of hours. I am a private pilot and an air trafficer. Between us we have a reasonable amount of experience. We both know what we are talking about and have a good understanding of the principles of flight. We are both telling you that you are wrong. Accept it!
 
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