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  • EADD Moderators: axe battler | Pissed_and_messed

Will the plane be able to take off?

There is no mention of the jet engines being on.

However the plane would be able to get off the ground (very briefly) as the air speed over/under the wings relative to the ground would be the same as if it were being powered by the jets. This would provide sufficient lift to make the wheels leave the ground.

At this point, the method of propulsion is lost (ie contact with the conveyor belt) so the plane would drop back onto the conveyor.

It would then run out of conveyor, crash and explode into a fireball killing everyone onboard. Sorry these are the facts.
 
swedger77 said:
There is no mention of the jet engines being on.

However the plane would be able to get off the ground (very briefly) as the air speed over/under the wings relative to the ground would be the same as if it were being powered by the jets. This would provide sufficient lift to make the wheels leave the ground.

At this point, the method of propulsion is lost (ie contact with the conveyor belt) so the plane would drop back onto the conveyor.

It would then run out of conveyor, crash and explode into a fireball killing everyone onboard. Sorry these are the facts.
Click to expand...

I'm sorry, but I can't see how there would be any airflow over the wings other than the turbulence created by the movement of the belt. The plane is stationary in relation to the ground and the atmosphere. The forward thrust of the engines is exactly counteracted by the reverse movement of the belt.

Furthermore, a jet engine requires forward motion to ram enough air into it to provide enough thrust to take off. No airflow, no takey offy.

However, I do agree that it would crash and burn...
 
mmmmm, its a bit ambiguous.

I get your point, ie the plane body is stationary as the wheels are spinning, counteracting the movement of the conveyor.

But would that actually happen?


I conclude........................


fuck knows
 
swedger77 said:
mmmmm, its a bit ambiguous.

I get your point, ie the plane body is stationary as the wheels are spinning, counteracting the movement of the conveyor.

But would that actually happen?


I conclude........................


fuck knows
Click to expand...

That's a very similar flavour to where my head was at about tea time yesterday. I haven't even given it any thought since. I trust Don's NSFW implicitly, so much that I haven't even looked at it yet, but knowing the solution is their waiting is satisfying enough to maybe give it another crack myself later before I put to bed by looking at the answer.
 
ponch said:
Think of it in reverse if the plane comes in to land at 200mph and the belt is travelling in reverse at 200mph does the plane stop dead when it hits it or does it freely roll?
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I think that's a completely different scenario. Landing a plane utilises gravity. If the forward momentum can be totally cancelled out by the reverse motion of the belt, then landing on a sixpence should be possible. Taking off relies upon fighting gravity. Landing merely utilises gravity.
 
Gravity is still exerting the same force in the system whether the plane is in the air or on the ground.

Think of it another way you hold a toy car on a conveyor belt in the supermarket completely still while the belt moves backwards. Are you able to push it forwards or not?
 
ponch said:
Think of it another way you hold a toy car on a conveyor belt in the supermarket completely still while the belt moves backwards. Are you able to push it forwards or not?
Click to expand...

Of course you can. The toy car has no propulsion of its own, so as long as you can exceed the reverse speed of the belt then you can do what you like.
 
Pushing the car forward with your arm is exactly the same as a plane pushing it's self forward via jet engines, effectively a force of X pushing from the back. Why can't the plane move forwards?
 
ponch said:
Pushing the car forward with your arm is exactly the same as a plane pushing it's self forward via jet engines, effectively a force of X pushing from the back. Why can't the plane move forwards?
Click to expand...

Because you said the forward thrust from the engines was exactly counteracted by the reverse motion of the belt in contact with the wheels. in this case the net movement is zero, therefore no airflow over the wings and into the jet engines, therefore no lift. QED.
 
No mention of the jet engines being on.

It does say the wheels are spinning at the same speed as the belt, thus the plane is stationery relative to the ground.

Its not taking off.

I should be a Tory. What an epic U-turn
 
Aircraft require air to be sent at velocity over the wing, without this, no lift can occur, and no matter how fast the wheels may turn on a conveyor belt, it wouldnt provide lift.
 
Judging by the illustration, it looks as though there is nothing fixing the conveyer belt in position - I'm kind of picturing some mad contraption that is basically comprised of some round wheel like objects within the outer material - meaning that the conveyer belt itself would actually drive along the ground in the opposite direction of whatever way the plane was accelerating.

Therefore, if the plane is able to reverse at sufficient speed, it would be propelled forward by the conveyer belt fast enough to take off.

(This also assumes that the runway sized conveyer belt is on an even bigger actual runway with enough ground to accelerate to full speed.)
 
F.U.B.A.R. said:
Furthermore, a jet engine requires forward motion to ram enough air into it to provide enough thrust to take off.
Click to expand...
no it doesn't. i think you're confusing a jet and a ramjet.

if a jet requires forward motion for thrust, how does any jet take off from a standing start ever?

alasdair
 
alasdairm said:
no it doesn't. i think you're confusing a jet and a ramjet.
Click to expand...

Aye, I think you're right there.

But the rest of my point still stands.

If there was a big fuck off fan in front of the plane blowing air back over the wings then I could imagine it leaving the ground, but it seems like a bit of a faff for the sake of a bit of tarmac...
 
It_flies.jpg

i guess this will happen
 
The fucker better tonight when i get on it. Any sign of FUBAR with a conveyer belt and i am declaring war.
 
I'm imagining the conveyer belt moving at exactly the right speed to keep the plane stationary, and the whole system perfectly horizontal. Like in a physics exam question. So with this in mind, let's analyse the forces at play here.

The engines are exerting a force on the exhaust gases, propelling them backwards. This means there is an equal and opposite reaction pushing the engines (and therefore the plane, which is attached to them) forwards. The conveyer belt is exerting an equal and opposite force on the plane. It will be doing one joule of work keeping the plane from otherwise moving forward one metre, for each newton of forward thrust of the engines. The plane's wheels will be spinning very fast against the belt, and probably will go on fire from heat generated by friction in the bearings (which itself is opposing some small portion of the engines' thrust).

Anyway, for as long as the setup retains its integrity, the plane is not moving forward through the air. And this is what generates lift. The top of the wing has a larger surface area than the underside, so air travelling over it has to expand in order to meet the air travelling under it at the same time, otherwise you would create a vacuum. The volume increases, so the pressure must decrease. With less air pressure above the wing and more pressure below, there exists an upward force on the wing. Also, the air leaving the wing is travelling at a slight downward angle. This means the plane must have exerted a downward force on the air; so per Newton's Third Law, there must be a reaction pushing up on the plane. The combined effect of the two forces acting in the same direction is an upward lift on the plane. All these forces are acting on the wing; the fuselage keeps the plane stable, by adding inertia and so reducing the effect of any forces on its motion.
 
The plane would perform as on a runway of equal size,wheel bearings may get hot
 
Once it gained enough speed it would take off.The jet engines are pushing on the air behind them,it dont matter how fast the wheels are moving in the other direction.
 
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