No, there is very little force on the plane from the wheels. The wheels rotate pretty much freely (with almost negligible resistance), and when you have the engines providing a huge force going forwards the plane moves forwards.Byron5184 said:
Who's right?
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****read op and answered cos im too blitzed to read 13 pages****
Nope the plane has to displace the air around it to get lift
The plane is not actually moving forward so no air is actually displaced
/me thinks
or is it a kind of "88 miles per hour speed" that the engines need to create lift and its air moving through engines and not engine moving the plane through air
/quits thead and hope the bad man stops
Nope the plane has to displace the air around it to get lift
The plane is not actually moving forward so no air is actually displaced
/me thinks
or is it a kind of "88 miles per hour speed" that the engines need to create lift and its air moving through engines and not engine moving the plane through air
/quits thead and hope the bad man stops
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Byron5184 said:I'm gonna toss my two pence into this cause im in a debate mood
The question asked is if the conveyor is moving in the opposite direction at the same speed the plane should be travelling forward. (i.e. if the tyres are spinning at a rate to move the plane at 100MPH, the conveyor would be moving at 100MPH the other way) Oviously, to achieve this effect in the real world the conveyor would have to be motorised or designed like a rolling road like you see in a car garage etc... both would have exactly the same effect.
While the plane is on the ground, all the engine thrust is used to overcome the friction between the planes tires and the ground. Sufficient force will propel the plane forward. The forward motion on the plane forces air over the wings to generate lift. When the plane is travelling at sufficient speed the lift is strong enough to allow the plane to become airborn.
However, if the conveyor is moving in the opposite direction at the same as the aircrafts tyres. All that thrust the engines provide is transferred through the freewheeling tyres into the conveyor belt instead of the moving the plane forward. Because of this no lift is generated on the wings, therefore, the plane is completely incapable of taking off. The only way the plane could take off in these circumstances would be if the wind was blowing fast enough over the wings to generate the sufficient lift. But if a plane requires a speed of (for example) 200MPH in zero wind conditions, the head wind would have to be going 200MPH to cause the plane to lift off from a stationary position.
Think of it like a Formula 1 car sat on a rolling road. You can rev the engine all you like, all that will happen is you make the rollers spin faster all those aerodynamics will be useless because no air will be flowing over them. But a rolling road is rollers that are freewheeling. The conveyer for the plane would have to be motorised and controlled to allow it to travel in the opposite direction at the same speed the tyres are going.
Hell, replace the conveyor with a rolling road like in car garages and you've got exactly the same effect. All that thrust is transferred into the conveyor/rolling road through the tyres. The tyres are spinning which is the aim of the thrust but the ground is moving where as normally it isn't.
So simply put. If the ground (conveyor) is moving in the opposite direction at the same speed to keep the plane stationary, then NO, it will never take off.
Enjoy
The difference is that with a car the force/drive to propel it forward is applied to the road or conveyor through the tyres, so yes the car goes nowhere.
However with the plane it is pushing against the air around it and not the road. therefore the plane pushes itself through the air building up airspeed irrelevant of the rpm of the tyres which have no drive they will spin but no force will be acting through them.
Yes it is, as a pilot I am required to understand the principles of flight, and yes it also is basic physics.Athanor said:
The engines of the aircraft propel the aircraft relative to the airmass, regardless of whether or not the wheels are up or down. On this conveyor runway, when the engines are spooled up to full power, the aircraft will accelerate through the airmass. Any counteracting force provided by the conveyor will be lost as the wheels of the aircraft will freewheel. The aircraft will accelerate as normal to it's nominated rotation speed and begin to fly. As a result of the example, the wheels on the aircraft will be spinning at twice the speed of the aircraft at rotation (in nil wind conditions).
No resistant force is applied by the conveyor as the wheels do not transfer the conveyors motion to the aircraft. They spin or'freewheel'.
Errr.... we're not talking about the same thing here but if it was the same is this and assuming the rolling road could run at the same speed as the cars wheels could rotate then no (all other things being equal).clv101 said:
It's just a case of equal and opposite forces canceling each other out.
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Exactly there is nothing (no force) to stop the plane moving forward
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I'd hate to think what he would be doing if he read the thread in the OP then. At least the majority in here say it will take offThe point is the aircraft never atains any forward motion through an airmass because as the wheels rotate to enable it to move forward the runway/treadmill is powered away in the opposite direction.Scuzi said:
So the wheels end up rotating at 120knts but as the surface they are rotating on is going at 120knts in the opposite direction there is no net forward motion so the plane does not move through the air mass to create lift.
The wheels are irrelevant in as much as they provide no power, they do however provide the means for the aircraft to move forward through the air down the runway.
The opposite force is being produced by the motors turning the treadmill in the opposite direction.... /sighScuzi said:
The OP has stated the treadmill matches the speed with a device, the original post doesn't mention the treadmill "freewheeling". He specifically says it adjusts it's speed to match the rotation of the wheels. the only way it could do that is through being powered itself.
**edit** Just to add this is why treadmills in a gym have a motor, the motor matches the force you exert tring to move forward by moing the treadmill back with an eual and opposite velocity so you make no net movement forward
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clv101 said:
I kinda second guessed myself in the end of my post
suzi has the answer i recon
No, we just covered this.Athanor said:
As the treadmill just matches the speed the wheels spin at the no friction, no force, they are out of the equation. Just think about it in your head. 747 sitting there, engines fire up, massive thrust... the thing just sits there? Of course not.
Ok, think one step further, the engines fire up, the wheels roll and instead of working it's way down the runway the treadmill runs in the opposite direction at the same speed, so although the wheels are rotating rlative to the treadmill it's not moving forward relative to the air because it never moves forwardclv101 said:No, we just covered this.
As the treadmill just matches the speed the wheels spin at the no friction, no force, they are out of the equation. Just think about it in your head. 747 sitting there, engines fire up, massive thrust... the thing just sits there? Of course not.
See what I mean?
There is no opposite force. Yes, the treadmill turns in the opposite direction but as the wheels of the aircraft freewheel, this motive force is not transferred to the airframe. What the wheels do on the ground is completely irrelevant. Whether or not the original question mentions freewheeling, the fact remains that drive is not transferred through an aircrafts wheels. The reason the wheels are on an aircraft is to get rid of friction and enable it to move forwards on the ground.Athanor said:
I get the feeling I'm talking to a brick wall here. I wish I could explain it in simpler terms but if you can't grasp physics at this, it's most basic level then there's no hope of getting you to understand the principles of flight and motion.
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How do you know its got thousands of pounds of thrust?clv101 said:
The question just says a plane. Not what type.
What if the plane were a Sopwith Pup for example.
How would that get enough thrust to move against the treadmill.
Say for example the treadmill was a muddy field.
The Sopwith Pup is trying to take off from the muddy field, but its wheels are stuck in the mud, just going round and round.
Surely it couldn't take off.
It would need sufficient force to get moving fowards to fly.
(I need sleep.
)Read here - http://www.kottke.org/06/02/plane-conveyor-belt