Principles of flight?

[RomanV]

It would be awesome if they got in a punch up over it.

hehe, I could just imagine it.

"but the plane isnt moving!" *SMACK*

"Wheres the force of the thrusters going then?!" *SMACK*

[malc]

I just find the whole thing very interesting

Maybe fivebob is just a researcher, using toyspeed as a focus group to find out ratios of optimists to pessimists....

I dont think the plane will ever take off, and I bet its fuel tanks are half empty too

[no_8wire]

I have reformed my opinion to say no...it needs speed in relation to the ground, since there is no air speed...

I dont know but this make the most sense to me...

[riddles]

I think I can see where both sides are going here. But what if as in a real runway situation, the conveyor isn't moving, the brakes are on and the engines are at full thrust, the brakes are released and the conveyor starts moving at the same time?

Everyone seems to agree that the engines provide thrust, what appears to be the argument is does the conveyor provide reverse thrust (drag) ie the plane is moving forward because of thrust at 100Kph, the canveyor backwards at 100Kph and the wheels are turning at 200Kph, The engines cease to thrust, will the plane still continue forwards?

Where does weight transfer come into this? When in flight then the weight of the plane is carried by the wings and supported by the low air pressure above them caused by the air flowing faster above than below. When on the ground the weight of the plane is supported by the under carriage and pneumatic tyres. A plane takes off when the airspeed is great enough to transfer the weight from the tyres to the wings (v simplified) and the wheels still rotate as the disapper up into the body of the aircraft. At what point does the transfer of weihgt from tyres to wings affect the drag of the conveyor?

[RomanV]

You know how you drive past a horrible car crash, and cant help but look?

Well this thread is like driving past a horse crash, where you cant help but get out of the car and go flog the shit out of all of the dead horses lying around.

[Punter]

**** That horse isn't dead yet **** (is it?)

Everyone seems to agree that the engines provide thrust, what appears to be the argument is does the conveyor provide reverse thrust (drag) ie the plane is moving forward because of thrust at 100Kph, the canveyor backwards at 100Kph and the wheels are turning at 200Kph, The engines cease to thrust, will the plane still continue forwards?

The wheels cannot provide that much drag, as the brakes are off and they are FREE TO SPIN.

Don't think of the conveyor belt as pushing the plane backward (because it can't) think of it as making the wheels spin faster which has NO EFFECT ON THE PLANE.

[snwtoy]

You know how you drive past a horrible car crash, and cant help but look?

Well this thread is like driving past a horse crash, where you cant help but get out of the car and go flog the sh*t out of all of the dead horses lying around.

HAHAHHAHA... hahehehahahahhehehehehehehehaah /HHAHAHAHAHHA

[snwtoy]

Push matchbox car on treadmill against the motion of the belf. Can you push the car from one end to the other?

like above, it would move forward, and that is because your normal treadmill moves at a constant speed. It makes no odds whether the car is pushed very quickly or with a huge amount of thrust.
For something to move forward it must gain traction or be moving faster than the surface below. In the case of the plane, its forward speed is transfered through its wheels.

*flogs a bit more*

I said that your mate has to accellerate the treadmill (ie turn it up) while you are pushing the car along it. Can you still push from one end to the other when the treadmill is accelerating?
A plane's forward speed has no relationship to it's wheels (apart from drag coefficient). The wheels are irrelevant. A plane is only ever acted on by four forces:

Thrust
Drag
Weight
Lift

We all agree that in order for lift to overcome the weight of the plane, sufficient airflow over the wings must be achieved - this is called airspeed and is not to be confused with groundspeed.

In order to gain airspeed, thrust must overcome drag. While in the air the only drag on the plane is caused by air friction. While on the ground, the friction comes from both air friction and friction with the ground.
If the thrust from the engines can overcome the friction generated by the bearings in the wheels, the plane will accelerate, gain airspeed and thus lift.

Now why are so many people convinced that the conveyor will provide enough friction that the engines will prove ineffective?

[MrOizo]

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

Explain why it can, or cannot, take off?

After reading it again i still go with Yes.

I see the plane taking off as normal other than the wheels spinning twice as fast as they should.

Question is saying that the conveyor is making only the WHEELS go faster in the opposite directioin to the planes movement.

What if the belt was to go the same way as the plane? still wouldnt make any difference.

[V8MOFO]

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

Explain why it can, or cannot, take off?

After reading it again i still go with Yes.

I see the plane taking off as normal other than the wheels spinning twice as fast as they should.

Question is saying that the conveyor is making only the WHEELS go faster in the opposite directioin to the planes movement.

What if the belt was to go the same way as the plane? still wouldnt make any difference.

I think we can all agree now that the plane can move forward relative to the ground. Although I still dont believe the plane will take off. But it also unfair to state that the plane can't take off. There really is no way of testing this. I was thinking about it today.
IF you could get all forces even ( acceleration, time, speed ) I think the speed of the wheels and the travelator would accelerate to infinite.

[malc]

I think we can all agree now that the plane can move forward relative to the ground.

No I do not agree at all, the plane is simply not moving.

Example,
float plane on a river, the float plane will achieve lift off at a speed of 60kts, the river is flowing at 60kts in the other direction, The plane is not making headway up stream. It simply cannot.
I dont think there would be one float plane pilot who is willing to try going against a large current, they are simply not that daft!!

Ok, a boat is on the river, the boat is trying to go upstream, the water current is matching the boats speed going downstream, the boat is staying in the same spot. If the water goes faster than the boats maximum speed, then the boat will go backwards.

[snwtoy]

I think we can all agree now that the plane can move forward relative to the ground.

No I do not agree at all, the plane is simply not moving.

In order to stop the plane moving forward, you need to counteract the thrust of the engines.
Are you telling us that the conveyor belt, which is simply spinning the wheels of the plane, can counteract the engines?

[malc]

the belt is counteracting foward movement or acceleration

[snwtoy]

the belt is counteracting foward movement or acceleration

All the belt is doing is spinning the wheels of the plane, how does a spinning wheel affect the motion of the plane? Think about it.

[MrOizo]

The belt is making the velocity of the plane RELATIVE to the belt, 0.

[V8MOFO]

I understand the principle now. Sit on a bike on a moving travelator. Hold onto a rope which is tied somewhere down the end ( the way you're facing ) and pull yourself along it. No matter how fast the travelator is going you can still pull yourself along. ( In theory )

BUT the plane simply wont take off due to the surrounding conditions. Travelator going one way, wheels turning the other way. Like I said, the travelator and the wheels will be spinning at infinity.
Similar concept to a spinning circle. The top of the wheel is moving right, whilst the bottom of the wheel is spinning left. In theory the centre is not moving at all, yet you would have to go to the infinity to get to the centre...

[blitza]

I think we can all agree now that the plane can move forward relative to the ground.

No I do not agree at all, the plane is simply not moving.

aaaand if the plane was stationary, the wheels would not spin at all

lets think some more, fed by fivebob's mention of wind created by the belt, I propose there is LESS chance of the plane taking off if the belt were to spin in the direction of plane travel......

[EVOGTX]

Think of it this way, you are on a treadmill wearing rollerskates (pretending to be the plane ) If the treadmill/conveyor starts to move in reverse then the wheels on the skates will turn also. Now imagine a handrair next to the treadmill (representing thrust). Pull yourself along the treadmill using the hand rail. The skates spin faster and you can turn the treadmill speed up to whatever you like but the force exerted by you pulling on the handrail (thrust) is not dependant on anything that happens with the treadmill. It could be there, it could not be there the result would be the same, you move forward. AKA Plane takes off. Because the engines that drive the plane (NOT THE WHEELS!) are exerting thrust on the air NOT the ground therefor anything that the ground is doing is negligable.

And I'm tired so this probably makes no sense

We had this question in a physics exam and the whole class apart from me and another guy got it wrong, the people who got it wrong still didn't grasp the concept after over an hour of explaining.

And I'll bet they still dont get it

[matt dunn]

The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

So,

The plane moves forward at say 10kmh, the bottom of the wheel moves towards the back of the plane and the top of the wheel moves to the front as the wheel is rotating.
The convey moves in the opposite direction to the part that contacts it.
so the conveyer moves forward in the same direction as the plane.

The plane moves forward, the conveyor moves forward, and.....

THE WHEELS DO NOT TURN AT ALL,

no matter how fast the plane moves.

[V8MOFO]

The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

So,

The plane moves forward at say 10kmh, the bottom of the wheel moves towards the back of the plane and the top of the wheel moves to the front as the wheel is rotating.
The convey moves in the opposite direction to the part that contacts it.
so the conveyer moves forward in the same direction as the plane.

The plane moves forward, the conveyor moves forward, and.....

THE WHEELS DO NOT TURN AT ALL,

no matter how fast the plane moves.

Good try, but no ''opposite direction of rotation'' meaning, one moves clockwise, the other moves anti-clockwise.