conveyor belt and plane answered at last ??

[big-all]

watch mythbusters at 2000hrs on quest

origional thread or at least one off
//www.diynot.com/forums/viewtopic.php?t=276712&start=0

 

[snico]

Dont forget that mythbusters are never always right

 

[Brigadier]

Or Brazilian ladies playing beach volleyball on the beeb........

 

[crank39]

watch mythbusters at 2000hrs on quest

origional thread or at least one off
//www.diynot.com/forums/viewtopic.php?t=276712&start=0[/QUOTE]

I think it was mythbusters that started the disgreement to be honest

I still stick by my view that the plane cannot take off, it needs forward movement for the wings to generate lift

 

[AronSearle]

I still stick by my view that the plane cannot take off, it needs forward movement for the wings to generate lift

People who think it won't take off are being a bit silly, and not really thinking about it.

Forward motion is provided by the engine thrust. It's not a car, motion is not provided by the wheels.

The wheels act as ball bearings.

If you put the plane on ball bearings, what difference do you think a conveyor belt will make no matter which direction it's running and at what speed, the engine will pull it forward regardless.

 

[pred]

Aircraft take off due to airflow over the mainplanes (wings) if an aircraft carrier were capable of about 100mph the the aircraft would become airbourne like a glider. The only gas turbine (military) aircraft to glide that i am aware of was the Hawker Hunter, about 40yrs ago one had a flame out and would not relight, he was if memory serves me 25miles out of RAF Chivenor at 20,000ft and managed to glide back onto the runway, the glide angle of a Vulcan was 50' from the verticle and the lightning 8', fortunatly they were fitted with good bang seats.

Different aircraft have diferent take off and landing speeds/stall speeds, as the air flows over the mainplane it takes the air the same time to travel from the leading edge to the trailing edge, as it has to travel further up and over the top of the wing there is an increase in velocity which gives you a decrease in pressure so the wing is sucked up not pushed up from underneath the wing, same principle in the old carburettor, the air flow through a ventury, this caused an increase in velocity and a decrease in pressure, hence the fuel was sucked up through the jets. SIMPLES.

 

[chapeau]

Ah pred, you were doing so well, until....

as the air flows over the mainplane it takes the air the same time to travel from the leading edge to the trailing edge,

Not so....

The air is accelerated over the top of the wing so gets to the trailing edge a lot faster.

Funny old things are wings, they work upside down too, and it's to do with 'angle of attack' and circulation.

 

[snico]

The actual question itself need to be given correctly with more detail, once you do that...the answer is very straight forward.

Is the conveyor at a fixed speed, motor run? if so....the plane WILL eventually take off as the eggines give forward momentum, not the wheels. The wheels would turn faster until a point where the plane would start to move forward, giving the plane lift.

If the conveyor was free moving, and accelerated with the speed of the plane wheels, then the plane would NOT take off, as the thrust becomes greater, the planes wheels would turn faster. No forward movement of the plane and wings through the air.

Its pretty simple really

 

[rjm2k]

The actual question itself need to be given correctly with more detail, once you do that...the answer is very straight forward.

Is the conveyor at a fixed speed, motor run? if so....the plane WILL eventually take off as the eggines give forward momentum, not the wheels. The wheels would turn faster until a point where the plane would start to move forward, giving the plane lift.

If the conveyor was free moving, and accelerated with the speed of the plane wheels, then the plane would NOT take off, as the thrust becomes greater, the planes wheels would turn faster. No forward movement of the plane and wings through the air.

Its pretty simple really

I think the question covers that, since it states that the belt travels at the "same speed" as the wheels you have to assume it always matches the speed no matter how much it's accelerated.

I haven't seen anything which covers the direction of the belt, if it opposes the direction (I think this one) of the plane then it won't take off, if it's in the same direction then it will take off sooner.

A simpler way to think of it is to forget the plane, think of a car on a rolling road, if you sit on the bonnet will you feel increased airflow the faster the car goes? Nope. So no airflow over the wing = no lift.

I suppose if it were a wing where the airflow is generated by the engine itself and directed over the wing then it could generate its own lift maybe, boats do this with their prop in order to provide stearage sooner than would be provided simply by their motion through the water.

 

[doitall]

The plane cannot take off because there is no air flow.

The videos showing the plane taking off has the conveyor sandwich between the wheels and the ground, whereas if the plane was on a conveyor that was not in contact with anything solid the plane would for example be going backward at 85mph, starting the engine would at best hold the plane in a static position>

To get lift off the plane would have to have a forward motion of say 85knots, other wise it will just sit on the conveyor until it runs out of juice.

 

[big-all]

the conveyor cannot excelerate the plane to any extent as the only energy tranferred is the friction contact off the tires and the small amount drag by the bearing there is no other energy transfered to the plane from any source

 

[doitall]

the conveyor cannot excelerate the plane to any extent as the only energy tranferred is the friction contact off the tires and the small amount drag by the bearing there is no other energy transfered to the plane from any source

BA next time you go to tesco's place a small plane on the conveyor belt and it will go shooting down to the checkout person. The same will happen to a big plane and you need the engine power just to stop it doing that.

Now understand.

The toy plane is going backwards towards the cashier but the wheels are not turning.

To prevent the plane going backwards you need an equal power to overcome the conveyor.

Start the engine and the plane has matched the speed of the conveyor so the plane is stationary but now the wheels are turning.

Still no air flow over the wings because there is no forward motion.

Give it more power in that case, but the question states the conveyor matches the speed, so still no forward movement.

Assuming you could build a big enough conveyor the plane cannot take off.

 

[Trazor]

Hands up, all those that think free wheeling wheels can brake 120,000lb of thrust.

 

[AronSearle]

Hands up, all those that think free wheeling wheels can brake 120,000lb of thrust.

But but but

What if the conveyor belt turns REALLY REALLY fast, then it will spin the wheels in the other direction so fast, the engine won't be able to counter the force of the free wheeling wheels, the errrm, ahh, friction provided by the free wheeling, errm wheels, so what you have is, errm, aha.......

Sorry, the door bell is ringing, back in a jiff....



Seriously people, stop over thinking it, you look really really silly. The wheels are nothing more than ball bearings, if you put something on ball bearings, on a conveyor, what difference do you think the conveyor is going to make to against jet engines.

 

[doitall]

If you sit a plane on a conveyor belt going at 100mph, the plane will move in the direction the belt is running at 100mph, and the wheels are not turning, all the power is used to stop you going the wrong way.

Take a treadmill running at 5mph, if you stand on it you'll go flying of the end at 5mph, now for the clever bit.

If you start walking at 5 mph you'll stay where you are, if you start walking faster the belt goes faster so you are walking on the spot, at no time can you walk off the end.

And the question is not about jets but prop engines, that need an air flow to get off the ground.