For those that hate the BNP .......

[Maverick]

Alright then. An alternative approach.........

Please, cause I can not work out where I'm going wrong in order to get your conclusion.

[MattF]

Don't know about you, but at that moment my attention is occupied with holding the book open on the floor with my foot. Couldn't tell you what speed the bog rolls doing

You wipe before you've finished the book?

[biosurf]

You wipe before you've finished the book?

It might be a long book...



Having said that, with the credit crunch for all you know I might be wiping with the pages

[Dodge]

for the plane to take off, the jet engines will have to match this force just to remain stationary plus additional force to gain speed and take off.
however, in this situation the conveyor provides as much force one way as the jets provide in the opposite direction and therefore the plane does not take off it remains stationary.

You have countered your own argument. The conveyor doesn't provide any force, directional speed maybe but not force, the only force or "drag" to speak of is the friction of the wheel bearings. The force created by the engines to get several hundred tons of steel to travel at hundreds of miles an hour requires such force that the fact the there is a little drag from the wheel bearing is negligible in comparison.

This is how I see it, I am willing to be proven wrong.

The planes engine (prop or rocket) produces forward force, now initially this is displaced through the contact with the ground surface (earth, water, concrete, whatever), until forward momentum creates enougth air speed to produce lift.

Now if that forward force was displaced onto an item (conveyor belt) that absorbed it (by being equal or greater), then it could not get the forward momentum, so no air speed, no lift.

Unless you're informing me that the engine can disturb enougth air around the plane get the wind up to take off speed and thus create lift (of course in the case of virtical take off and landing aircraft this is the case).

This is the case with every aircraft, the forward motion is provided by the engines pushing the air behind it, not the ground underneath.

Air might not feel solid enough to provide something to push against, but it is, if it weren't, as soon as an aircraft were to leave the ground it would fall out of the sky. For examples of the "strength" of air you only have to look at the small amount in tyres to hold up the weight of whatever is riding on them, from a ton of car to hundreds of tons of aircraft . . . or air tools, how can air drive a chisel with enough force to cut through steel . . . or just put your finger over the end of a pump.

Yes, but I'm not pulling bog roll.

If I sit on a skateboard (I never managed the balance to stand) with a leaf blower pointed backwards and switched on will I move forwards?.....Yes.

Now if I move that skateboard onto a running machine and (with the leaf blower switched on) accelerate the running machine until it matches the speed of wind that the leaf blower is blowing will I move forward, or will I be stationary? The laws of physics as I understand them make me believe that I would effectively (to anyone who wasn't on the running machine with me) be stationary.


Now do you see why I'm not seeing your logic. It goes against the laws of physics as I have understood them.

A leaf blower on a running machine it is no comparison. The belt doesn't provide any force it is gravity and the friction of the wheel bearings, hard to counter these with a leaf blower, but with thousands of pounds of thrust from an aircraft engine only a micro fraction of this force is actually required to counter the rotation of a few bearings . . . if the wheels were jacked up off the grounds, brakes off you could turn them with your hand and maybe even a leaf blower.

[Maverick]

The only way I can see that a plane would take off, is if the conveyor belt is not moving backwards.

[gwh200]

Please, cause I can not work out where I'm going wrong in order to get your conclusion.

Wow...I'm sure glad my internet has been off for a week...its so hard to reply by phone

[lord lucan]

You have countered your own argument. The conveyor doesn't provide any force, directional speed maybe but not force, the only force or "drag" to speak of is the friction of the wheel bearings. The force created by the engines to get several hundred tons of steel to travel at hundreds of miles an hour requires such force that the fact the there is a little drag from the wheel bearing is negligible in comparison.

This is the case with every aircraft, the forward motion is provided by the engines pushing the air behind it, not the ground underneath.

Air might not feel solid enough to provide something to push against, but it is, if it weren't, as soon as an aircraft were to leave the ground it would fall out of the sky. For examples of the "strength" of air you only have to look at the small amount in tyres to hold up the weight of whatever is riding on them, from a ton of car to hundreds of tons of aircraft . . . or air tools, how can air drive a chisel with enough force to cut through steel . . . or just put your finger over the end of a pump.

A leaf blower on a running machine it is no comparison. The belt doesn't provide any force it is gravity and the friction of the wheel bearings, hard to counter these with a leaf blower, but with thousands of pounds of thrust from an aircraft engine only a micro fraction of this force is actually required to counter the rotation of a few bearings . . . if the wheels were jacked up off the grounds, brakes off you could turn them with your hand and maybe even a leaf blower.

yes thats what i said

[Dodge]

The only way I can see that a plane would take off, is if the conveyor belt is not moving backwards.

OK, again . . . an aircraft takes off when it reaches the required air speed for the aerodynamics of the wing to lift it off the ground.

This speed, or forward motion is provided by the engines pushing the aircraft forward.

What is happening underneath the aircraft is irrelevant.

The engines will push the air backwards this will make the plane move forward, the air is not "on" the conveyor.

Aircraft speed is measures in knots, not mph or kph as the distance travelled may vary according to wind speed, in a head wind an aircraft will take off in a shorter distance as the wind speed over the wing will be increased as there is already wind travelling over the wing, conversely a tail wind will mean the aircraft needs a longer distance to take off.

Whatever the wheels, skis, floats etc are doing the aircraft will always require the same amount of air speed over the wings to generate enough lift for take off.

Lift, created by the air speed over the wings, created by the force from the engines pushing the air backwards ergo the aircraft forwards, is the only thing that an aircraft needs to take off, it is on wheels purely to allow it to roll whist still on the ground, these rolling wheels do not drive the plane nor do they slow it down (except when the brakes are applied).

Put an aircraft on a conveyor the length of a runway and turn it on the plane will move backwards, but as soon as you apply a little force, thrust, from the engines, it will remain stationary, increase speed of the conveyor and all you will do is increase the rate at which the wheels on the aircraft turn, apply even more thrust and the aircraft will move forward and take off, you cannot apply force to the plane through the conveyor only ground speed (apart from a little friction in the wheel bearigs), this is easily countered by the thrust of the engines which provide air speed, which is what is required to generate lift.

There is no point in continuing if you can't grasp how a wing works, the physics of lift, air over a wing.

[RodLeach]

I think its best to think that the 'landing gear' is just there to hold the plane off the ground.

[Maverick]

Right I've got it.

You're moving the wind.

The plane is resting is a gravity free zone, and the wind is rushing at it.

All I'm asking is how are you getting the air to move, in order to create lift.

I have to presume that a single prop can create enougth force to blow enougth wind past the wings to create lift. Otherwise it's ain't going nowhere.

[lord lucan]

Right I've got it.

You're moving the wind.

The plane is resting is a gravity free zone, and the wind is rushing at it.

All I'm asking is how are you getting the air to move, in order to create lift.

I have to presume that a single prop can create enougth force to blow enougth wind past the wings to create lift. Otherwise it's ain't going nowhere.

ficking hell

[Albannach]

Here's a question for those who don't think it will fly.

Lets hust say that by some fluke, the plane manages to take off, it circles once and comes in to land on the conveyor belt. Plane is landing at 160mph, belt is spinning in the opposite direction at 160mph. When the plane hits the belt, will it stop dead? If not, why not?

[Dodge]

Right I've got it.

You're moving the wind.

The plane is resting is a gravity free zone, and the wind is rushing at it.

All I'm asking is how are you getting the air to move, in order to create lift.

I have to presume that a single prop can create enougth force to blow enougth wind past the wings to create lift. Otherwise it's ain't going nowhere.

Yeah that's it.

No, *shakes head*, you move the aircraft, or more correctly the engines move the aircraft by pushing the air.

An aircraft an inch above the ground can fly and it can accelerate, if the wheels touch the ground they spin it doesn't come to a dead stop!

An aircraft will take off when it reaches it's take off speed, the airspeed at which the aerodynamics of the wing comes into effect. This airspeed is reached by the engines pushing it, the thrust from the engines pushes the air behind it and this airspeed is not related to the speed of the ground, it can be affected by the direction and speed of the wind.

An example using extremes for simplicity's sake, a light aircraft has a take off speed of 50mph (airspeed), if it tries to take of into a headwind of 50mph it will do so without moving therefore the wheels won't be turning, if it tries to take off in a tailwind of 50mph it will need to reach an airspeed of 50mph but as it has to counter the tailwind it's ground speed will be more like 100mph and the wheels will be spinning twice as fast as at normal (dead air) take off speed. The speed at which the wheels rotate is not related to the aircraft's take off speed and therefore not relevant to whether the aircraft will take off or not.

Simply put . . . For an aircraft not to take off it needs to remain stationary, or not reach it's take off speed at least, a conveyor cannot stop an aircraft from moving as the thrust from it's engines push against the air not against the conveyor.

[wishbone]

Ok so if I've got my old school roller boots on with leg warmers n all.. and I get on one of them flat conveyor belts at the airports... 1/2 the people here will say I'll not be moving but my little roller skate wheels will be.. The other half of people will say my wheels ain't moving and I'm moving at the speed of the belt...


So.. this plane on the belt... is it moving backwards on the belt at 150mph with stationary wheels or is it not moving at all with the belt doing 150mph and its wheels spinning like a goodun ?


Don't care either way but this seems to be where the arguments stem from..

Didn't really pay much attention to the original thread so ignore this if I'm stating the bleedin obvious

[Albannach]

The arguement arises because of folk's fixation for driven wheels. In reality, the wheels on the 'plane and the conveyor belt are irrelevant.

I love this arguement, I'm truly surprised it took off as well this time. Normally it fizzles out quite quickly.