Plane and conveyor belt...

[crank39]

but to move forward, to wheels would roll along the runway. but here the runway counteracts that forward motion, so the plane can't move forward !!!

Yes correct assuming no friction in the wheel bearings the plane would stand still, but as i said before.........to get it to seemingly take off from that stand still you need to have air going across the wings to provide lift.

But as inky says the bearings will have friction so the plane will ever so slowly go backwards with the conveyor, depending on the friction eventually over several miles the plane would be going the same speed as the conveyor.

Lets put it this way, i strap myself to a handglider then i step onto a treadmill and turn it on till im sprinting like a man possesed, i will still not take off because there is no air running over the wings

 

[Inky Pete]

but to move forward, to wheels would roll along the runway. but here the runway counteracts that forward motion, so the plane can't move forward !!!

Turn your belt sander upside down. Turn it on.

Put a block of wood on the belt and hold it from shooting off backwards with one finger. Takes quite a lot of force from your finger to hold it there, doesn't it?

Now put a toy car of about the same weight on the belt and hold it there with one finger.

The wheels will be spinning like b*ggery, but it will take MUCH less force from your finger to hold the car there. And very little extra force will be needed to push the car forwards.

That's friction for you.

With the block of wood you're finger is having to supply a force big enough to overcome the friction between the block and the sanding belt.

With the toy car, you're finger is only having to overcome the much lower friction in the wheel bearings.

Your belt sander is the runway, the toy car is the plane, your finger is a jet engine.

If the plane didn't have wheels then the jet engines would have to work REALLY hard to prevent the conveyor from dragging the plane backwards - but the plane does have wheels so the jet engines can do that very easily, virtually all of the thrust can then go into accelerating the plane forwards through the still air and generating lift.

 

[Nige F]

There are so many new people on here, and so many of the old crowd not, is it worth digging up this little treasure? I still don't think we ever got a definitive answer?

FFS it`s bleedin obvious why not have a flying boat on a river - or an endless pool - of course it`ll take off

 

[imamartian]

belt sander and wood... suggest slippage... conveyor and wheels are attached together..... and the wood fighting against the belt sander is wrong....

the conveyor reacts directly to the speed of the wheels....thereby taking away the possibility of forward motion !

 

[Mickymoody]

The wind resistance against the wings causes a plane to have lift. You could run a plane on a treadmill, but it would fall off the back of the giant treadmill, as the wheels aren't powered.

On a treadmill there is no wind resistance to the wings, so a massive fail would occur.

2nd time I said that methinks..?

 

[imamartian]

The wind resistance against the wings causes a plane to have lift. You could run a plane on a treadmill, but it would fall off the back of the giant treadmill, as the wheels aren't powered.

On a treadmill there is no wind resistance to the wings, so a massive fail would occur.

2nd time I said that methinks..?

dear oh dear.... it really is not wind resistance against the wings that causes a plane to have lift.... it's the speed of the air OVER the wing compared to the speed of the air under the wing, and therefore their relative pressures that provides lift...

and please re-read... the conveyor MATCHES the speed of the wheels !!

 

[Inky Pete]

So the conveyor doesn't have a constant speed? Please explain the set-up in more detail.

Not that it makes any difference since the wheels are free to spin at whatever speed they want to regardless of the motion of the plane through the air. And the forward speed of the plane is due entirely to the thrust from its engines.

 

[imamartian]

So the conveyor doesn't have a constant speed? Please explain the set-up in more detail.

Not that it makes any difference since the wheels are free to spin at whatever speed they want to regardless of the motion of the plane through the air. And the forward speed of the plane is due entirely to the thrust from its engines.

It's a theoretical situation, not of my making, i might add... but the idea is that whatever speed the wheels attain, then the conveyor counteracts it.....

so for me it's a clever way of isolating the friction with the floor... there must be a definition in physics.... so is it like a hovercraft? i don't think so, because a small force pushes a hovercraft forwards.... it's almost like the conveyor pushes the plane back at the same rate tha the engines push it forward !!! so a static plane for me !!

 

[Norcon]

Did that close encounter last night scramble your brain Imam cos you're talking shyte.

 

[imamartian]

Did that close encounter last night scramble your brain Imam cos you're talking shyte.

I'm not talking shyte.... the idea of this thread is to explain why you disagree, not just fire off bullshyte and insults.

If you're that clever, that make me see how the plane will move forwards....

 

[joinerjohn]

The aircraft pushes against the atmosphere. Doesn't matter what's underneath the wheels. The aircraft has to move through the air to create lift. All it means is that the aircraft's wheels would be rotating much faster than they normally do when the aircraft was hurtling down the runway.
In this situation, it's airspeed that matters, not groundspeed.

 

[imamartian]

The aircraft pushes against the atmosphere. Doesn't matter what's underneath the wheels. The aircraft has to move through the air to create lift. All it means is that the aircraft's wheels would be rotating much faster than they normally do when the aircraft was hurtling down the runway.
In this situation, it's airspeed that matters, not groundspeed.

agreed, except,,, replace the wheels with usain bolt....and he's on a treadmill.... if he runs at 10 mph... the treadmill runs at 10 mph in the other direction... and at 15mph.... so does the conveyor... it doesn't matter how fast Usain Bolt is !!

 

[Nige F]

More shyte.

Indeed - more shyte than in the shyte tank on the plane that`s been on the poxy conveyor for years

 

[Space cat]

-- the wheels are free to spin at whatever speed they want to --

Not quite; there will come a point where centrifugal force causes them to fly apart. But, for the sake of argument, let's ignore that and assume we have perfect, indestructible wheels.

I remember the original question and it was badly posed. The conveyor will move at whatever speed it takes to try and stop the plane from moving. Now our wheels can have frictionless bearings but they still have inertia. What will happen is that all the thrust of the engine will be consumed in accelerating the wheels.

 

[Inky Pete]

If the speed of the conveyor is modulated to prevent the wheels from turning, then the conveyor will be moving forwards at the same speed as the aircraft.

No rotation of the wheels = no rolling friction = plane takes off easier than it would on a tarmac runway.

If the conveyor is modulated to run backwards at whatever speed the aircraft is moving forwards, then all that will happen is that when the aircraft reaches its take-off airspeed the wheels will be free spinning at twice that speed.

No big deal if we assume the wheel bearings can take it, slight increase in engine thrust required to overcome the slightly increased rolling friction but the plane still takes off.