Who's right?

Jotun · 20 Jan 2007 at 01:52

Athanor said:
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 forward

See what I mean?

It would move forward relative to the air because that is exactly what the engines are there for, to move the plane forwards relative to the air.

Jotun · 20 Jan 2007 at 01:54

Digital Punk said:
How do you know its got thousands of pounds of thrust?
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. )

There is no force on the airplane from the treadmill though as the wheels can spin freely.

Why on earth would the wheels of an airplane stuck in mud be rotating? :confused:

Airplanes are not like cars, there is no power to the wheels, all the power is from the engines which suck air in and force it out the back.

tim_enchanter · 20 Jan 2007 at 01:54

clv101 said:
No not at all, the wheels can spin forwards, backwards, any which way they like, the treadmill will match and the body of the plane will be forced forward by the engines, unimpeded by any other force.

Yep, going back to scams shopping trolley.

If you hold the shopping trolley on the conveyor and stand on solid ground next to it, you can run forwrd moving the trolley forward.
While doing that the conveyor and trolley wheels can go at any speed or direction they like, there is no way it can stop you pushing the trolley forward.
The same goes with the planes engines pushing against the air

Digital Punk · 20 Jan 2007 at 01:56

Jotun said:
Why on earth would the wheels of an airplane stuck in mud be rotating? Airplanes are not like cars, there is no power to the wheels, all the power is from the engines which suck air in and force it out the back.

Thats true. Told you I need sleep.

Macro · 20 Jan 2007 at 01:58

Scuzi said:
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.

I get hte 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 if getting you to understand the principles of flight and motion.

I understand them just fine. There's really no need to get rude about it...

In your terms I'll make it simple for you.

The wheels as you say allow it to move forward on the ground. As the treadmill is moving backwards the plane would (with no power) go backwards with the treadmill with the wheels stationary.

The egines of the plane however provide thrust to move it forward.

However in order for it to move forward the wheels must rotate faster than the ground is moving backward tomake positive progress (in the case of a normal runway it's no problem as the ground isn't moving)

The plane cannot move forward until it's foward speed, relative to that of the treadmill is positive.

The wheels must have friction against the ground to allow the plane to move forward.

This works for just the same reason as having square wheels wouldn't.

Unless the forward power of the plane can allow the wheels to rotate making progress forward along the runway the plane never moves through the air mass and therfore never generates lift.

As the treadmill moves backwards at the same speed the wheels rotate it never progresses.

Now if you were talking about just a freewheeling un powered treadmill you would be right as the power was not being applied through the wheels so you would just roll along the treadmill.

However the OP posted that the treadmill matches speed via a device so it must be powered.

See what I'm getting at?

Scuzi · 20 Jan 2007 at 02:01

Athanor said:
I understand them just fine, i'm afraid it's you that can't grasp the basic facts.

HAH HAH! I'm not even going to try any more. I admire your tenacity however

Athanor said:
See what I'm getting at?

I can see that your understanding is flawed. The speed of the aircraft relative to the treadmill is IRRELEVANT.

I think I've said all that I can say in this thread. Have fun

Jotun · 20 Jan 2007 at 02:02

Athanor said:
The wheels as you say allow it to move forward on the ground. As the treadmill is moving backwards the plane would (with no power) go backwards with the treadmill with the wheels stationary.

If the wheels are stationary then the treadmill is stationary, so the plane will not be moving. Wheels have no bearing on the situation as you said earlier. As they freewheel there is little resistance transfered to the plane, so the plane could be on a sled on a huge block of ice and it would be the same.

jhmaeng · 20 Jan 2007 at 02:05

Athanor said:
I understand them just fine. There's really no need to get rude about it...

In your terms I'll make it simple for you.

The wheels as you say allow it to move forward on the ground. As the treadmill is moving backwards the plane would (with no power) go backwards with the treadmill with the wheels stationary.

The egines of the plane however provide thrust to move it forward.

However in order for it to move forward the wheels must rotate faster than the ground is moving backward tomake positive progress (in the case of a normal runway it's no problem as the ground isn't moving)

The plane cannot move forward until it's foward speed, relative to that of the treadmill is positive.

The wheels must have friction against the ground to allow the plane to move forward.

This works for just the same reason as having square wheels wouldn't.

Unless the forward power of the plane can allow the wheels to rotate making progress forward along the runway the plane never moves through the air mass and therfore never generates lift.

As the treadmill moves backwards at the same speed the wheels rotate it never progresses.

Now if you were talking about just a freewheeling un powered treadmill you would be right as the power was not being applied through the wheels so you would just roll along the treadmill.

However the OP posted that the treadmill matches speed via a device so it must be powered.

See what I'm getting at?

What you are saying would match perfectly what would happen to a motorcar with wings on a treadmill. However, we are talking about an aeroplane.

How do you suppose seaplanes manage to get off the water with no wheels?

clv101 · 20 Jan 2007 at 02:07

Athanor said:
The wheels as you say allow it to move forward on the ground. As the treadmill is moving backwards the plane would (with no power) go backwards with the treadmill with the wheels stationary.

Okay, try this. With no power the plane sits on the treadmill, you turn the treadmill on and the plane moves backwards.

I could stand on solid ground behind the treadmill, raise my hand and hold the plane in place. The treadmill moves, the wheels spin, my hand holds the plane in place. Yeah?

Now what if I was to push a little harder? The plane would move forward wouldn't it? Now what if the pilot lights the engines? I get a face full but the plane move forward, picks up speed and takes off.

Macro · 20 Jan 2007 at 02:07

You're missing the basic point that the treadmill is powered to match the speed.

If it was just an unpowered loop of treadmill you would be right as the wheels are not applying any forward force and so it would roll down the treadmill and the treadmill would never move (although obviously if they were powered wheels the treadmill would, allowing for friction, just spin out from under it).

With a powered treadmill however it's completely different, if you stopped being a smart**** long enough to think it through you'd see the two different scenarios.

The treadmill is powered rolling backwards at say 5mph so the plane needs to produce 5mph of forward speed just to stand still (relative to the air, and the ground outside of the treadmill).

With me yet?

clv101 · 20 Jan 2007 at 02:09

Athanor said:
You're missing the basic point that the treadmill is powered to match the speed.

No, my example includes that. Assume that and read it again.

Macro · 20 Jan 2007 at 02:09

clv101 said:
Okay, try this. With no power the plane sits on the treadmill, you turn the treadmill on and the plane moves backwards.

I could stand on solid ground behind the treadmill, raise my hand and hold the plane in place. The treadmill moves, the wheels spin, my hand holds the plane in place. Yeah?

No what if I was to push a little harder? The plane would move forward wouldn't it? Now what if the pilot lights the engines? I get a face full but the plane move forward, picks up speed and takes off.

Right, we're almost there

I agree with you except one thing...

As you push harder forward (increasing the planes forward speed) the treadmills motors increase the speed of the treadmill in the opposite direction to match so you end up with no net forward movement.

Been a while since I've done this stuff but hopefully you see what I mean there

tim_enchanter · 20 Jan 2007 at 02:10

Athanor said:
You're missing the basic point that the treadmill is powered to match the speed.

If it was just an unpowered loop of treadmill you would be right as the wheels are not applying any forward force and so it would roll down the treadmill and the treadmill would never move (although obviously if they were powered wheels the treadmill would, allowing for friction, just spin out from under it).

With a powered treadmill however it's completely different, if you stopped being a smart**** long enough to think it through you'd see the two different scenarios.

The treadmill is powered rolling backwards at say 5mph so the plane needs to produce 5mph of forward speed just to stand still (relative to the air, and the ground outside of the treadmill).

With me yet?

No I doubt he is because you are wrong

clv101 · 20 Jan 2007 at 02:11

Athanor said:
The treadmill is powered rolling backwards at say 5mph so the plane needs to produce 5mph of forward speed just to stand still (relative to the air, and the ground outside of the treadmill).

No, could you explane to me the difference between the wheels driving it (like a car) and the thrust from the engines driving it (like a plane)?

Macro · 20 Jan 2007 at 02:11

jhmaeng said:
What you are saying would match perfectly what would happen to a motorcar with wings on a treadmill. However, we are talking about an aeroplane.

How do you suppose seaplanes manage to get off the water with no wheels?

Err they still have to make progress against the sea current. If the seaplane was trying to take off against 30mph of sea current coming towards it, it would have to exceed that to get any nett forward motion to take off. Otherwise it's be going backwards at 30mph

Jotun · 20 Jan 2007 at 02:13

Athanor said:
As you push harder forward (increasing the planes forward speed) the treadmills motors increase the speed of the treadmill in the opposite direction to match so you end up with no net forward movement.

The key though is that the wheels can spin freely, this means there is no resistance on the plane from the treadmill. The speed of the wheels and treadmill are irrelevant, as there is no force on the plane as a result of them.

clv101 · 20 Jan 2007 at 02:13

Athanor said:
As you push harder forward (increasing the planes forward speed) the treadmills motors increase the speed of the treadmill in the opposite direction to match so you end up with no net forward movement.

Okay - so you agree that my hand could stop it rolling backwards? Yeah? And you agree that if I took my hand away it would continue to roll backwards, yeah? But you don't think that I could apply a little more presure than it took to hold it still and it would move forward?

tim_enchanter · 20 Jan 2007 at 02:14

Athanor said:
Err they still have to make progress against the sea current. If the seaplane was trying to take off against 30mph of sea current coming towards it, it would have to exceed that to get any nett forward motion to take off. Otherwise it's be going backwards at 30mph

Thats actually a bad example because the skis on the seaplane do not rotate freely, there is friction between plane and the sea. A normal plane has bearing which remove 99% of the friction/ forces between the plane and the treadmill

tim_enchanter · 20 Jan 2007 at 02:16

Sorry to quote myself but read this again

tim_enchanter said:
Yep, going back to scams shopping trolley.

If you hold the shopping trolley on the conveyor and stand on solid ground next to it, you can run forwrd moving the trolley forward.
While doing that the conveyor and trolley wheels can go at any speed or direction they like, there is no way it can stop you pushing the trolley forward.
The same goes with the planes engines pushing against the air

jhmaeng · 20 Jan 2007 at 02:18

Athanor said:
As you push harder forward (increasing the planes forward speed) the treadmills motors increase the speed of the treadmill in the opposite direction to match so you end up with no net forward movement.

Theoretically, the wheels of an aeroplane can spin as fast as they want, without the plane moving. No energy is transferred to/from the wheels to the rest of the mass of the plane, except for the unavoidable inherent friction of the wheels. If the wheels were truly friction-less, the plane itself will absolutely not move even if the treadmill was moving at 100mph+. But even the friction of the wheels becomes negligible once the initial resistance of the friction is overcome.

Unless you're trying to insist that take-off power is provided by the wheels, I'm just failing to see how you can insist that a treadmill on the ground, which theoretically only affects the wheels and not the mass of the plane itself (and providing very little energy transfer in practice) can prevent the thrust of the engine (that is powered highly enough for the entire mass of the plane, and have nothing to do with driving the wheels) from starting to move the plane forward, irrespective of how fast the wheels are spinning on the ground.

But as Scuzi said already, I fear I'm wasting precious sleeping time, so I'll leave it to some other hapless soul to keep trying.