Aeroplane on a conveyor belt puzzle

[Yenn]

Re Kens comment about time to take off heading East or West. It gepends upon wind velocity'

 

 

[Ultralights]

yes. it will take off at normal speed, as the prop drives it through the air...

 

just as a seaplane does on floats. the prop and wing dont care about whats under the wheels..

 

 

[slartibartfast]

yes. it will take off at normal speed, as the prop drives it through the air...just as a seaplane does on floats. the prop and wing dont care about whats under the wheels..

Glad you brought that up. What about chocks. The prop and wing care if it's chocks under the wheels. Will it take off anyway? That's exactly the effect of the postulated conveyor. The aircraft wants to move forward but can't. Nett effect - no ground speed, no airspeed, no take-off.

 

 

[Sky Gazer]

Yes guys I'd have to agree -the thrust acts to propell the AC down the runway/converoy belt and not through the wheels -they simply reduce rolling friction.

 

Peter

 

 

[Deskpilot]

Back to the original question. I don't often say this but I was wrong.:confused: Of coarse it can take off, and the wheels will rotate a lot faster than normal. In fact it's because it has free spinning wheels that make it possible. They are the interface, the oil if you like, between the plane and the conveyor. If it were a car where the wheels are driven, then it would stay where it is as on a Dyno test rig, or the same as a person running on a frictionless, unpowered tread mill. With the plane, the prop pushes or pulls the plane forward, the runway speeds up to the equal and opposite speed and the wheels take up the difference by rotating twice as fast as normal. The old grey matter takes its time nowadays but gets there in the end.:big_grin: Well done to those who got it right first time.

 

Now, about that bolt falling out of your main wheel..............

 

 

[Deskpilot]

Back to the original question. I don't often say this but I was wrong.:confused: Of coarse it can take off, and the wheels will rotate a lot faster than normal. In fact it's because it has free spinning wheels that make it possible. They are the interface, the oil if you like, between the plane and the conveyor. If it were a car where the wheels are driven, then it would stay where it is as on a Dyno test rig, or the same as a person running on a frictionless, unpowered tread mill. With the plane, the prop pushes or pulls the plane forward, the runway speeds up to the equal and opposite speed and the wheels take up the difference by rotating twice as fast as normal. The old grey matter takes its time nowadays but gets there in the end.:big_grin: Well done to those who got it right first time.

 

Now, about that bolt falling out of your main wheel..............

 

 

[Deskpilot]

oops, sorry, double posted Doug

 

 

[slartibartfast]

This is getting a little frustrating.

 

How about if we scale it down.

 

Picture a model plane sitting on an exercise treadmill. We can control the speed of the treadmill.

 

Now fire up the model plane. As you see it move forward, increase the treadmill speed so it can't. Pretend you can control the treadmill so well, that you can keep the model plane exactly in the middle of the treadmill length, no matter what it tries to do. Now imagine the air it is sitting in. You are in a room, so there's no wind. Is the air moving over the wings any faster? Remember the air is not affected by the treadmill, except for a little surface friction. The wings are not moving through the air in the room, they remain still in relation to it.

 

What do you think now?

 

I reckon that unless the surface friction moves the air enough to pass over the wings more than min flying speed, it ain't going anywhere.

 

That's the problem with the "earth is one big conveyor belt" theory. The air is moving with the earth also at 900 knots more or less. With our runway conveyor, the air isn't moving with it.

 

Ross' last effort.

 

 

[Guest pelorus32]

Ross,

 

sorry to say this mate but ahhhhh you are lost in extraneity:cool:

 

Forget about the air moving, forget about the earth turning - we're all flat earthers here.

 

The only thing that the conveyor belt affects is the wheels of the a/c. Those wheels are free to spin, so with the tiniest amount of propeller thrust (to overcome friction in the wheel-conveyor interface and in the wheel bearings) the aircraft will stand still on the conveyor belt. The thrust required will hardly change with the speed of the conveyor. So then any additional thrust will be used to move the aircraft down the conveyor belt at the speed necessary to get enough lift to put you into the air.

 

Voila the a/c flies - the conveyor is near enough to an irrelevance.:;)3:

 

Kind regards

 

Mike

 

 

[hihosland]

Imagine a tethered aircraft at full power.

 

It is not going anywhere. All the energy is going into stretching the tether. Cut the tether and the plane will shoot forward until it reaches flying speed and fly away.

 

Imagine same situation with the wheels on the hypothesised conveyor belt.

 

If the tether is cut where is the energy going to go that launched the plane in the above example if it is not going to accelerate the plane?.

 

The plane will fly.

 

That’s what aeroplanes do.

 

Davidh

 

 

[Guest Ken deVos]

Re Kens comment about time to take off heading East or West. It gepends upon wind velocity'

Hi Ian

 

We have all assumed a 'no wind' situation. However, to add more fuel to the argument that the aircraft will fly... lets consider the headwind that would be created by the friction layer of the high speed conveyor belt.

 

 

[Deskpilot]

Ross, sorry to have swapped sides but let me attempt to explain in more detail. The plane moves forward a fraction, at a given rate. The conveyor reacts by moving in the opposite direction at the same rate. The wheels revolve but the plane is not pushed back to its original point because the thrush won't allow it, the conveyor just moves under it. The plane moves forward again. the conveyor react, the wheels turn but again the plane connot be pushed back due to the freely revolving wheels. Now, the plane moves again and so on. Its speed increases, as does the conveyor and the wheels turn faster. At no time can the plane be pushed backwards by the conveyor because there's no fixed, mechanical connection between the conveyor and the plane. The wheels are only holding the plane off its fixed axiles.Eventually the plane has enough speed to take off. I hope this helps. Doug

 

 

[Guest Nomad]

Whew. I was worried for a while that this thread wouldn't "take off"

 

The answer is that the plane CAN take off. The plane moves forward (relative to some stationary external observer, just as normal. In still air its speed will be shown on the ASI). The conveyor belt responds by moving in the opposite direction. As several people above (tonymcg, brentc, hiperlight, Teenie2, Ken deVos, Yenn, Ultralights, Sky Gazer, pelorus32 and Deskpilot - apologies to those I missed) have pointed out, this merely results in the wheels spinning faster (twice as fast, to be precise) than normal. That's what the wheels on an aeroplane are for - to reduce the friction between the ground and the plane towards zero.

 

The intuitive error many people make is to 'feel' that it's like a dyno - and that the speed of the aircraft is relative to the treadmill, giving an absolute or real speed of zero. Hopefully people can see that that leads to a logical absurdity: If the plane is stationary because the moving belt is cancelling its speed out, then shouldn't the belt (which is matching the speed of the plane) be stationary too?

 

The question is very sensitive to the way it's interpreted - and I've been really careful in the way I've phrased it. I've seen it written sometimes with ambiguous phrases like "...matches the speed of the wheels". Which is a recipe for debate disaster. The best example I've seen of an argument over this question was on another forum where the thread ran to over 230 pages.

 

Glad you all had fun with it, and mega-props to Deskpilot for leaving the Dark Side for the cause of Justice and joining with the "can take off" team. ;)

 

 

[slartibartfast]

Well that was fun.

 

Glad I could play Devil's advocate so completely.

 

Thanks for the explanation too Doug. It makes sense in a way, but I'm still not completely convinced. I want to try my model on a treadmill test. I'll get back to you. "logical absurdity" is my middle name.

 

But yeah - I can see that you can try to speed up the treadmill, but there's nothing for it to act on. The wheels just spin faster. Funny how the brain works. I thought I could see exactly what was going on.

 

Next!

 

 

[BigPete]

I'd just like to say..............

 

There are no bones in icecream!!!

 

regards

 

 

[Admin]

and no nuts in donuts...

 

and steam rollers don't roll steam :big_grin:

 

 

[Ben Longden]

Hark back to the heady days of James Watt, his bretheren and decendants!

 

Steam Rollers USED to steam... they were powered by coal or wood. ;)

 

Ben

 

 

[rick-p]

What colour is the aeroplane?

 

This is a very important factor as everyone knows that unless it is red it will not take of.

 

Red makes it go faster.

 

You have all said so in other threads.

 

 

[rick-p]

Sorry I meant OFF not of because of is not going anywhere.

 

 

[Guest Maj Millard]

OK, If your flying along at the speed of light, and you switch the landing light on, would it work ??..........................................................................................................

 

 

[Captain]

OK, If your flying along at the speed of light, and you switch the landing light on, would it work ??..........................................................................................................

Yes it would work .... if the switch is good, the globe is in tact, the battery is charged the circuit is in good nick and the circuit breaker isn't tripped.

 

But would it be seen from a position in front?

 

Or would it leave a trail of light particles streaming out behind?

 

 

[Yenn]

My theory is that if I can exceed the speed of light, I can turn around and see myself coming. Rather after the reasoning that the military decided not to use the Concorde, if they fitted it with guns which fire slower than the plane flies it would shoot itself down.

 

 

[facthunter]

What?

 

You can't be serious about that last comment, can you Yenn? When the bullet is fired the charge adds energy to the bullet. It already has kinetic energy due to the planes motion, so it will move away from the aircraft forward of it. That is normal Newtonian physics. Those rules do not apply where the speed of LIGHT is concerned. Nev

 

 

[Powerin]

OK, If your flying along at the speed of light, and you switch the landing light on, would it work ??..........................................................................................................

Actually (according to Einstein) it's impossible to travel at the speed of light because it takes an infinite amount of energy to go that fast.

 

BUT if Maj was on final to the airport going 99.9% of the speed of light (!) and switched on his landing lights he would see the beam travelling away from him at the speed of light. Even though he's already at 99.9% and nothing can go faster than light, the light will still travel forward at the speed of light from his perspective.

 

However the good Captain, waiting to takeoff at the airport, would see the same beam of light travelling towards him also at the speed of light...not at the speed of light plus 99.9% that Maj was travelling at.

 

So yes, your landing light would work.

 

Does your brain hurt yet? :baldy: Ok I'll stop now...I know I'm a nerd

 

Peter

 

 

[Guest eland2705]

Yep! My brain hurts!

 

Owch.