Imagine a plane is sitting on a treadmill

@ parnell

If you're going to argue about it, do it here. Unless you're chicken of course.

Out of interest, I just did a Google on the phrases Plane on a treadmill and Plane on conveyor.

Have you any idea how many physicists are arguing around the world at any one time on this question???

There are some that have proved (with scaled apparatus) that the plane will not fly, there are others (with scaled apparatus) who have made the plane fly, and there are yet more who have worked out a conspiracy theory that the US DoD is spending billions on new conveyor belt technologies.

She is ALWAYS watching, from near and afar...
Just kidding, but this thread is like a car crash - I can't seem to look away...what's it about again?

At least the conveyor belt nonsense is realistic. What you describe is so far beyond reality as to not even merit discussion. What you are talking about could not even happen to the french.

@wheel, parnell sent me a PM on another, much larger, problem. On the plane thingy, we are in agreement: dat sheeit will not fly.

I think it's a continuation of the 'Personal Attacks R Us' theme.

boy u sure nailed me there ... woo hoo ... man am i ever your bitch... do u post on internet chat forums for money ? cos like u could... u and ur sharp wit and ur cunning and ability to back ur opponent into corners...all hail the King!

gideon,
I heard this problem posed in a slightly different way:

you're a major airplane manufacturer with a new ground breaking plane having past its prototype stage.
your order books are filling up and the break even is in sight.
unfortunatley, even though your engineers clearly reported that there were unresolved issues in the implementation the project management and marketing guys shut their ears and dismissed the risks.
you start to lose order and face massive delay payments. what do you do?

I vote we boil project management and marketing alive.

I still can't believe that Baddoggie hasn't come 'round! He is usually incredibly intelligent in his posts! (and I'm being sincere here, not sarcastic)

Next time you're at the airport, put your rolling suitcase onto the flat "people mover" but walk next to it going the opposite direction. The belt doesn't stop the suitcase from rolling, the wheels just have to move twice as fast. Even if the conveyor belt goes 3 or 4 times as fast as you are walking, your suitcase will match your speed.

Do we need a poll here?

@ parnell

Just popping up on this thread, saying 'it won't fly' and then going again is a bit sad though. Argue your point or shut up. Seems fair.

Oh C'mon kitty. That suitcase'll NEVER fly, you dumb c*nt.

Yeh that's the problem, people who don't have an understanding of physics and relying solely on personal intuition. Makes a fun discussion though, and personally I hope a few peopel have learnt a thing or two about physics. Otherwise I wouldn't bother posting.

And calling me "chicken" to snare me back into this cock circle of a thread is what exactly ?

No adi after this thread i say (tounge in cheek as i know a few of the engineers in hamburg)

unfortunatley, even though your engineers thought they clearly had reported that there were unresolved issues in the implementation the project management and marketing guys couldnt understand a bloody word they were on about and never knew there were any risky bits involved. apart from it crashing and being a bit more bendy in parts than the original computer simulation had shown. CEO went on holiday.

I believe we've all got that point kitty-kat. However, the question states, The conveyor belt is designed to match the speed of the plane exactly but moves in the opposite direction.. The speed of the wheels is never mentioned. Only the speed of the conveyor belt and the plane.

I think we're straying into the realms of conveyor-belt rage now.

OK fair enough, that was stoopid. I apologise.

oh its been fun quiet enjoyed it. if anything its shown a shocking ability for grease monkies to communicate in normal language to non-specialised people. and for non-specialised people's attention span to go further than ughhh. scary communications problems that.

EDIT apart from Silly Point, who below, after 38 pages has finaly made an understandable GM statement which didnt involve my brain going into overheat.

maybe it would fly...

Yes, yes. Now forget the jet and imagine a glider being pulled by a winch. The winch is reeling in the glider at 300mph (for example), so the conveyor belt is travellng at 300mph in the opposite direction. Will glider fly? Of course it will. Now replace winch with jet engine ...

@gideon

Assumption: The engineers used words instead of a traffic-light picture in their presentation to project management & marketing. This was where it all started to go pear-shaped...

Fiar fucks to ya boyo fer bein man enuff ta see it. Peace.

No, no, no. I agree fully with that statement. I'm playing Devil's Advocate a little here. In this interpretation the forward speed of the glider and the opposing speed of the conveyor belt are the same (300mph), so the glider is sliding along a surface at 600mph. No problem at all with that... unless the winching mechanism is also attached to said conveyor... and hurtling towards our glider at 300mph.

Do you see the conudrum now?

I expected that. No the winch is not attached to the conveyor. Neither is the jet engine.

Even the muppets that are trying to argue with the wording of the question, and have this theoretical zillion mile an hour conveyor - its still cock - cos the tyres will just not grip.

unless the winching mechanism is also attached to said conveyor

Sin, I think this is the crux of the matter. The difference is that the jets are not directly connected to the belt because they are free-wheeling and exert negligible drag through the bearings.

EXACTLY!

OK, (and I'm not trying to be rude) now you confused me.

I mean, the jets suck in air and provide forward thrust. What the wheels are doing has negligible effect on that forward thrust.

How is the atmosphere, against which the engines act, tied to the conveyor?

It isn't.

Sorry that was to Sin.

@Adi Lets just say each person talked his own language and didnt attempt to engage in active listening. engineers do not general use language understood by anybody else. Project management dont always understand exactly what problems have to be over come, and marketing rarely has a look in nor deceide your launch date. though your sales guys must have committed collective suicide after rereading the delay penalty paragraphs. The project was doomed from the time a certain CEO was hired who thought "but i didn't know of any problems" was a sufficient and adequate reply.

Yes, but a very normal way of measuring speed is at the tire. So not really dim witted to make that assumption. In fact Id say it a toss up how you assume the speed is being measured.

The problem with that is that the engines don't drive the wheels, they drive the whole plane forward.

It isn't.

Then how do you get to tying the winch to the conveyor?

I'd say that the speed should be measured by how far the plane moves from a static index point over a fixed period of time. The rotational speed of the wheels will depend on their diameter.

Going back to the original puzzle...

What would happen to the plane if there was a tail-wind which exactly cancelled out the air-speed of the wind going over the wings?

Is that how they produce those air-speed displays to keep you amused when your in a 747. They let the undercarriage down and see how fast the wheels spin?
Speed = distance travelled / time
in this case, because the ground is moving, the forward speed of the plane and the rotational speed of the wheels are different.

Airplane + conveyor belt = CRASH!



Case closed!

By the wit and charm of Devil's Advocacy.

Ah. Silly me.

if the "no fly" people want to dick around with random points of reference (Saying that the planes speed is measured relative to the conveyor belt) then I can do the same. For my new made-up scenario, I will say that the treadmills speed is measured relative to the plane. Therefore...

Planes Speed = 0 - treadmill speed = 0

Plane moves along at 10mph, treadmill stays still (As its moving at -10mph wrt the plane - exactly the same speed but in the other direction)

Plane moves along at 100mph, treadmill stays still (As its moving at -100mph wrt the plane - exactly the same speed but in the other direction)

Plane moves along at 300mph and takes off.

The fact is, no frame of reference was given for measuring the planes speed so in any scenario where simply a speed is given you should use the nutral frame of reference for the speed measurements.. which is what the "fly" people here are doing. Its the most logical way.

Sin.

I originally thought that it would fly. Seemed obvious to me, so I voted that way. Then I started to think some more and tied myself in knots with points which were not part of the scenario.

Key things:
1. Forward motion comes from the jets, which are not tied to the belt (they are separated by the free-wheeling wheels). This is fundamentally different than the scenario with a car, where forward motion is obtained through driven wheels and the friction from the tires on the ground.

2. Because forward motion is not related to what the wheels are doing, the jets are free to propel the aircraft (to which they ARE attached) up to it's take-off speed. The take-off speed required would be, I guess, very very marginally higher than if the plane was not on a belt moving in the opposite direction. So marginal, that other effects (such as prevailing head-wind speed, air-density, etc.) would be far greater.

Are you then saying that as it is the most obvious way, then therefore it is the most logical?

I think so.. It makes more sense than making up random arbritary frames of reference that were not posed in the original question... "you are in a car that is going 50mph, how fast are you going?"

But consider.. what is more logical, measuring the planes speed relative to the treadmill, or measuring the treadmills speed relative to the plane? They both sound just as (un)feasible yet both give entirely different outcomes (warp speed treadmills Vs non-moving treadmills). You choose

No, what he means is that whichever way you look at it that plane is going to fucking well fly!

Wot sort of 'plane is it?

How so? Is the conveyor belt powered by the car's wheels or some such nonsense?

For people who claim to know physics, ya'll fail miserably on this point.

We all know that using a GPS is the best way to measure speed accurately :-) BTW, what plane measures its speed through the wheels?