Aeroplane Riddle

[Resolve]

Come on B. Piers! Don't throw a grenade and watch! What's your opinion?

[Sledgehead]

This was always my position.

no airflow over the aerofoil == no lift.

I think what is on the tip of other poster's tongues is: Bernoulli's principle!

yeah, right

[twatmangle]

Do I win a prize?

Mythbusters

http://www.youtube.com/watch?v=IbRcg3ji_Pc

[daniel stallion]

yeah, right

?

They were talking about Bernoulli's principle (even if they didn't know it). My next post pointed out that the equivalent air time (which is NOT the same thing) was a fallacy.

[Sledgehead]

?

They were talking about Bernoulli's principle (even if they didn't know it). My next post pointed out that the equivalent air time (which is NOT the same thing) was a fallacy.

Yeah, well, my next post after my windtunnel foray got it right too, so, like I say, don't act so smug

[daniel stallion]

Yeah, well, my next post after my windtunnel foray got it right too, so, like I say, don't act so smug

I have no idea what you are accusing me of, but okay fine - I won't. Well done. Sorry. Whatever.

[Sledgehead]

I have no idea what you are accusing me of, but okay fine - I won't. Well done. Sorry. Whatever.

Don't mind me.

I've just realised something while filling the bath: I hate riddles because they test the opposite of knowledge.

I reckon all riddles are composed by people who studied english language or lit and are pissed that they don't understand anything technical, so they construct problems designed specifically to reel in those who have a grasp of a particular technical field. Then, after those poor techies have laboured and fretted an come up with a solution they say "er, no idiot, actually you are wrong", when those people aren't wrong, they were just too eager to chew over a problem. What they weren't expecting was some semantic twist that turned the whole exercise into a game of comprehension.

So there's my theory: riddles are written by non tech people who have a frikkin great chip on their shoulders and wanna catch out the kids who always made them look stupid in class.

[daniel stallion]

Don't mind me.

I've just realised something while filling the bath: I hate riddles because they test the opposite of knowledge.

I reckon all riddles are composed by people who studied english language or lit and are pissed that they don't understand anything technical, so they construct problems designed specifically to reel in those who have a grasp of a particular technical field. Then, after those poor techies have laboured and fretted an come up with a solution they say "er, no idiot, actually you are wrong", when those people aren't wrong, they were just too eager to chew over a problem. What they weren't expecting was some semantic twist that turned the whole exercise into a game of comprehension.

So there's my theory: riddles are written by no tech people who have a frikkin great chip on their shoulders and wanna catch out the kids who always made them look stupid in class.

[Britney's Piers]

Don't mind me.

I've just realised something while filling the bath: I hate riddles because they test the opposite of knowledge.

I reckon all riddles are composed by people who studied english language or lit and are pissed that they don't understand anything technical, so they construct problems designed specifically to reel in those who have a grasp of a particular technical field. Then, after those poor techies have laboured and fretted an come up with a solution they say "er, no idiot, actually you are wrong", when those people aren't wrong, they were just too eager to chew over a problem. What they weren't expecting was some semantic twist that turned the whole exercise into a game of comprehension.

So there's my theory: riddles are written by non tech people who have a frikkin great chip on their shoulders and wanna catch out the kids who always made them look stupid in class.

That's why they're called riddles. If they were to test knowledge they would just be called "questions".

Here's an explanation for the riddle http://www.straightdope.com/columns/read/2638/an-airplane-taxies-in-one-direction-on-a-moving-conveyor-belt-going-the-opposite-direction-can-the-plane-take-off

[Sledgehead]

snap!

EDIT : I've just realised that my radox bubble bath claims to have been formulated specifically to remove my stress. This has caused me more stress as I know this is pure BS. Just how f**ked up am I that a stress relief shampoo is causing me stress!!!!!

I blame 13 years of new labour

[Sledgehead]

That's why they're called riddles. If they were to test knowledge they would just be called "questions".

DOH!

Actually, following on from my (crazy and paranoid) assertion about riddles, what say we invent a few riddles specifically aimed at luring in english lit and lang students and then push them out over the net, just so as we can let 'em know it ain't all gonna be one way traffic!

Come to think of it, I bet a few politics students are behind these riddles too - you know, devious Mandy types, so maybe a few political riddles wouldn't go amiss.

[Snow Birds]

Yea, like duh, the summing up would be that the question is flawed. It is not possible to stop the plane moving forward with a moving runway. Good catch! Shoulda seen it.

[Sledgehead]

Yea, like duh, the summing up would be that the question is flawed. It is not possible to stop the plane moving forward with a moving runway. Good catch! Shoulda seen it.

Stop feeliong sorry for yourself and help me write some english lit / land / polics riddles. And religion too. Those lot hate techie sorts ever since they had to concede the world was spherical. Bet they are behind a good half of these "riddles". Fiends!

[Mikhail Liebenstein]

Yep, there's something in what you say, but if you'll forgive me, you haven't explained the issues.

The issue is this is a plane, so its forward motion on the tarmac comes not from surface traction but from air displacement through the prop / jet engine. The plane is not "gripping" the road surface at all during this process, so the conveyor's action is not relevant to producing a static plane. To make the plane static we need an "air conveyor", that negates the "gripping" of the jet engine / prop on the air. In otherwords, to get the plane to stay still, we need the air to flow through the engine / prop at the same speed it would normally flow though during applied power. Only then will the plane be "stationary". The belt is therefore a red herring. Of course, with air flowing through the prop / jet at the kind of speeds we are talking, and, assuming the same air is allowed to flow over the wings in the sam edirection, lift off is inevitable, so yes, the plane plane takes off.

I go for a yes. 

The plane itself moves by displacing air through the engines, not by rotating its wheels like a car. The plane will transfer momentum (equal and opposite) between itself and the gases it expels to generate thrust. The fact that there is a conveyor is almost irrelevant, as the wheels will simply just rotate twice as quickly covering twice the aggregate distance on the tread mill as they would on a runway - hopefully the tires hold out.

[Snow Birds]

Stop feeliong sorry for yourself and help me write some english lit / land / polics riddles. And religion too. Those lot hate techie sorts ever since they had to concede the world was spherical. Bet they are behind a good half of these "riddles". Fiends!

OK Oldie but goodie: A hunter makes camp and then walks five miles due South but finds nothing to shoot. He then walks five miles due West and shoots a bear. He then walks five miles back to camp to get his buddy and vehicle to retrieve the bear.

What colour was the bear?

[Guest Skinty]

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?

Yes. When I worked in an aerospace company in Southampton someone came up with this and it took them all a while to figure out.

The plane is not driving forward like a car through the turning of its wheels. It's being pushed forward by a jet and the air flow over its wings generates lift. Like a paraglider above your head when you're still standing on the ground is still flying.

[Snow Birds]

If air is being dragged over the wing the plane will lift. It is irrelevant whether the plane is on the ground or whether the ground moves or remains static, all you need is air moving over the wing.

Sort of but the point is the conveyor belt cannot stop the plane moving forward and the plane will take off normally.

[happy_renting]

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?

The plane moves. As long as it is fast enough( and forwards) , that's all you need to know.

The puzzle does not state that the moving conveyor negates, or in any way reduces, the forward motion of the plane. What the runway does underneath the plane is irrelevant.

[sigma]

Sort of but the point is the conveyor belt cannot stop the plane moving forward and the plane will take off normally.

Strictly speaking the belt can stop the plane moving by friction alone.

[acer]

OK Oldie but goodie: A hunter makes camp and then walks five miles due South but finds nothing to shoot. He then walks five miles due West and shoots a bear. He then walks five miles back to camp to get his buddy and vehicle to retrieve the bear.

What colour was the bear?

White.

[Snow Birds]

Strictly speaking the belt can stop the plane moving by friction alone.

No because the rolling friction of the wheels is not related to the speed, or at least only marginally. As long as the bearings and tires hold out, and that is likely because the plane will take off in normal time, then there is no extra friction from the wheels because of speed.

[Snow Birds]

White.

gold star

[Guest Skinty]

I used to have a reputation for taking off vertically in a paraglider like a Harrier. I'd be standing on the ground keeping the wing above my head and very gently pull down on the brakes until I could fly up vertically (the brakes convert the speed of the wing to lift). When I was about 20 - 30 feet high I'd then release the brakes and fly forward.

The reason I got the reputation though is because I learnt on a wing that was slightly too large for me and I'd do this in light winds when everyone else couldn't get off.

Trouble was that sometimes i didn't realise that I had left the ground because I was looking up at the wing.

[The Generation Game]

White.

Or transparent?

[happy_renting]

No because the rolling friction of the wheels is not related to the speed, or at least only marginally. As long as the bearings and tires hold out, and that is likely because the plane will take off in normal time, then there is no extra friction from the wheels because of speed.

But it is stated that the plane is moving. The conveyor moves in the opposite direction at the same speed. If the plane is moving forward at say 100mph, it is moving at 100mph, irrespective of whether the conveyor is stationary or doing -100mph.

If the moving conveyor were to slow the plane down, then the conveyor would also slow down, because it moves, by definition, at the same speed as the plane, but in the opposite direction.

The case where the plane is stationary, because of the conveyor, is only true if the conveyor is stationary, as it moves at the same speed as the plane.