A Riddle To Do Your Head In...

Slither · Post by **Slither** » Fri Nov 25, 2005 9:08 pm

Pinched from another forum

"A plane is standing on a runway that can move (some sort of conveyer belt). 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 opposite direction).

The question is:

Will the plane take off or not?"

SchumieFan · Post by **SchumieFan** » Fri Nov 25, 2005 9:14 pm

um........ no? same as running on a treadmill?

dimi · Post by **dimi** » Fri Nov 25, 2005 9:16 pm

lol, here goes nothing

Its probably something like planes can't stand or something.

But, my guess would be because the belt is going in one direction at the same speed this would not affect the speed of the plane as the wheels will be spinning at more revolutions per second or something, allowing it to take off.

SO my answer is yes it will take off, now tell me im a dummy and tell me the real answer

dimi · Post by **dimi** » Fri Nov 25, 2005 9:18 pm

SchumieFan wrote:um........ no? same as running on a treadmill?

yes but feet dont exactly work like wheels

Post by **kazbah** » Fri Nov 25, 2005 9:30 pm

I'm going to throw my two cents in here.... No it wouldn't cos in essence the plane is standing still.... The thread mill is going in the opposite direction to the tyres at the same speed therefore nullifying any movement... phew!

PaddyOFurniture · Post by **PaddyOFurniture** » Fri Nov 25, 2005 9:47 pm

This could make airports a lot smaller

SchumieFan · Post by **SchumieFan** » Fri Nov 25, 2005 9:52 pm

air plane wings need air pressure to give themn lift, no air rushing pastr the wing, no lift! even if the wheels r moving.

IE a car on the dyno.... its rear wing isnt pushing itr to the ground case theres no air rushing past it... case closed

Teania · Post by **Teania** » Fri Nov 25, 2005 9:53 pm

hmmmmm

You do pose interesting questions.....

Planes usually take off into a headwind as they require lift to become airborne. If the treadmill was going the same speed (but the opposite way) to the plane - technically the plane wouldnt be moving forward so it wouldnt be going against the wind so couldnt gain lift and wouldnt take off....

but then again....

Roberts 2 cents coming in - Planes are not driven by their wheels - they have engines that move air.... so if you look at something like the harrier jump jet - doesnt matter if the wheels move or not

.....

oh I dont know!!!!! Too hard!!!!

PaddyOFurniture · Post by **PaddyOFurniture** » Fri Nov 25, 2005 10:00 pm

A jet engine does not move the wheels - it flys through the air around it - so if the air is being moved at proper take off speed - it WILL take off.

And the ground under every plane on the planet is moving east for example at thousands of km an hour Can a plane take off headed West?

BuCkEt · Post by **BuCkEt** » Fri Nov 25, 2005 10:09 pm

The air plane could take off......get to a high speed on the treadmill and then just raise the landing gear.

EDIT: Actually, no that doesn't make sense.

If the plane's flaps are down ( ie providing lift) then once the engines reach a high enough turbine speed the thrust would lift the plane up.

Double EDIT: Oh shizzle, I've reached 1k posts and I didn't even notice!

Post by **kazbah** » Fri Nov 25, 2005 11:03 pm

LOL I love the edits and the double edits.... but have we reached a consensus yet

scarecrow · Post by **scarecrow** » Sat Nov 26, 2005 8:20 am

The plane would take off

Unless the brakes are applied the wheels spin freely, they'd just be spinning at twice the normal rate before the plane has enough forward momentum to take off.

It's like putting a car in neutral and towing it across a treadmill going in the opposite direction. The car would still be moving because it is being towed, but the wheels would be spinning twice as fast.

scarecrow · Post by **scarecrow** » Sat Nov 26, 2005 8:23 am

Neglecting friction that is

It would take slightly more thrust to push the plane that bit faster. Remember at a standstill the conveyor is at a standstill, but once it starts moving because of the planes weight the motion of the wheels would retard it's ability to reach full speed, until of course the plane is subject to slight lift, in which case the friction between the wheels and the tarmac would dissappear.

Post by **Bennoz** » Sat Nov 26, 2005 10:04 am

The plane wont go anywhere.

Planes fly because of pressure differences on the top and bottom of the wing - caused by air passing the specific shape of the wing at speed:

The low pressure caused by the air passing at speed over the shape, must be equalized, causing the high pressure below the wing, therfore causing lift. All plane engines do is get the plane moving forward quick enough to create that pressure unbalance.

Heaps of wizz bang formulas to work it out.

Next time you have a dead bird in your back yard (and if your feeling like a 'scientist') cut its wing in half cross sectionally. You find that the shape will be very similar to the above picture. They get flight by flapping, causing the air to pass their wing shape at speed.

Sorry to waffle on & sound like a sick fcuk cutting up birds! I struggled through 6 months of aeronautical engineering at uni.

ahew · Post by **ahew** » Sat Nov 26, 2005 12:34 pm

umm.. agree with Bennoz. plane will not be able to take off as there is no air velocity to create lift over the wings which is the whole basis for being able to fly in the first place.

sure the wheels on the tarmac are spinning, but it's sorta like saying "i can get from 0-100kmh in 1 sec" yeah.. you'll be doing a burnout on the same spot for ages with the needle shooting past 100km/h but in actual fact an old man in a mobility chair is moving faster than you (he's got more chance of flying too!). it's great if you like your wheels to rotate very fast though

Post by **Supplanter** » Sat Nov 26, 2005 5:46 pm

The wheels on the plane are free-wheeling, therfore the plane will take off

The wheels will probably spin twice as fast but the plane will still be moved forwards by the thrust of the engines

What do I win?

[edited because this flu is making my brain wonky]

akuma3 · Post by **akuma3** » Sat Nov 26, 2005 6:12 pm

don't make me think on a weekend dammit, it won't fly

how about answer now?

ahew · Post by **ahew** » Sat Nov 26, 2005 6:40 pm

the plane will not be able to move forwards as there is no friction on the ground (between tyres and ground) to create any forward movement. the "conveyor belt" basically means there is no friction. no forward movement people! means no thrust (hehe... thrust) - no nothing, and especially no lift. it's dead simple.

afterburner · Post by **afterburner** » Sat Nov 26, 2005 7:37 pm

Seems pretty simple to me. The plane is essentially standing still, so there is no airflow over the wings. No airflow, no lift, no flight. So it won't go anywhere.

I've also done a bit of aeronautical engineering, but I still can't get the g/f to understand why planes take off into a head wind

Post by **Supplanter** » Sat Nov 26, 2005 8:37 pm

The engines suck air through them and push the air out at a faster rate to make the plane move, they do not drive the wheels.

Stick a fire cracker on a matchbox car, borrow your Dad's belt sander and do the experiment yourself