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Title: Brainteaser: There's an airplane on the runway..
Source: Elsewhere
URL Source: http://www.someplaceelse.com
Published: Dec 1, 2005
Author: I have no idea
Post Date: 2005-12-01 01:10:02 by Jhoffa_
Keywords: Brainteaser:, airplane, runway..
Views: 1086
Comments: 202

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation. There is no wind.

Can the plane take off?

Post Comment   Private Reply   Ignore Thread  

"It doesn't matter what the ground is doing with respect to the wheels, because the wheels don't propel the craft down the runway."

Bingo. Give that man a happy face.

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:22:23 ET  Reply   Trace   Private Reply  

"...All engine power would be merely transferred to the conveyor belt through the wheels ..."

What? How do you figure?

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:27:33 ET  Reply   Trace   Private Reply  

does the weight of the fly count in the total weight of the aircraft?

yep

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:28:47 ET  Reply   Trace   Private Reply  

I doubt that would be much of a factor.

me too

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:30:02 ET  Reply   Trace   Private Reply  

The plane would have forward motion thanks to the thrust caused by the engines.

there it is

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:31:53 ET  Reply   Trace   Private Reply  

I misread that earlier, the plane would be stationary

and, you've misread it again

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:34:17 ET  Reply   Trace   Private Reply  

Where's this runway at.

that's not near as important as the color of the plane and whether it is being hijacked

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:38:21 ET  Reply   Trace   Private Reply  

In this hypothetical, increasing thrust of the engines would only translate into higher wheel and conveyor belt counter rotation.

nope, you missed it entirely, embarrassing, very embarrassing

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:41:12 ET  Reply   Trace   Private Reply  

he plane wouldn't care about little spinny wheels and would shoot off into the air

and now the plane has feelings

what if the plane just said, I DON'T WANT TO FLY

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:45:45 ET  Reply   Trace   Private Reply  

There are too many unaccounted-for factors for this to be a classic brain teaser.

Nope. The question is complete.

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:50:20 ET  Reply   Trace   Private Reply  

he plane would have forward motion thanks to the thrust caused by the engines. That is, BTW, very true ONCE AND ONLY AFTER a plane is airborne.

wrong, thrust moves it forward and the plane lifts off once air speed is sufficient

give it up, it's starting to hurt

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   1:54:36 ET  Reply   Trace   Private Reply  

if it used a high bypass turbo fan jet for it's propulsion, as is typical for jetliners, the answer is never,

wrong

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:00:20 ET  Reply   Trace   Private Reply  

A jet would throttle up and not give a damn about what the tires were thinking.

tires were thinking

as you all know, tires don't think until they reach terminal velocity

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:03:28 ET  Reply   Trace   Private Reply  

get some bottlerockets and visit your local supermarket

good image, gets to the point, thanks

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:05:54 ET  Reply   Trace   Private Reply  

sad, very sad

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:08:14 ET  Reply   Trace   Private Reply  

The bottle rockets would fly, no matter what the conveyor was doing. They are a self contained control system. The propellent contains an oxident. Thrust here is independent of external conditions.

oh, my God

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:10:32 ET  Reply   Trace   Private Reply  

How would sitting on conveter belt with wheels spinning be different from idling on tarmac

nice, clean, clear

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:12:15 ET  Reply   Trace   Private Reply  

And anyway, back to the question: if this plane could take off on a moving conveyor belt, we shouldn't need runways at all.

think of the poor souls who will agree with this

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:17:03 ET  Reply   Trace   Private Reply  

watch me take a airboat up a particularly wide escalator

that sells, I'm with ya

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:19:29 ET  Reply   Trace   Private Reply  

it all makes perfect sense

what patience and restraint you show, I'm impressed

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:23:24 ET  Reply   Trace   Private Reply  

I should have stopped at shooting bottle rockets at grocery clerks, but what do I know?

I'm going back to repetition. Making fun isn't fun anymore.

The plane will fly because it pushes against air in order to reach lift speed in contrast to a car which would push against the conveyer belt which never allows it to move forward. The car spins it's wheels in place and the plane moves forward.

Best analogy... a bike and a bottle rocket. No matter how fast you peddle the bike the conveyer belt negates the forward motion. Yet, the bottle rock on wheels or not, is out of here.

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:32:51 ET  Reply   Trace   Private Reply  

There is a force applied by the thrust of the engines to propel the plane forward. Where is the opposite force to counter it and hold the plane motionless?

I like it. You can't argue with it or...

I've been keeping score and some of you folks are sad, real sad.

Just goes to show you how forums are not a good place to persuade. No matter how much explanation, logic, patience and repetition of same, folks stick to their guns. Did anyone here change their mind? No progress was made. Yet, there is a correct answer to the question. The plane does fly. No doubt, absolutely a fact. It will fly. It's not a matter of opinion. It's a fact.

Lesson to be learned: You may have the right to your opinion but, isn't it more important that your opinion be right? Isn't truth more important than ego? Isn't right more important than wrong?

Now, let's go one more round and work towards a consensus.

Their coming to take me away, ha ha

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:47:28 ET  Reply   Trace   Private Reply  

Forgive me. They're coming to take me away.

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   2:53:05 ET  Reply   Trace   Private Reply  

Now, let's go one more round and work towards a consensus.

Well, we could hang a "Mission Accomplished" banner from the control tower.

I'm not helping our case, am I? Sorry about that. ;)

When prosperity comes, do not use all of it. - Confucious
The nation is prosperous on the whole, but how much prosperity is there in a hole? - Will Rogers
There are 9,000 hedge funds out there. There aren't that many smart people in the world. - Michael Driscoll, a trader at Bear Stearns & Co. in New York
Some days you just want to pull out the Bonehead Stick and beat people senseless. - mirage

markm0722  posted on  2005-12-02   3:25:14 ET  Reply   Trace   Private Reply  

Clever.

Mission Accomplished fits, though.

It's a lie that will send most to another issue.

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup  posted on  2005-12-02   3:37:15 ET  Reply   Trace   Private Reply  

Interestingly, the place I first saw this question posted did not have a answer. Actually, that's part of the reason I posted it... because there was such a debate over it.

IMO, Yes.. The plane will fly.

As markm0722 pointed out above, it's generating thrust.

If you make 100,000lbs of thrust, where does it go? You can't destroy it, that's impossible.

You're not expending it on the runway, because the wheels don't drive. You're not burning it up with friction, either.. as that's not mentioned. Perfect hypotheticals here.

It's obviously going into forward motion. The wheels rotating (forcing the conveyor to match speed) is proof that the plane is indeed moving forward and regardless of what the conveyor is doing.

Dubya to the serfs: "It's Raining!"

Jhoffa_  posted on  2005-12-02   7:20:27 ET  Reply   Trace   Private Reply  

But if they had jet engines powerful enough and planes able to withstand the skidding, then it would take off.

Therein lies a problem made by many: confusion and/or equating the behavior/actions of solid fuel or liquid fuel rocket engines WITH turbofan gas turbines. Jets have the latter. Two extremely different propulsion systems-- two totally different engines.

Why should we hear about body bags and deaths. Oh, I mean, it's not relevant. So why should I waste my beautiful mind on something like that? -- Big Mama Bush

wbales  posted on  2005-12-02   8:03:31 ET  Reply   Trace   Private Reply  

The wheels rotating (forcing the conveyor to match speed) is proof that the plane is indeed moving forward and regardless of what the conveyor is doing.

The wheels rotating (forcing the conveyor to match speed) is proof that the plane is indeed transferring engine thrust to the conveyor belt while the plane remains stationary. Forward movement in a jet on the ground is created by friction between the ground and the tires. Remove that friction and no forward movement.

Again, jet planes DO NOT have rocket engines. High bypass turbofans DO NOT behave like rocket engines.

Why should we hear about body bags and deaths. Oh, I mean, it's not relevant. So why should I waste my beautiful mind on something like that? -- Big Mama Bush

wbales  posted on  2005-12-02   8:18:59 ET  Reply   Trace   Private Reply  

Again, jet planes DO NOT have rocket engines. High bypass turbofans DO NOT behave like rocket engines.

But it could be a window fan, so far as that goes.

It's making thrust, that's all that matters.

Dubya to the serfs: "It's Raining!"

Jhoffa_  posted on  2005-12-02   8:25:04 ET  Reply   Trace   Private Reply  

Forward movement in a jet on the ground is created by friction between the ground and the tires.

No it isn't, it is created by thrust from the jets. There are no drive motors for the wheels.

And I'm optimistic. See, I think you can be realistic and optimistic at the same time. I'm optimistic we'll achieve -- I know we won't achieve if we send mixed signals. I know we're not going to achieve our objective if we send mixed signals - gwbush

Dakmar  posted on  2005-12-02   8:29:52 ET  Reply   Trace   Private Reply  

Forward movement in a jet on the ground is created by friction between the ground and the tires.

Forward movement in a jet on the ground is impeded by friction between the ground and the tires.

I does not matter in the least whether the craft in question is a jet turbine, a turbofan, a pulse jet or a rocket. Wheels or skids or any other gear that serve to support an aircraft while it approaches takeoff speed only burn up energy or momentum. They do not transmit it.

They ain't no driveshaft on a 777.

randge  posted on  2005-12-02   8:34:33 ET  Reply   Trace   Private Reply  

I know I've been on jets that were able to utilise their engines for taxiing, don't tell me they are helpless if they come to a complete stop, I know better.

Of course. Not helpless, just inefficent.

tom007  posted on  2005-12-02   9:22:32 ET  Reply   Trace   Private Reply  

The bottle rockets would fly, no matter what the conveyor was doing. They are a self contained control system. The propellent contains an oxident. Thrust here is independent of external conditions.

oh, my God

Adolf Hitler... "What luck for rulers that men do not think."

John F. Kennedy... "Those who make peaceful revolution impossible will make violent revolution inevitable."

wakeup posted on 2005-12-02 02:10:32 ET Reply Trace Private Reply

Care to elaborate? Remember, we are talking about an air breathing engine here. By the way, I am using "Areospace Propulsion" by Dennis Sheppard, 1972, Cornell University, as my source.

tom007  posted on  2005-12-02   9:43:03 ET  Reply   Trace   Private Reply  

I'm back to my original conclusion that the plane in this scenario could not fly since it would not be moving. If the conveyor belt is turning at exactly the same speed as the wheels, then by definition the plane is standing still and thus could not get airborn. Of course this could never happen, but that's the way the question is phrased.

And I'm optimistic. See, I think you can be realistic and optimistic at the same time. I'm optimistic we'll achieve -- I know we won't achieve if we send mixed signals. I know we're not going to achieve our objective if we send mixed signals - gwbush

Dakmar  posted on  2005-12-02   10:35:04 ET  Reply   Trace   Private Reply  

The thrust from the engines will move the plane forward unless there is sufficient friction on the ground to offset the force. There is no indication in the question that this is the case. Thus, the plane will move forward.

Assuming the wheels maintain contact with the belt and the belt is moving in the opposite direction, the rate of rotation of the wheels is a function of the speed of the plane + the speed of the belt. Therefore, there is a flaw in the assumptions because it is impossible for the conveyor belt to move as fast as the wheels once the plane starts moving forward.

So perhaps, the trick answer is that the belt, in attempting to match the wheel rotation speed accelerates to infinity causing the wheels to fall off and the plane to crash.

Soren  posted on  2005-12-02   10:40:14 ET  Reply   Trace   Private Reply  

How does a multi-ton object become air born when it has no upward force being applied? The only way it could move forward is if it skidded down the runway and took off that way.

Moving forward generates the lift required to climb, of course.

Since the plane is not thrusting against the belt, but against the gases being expelled by the engine, it would accelerate.

On further thought, though, the only way the plane could move forward is if the wheels turned fasted than the conveyor belt, and the operation of the belt would make that impossible.

Ergo, as soon as thrust was applied, both the belt and the wheels would accelerate to an infinite speed, at which time the wheels, and probably the belt would both instantly explode, killing everyone and making the question moot. At that point the question would need to be redefined.

Pinguinite for Pinguins

Neil McIver  posted on  2005-12-02   12:09:27 ET  Reply   Trace   Private Reply  

Ya beat me to the punch.

Pinguinite for Pinguins

Neil McIver  posted on  2005-12-02   12:10:27 ET  Reply   Trace   Private Reply  

LOL. Amazing how similar our thought processes were.

Soren  posted on  2005-12-02   12:17:01 ET  Reply   Trace   Private Reply  

Think of running on ice--there is no traction--no friction to create forward movement despite a lot of thrust. Or think of a car wheel spinning on ice-- lots of thrust--no forward motion.

You are still making the incorrect assumption that an airplane moves forward the same way a car does, by turning the wheels against the ground.

If I were standing on ice and had a jetpack on, it wouldn't matter if my feet couldn't get any traction. If my car had jato jets strapped to the trunk, I wouldn't even have to put it in gear to move forward.

Airplane wheels don't produce thrust. They're just along for the ride.

"Liberty is the solution of all social and economic questions." ~~Joseph A. Labadie

Mr Nuke Buzzcut  posted on  2005-12-02   13:49:03 ET  Reply   Trace   Private Reply  

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