# Plane On A Conveyor Belt



## Guest (Jan 24, 2008)

Okay ... let's hear it - Fly or No Fly!

Poll closes at 8PM EST - 1 hr before the Mythbusters Show!

JR


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## cement (Jan 24, 2008)

I done been to the FAA Academy in OK City. Unless there is wind over the wing, it is a doorstop.


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## Desert Engineer (Jan 25, 2008)

My vote is that the plane will take off.

Since, the plane is not tethered to the ground, so it should only have to overcome the additional rolling resistance to take off. The only change should be that the wheels will roll at airplane speed plus treadmill speed. If the plane used its wheels to power the takeoff then you would have a problem.


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## cement (Jan 25, 2008)

the wheels are a distractor.


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## FusionWhite (Jan 25, 2008)

Desert Water said:


> My vote is that the plane will take off.Since, the plane is not tethered to the ground, so it should only have to overcome the additional rolling resistance to take off. The only change should be that the wheels will roll at airplane speed plus treadmill speed. If the plane used its wheels to power the takeoff then you would have a problem.


DING DING DING!!!! We have a winner! An elegant summary of why it will take off.


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## benbo (Jan 25, 2008)

Shouldn't we be having this discussion in the 5000 post thread?


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## SuperAlpha (Jan 25, 2008)

Thrust from the engines is what causes the plane to move. The moving air across the wing causes lift.

Now what part of that involves ground speed or wheel speed?

The wheels are there simply to keep it raised off the ground and able to roll.


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## Capt Worley PE (Jan 25, 2008)

The wheels and the treadmill would be moving at a furious rate!


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## DVINNY (Jan 25, 2008)

Desert Water said:


> My vote is that the plane will take off.Since, the plane is not tethered to the ground, so it should only have to overcome the additional rolling resistance to take off. The only change should be that the wheels will roll at airplane speed plus treadmill speed. If the plane used its wheels to power the takeoff then you would have a problem.






SuperAlpha said:


> Thrust from the engines is what causes the plane to move. The moving air across the wing causes lift.Now what part of that involves ground speed or wheel speed?
> 
> The wheels are there simply to keep it raised off the ground and able to roll.


WHere were you two back at the beginning of the montrosity known as "riddle me this batman" thread??

well said BTW


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## Wolverine (Jan 25, 2008)

The question is dividing by zero. It's an infinite feedback loop.

As soon as the plane has groundspeed of 0+, the conveyor reacts to counter that speed through friction in the wheel bearings. At anything 0+ knots, the conveyor moves up to infinity.

Somewhere prior to infinity, the wheelbearings explode. Unless you install magical frictionless wheel bearings

The only way to make the plane take off is to push it backwards slightly. Then it will immediately pop into the air.


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## BluSkyy (Jan 25, 2008)

This question causes me great concern. If we as technical persons/professional engineers cannot come to a consensus we're in trouble.


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## IlPadrino (Jan 25, 2008)

Wolverine said:


> As soon as the plane has groundspeed of 0+, the conveyor reacts to counter that speed through friction in the wheel bearings. At anything 0+ knots, the conveyor moves up to infinity.


No conveyor known to man is capable of countering the speed through friction in the wheel bearings (aka axle friction) or tires (rolling resistance). Or at least that was implied by Fact 4 (Rolling resistance is a function of [what?] and axle friction is a function of [what]?"; the rolling resistance and axle friction of an airplane is orders and orders of magnitude less than the thrust provided) in the thread Riddle me this batman, (airplane-conveyor thread).


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## Dleg (Jan 25, 2008)

Wolverine said:


> The only way to make the plane take off is to push it backwards slightly. Then it will immediately pop into the air.


:Locolaugh:


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## Sschell (Jan 25, 2008)

Wolverine said:


> The question is dividing by zero. It's an infinite feedback loop.
> As soon as the plane has groundspeed of 0+, the conveyor reacts to counter that speed through friction in the wheel bearings. At anything 0+ knots, the conveyor moves up to infinity.
> 
> Somewhere prior to infinity, the wheelbearings explode. Unless you install magical frictionless wheel bearings
> ...


this depends on the phrasing of the challenge, my understanding is that the treadmill moves backwards at the same speed as the plane's wheels roll forward.... not a a speed fast enough to to counter the speed through friction... don't overcomplicate!

Anyways, we live in a univerise governed by physics... your conveyor belt will have a top speed.

If the top speed is not fast enough to burn up the wheel bearings, we have forward motion and therefore flight.

If that top speed is fast enough to burn up the bearings, the thrust from the engine will overcome the friction between (the no longer rotating) tire and the (hauling ass) conveyer, thus forward motion, thus flight!


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## SkyWarp (Jan 26, 2008)

I always thought the spirit of the question was that the plane was forced to remain horizontally stationary, but that's not how the question is worded so I voted yes.


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## DVINNY (Jan 26, 2008)

The plane will take off, it has no horizontal resistance keeping it from doing so, as long as the wheels spin freely.

I highly suspect that anyone stating the plane will just sit there, is simply stating that to get the arguement stirred up.


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## cement (Jan 26, 2008)

if it is just sitting there, how is there wind flow over the wing? A helicopter or a Vertical Take Off aircraft have downward thrusting force for lift (actually a helicopter is a spinning wing, but we can save that for another day) but a traditional fixed wing aircraft has it engine provide thrust parallel to the ground. it needs to move forwad for the wing to achieve lift. the conveyor belt in theory prevents forward movement, so there is no airflow over the wing.

if they do the stunt correctly, the airplane will not take off. seriously.

but the dragging a tarp to replace a conveyor belt I see on the preview looks pretty sketch to me.

here it is Visit My Website


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## DVINNY (Jan 26, 2008)

Cement said:


> if they do the stunt correctly, the airplane will not take off. seriously.


100% wrong ^^.


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## DVINNY (Jan 26, 2008)

[No message]


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## cement (Jan 26, 2008)

I don't know what those toys are doing there buddy. most likely what will happen is the conveyor will start bouncing at high speed, or will max out and the airplane will creep off the end and fall off because it is going too slow to fly.


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## DVINNY (Jan 26, 2008)

> About This Video
> Ok, since some people were confused by the tape to stop it the plane from falling off, I run the plane at a low throttle to match rolling friction w/ thrust. I then accelerate the treadmill to almost 10 MPH w/o changing the throttle position. Then I throttle it up to prove that the plane can move at the high treadmill speed.
> 
> The treadmill does not affect the airplane's performance; this shows that no matter what the treadmill does (accelerate the same as the plane, faster than the plane, or less than the plane) the plane will still move forward.
> ...


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## MEPE2B (Jan 26, 2008)

Excuse me if I am missing the sarcasm, but are you guys really serious?? A wing produces lift from motion relative to the air, not movement relative to the ground or relative to a treadmill. An airplane on a treadmill will not take off by virtue of the belt rolling under it's wheels.

I am going to assume you are all joking and too much studying has killed my sense of humour. Is this like that guy on the radio who pretends to espouse ridiculous beliefs just so listeners will call up in an outraged tizzy, so as to derive a laugh at the people who were taking it all so seriously?


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## DVINNY (Jan 26, 2008)

Okay,

I'm really suspecting everyone is PM'ing each other and saying "get on there and tell DVINNY that the plane won't fly, it'll be funny"

^^^ gotta be something like that. You can't be serious that it won't move. Not at this point.


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## MEPE2B (Jan 26, 2008)

MEPE2B said:


> Excuse me if I am missing the sarcasm, but are you guys really serious?? A wing produces lift from motion relative to the air, not movement relative to the ground or relative to a treadmill. An airplane on a treadmill will not take off by virtue of the belt rolling under it's wheels.
> I am going to assume you are all joking and too much studying has killed my sense of humour. Is this like that guy on the radio who pretends to espouse ridiculous beliefs just so listeners will call up in an outraged tizzy, so as to derive a laugh at the people who were taking it all so seriously?



Oh, ok I see now that I did not understand the question. No, the treadmill should not prevent the airplane from gaining wind speed and taking off. I first thought the question was whether the airplane could take off with no motion relative to the ground simply because it was rolling on the treadmill. lol


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## DVINNY (Jan 26, 2008)

MEPE2B said:


> A wing produces lift from motion relative to the air, not movement relative to the ground or relative to a treadmill.


Correct ^^^ and an airplane (jet or prop) produces thrust through the air not through the ground via its wheels. It's wheels just roll along freely.



MEPE2B said:


> An airplane on a treadmill will not take off by virtue of the belt rolling under it's wheels.


Nope, see above.


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## MEPE2B (Jan 26, 2008)

DVINNY said:


> Correct ^^^ and an airplane (jet or prop) produces thrust through the air not through the ground via its wheels. It's wheels just roll along freely.
> 
> Nope, see above.



Yes, I agree. I simply misunderstood the question being asked.


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## Desert Engineer (Jan 26, 2008)

I'm with you DV,

The plane will f-ing fly. You could never spin a treadmill fast enough to make the wheels provide enough resistance to overcome the thrust of the prop. Are you guys assuming the treadmill speed goes to infinity or something?

Think about it how little force would it take to make the plane remain stationary on the moving treadmill. I havent done the calculations, but i know it is not that much. The plane is on round wheels not blocks. I know for sure that the thrust of the props is well enough to overcome the resistance of the wheels moving at a higher speed.


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## cement (Jan 26, 2008)

your assertion that the plane will fly only works if you change the rules and state that the conveyor can not keep up.

this discussion is predicated on the fact that the conveyor will match the thrust and prevent the airplane from moving forward.

the plane does not move forward, then no flow over the wings.

it does not take off.


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## Desert Engineer (Jan 26, 2008)

Ok, I agree with you that if you could (some how, maybe by removing the wheels completely) make the plane stand still via the conveyor belt, then it wouldn't take off due to lack of air movement by the wings. But, I don’t think that is possible. The rolling/bearing friction will always be negligible compared to the thrust of the motor.


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## ktulu (Jan 26, 2008)

WGASA


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## cement (Jan 26, 2008)

ktulu said:


> WGASA


killjoy


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## Sschell (Jan 26, 2008)

Cement said:


> your assertion that the plane will fly only works if you change the rules and state that the conveyor can not keep up.
> this discussion is predicated on the fact that the conveyor will match the thrust and prevent the airplane from moving forward.
> 
> the plane does not move forward, then no flow over the wings.
> ...






sschellhase said:


> this depends on the phrasing of the challenge, my understanding is that the treadmill moves backwards at the same speed as the plane's wheels roll forward.... not a a speed fast enough to to counter the speed through friction... don't overcomplicate!
> Anyways, we live in a univerise governed by physics... your conveyor belt will have a top speed.
> 
> If the top speed is not fast enough to burn up the wheel bearings, we have forward motion and therefore flight.
> ...


IT FUCKING FLYS!!!!!!!!!!!!!


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## DVINNY (Jan 26, 2008)

Cement said:


> your assertion that the plane will fly only works if you change the rules and state that the conveyor can not keep up.


The rules are, the conveyor keeps up. No problem.



Cement said:


> this discussion is predicated on the fact that the conveyor will match the thrust and prevent the airplane from moving forward.


Conveyor matches the "SPEED" of the airplane, not the thrust. It would have to go MANY MANY times faster than the plane to have the wheel friction match the thrust of the plane. This is where you are missing it. Thrust and Speed are quite different. If the _THRUST_ was matched then Sapper's free body diagram would have equal forces in the horizontal direction, causing the plane to sit still. If the _SPEED_ is matched by the conveyor, then the wheels just spin twice as fast.


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## cement (Jan 27, 2008)

this may be a disagreement between the theoretical and the practical.

when you run on a treadmill, it keeps up with you (or you adjust your speed to stay on)

regardless, there is no forward motion, no apparent wind created by running, so you sweat.

there is a finite amount of thrust provided by the engines, the treadmill is set to match it, and the airplane goes nowhere.

no sweat!


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## mudpuppy (Jan 27, 2008)

Ok, I haven't weighed in on this. So let me try (yet) another approach at explaining this in the off chance that DV is not correct in his conspiracy theory.

Let's say we have the plane sitting motionless on the conveyor. Let's say it's a small plane; small enough for a couple of people to easily push around. Now say a couple people off to the side of the conveyor (feet on solid ground) approach the plane, one on either side, and push forward equally on each wing with enough force to overcome friction. Does the plane move relative to the ground?

If you think it does not, please explain what the conveyor is doing to prevent the plane from moving when an external force is applied to it. In order to keep the plane from moving, an opposite force of equal magnitude must be applied. As far as I can see, there is no way for the conveyor to apply this force--if the conveyor moves forward, the plane moves forward with it. If the conveyor does not move, the plane rolls forward. If the conveyor moves backward (as the riddle states), the plane rolls forward with its wheels spinning faster.

If you think the plane does move relative to the ground, then (assuming no wind) it must be moving relative to the air around it as well, which I think we all agree causes lift. If you replace the force applied by the people with the thrust provided by an engine (propeller, turbine or whatever), it will still move--force is force, whether it is applied against the ground or against a fluid. And I think we all agree that if the plane can move forward it can continue to accelerate to takeoff velocity.

Please feel free to voice disagreement with anything above.


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## mudpuppy (Jan 27, 2008)

Cement said:


> this may be a disagreement between the theoretical and the practical.
> when you run on a treadmill, it keeps up with you (or you adjust your speed to stay on)
> 
> regardless, there is no forward motion, no apparent wind created by running, so you sweat.
> ...


Similar to what I'm trying to illustrate in my post above, the key point is the application of an *external* force. When you are running on a treadmill, you are applying force against the treadmill itself and you are moving relative to the treadmill but not relative to the surrounding air. The thrust from the plane's engines is not applied to the conveyor, it's applied to the air around the conveyor and thus it moves forward relative to the air.


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## cement (Jan 27, 2008)

^^ My eyes unfurled!

you win.


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## Desert Engineer (Jan 27, 2008)

^^^ Now that we've come to a consensus... Lets all watch the show, when the plane fails to take off! LOL


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## Dark Knight (Jan 27, 2008)

I cannot wait to see the end of this conflict!!!!!!!!!!!!


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## DVINNY (Jan 27, 2008)

good explanations mudpuppy. Nicely done.


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## mudpuppy (Jan 27, 2008)

Thanks. I must admit I thought at first it wouldn't fly either and had to convince myself otherwise.

I've thouroughly enjoyed this riddle. It's deceptively simple and surprisingly hard to explain in a straightforward way.

Problem is, what do we argue about now that the last holdout is convinced?


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## cement (Jan 27, 2008)

if you want, I could pretend otherwise 

the external force arguement was the clincher for me.


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## Guest (Jan 27, 2008)

mudpuppy said:


> Problem is, what do we argue about now that the last holdout is convinced?


There is STILL the three doors + two :goat: Monty Hall Problem!

:bio:

JR


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## mudpuppy (Jan 27, 2008)

Oh no, now I'm going to have that one stuck in my head for the next week!


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## Capt Worley PE (Jan 28, 2008)

mudpuppy said:


> Thanks. I must admit I thought at first it wouldn't fly either and had to convince myself otherwise.


I was too until someone pointed out the wheels were just there to support the planeand minimize friction, noit apply tractive force. Then the light came on and I felt a huge "DUH!" moment.


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## RIP - VTEnviro (Jan 30, 2008)

My prediction: Buster gets mutilated, the plane explodes.


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## frazil (Jan 30, 2008)

Ok - At risk of being banned from the site, I'm just going to say I still don't see how the plane will move, let alone take off. The way I understand the question the conveyor belt moves in the opposite direction at the same speed the plane moves forward. So relative to anyone standing on the ground, the plane doesn't move. The thrust from the engines can be as big as you want but if there's no wind over the wings it's going to sit there.

well, we'll see...


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## Sschell (Jan 30, 2008)

frazil said:


> Ok - At risk of being banned from the site, I'm just going to say I still don't see how the plane will move, let alone take off. The way I understand the question the conveyor belt moves in the opposite direction at the same speed the plane moves forward. So relative to anyone standing on the ground, the plane doesn't move. The thrust from the engines can be as big as you want but if there's no wind over the wings it's going to sit there.
> well, we'll see...


The engines force acts on the air (not the ground or conveyor belt), there fore the conveyor belt can move at any speed it wants to, it just causes the (free rotating) wheels to spin faster as the plane moves forward.

Now if you put a giant vacuum behind the engines that sucked the same volumetric flowrate that the engines put out... that would keep the plane from flying


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## Sschell (Jan 30, 2008)

how about a harrier... can that take off on a conveyor?


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## BluSkyy (Jan 30, 2008)

are its wheel brakes engaged?


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## Sschell (Jan 30, 2008)

BluSkyy said:


> are its wheel brakes engaged?


willing to bet thrust beats tire friction...


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## Brody (Jan 30, 2008)

Excitement builds. A lot of my friends say it won't fly. I say it does. The truth will be revealed shortly.


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## BluSkyy (Jan 30, 2008)

sschellhase said:


> willing to bet thrust beats tire friction...


Sorry meant that tongue in cheek. I don't really care whether it flies or not anymore


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## IlPadrino (Jan 30, 2008)

sschellhase said:


> willing to bet thrust beats tire friction...


That would be interesting... I'd get on a jet, but not a prop. That's a lot of skidding down the runway. I wonder how hard it would be to keep it going straight - probably no worse than a strong cross-wind.


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## Road Guy (May 16, 2016)

last page bump


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## cement (May 17, 2016)

Did I really think it wouldn't fly or was I just being a troll?  Those were dark times for me.


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## jeb6294 (May 17, 2016)

Road Guy said:


> last page bump


Why would you do that?!?! :banhim:

It's like getting an irrelevant email to a large group at work.  You do the normal thing and delete it, but then the idiots all have to start replying to all asking to be removed from the email.


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## Wolverine (May 17, 2016)

Please delete me from this reply all email.

*Everybody #&amp;$^ing knows the #&amp;$^#  plane WILL NOT FLY!*

(but only because it's an infinity paradox: if the wheels move at the same speed as the conveyor, both will instanstly reach infinite speed and the bearings will explode. BOOM, solved it!)


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## Dleg (May 17, 2016)

This question is old news.  It's time to update the question.  Let's say there's a treadmill mounted on an airplane. If the airplane is flying at 1 mph slower than the speed of sound, but you are running on the treadmill at a speed of 6 mph, will your body be harmed when it breaks the sound barrier?


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## Wolverine (May 17, 2016)

Wait, is the treadmill INSIDE the airplane or outside?

And what color is the airplane?  Need to define these _seemingly _insignificant details first.


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## Dleg (May 17, 2016)

The treadmill is outside the airplane, and the airplane is white.


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## matt267 PE (May 17, 2016)

What's the drag coefficient on the person, and are they plump or twiggy?


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## Dleg (May 17, 2016)

Assume it is negligible.

Oh, and for anyone who has never read the original thread on this topic, it is EPIC.


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## matt267 PE (May 17, 2016)

Are you saying they're in a perfect vacuum? If so, the plane wouldn't even be able to fly, making your question invalid.


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## Dleg (May 17, 2016)

The person is running 5 mph on a treadmill, which is attached to the outside of an airplane that is travelling at 1 mph less than the speed of sound (for that pressure and temperature).  Someone else did the engineering necessary to get the situation to this point.

Now answer the damn question.


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## Wolverine (May 17, 2016)

Not yet.  Is the white plane going 1mph slower than the speed of sound with a person on a treadmill on top accelerating or decelerating?

And is there any sort of power connection between the treadmill and the airplane, either absorbing power to run the treadmill motor or producing power from the motion of the running?

This is critical for my calculations.


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## Audi Driver P.E. (May 17, 2016)

flight involves... nay... REQUIRES air movement to provide lift.


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## matt267 PE (May 17, 2016)

Dleg said:


> This question is old news.  It's time to update the question.  Let's say there's a treadmill mounted on an airplane. If the airplane is flying at 1 mph slower than the speed of sound, but you are running on the treadmill at a speed of 6 mph, will your body be harmed when it breaks the sound barrier?






Audi driver said:


> flight involves... nay... REQUIRES air movement to provide lift.


@Audi driver, P.E., have you considered Dleg's new question? I think it's invalid and Dleg is not providing enough info to Wolverine. What do you think?


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## Audi Driver P.E. (May 17, 2016)

matt267 PE said:


> @Audi driver, P.E., have you considered Dleg's new question? I think it's invalid and Dleg is not providing enough info to Wolverine. What do you think?


I had not considered it.  But obviously there is information missing.  Is the treadmill moving at 6mph?  If not, then you're already beyond the speed of sound and obviously you survived.  But the bigger question is why would I be running on a treadmill on an airplane.  Am I sufficiently drunk?


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## scatsob (May 17, 2016)

If the plane is flying that fast there would already be local flow in various locations already faster than sound, on the plane, person, and treadmill.  But yes, you will be very harmed and likely dead already as the plane accelerated to ~0.99 Mach.  Unless the person has some sort of suit on for protection. Is the person Spider-Man?

As a classically trained aeronautical engineer I find these questions disturbing.


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## Dleg (May 17, 2016)

Wolverine said:


> Not yet.  Is the white plane going 1mph slower than the speed of sound with a person on a treadmill on top accelerating or decelerating?
> 
> And is there any sort of power connection between the treadmill and the airplane, either absorbing power to run the treadmill motor or producing power from the motion of the running?
> 
> This is critical for my calculations.


The treadmill is accelerating from zero to 6 mph, with the person matching that with his /her running speed.  So, the person and treadmill are traveling at 1 mph less than the speed of sound at the start of the scenario. 

Let's assume the person is wearing high speed running clothes that sufficiently protect him/her against the windspeed at 1 mph less than the speed of sound.

The treadmill is plugged in to a 120V AC outlet powered by the aircraft's electrical power system.


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## FLBuff PE (May 17, 2016)

How much hair does the treadmill runner have? The amount of hair (both on the head and on the body) would increase the drag coefficient.


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## Dleg (May 17, 2016)

none.


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## wilheldp_PE (May 17, 2016)

Dleg said:


> The treadmill is plugged in to a 120V AC outlet powered by the aircraft's electrical power system.


Most airplanes use 115 VAC at 400 Hz.  If you use a treadmill designed for 115 VAC at 60 Hz, it's going to run ~7 times faster than it would in the US.  So now your 5 mph treadmill is going ~33 mph.


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## jeb6294 (May 18, 2016)

The plane will be fine.  The extra speed of the person on the treadmill will allow them to break the sound barrier and explode...but since they're going faster than the speed of sound, you won't hear them explode.


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## Dleg (May 18, 2016)

Are you certain?  Wouldn't they cause a sonic boom, IF they accelerated through the speed of sound?


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## matt267 PE (May 18, 2016)

Isn't there something about the theory of relativity that should be applied here?


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## Dleg (May 18, 2016)

That's another topic.  The guy walking forward in the spacecraft traveling 1 mph less than the speed of light.


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## csb (May 18, 2016)

Why's the plane gotta be white?


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## matt267 PE (May 18, 2016)

csb said:


> Why's the plane gotta be white?


Because the other color plane didn't want to work.


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## csb (May 18, 2016)

Guys, I think we're forgetting a crucial step. Does the plane need to wear the little safety clip that will stop the treadmill if the plane falls off?


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## envirotex (May 18, 2016)

Did the person on the treadmill get charged a baggage fee for the treadmill?


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## Audi Driver P.E. (May 18, 2016)

jeb6294 said:


> The plane will be fine.  The extra speed of the person on the treadmill will allow them to break the sound barrier and explode...but since they're going faster than the speed of sound, you won't hear them explode.


Sure you will, you just won't hear it when it happens.


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