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Can this airplane lift off?

yes
no

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Offline sangyo soichiro

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Re: Can this airplane lift off?
« Reply #250 on: April 06, 2009, 11:59:20 AM »
As some of you have pointed out, this is not a simple 'yes/no' question.  It depends on how you interpret "the runway will match the speed of the airplane's wheels."

The best possible answer is one that addresses all possible scenarios.


The main motivation for this problem was to have a bit of fun and to exercise our brains.  I think we succeeded.



For anyone wanting to think about the more difficult version, forget about bearings wearing out and tires blowing (which they indeed would!)... there is a more fundamental issue here and one that we cannot escape, even if we had bearings and tires that wouldn't fail.  It is the wheel's moment of inertia.
« Last Edit: April 06, 2009, 12:07:08 PM by soichiro »
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Offline sangyo soichiro

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Re: Can this airplane lift off?
« Reply #251 on: April 06, 2009, 12:05:07 PM »
Oh...
And no one should feel bad or get defensive (unless they displayed some behavioral volatility toward others)... this is a difficult problem. 
« Last Edit: April 06, 2009, 12:07:45 PM by soichiro »
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Offline my78k

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Re: Can this airplane lift off?
« Reply #252 on: April 06, 2009, 12:08:24 PM »
well in that case wouldn't the biggest factor be the type of plane???

i.e. one that has the lowest air speed requirement would behave and react far differently than one that has far less lift etc? The speed (wind speed) would be less therefore less wheel spin therefore less "doubled" wheel spin blah blah blah....

Dennis

P.S. I just realized that this whole thing wasn't really a thought experiment at all but rather a Shameless Post Boost Thread in disguise...

Offline HavocTurbo

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Re: Can this airplane lift off?
« Reply #253 on: April 06, 2009, 12:10:37 PM »
well in that case wouldn't the biggest factor be the type of plane???

i.e. one that has the lowest air speed requirement would behave and react far differently than one that has far less lift etc? The speed (wind speed) would be less therefore less wheel spin therefore less "doubled" wheel spin blah blah blah....

Dennis

P.S. I just realized that this whole thing wasn't really a thought experiment at all but rather a Shameless Post Boost Thread in disguise...

post boost thread?? this?? one could only be so lucky.  ;) ;D 8)
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Offline Gordon

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Re: Can this airplane lift off?
« Reply #254 on: April 06, 2009, 12:14:55 PM »
gordon

"Of course it can, but it's not flying because of the wind created by its own propeller. "


Nope.  You're reading more into that than the words that I typed.  The plane is NOT flying because of the wind created by its own propeller.  It's flying because of the air moving over it's wings, which was not created by its propeller.  It's being pulled through the air by its propeller. 

It's irrelevant, though.  I think I was confusing you with someone earlier who said the plane would gain lift because its propeller would push enough air over its own wings, which is not the case.   

Offline sangyo soichiro

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Re: Can this airplane lift off?
« Reply #255 on: April 06, 2009, 01:44:18 PM »
OK soichiro, what's the answer?

That would be a much too vulgar display of power.   

:)
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Markcb750

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Re: Can this airplane lift off?
« Reply #256 on: April 06, 2009, 02:08:30 PM »
OK soichiro, what's the answer?

That would be a much too vulgar display of power.   

:)


Seriously,  moment of inertia...

Moment of inertia does not increase until relativistic speeds. In this situation the power the engine must provide to accelerate the wheels to twice rotary speed will make the net take off distance a little longer. Twice as much energy is required to accelerate the wheel leaving less net thrust to accelerate the plane,  but this is still a fairly small number.  Not relevant to the thought experiment. 

Something as important as causing the wheels to spin at a radial velocity equal to 99% C is too important to leave out. 

Unless,


Methinks you might be obfuscating for entertainment.
« Last Edit: April 07, 2009, 04:00:28 AM by Markcb750 »

Offline toycollector10

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Re: Can this airplane lift off?
« Reply #257 on: April 07, 2009, 03:33:34 AM »
In answer to the original question, the answer is YES. The aircraft can take off. The proof of this is exhibited by the fleet of 50 yard long aircraft carriers now in service with the US Navy. You know, the ones with the supermarket like conveyor belt things (they don't exist because the physics doesn't make sense) in the flight decks instead of steam powered catapult launchers.

It's all down to the airflow over the wings, angle of attack (the angle the airfoil meets the oncoming air) and the thrust of the engines. But let's not get overwhelmed with science here boys.

You should all stick to motorcycles if you don't know sh*t about the principles of flight!

I'm so over this! It's just so much fluff and mirrors and crap and it doesn't make any sense. And the original poster getting all superior and using red text when even a 14 year old can see that the physics is all wrong.
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Offline mystic_1

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Re: Can this airplane lift off?
« Reply #258 on: April 07, 2009, 05:02:54 AM »
Wouldn't the conveyor and therefore the wheel speed accelerate to infinity.  Each time the plane moved forward relative to the ground (not the conveyor), the conveyor would sense an increase in speed and then match that speed.


No.  The speed of the hypothetical conveyor would always equal twice the groundspeed of the aircraft.  This is established as one of the initially stated conditions in your first post:

Quote
When the runway senses the wheels moving, the runway will match the speed of the airplane's wheels, but in the opposite direction.

The speed of the conveyor would only approach infinity if the ground speed of the aircraft did.

Your new question confuses movement with acceleration.

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Offline sangyo soichiro

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Re: Can this airplane lift off?
« Reply #259 on: April 07, 2009, 12:11:42 PM »
Wouldn't the conveyor and therefore the wheel speed accelerate to infinity.  Each time the plane moved forward relative to the ground (not the conveyor), the conveyor would sense an increase in speed and then match that speed.


No.  The speed of the hypothetical conveyor would always equal twice the groundspeed of the aircraft.  This is established as one of the initially stated conditions in your first post:

Quote
When the runway senses the wheels moving, the runway will match the speed of the airplane's wheels, but in the opposite direction.

The speed of the conveyor would only approach infinity if the ground speed of the aircraft did.

Your new question confuses movement with acceleration.

mystic_1

Then I guess what I'm saying is forget the 'old version' and consider the new.  It's more interesting.  The old version is solved - the plane will fly.  The fun is gone.  Now tackle the infinite problem.
 

Seriously,  moment of inertia...

Moment of inertia does not increase until relativistic speeds. In this situation the power the engine must provide to accelerate the wheels to twice rotary speed will make the net take off distance a little longer. Twice as much energy is required to accelerate the wheel leaving less net thrust to accelerate the plane,  but this is still a fairly small number.  Not relevant to the thought experiment. 

Something as important as causing the wheels to spin at a radial velocity equal to 99% C is too important to leave out. 

Unless,


Methinks you might be obfuscating for entertainment.
First thing to note is that I'm suggesting we no longer consider the conveyor that goes to twice the plane speed.  That problem is indeed trivial.

Considering a conveyor that goes to infinity:
Not sure if the moment of inertia needs to increase...  the wheels have a moment of inertia that's non-zero, compounded with something that goes to infinity. 

That alone is an interesting challenge.


Another challenge is if we consider relativity.  Nothing can travel faster than light.  If we have a conveyor that's moving at (or near) the speed of light, then it's interesting to consider the possibilities of
a. the motion of the bottom of the wheel,
b. the motion of the top of the wheel,
c. the motion of the center of the wheel,
d. all the above in relation to each-other, the ground, and the conveyor.



Compound all that with this little paradox:
Imagine we are sitting still on the conveyor waiting to test this experiment (if it were possible).  Everything is still - the plane relative to the ground is still, the wheels are not rotating, and the conveyor is motionless.  Then the pilot releases the brake...
This is the paradox:  How do the wheels start to rotate?

Do I claim that this plane will fly?  No.
Do I claim that this plane will not fly?  No.
I claim that this problem is, at the very least, not trivial.

Again, all the above is in the context of the infinite conveyor.  If anyone's still thinking in terms of a conveyor that goes to twice the speed of the plane, then the above does not apply.  And the 2-times the wheel speed conveyor problem is solved.  That plane will fly.



You should all stick to motorcycles if you don't know sh*t about the principles of flight!

I'm so over this! It's just so much fluff and mirrors and crap and it doesn't make any sense. And the original poster getting all superior and using red text when even a 14 year old can see that the physics is all wrong.


To whom it may concern, this riddle is a difficult problem and is not for everyone.
« Last Edit: April 07, 2009, 12:48:03 PM by soichiro »
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Markcb750

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Re: Can this airplane lift off?
« Reply #260 on: April 07, 2009, 02:16:26 PM »
Socichiro.

You are obfuscating again.

Moment inertia is a function of radius and mass, The energy required for each change in rpm is the same regardless of where that change in rpm is.

Energy from 0 to 100rpm is the same same as 100 to 200.**given the same time is taken  for each... :-[ ***

As you approach the speed limit of the bearing, several thousand RPM, the bearing might seize up but little else would effect the prop pulling the aircraft forward...
« Last Edit: April 07, 2009, 02:25:05 PM by Markcb750 »

Offline sangyo soichiro

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Re: Can this airplane lift off?
« Reply #261 on: April 07, 2009, 02:39:49 PM »
Energy from 0 to 100rpm is the same same as 100 to 200.**given the same time is taken  for each... :-[ ***

I see what you're saying, but I'm considering that the problem is such that the conveyor quickly accelerates toward infinity as it tries to keep up with the wheels.  (I cannot emphasize enough that it's the infinite problem that these concepts are concerned with.)

As you stated,
Quote
Energy from 0 to 100rpm is the same same as 100 to 200...
But... the energy from 0 to 200 rpm is the energy from 0 to 100 plus the energy from 100 to 200. 

...now consider the problem where the conveyor (and hence, the rpm) goes to infinity.  It would take an infinite amount of energy.

You may recall a concept from calculus called convergence.  I suspect to resolve this problem involves the relative rates of convergence of the appropriate quantities.



I honestly don't know the answer...
I'm just saying it's tricky.
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Offline Inigo Montoya

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Re: Can this airplane lift off?
« Reply #262 on: April 07, 2009, 02:48:29 PM »
I like pie.

Offline sangyo soichiro

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Re: Can this airplane lift off?
« Reply #263 on: April 07, 2009, 02:58:24 PM »
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Offline mlinder

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Re: Can this airplane lift off?
« Reply #264 on: April 07, 2009, 02:58:52 PM »
Energy from 0 to 100rpm is the same same as 100 to 200.**given the same time is taken  for each... :-[ ***

I see what you're saying, but I'm considering that the problem is such that the conveyor quickly accelerates toward infinity as it tries to keep up with the wheels.  (I cannot emphasize enough that it's the infinite problem that these concepts are concerned with.)

As you stated,
Quote
Energy from 0 to 100rpm is the same same as 100 to 200...
But... the energy from 0 to 200 rpm is the energy from 0 to 100 plus the energy from 100 to 200. 

...now consider the problem where the conveyor (and hence, the rpm) goes to infinity.  It would take an infinite amount of energy.

You may recall a concept from calculus called convergence.  I suspect to resolve this problem involves the relative rates of convergence of the appropriate quantities.



I honestly don't know the answer...
I'm just saying it's tricky.

But it's only a factor of wheel bearing and tire to conveyor-belt friction. The speed of the conveyor means nothing without this, and it appears we are ignoring such frictions? (If this is the case, lets assume only the bearings are frictionless, as frictionless tires would mean the conveyor belt doesn't even cause the wheels to turn...)
Without ANY of this friction, the plane would actually stay stationary, no engine running, no power, no matter how fast you run the damn conveyor-belt. Without the aforementioned friction, there is nothing compelling the plane to move the same direction as the conveyor belt. Now, as soon as you fire up the planes engine (assuming friction is working normally for the rest of the plane... :/ ) it would take off without issue, as if the conveyor belt did not exist.

However, if we DO include friction, then we need to consider that the increase in friction is probably not linear (unless we just want to say, that yeah, it's linear), and we also cannot give a real number of what that friction is, if the speed can increase to ∞. I mean, linearly, x*∞=∞. non linearly, the final result is STILL ∞.
« Last Edit: April 07, 2009, 03:02:46 PM by mlinder »
No.


Offline sangyo soichiro

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Re: Can this airplane lift off?
« Reply #265 on: April 07, 2009, 03:02:54 PM »
Hey!  Where did you get this?


I want one! 

(Seriously, how did you do that?  HTML?  Do we have a symbol palette here somewhere?)

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Offline bunghole

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Re: Can this airplane lift off?
« Reply #266 on: April 07, 2009, 03:04:21 PM »
I like pie.


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Offline mlinder

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Re: Can this airplane lift off?
« Reply #267 on: April 07, 2009, 03:05:33 PM »
Switch on the 'Num lock' and press and HOLD the 'Alt' key
type 236 on the num-lock keypad.
Release 'Alt' key. You get ∞
« Last Edit: April 07, 2009, 03:11:30 PM by mlinder »
No.


Offline TwoTired

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Re: Can this airplane lift off?
« Reply #268 on: April 07, 2009, 03:06:59 PM »
∞∞∞∞  Is option and 5 keys on the mac keyboard.


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Re: Can this airplane lift off?
« Reply #269 on: April 07, 2009, 03:10:46 PM »
I don't see the point of this diversion of your thought problem, It is not implied or explicitly denoted in your original post.

If the math in my head is correct even 1% of 1% (18.6 miles per second) of the speed of light would be 2,500,000 rpm on a 1.5 ft diameter tire. An absurdity. Let alone an "infinite" belt speed.


As I stated, if you accelerated to relativistic speeds, 0.9C (90% of 186,000 miles per second) the moment of inertia would become larger as the mass would start to significantly increase due to the fact that mass and energy are equivalents. (E=MC^2) at 99.999% of C would require more energy then we can create in the whole world...

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Offline sangyo soichiro

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Re: Can this airplane lift off?
« Reply #270 on: April 07, 2009, 03:11:24 PM »
∞∞∞∞  Is option and 5 keys on the mac keyboard.





∞  Nice!  Thank you, I'm actually on a Mac.  And thanks to you too mlinder.

¡™£¢∞§¶•ªº–≠

Had to test what the others did.   :)
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Offline sangyo soichiro

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Re: Can this airplane lift off?
« Reply #271 on: April 07, 2009, 03:14:37 PM »
I have a rattle in the Mean streak pipes I put on my Vulcan Classic last month, I am going out to fix it. I need to get ready for a nice 200 mile road trip tomorrow. I am going to hook up with my '76 750 I have staged there and ride the next few days. :) :)

Look for a PM from me.


Good luck with the pipes.  And have a safe ride.
(If you, by chance, rode on a conveyor, it would be safe, and would provide a unique insight into this problem that the rest of us lack.)   ;D
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Offline mlinder

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Re: Can this airplane lift off?
« Reply #272 on: April 07, 2009, 03:18:20 PM »
I have a rattle in the Mean streak pipes I put on my Vulcan Classic last month, I am going out to fix it. I need to get ready for a nice 200 mile road trip tomorrow. I am going to hook up with my '76 750 I have staged there and ride the next few days. :) :)

Look for a PM from me.


Good luck with the pipes.  And have a safe ride.
(If you, by chance, rode on a conveyor, it would be safe and would provide a unique insight into this problem that the rest of us lack.)   ;D

...I'm not sure we are lacking...
Now, I'm no physisssiist..ist... nor a maffmatician, but your scenario just doesn't work without knowing the friction values of the bearings in the wheels of the airplane. That friction is the ONLY cause of plane movement caused by the conveyor-belts motion.
∞ or no. Just doesn't matter.
« Last Edit: April 07, 2009, 03:20:39 PM by mlinder »
No.


Offline Joel

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Re: Can this airplane lift off?
« Reply #273 on: April 07, 2009, 03:35:11 PM »

Offline mlinder

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Re: Can this airplane lift off?
« Reply #274 on: April 07, 2009, 03:41:22 PM »
No.