Topic: Can this airplane lift off?

[Buber]

Well, I beg to differ.
 I my opinion, the fault in Gordon thinking lies in fact that "propeller tows the plane through the air". Yes it does, but plane flies not because it is being towed, but because the air goes around the wings, which in turn generate lift.
Now, the propeller may turn as fast as it like, creating as much trust as it like, but UNLESS the air will start flowing around WHOLE wings the plane will NOT take off.
Of course a bit of air may go around the base of wings, but lift so generated will be waaay to small..

So, sorry, but unless you could direct somehow the stream of air to go over the WHOLE wingspan, it won't fly.

Imagine this - take a small model of a plane and direct on it narrow stream of air, like from hair-dryer, directly on its nose. It will stay put. Now, take a big fan, that covers the wingspan - the model will lift....

And THAT folks is all there is to it.... or, Dukie is right, Gordon is wrong... If you don't believe, take a model and try... The Myhtbusters AS USUAL take a lot of liberties with conditions. This plane on the movie, was moving forward.

I just can't imagine that so many of you don't realize why do the planes fly... because that's why - because of the lift created by the airflow around the profile of the wing... the whole wing, BTW....

[mystic_1]

Buber, re-read Gordon's post.

the plane will still move forward through the air regardless of what the conveyor belt runway beneath it is doing.

Once the plane is moving forward through the air, air will be passing over the entire wing surface and the plane will therefore take off. 

The air isn't moving over the wings due to being impeled by the propeller, it's moving over the wings due to the fact that the plane is moving forward through the air.

We know this works because this is how plane actually fly in the real world.  Their forward motion results in air moving over the wings which generates lift.

mystic_1

[Bob Wessner]

See http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html and scroll down to airfoils. It's a pretty good illustration.

[Buber]

Ok, it seems that the question posed is misunderstood.

When the runway senses the wheels moving, the runway will match the speed of the airplane's wheels,

Ok, formulated this way, plane will eventually take off.
BUT most people understand this that he conveyor is to keep the plane stationary. In such case, it won't fly.

So, maybe we should look at this question as similar to:
what is heavier? 1kg of dawn or 1kg of steel? On the first quick shout many people will say "steel", but when they analyze the questions, the answer is obvious.

So, looks like those who say "it won't fly" are falling for it, i.e. we are not reading teh question properly, but we are ASSUMING that the conveyor belt is to keep plane stationary.

A case of misunderstanding....

If the question would be...

When the runway senses the wheels moving, the runway will match the speed of the airplane's wings,

Then there's no other answer... it won't fly.

[333]

Ah, Grasshopper.  One thinks that Soichiro needs a good a$$ whooping for starting this thread.

[Gordon]

Buber,

  Go read the first 21 pages of this thread.  It's already been explained in every way humanly possible, and not just by me.  The plane will fly.  If you don't want to accept that fact, it makes no difference to me.  I'm not going to re-type all of my previous posts, but perhaps somebody else won't mind re-typing theirs.

The fact you're not understanding is that the conveyor can't match the speed of the wings, only the wheels, and since it's the wings that make the plane fly (not the wheels), the plane will take off normally.

[sangyo soichiro]

Imagine the conveyor adjusts itself to the speed mentioned above in setup 1 plus the reading on the plane's speedometer (which measures the speed relative to the conveyor itself).

I didn't see where this new condition was stated before this post.  I checked back through several pages of the thread just to make sure.

mystic_1

It is not a new condition - it comes from how you interpret the original problem.  That is, how the conveyor senses the wheel speed, and which "speed".  Is the conveyor sensing the speed of the plane relative to the ground?  Or is it sensing that plus what the speedometer of the plane reads?  The original question does not specify and, for fun, why not consider both...

In the original scenario, there was no need to consider infinite conveyor speed as it would never occur.

In the revised scenario, infinite speed is assumed.

If we're going to start changing the scenario by adding more and more vairables (infinite speed, frictionless bearings) than the whole thread becomes even more pointless than it was to begin with.


That's been my point all along.




Let's just go ahead and presume the existance of magical fairies why will use psionic powers to keep the wheel bearings from exploding.  After all, what do you suppose is holding the bearings in the conveyor together?

mystic_1

As I said above, it has always been there.  It has not been revised.  No one is moving the goal posts. 

Because this is important to the understanding of where infinity comes from, I'm going to label it in a bold font.

How the runaway-conveyor scenario works:

Setup 1:
Imagine the conveyor adjusts itself to the speed of the plane relative to the ground.  This is the scenario where the wheels rotate at twice their normal speed.

Setup 2:
Imagine the conveyor adjusts itself to the speed mentioned above in setup 1 plus the reading on the plane's speedometer (which measures the speed relative to the conveyor itself).  In this case, the conveyor quickly speeds up to infinity.


Anyway, that's where infinity comes from.

Nope, not part of the original problem statement.   I believe you are injecting "info" simply to further the thread life.

There is an airplane on a runway. The runway is like a conveyor belt, and can detect the speed of the wheels of the airplane. When the runway senses the wheels moving, the runway will match the speed of the airplane's wheels, but in the opposite direction.

I must insist, it was always a possibility.  The conveyor senses the wheels moving with respect to what?






P.S.  When I have stated "infinite conveyor," I've always meant that in terms of infinite speed, not length.  I mention this because I don't think I was clear before.

[sangyo soichiro]

This may be a thread killer, but I'll post it anyway.  I am in no way associated with the person who wrote this.  It's just something I found.

http://blag.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/comment-page-8/


I post this to illustrate that I have not introduced a new concept into the problem (that of the infinite-speed conveyor).

This blog entry gives away one of the paradoxes of this problem, so in a way, it's spoiling your "fun."  But then again, I still think there are other things to speculate on, for fun, that this blog entry doesn't address.


Either way, if this problem is causing trouble... then forget it.


Cheers

[sangyo soichiro]

And I must confess a dirty little secret...
I stole the original question from another forum.  I thought it was a cute problem and it seemed to generate a LOAD of havoc over there.  I am not the author of that thread... he was smart enough to stay out of the conversation (look at his post count - it's 1).   

This other forum is a "science" forum.  You may find it interesting that, according to their poll,
73 people voted,
42 (57%) said no,
31 (42%) said yes. 
Compare that to our poll.  The question there was exactly the same as the one here.  It went on for 24 pages there.

http://www.thescienceforum.com/viewtopic.php?t=9419&postdays=0&postorder=asc&start=0&sid=a69a53212ad8f42841f3775aa08b32a1

[mattcb350f]

Imagine the conveyor adjusts itself to the speed mentioned above in setup 1 plus the reading on the plane's speedometer (which measures the speed relative to the conveyor itself).

An aircrafts 'speedometer' is called an Air Speed Indicator, which measures the velocity of the aircraft through the air, not how fast it is moving relative to the ground.

Aircraft don't have traditional speedometers in the way we think of them.

There is no connection between how an aircraft flies and wheels it takes off on. 

If, as the original problem states, the runway was a conveyor belt...bla, bla, bla, would the plane takeoff?. The problem gets people to think about how they interpret how an aircraft flies and tries to get them to decide if ultimately ground speed has anything to do with it.

The answer: It will, provided the conveyor is long enough to allow the plane to achieve FORWARD MOVEMENT THROUGH THE AIR, NOT RELATIVE TO THE CONVEYOR to an airspeed high enough for it to lift off of the conveyor. In the original problem, the runway is said to be like a conveyor belt...which says yes, it is big enough. It's a runway, not a wee conveyor like the pic I put up.

And while it is theoretically posible that the conveyor be able to reach an infinate speed as stated earlier, it never would. I already explained that part too.

[Inigo Montoya]

It does not matter what happens to the plane! My inter Galactic Spam cruiser will destroy it!!!!

[mystic_1]

Nowhere did the original question mention a speedometer.  There's your new factor.  Suddenly you want to introduce a speedometer and connect that to the treadmill.  Pfft.






At least you've finally admitted that you're just being a troll and trying to stir the pot on this forum.  Glad you had fun.  Please stop trolling with threads reposted from other sites now.

And I must confess a dirty little secret...
I stole the original question from another forum.  I thought it was a cute problem and it seemed to generate a LOAD of havoc over there.  I am not the author of that thread... he was smart enough to stay out of the conversation (look at his post count - it's 1).  

This other forum is a "science" forum.  You may find it interesting that, according to their poll,
73 people voted,
42 (57%) said no,
31 (42%) said yes. 
Compare that to our poll.  The question there was exactly the same as the one here.  It went on for 24 pages there.

http://www.thescienceforum.com/viewtopic.php?t=9419&postdays=0&postorder=asc&start=0&sid=a69a53212ad8f42841f3775aa08b32a1

mystic_1

[sangyo soichiro]

Nowhere did the original question mention a speedometer.  There's your new factor.  Suddenly you want to introduce a speedometer and connect that to the treadmill.  Pfft.






At least you've finally admitted that you're just being a troll and trying to stir the pot on this forum.  Glad you had fun.  Please stop trolling with threads reposted from other sites now.

And I must confess a dirty little secret...
I stole the original question from another forum.  I thought it was a cute problem and it seemed to generate a LOAD of havoc over there.  I am not the author of that thread... he was smart enough to stay out of the conversation (look at his post count - it's 1).  

This other forum is a "science" forum.  You may find it interesting that, according to their poll,
73 people voted,
42 (57%) said no,
31 (42%) said yes. 
Compare that to our poll.  The question there was exactly the same as the one here.  It went on for 24 pages there.

http://www.thescienceforum.com/viewtopic.php?t=9419&postdays=0&postorder=asc&start=0&sid=a69a53212ad8f42841f3775aa08b32a1

mystic_1

I was not being a troll.  It's an interesting problem.  I simply copied the question from somewhere else and gave a link to the other place in case anyone else was interested in how this question fared elsewhere.

Your comment is very offensive.

And there is no need to get so defensive.  Really. 

[mlinder]

I found it an interesting problem, but not a difficult one, until we started dealing with theoretical physics (and absolutes like ∞ and an 'f' value of 0). 

[333]

Regarding the "/the-goddamn-airplane-on-the-goddamn-treadmill/comment-page-8/" link, the best part is at the end;

All in all, it’s a lovely recipe for an internet argument, and it’s been had too many times. So let’s see if we can avoid that. I suggest posting stories about something that happened to you recently, and post nice things about other peoples’ stories. If you’re desperate to tell me that I’m wrong on the internet, don’t bother. I’ve snuck onto the plane into first class with the #5 crowd and we’re busy finding out how many cocktails they’ll serve while we’re waiting for the treadmill to start. God help us if, after the fourth round of drinks, someone brings up the two envelopes paradox.

Seems like the perfect answer to me.


I'll have champagne, thank you.

[mystic_1]

And I must confess a dirty little secret...
I stole the original question from another forum.  I thought it was a cute problem and it seemed to generate a LOAD of havoc over there.

The logical inference is that you wanted to generate a LOAD of havoc over here too.

mystic_1

[mlinder]

This thread was not political, not religous, nor did it challenge anyones moral or ethical beliefs. It did not even cross boundries such as "honda vs harley" or "ford vs chevy".
The only havoc it caused is what the contributors to the thread allowed it to cause them.

[mystic_1]

I wasn't commenting about what the result of this thread was, just about what it seems the op's goal was, which was to generate arguments over semantic interpretations of intentionally misleading questions.

mystic_1

[sangyo soichiro]

And I must confess a dirty little secret...
I stole the original question from another forum.  I thought it was a cute problem and it seemed to generate a LOAD of havoc over there.

The logical inference is that you wanted to generate a LOAD of havoc over here too.

mystic_1

Perhaps I should have said 'lots of discussion.' 

I wasn't commenting about what the result of this thread was, just about what it seems the op's goal was, which was to generate arguments over semantic interpretations of intentionally misleading questions.

mystic_1

No one forced you to partake in this thread.

[mlinder]

I do get perturbed by lack of data, and would have preferred tangible values be stated, but it was still fun (though I entered late.)

[mystic_1]

Just as no one forced you to post it, or to keep prodding and provoking people in the direction you wanted it to go in.

So, what now?  What's the point of this thread?

mystic_1

[sangyo soichiro]

Just as no one forced you to post it, or to keep prodding and provoking people in the direction you wanted it to go in.

So, what now?  What's the point of this thread?

mystic_1

If you wish to continue this, it should be done via PM.

[masonryman]

when I brought up practical application verses theory I had never seen that article.


http://blag.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/comment-page-8/

As a tradesman I look at the practical verse theory, mostly because I have little formal education beyond HS, this is the point I was trying, unsuccessfully, to make


It was fun

peace

[my78k]

24 pages now eh? Can you tell it is still not quite riding season???

Dennis

[HavocTurbo]

And whats this with everyone throwing around my name like it will evoke some sort of madness....

I think I'm perfectly sane thank you.

And I do NOT cause trouble.







Yet.