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#607385 - 05/11/07 03:15 PM Re: Airplane on a treadmill question
Samueul Offline
Member

Registered: 10/04/01
Posts: 4114
Loc: Pittsburgh, PA. USA
Quote:
Originally posted by ndxterra:
Quote:
Originally posted by Samueul:
[b]
Quote:
Originally posted by JMo:
[b]Being a pilot, the myth that a plane could take off from a tredmill is impossible. Its not the speed the wheels are travleing that make the plane take off. its the speed of the air iver the wings which creates the lift. Now, it would be possible for a plane to land or i guess even take off vertically, given the right wind conditions for the specific plane. I've heard of a navy pilot land on an aircraft carrier the was heading into hurricane force winds. he practically hovered over the ship into the wind and touched down. his relative motion was very slow but his airspeed was still over 100 knots. just like i've had my cessna start to go back watds druing slow flight.
Um,,, That's exactly why it would take off, because the ground speed and the wheels don't matter and it's the initial thrust pushing the plane through the air that generates lift below the wings etc. Since the plane isn't anchored to the treadmill, it's going to take off no matter how fast the treadmill goes in the opposite direction.[/b]
What "initial thrust"? I'm not following your explaination.

An airplane on a treadmill would not generate the necessary airspeed over its wings to produce lift required for flight.

Here is an example:
An airplanes takeoff airspeed is 80mph. This means the air must travel over the wings at 80 mph, the ground speed is irrelevant. If it takes off in a no wind condition, it must have a ground speed of 80 mph to have the required 80 mph airspeed. If the plane takes off into a 20mph headwind, it only needs to travel at 60mph ground speed to generate an 80 mph airspeed over its wings. Now if it has a 20 mph tailwind, it must have a 100mph ground speed to achieve a 80mph airspeed.

So if this same plane was on a treadmill going 80mph (ground speed), what would the airspeed over the wings be?

The answer is zero. With a zero mph airspeed over the wings the plane would generate no lift, and it would be unable to overcome the force of gravity.[/b]
What's powering the plane? I would assume its engines right? How else is it staying on the belt at all then? The wheels of the plane are just there for it to have something to sit on. If those engines turn on, there is nothing holding that planes wheels to the belt. That plane will move forward via the thrust of the engine. That forward motion will create airspeed and lift, and those wheels will lift off the belt and that plane will fly.

How does a black cat bottle rocket fly when it's laid on its side? It doesn't even have wheels! Its thrust moves it. What if you glue small wings to it?
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#607386 - 05/11/07 03:20 PM Re: Airplane on a treadmill question
Samueul Offline
Member

Registered: 10/04/01
Posts: 4114
Loc: Pittsburgh, PA. USA
Quote:
Originally posted by Auditor_Kevin:
I can't believe the airplane on a treadmill is even a debate. Of course it can't take off. If it did, it would be hovering, not flying.

C'mon people!
How does a vtol plane like the harrier jump jet fly. It hovers then as the engine "ports" are slowly turned rearward, it gains forward thrust and momentum and flys. It's the same principle. The belt under a plane makes no difference.
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#607387 - 05/11/07 05:33 PM Re: Airplane on a treadmill question
Anonymous
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#607388 - 05/11/07 05:44 PM Re: Airplane on a treadmill question
Anonymous
Unregistered


Quote:
Originally posted by Samueul:
Quote:
Originally posted by Auditor_Kevin:
[b]I can't believe the airplane on a treadmill is even a debate. Of course it can't take off. If it did, it would be hovering, not flying.

C'mon people!
How does a vtol plane like the harrier jump jet fly. It hovers then as the engine "ports" are slowly turned rearward, it gains forward thrust and momentum and flys. It's the same principle. The belt under a plane makes no difference.[/b]
A VTOL or STOVL (Short TakeOff Vertical Landing) is a special case, and it uses thrust to take off. Most planes use lift to take off. To generate lift, you need sufficient air moving over the wings to overcome the force of gravity.

So I will agree with you that a VTOL can take off from a treadmill, but you might as well add helicopter to this category.

I will also say that maybe a STOVL or a plane with a thrust to weight ratio greater than 1 could do it.

But there is no way you are going to take off in a plane with a low thrust to weight ratio, when the aircraft depends on the lift generated by the wings to achieve flight.

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#607389 - 05/11/07 06:08 PM Re: Airplane on a treadmill question
Anonymous
Unregistered


READ ME before you guys reach any conclusion....

I know it's long, but the correct answer's explained dozens of different ways.

ETA: It's only on pages 1-53 of that thread.

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#607390 - 06/11/07 06:10 AM Re: Airplane on a treadmill question
Anonymous
Unregistered


Quote:
Originally posted by MattyX:
READ ME before you guys reach any conclusion....

I know it's long, but the correct answer's explained dozens of different ways.

ETA: It's only on pages 1-53 of that thread.
Alright, you got me, we're beating a dead horse here.

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#607391 - 06/11/07 08:24 AM Re: Airplane on a treadmill question
Anonymous
Unregistered


It's not that the horse is dead, it's that the right answer's in there. It's explained pretty well, I think.

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#607392 - 06/11/07 11:03 AM Re: Airplane on a treadmill question
Auditor_Kevin Offline
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Registered: 01/06/02
Posts: 1016
Loc: Dundee, IL
I'm not gonna click on 53 pages of debate. What's the answer (even though I know it's 'no')?

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#607393 - 06/11/07 11:17 AM Re: Airplane on a treadmill question
Samueul Offline
Member

Registered: 10/04/01
Posts: 4114
Loc: Pittsburgh, PA. USA
Quote:
Originally posted by Auditor_Kevin:
I'm not gonna click on 53 pages of debate. What's the answer (even though I know it's 'no')?
The answer is yes....basically for the reason I stated.

If you are running on a treadmill, and someone who is not on the treadmill pushes you from behind, will you move forward on the treadmill even though your running speed hasn't changed?

You = Airplane
someone pushing you = engine thrust.
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#607394 - 06/11/07 11:49 AM Re: Airplane on a treadmill question
GrayHam Offline
Member

Registered: 17/04/01
Posts: 8849
Do an experiment at home:

Put rollerblades on your brother.
Put him on a treadmill at any speed. Notice how (if the wheels are truly free-rolling) he doesn't move? Forward or backward, he doesn't move at all?

Now increase the treadmill's speed. He's still not moving. The wheels on the rollerblades are spinning wildly, freely, faster and faster, but he doesn't move.

Leave him like that for a few minutes. Get a sense for how all that energy from the treadmill is wasted on those free-rolling wheels.

Now, walk up to him while the treadmill and the rollerblade wheels are still spinning away. Push him in the back (maintain the push, just like a plane would maintain thrust!), and watch him roll forward into the treadmill's control panel.

Why?

Because the treadmill acts on the roller-blade wheels ONLY. The exact same way the treadmill will act on the free-rolling landing gear of an aircraft.

Your push acts on your brother's body the exact same way thrust from an aircraft's engines works on an airframe and the attached wings.

The energy being used and delivered at the wheels while on a treadmill simply has zero impact on the airframe.
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#607395 - 06/11/07 12:02 PM Re: Airplane on a treadmill question
XPLORx4 Offline
Member

Registered: 23/03/01
Posts: 1906
Loc: San Jose, CA
OMG, I simply cannot believe that this one has resurfaced! ARGH!

The irony of it all is that, with Mythbusters taking it on, I'm sure some of the "It WON'T fly" folks will find something wrong with the Mythbusters methodology, such as "Well, maybe an ULTRALIGHT can take off, but a 737 on a treadmill won't take off! They have to repeat the test with a 737 for me to be a believer!"

Some folks just don't get it, and never will. May they wallow in their ignorance.
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#607396 - 06/11/07 12:03 PM Re: Airplane on a treadmill question
XPLORx4 Offline
Member

Registered: 23/03/01
Posts: 1906
Loc: San Jose, CA
Quote:
Originally posted by Auditor_Kevin:
I'm not gonna click on 53 pages of debate. What's the answer (even though I know it's 'no')?
It's YES. You may as well start clicking through 53 pages of debate, 'cause this thread will start to get that long if you stick to your "Can't fly" position for much longer.
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#607397 - 06/11/07 12:14 PM Re: Airplane on a treadmill question
NY Madman Offline
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Registered: 09/05/02
Posts: 5232
Loc: Florida
Even standing on a treadmill with rollerblades on your feet, there will still be some backward force exerted on you. But, with a small push forward, that force can be easily overcome.

A plane would still be able to take off on a treadmill.

The debate and confusion on this issue comes from the wording of the question posed in the plane/treadmill scenario.

An even bigger question than whether the plane will take off is .... how come this is even being brought up again when the original thread is almost right beneath this new thread?

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#607398 - 06/11/07 12:17 PM Re: Airplane on a treadmill question
Anonymous
Unregistered


Alright, I'll concede that it can fly. Where my thinking was constrictive was the length of the treadmill.

If the treadmill is say...the length of a runway, then yes, the plane can take off. As stated previously the wheels will simply spin at a speed equal to the takeoff airspeed (assuming no head or tail wind) plus the velocity of the treadmill at the point of takeoff.

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#607399 - 06/11/07 12:25 PM Re: Airplane on a treadmill question
Anonymous
Unregistered


Quote:
Originally posted by NY Madman:

An even bigger question than whether the plane will take off is .... how come this is even being brought up again when the original thread is almost right beneath this new thread?
Because we enjoy beating dead horses here. Honestly I never knew what was being discussed in the thread "Know that if you do not post in this thread today the human race may cease to exist" because it was just too long to peak my interest, and the title doesn't exactly describe the topic of the thread.

It looks like we can add the "plane on a treadmill" question to to the status of "how do I improve my gas mileage?" and "what size tires can I run without trimming?".

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#607400 - 06/11/07 01:12 PM Re: Airplane on a treadmill question
Auditor_Kevin Offline
Member

Registered: 01/06/02
Posts: 1016
Loc: Dundee, IL
Quote:
Originally posted by ndxterra:
Alright, I'll concede that it can fly. Where my thinking was constrictive was the length of the treadmill.

Me too. I was assuming the word "treadmill" meant something roughly equal to the length of the plane, not something three miles long.

If someone had simply said "giant moving walkway the length of a runway" instead, we would have avoided 99% of the debate.

It's like starting a debate titled "you can't eat a sandwich in one sitting" without elaborating that the sandwich is the size of your house.

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#607401 - 06/11/07 01:28 PM Re: Airplane on a treadmill question
Anonymous
Unregistered



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#607402 - 06/11/07 01:54 PM Re: Airplane on a treadmill question
Anonymous
Unregistered


GrayHam - that was the best way to explain this problem I have ever heard. I went to the lengths of creating a drawing of a free body diagram, which seemed to not help at all. Physics gold star to grayham.

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#607403 - 06/11/07 02:15 PM Re: Airplane on a treadmill question
NY Madman Offline
Member
*

Registered: 09/05/02
Posts: 5232
Loc: Florida


Someone else also created a free body diagram that can viewed by clicking the image below....


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#607404 - 06/11/07 03:43 PM Re: Airplane on a treadmill question
Mobycat Offline
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Registered: 12/09/00
Posts: 8374
Loc: the hue of dungeons and the sc...
Quote:
Originally posted by ndxterra:

If the treadmill is say...the length of a runway, then yes, the plane can take off.


The length of the treadmill has no bearing on this. The plane will move no matter how long the treadmill is.

Well, ok, it matters in that if the treadmill is the length of the plane, the plane will move off it and on to the tarmac and then take off.

Quote:
As stated previously the wheels will simply spin at a speed equal to the takeoff airspeed (assuming no head or tail wind) plus the velocity of the treadmill at the point of takeoff.
Which is where, if I'm not mistaken, the original question is worded incorrectly (or badly, anyway) - say the wheels continuously match the speed of the treadmill.
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"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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#607405 - 06/11/07 04:09 PM Re: Airplane on a treadmill question
Anonymous
Unregistered


Are you people seriously going to chew this shit over again?

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#607406 - 06/11/07 06:49 PM Re: Airplane on a treadmill question
Anonymous
Unregistered


yes.

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#607407 - 07/11/07 11:52 AM Re: Airplane on a treadmill question
Anonymous
Unregistered


OMG! does the navy know about this!? Why don't they have treadmills on all the air craft carriers!?!?!?!?!

I'll tell you why, cause it won't work. Everyone keeps focusing on speed; speed is not directly responsible for a planes ability to take off. Planes fly because the air flowing over the wing is faster than the air under it. Therefore, the air under the wing pushes the plane up.

The treadmill does not provide any wind over the wings. The shape of the wing is what allows the air to flow faster over the top than the bottom, but in order for the air to flow over the wings at sufficient speed, the plane has to actually move. On a treadmill, no air is moving.

You would need a wind tunnel to make the plane take off. And in truth, this would work with or without the treadmill.

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#607408 - 07/11/07 11:55 AM Re: Airplane on a treadmill question
GrayHam Offline
Member

Registered: 17/04/01
Posts: 8849
Quote:
Originally posted by cadams7407:
OMG! does the navy know about this!? Why don't they have treadmills on all the air craft carriers!?!?!?!?!

I'll tell you why, cause it won't work. Everyone keeps focusing on speed; speed is not directly responsible for a planes ability to take off. Planes fly because the air flowing over the wing is faster than the air under it. Therefore, the air under the wing pushes the plane up.

The treadmill does not provide any wind over the wings. The shape of the wing is what allows the air to flow faster over the top than the bottom, but in order for the air to flow over the wings at sufficient speed, the plane has to actually move. On a treadmill, no air is moving.

You would need a wind tunnel to make the plane take off. And in truth, this would work with or without the treadmill.
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#607409 - 07/11/07 12:18 PM Re: Airplane on a treadmill question
Anonymous
Unregistered


LOL...really.

Welcome to 6 months ago when we went 20 pages on it then.

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