AVSIG: So, say a plane is on a moving runway.... wwswsigarch.jpg (7236 bytes)

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AVSIG Discussion Sections >> Aviation History

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Denny Cunningham
Top Gun


Reged: 09/01/01
Posts: 915
Loc: Gold Canyon, AZ
So, say a plane is on a moving runway....
      #83486 - 11/16/05 05:58 AM

The thread generated by this post on another forum got WAY more controversial than I would have expected. The average level of intelligence on that forum appears to be several orders of magnitude below this one, so I'm curious what the folks here have to say about the hypthetical question (repeated verbatim):

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The question is:

Will the plane take off or not?"

If you want to read the replies on the other forum, they're at:

http://forums.flightinfo.com/showthread.php?t=66860


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Tom Tyson [SUW]
Glider Guider


Reged: 05/27/04
Posts: 4691
Loc: KSUW
Re: So, say a plane is on a moving runway.... [Re: Denny Cunningham]
      #83491 - 11/16/05 06:12 AM

You know, life is SOOO much more pleasant here at the 'drome.

I think it's something we need to cherish and nurture.

- TT

--------------------
Tom Tyson-A&P

Pilots without Mechanics are just Pedestrians with fancy watches.


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Mick Ruthven
AVSIG Member


Reged: 05/15/04
Posts: 1320
Loc: San Francisco Bay Area
Re: So, say a plane is on a moving runway.... [Re: Denny Cunningham]
      #83497 - 11/16/05 06:39 AM

You have to be kidding, right? No I did not read the posts on the other forum.

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Sean Franklin
Top Gun


Reged: 08/15/04
Posts: 2566
Loc: Eureka Springs, Arkansas
Re: So, say a plane is on a moving runway.... [Re: Denny Cunningham]
      #83506 - 11/16/05 07:05 AM

I had to look... There are people who think it won't take off!!! Wow... I hope they're not pilots... That shows a lack of even a BASIC understanding of the physics of flight.

--------------------
Eureka Springs, Arkansas


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Stephanie Belser
Top Gun APC


Reged: 04/29/04
Posts: 5929
Loc: KFAM
Re: So, say a plane is on a moving runway.... [Re: Denny Cunningham]
      #83508 - 11/16/05 07:13 AM

Quote:

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The question is:

Will the plane take off or not?"




What is important is the speed of the aircraft through the relative wind, not the speed on the runway. That's why you can put an aiirplane on a flatbed truck (or the J-3 on the "world's shortest runway"), speed up the truck to the proper speed and launch the airplane. The airplane will fly and, if the prop is producing the required thrust, it will continue to fly. Airspeed is important here, not ground speed.

If you had perfect roller bearings, you could stand alongside the wingtips (on solid ground) and just hold the airplane by hand as the band runway moves. The prop, which will bite through the air, will do the same. The airplane will accelerate through the air and take off, assuming that the tires don't exceed their rated rotation speed and fail.

Stephanie


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Dan Barclay [ORG]
Top Gun


Reged: 05/06/04
Posts: 4492
So, say a plane is on a moving runway.... [Re: Denny Cunningham]
      #83514 - 11/16/05 07:23 AM

Code:

>> Will the plane take off or not?"

Assuming the plane is powered by moving mass via prop/jet/rocket (rather than
by wheels as in a car) it will take off.

The wheels, when it lifts off, will be spinning at twice their normal RPM.
If the wheels come apart (a la Concorde) the plane may or may not fly very
far.

>> http://forums.flightinfo.com/showthread.php?t=66860

Thanks, but...

Later,
Dan



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Bob Dubner
Super Imperial Member


Reged: 08/31/01
Posts: 4759
Loc: Extreme Upper West Side
So, say a plane is on a moving runway.... [Re: Denny Cunningham]
      #83528 - 11/16/05 08:17 AM

Denny, you need to stay in more.

I wonder if they've thought about taking off to the west.

Here in the New York area, the earth's surface is moving eastward at about
700 miles per hour. According to some of those folks, I'd have to be moving
at about 800 miles per hour over the ground in order to take off.

And how we keep any plane on the ground if its nose is facing east is a
mystery.


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John Graff
Top Gun


Reged: 05/19/04
Posts: 8596
Loc: KOJC
Re: So, say a plane is on a moving runway.... [Re: Denny Cunningham]
      #83535 - 11/16/05 08:48 AM

Denny:

____ Now - a plane is coming in to land on a conveyer belt that is operating at the speed of ...

Have fun!

John

Edited by John Graff (11/16/05 08:52 AM)


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Rick Durden
Top Gun


Reged: 06/07/04
Posts: 4366
Re: So, say a plane is on a moving runway.... [Re: Denny Cunningham]
      #83550 - 11/16/05 10:29 AM

Denny,

I look at a few of the other forums, but the dumbs$%^ factor is so high, and that little exercise proves it.

Wonder how they'd handle downwind turns? sigh

What really scares me is that some of those "it won't fly" morons may be pilots.

Warmest regards,
Rick


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Richard Palm (PAO)
Top Gun


Reged: 04/30/04
Posts: 5388
Loc: PUDBY
Re: So, say a plane is on a moving runway.... [Re: Denny Cunningham]
      #83554 - 11/16/05 10:34 AM

When I first saw the thread title I thought it was about aircraft carriers! <G>

BTW, I wonder if rolling friction increases with speed?

Edited by Richard Palm (PAO) (11/16/05 10:36 AM)


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