Will it fly
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Joined: Mar 2004
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From: Truro
Will it fly
I wonder if I may posit a question found on another forum (Nikon Cafe, used by many aviators, both fast jet and airline, plus my little rotary world). There is no further information than that included below. The theory will be tested on 'Mythbusters' in the states on Jan 30th and 31st.
Your opinions and reasoning would be appreciated. If this is in the wrong place please let me know where to post it, and if it has been covered previously again I apologise.
Let's say you have a single engine airplane sitting on a runway that is 3000 feet long, and through some great engineering the runway is actually a giant treadmill. It's engineered so that when the plane starts to move forward the runway moves in the opposite direction at exactly the same speed., i.e. as the airplane's wheels pick up speed the runway matches it.
Will the plane get airborne?
Your opinions and reasoning would be appreciated. If this is in the wrong place please let me know where to post it, and if it has been covered previously again I apologise.
Let's say you have a single engine airplane sitting on a runway that is 3000 feet long, and through some great engineering the runway is actually a giant treadmill. It's engineered so that when the plane starts to move forward the runway moves in the opposite direction at exactly the same speed., i.e. as the airplane's wheels pick up speed the runway matches it.
Will the plane get airborne?
Joined: Nov 2007
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From: Australia
I would of thought the 'runway' speed to be irrelavent, as mig 15 says, it is the airspeed that makes flight for fixed wing.
But of course myth busters will show how the 'moving' runway creats its own wind, so to speak....
But of course myth busters will show how the 'moving' runway creats its own wind, so to speak....
A Runyonesque Character
Joined: Apr 2004
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From: The South of France ... Not
The engine will pull (propeller) or push (jet) the aircraft towards the far end of the runway, regardless of whether or not the runway is moving relative to the ground on either side of it.
It is therefore a logical impossibility that the runway moves at the same speed as the wheels, the wheels will always be moving at the speed of the runway plus the forward speed of the aircraft.
Subject of countless Pprune threads about a year ago.
It is therefore a logical impossibility that the runway moves at the same speed as the wheels, the wheels will always be moving at the speed of the runway plus the forward speed of the aircraft.
Subject of countless Pprune threads about a year ago.
Per Ardua ad Astraeus
Joined: Mar 2000
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From: UK
http://www.pprune.org/forums/showthread.php?t=200511 from Jetblast which is where I suspect this one will go
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If the treadmill is matching the planes forward speed then it will take off. It will reach takeoff speed and lift off as normal with the treadmill running backwards at the same speed. The wheels will be travelling at twice the takeoff speed.
If, however, the treadmill is matching the wheelspeed of the plane the plane will remain stationary and both the wheels and the treadmill will rapidly accelerate upwards to the point where the friction in the wheel bearings exactly balances the thrust of the engines, either that or the wheel bearings seize.
If, however, the treadmill is matching the wheelspeed of the plane the plane will remain stationary and both the wheels and the treadmill will rapidly accelerate upwards to the point where the friction in the wheel bearings exactly balances the thrust of the engines, either that or the wheel bearings seize.
Last edited by NeoDude; 11th January 2008 at 08:58.
A Runyonesque Character
Joined: Apr 2004
Posts: 1,209
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From: The South of France ... Not
Moderation by popular vote, that's a novel idea for Pprune. I'll vote for that.
First time I've been in this forum, Genghis, you seem to look after it very well. All credit to you.
First time I've been in this forum, Genghis, you seem to look after it very well. All credit to you.
Joined: Aug 2007
Posts: 26
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From: UK
Why would the treadmill runway need to be 3000trs long??? after all a treadmill at the gym is only 1.5 mts approx yet i can run 5k>. and still not reach the end....never seem to achieve t/o either although i have sufferd u/c failure once!!!!
so the time saved constucting 3000mtrs can be used to build a large fan for that much needed airspeed.
so the time saved constucting 3000mtrs can be used to build a large fan for that much needed airspeed.
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From: UK
First time I've been in this forum, Genghis, you seem to look after it very well. All credit to you.
Genghis, I did apologise further back, please bin it. I hadn't searched prior to posting.
G
