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silverstan9
16th Apr 2009, 21:00
Hi,
Have just nipped over from my usual Football forum.

End of season non footy related question just been asked on our board and it goes like this ......

You are a pilot of an Aircraft and your runway is in fact a very large conveyor belt that is running in the opposite direction you are trying to take off, you then attempt a normal take off.

So what happens ?

Do you get into the air or stay in the same place.

Sorry if you have been asked this one a hundred times already.

Thanks. :ugh:

hellsbrink
16th Apr 2009, 21:02
Oh dear, this could get some fun responses :\

glazierflyer
16th Apr 2009, 21:05
I would be more concerned with landing

chiglet
16th Apr 2009, 21:06
ss9,
Do a search in jetblast for conveyor belt........:ok:

adverse-bump
16th Apr 2009, 21:06
it would take off, depending on the speed of the belt.

if it was 5 kts it would be the same as a 5 kts tail wind.

Rightbase
16th Apr 2009, 21:16
just go round faster. Normal take-off assuming the wheel bearings hold out..

daikilo
16th Apr 2009, 21:17
An airplane lifts off when the air flow over the wing creates excess lift over the drag and weight. The speed of the conveyor belt is totally irrelevant in this equation (excepting possibly induced ground effect - but that is another story).

Rainboe
16th Apr 2009, 21:18
Oh push off back to your stupid football forum creep. Wasn't the aim of the Priobationary thing that posts from newbies would be checked?

eliptic
16th Apr 2009, 21:39
Put on the breaks and take a backward lift:ugh:,,jissus what a question:sad:

Mohit_C
16th Apr 2009, 21:42
Back track the runway.

admiral ackbar
16th Apr 2009, 21:43
How would a rolling runway create lift for the wings again? :ugh::ugh:

B727
16th Apr 2009, 21:43
:bored:YouTube - Mythbusters - Plane on conveyor belt the practice! (http://www.youtube.com/watch?v=0ul_5DtMLhc&feature=PlayList&p=1E3C7CD1E1A3A620&playnext=1&playnext_from=PL&index=5)

mary meagher
16th Apr 2009, 21:45
Irrelevant answer to silly question.

Did you ever do a vertical circuit in a glider? Yes, if the wind is strong enough!

My mind also turns to thoughts of carrier planes, with a runway always into wind, and still moving.

sean maxwell
16th Apr 2009, 21:50
Nice one Rainboe. You couldn't just leave it could you?

Ballymoss
16th Apr 2009, 22:05
Leave it?.......he couldn't possibly. Fear not, one day he'll stew in his own handle!

Rgds
The Moss:ok:

SoundBarrier
16th Apr 2009, 22:36
ROFL...didn't I say this very thing in the "things that make you go Aaarrrg" forum just yesterday..maybe it's my fault!?
:}

Roger Sofarover
17th Apr 2009, 08:35
Rainboe

Oh push off back to your stupid football forum creep. Wasn't the aim of the Priobationary thing that posts from newbies would be checked?

I thought you had some sort of capacity as a Mod? Well whatever, what a nice welcome to the forum you gave the guy. Little wonder people think pilots are tossers.

maliyahsdad
17th Apr 2009, 08:42
it's ok, i have just got my own back. went on a football forum and asked if someone could explain the offside rule! :E

deltayankee
17th Apr 2009, 09:02
Whoever started this discussion in the pub has heard about the Mythbusters episode "Airplane on a Conveyor Belt" from 2008. For those who missed the show there is a summary of the conclusions here

MythBusters Episode 97: "Airplane on a Conveyor Belt" (http://mythbustersresults.com/episode97)

Rightbase was first with the right answer. This daft scenario is of no practical value, but does help people to understand the difference between wheel driven vehicles like cars and prop/jet driven aircraft.

Much more fun is to do a static takeoff on a seriously windy day (the "Vertical Circuit" described by Mary Meagher above). You'll not be able to do this with an airliner but gliders and very light bugsmashers can do it. In this case the problem is not taking off but staying on the ground the rest of the time.

tony draper
17th Apr 2009, 09:03
What happens if you sail up a river at five knots and the tide is ebbing at five knots?
:)

Sprogget
17th Apr 2009, 09:05
You put the kettle on, have a nice cup of tea?

Rollingthunder
17th Apr 2009, 09:07
Damn, i hate contributing to this thread.

Taxi onto said conveyor belt. Line up and wait.
Brakes on, engines at ground idle.
Belt starts moving - forward.
Halfway down bring power up, release brakes, V1, Vr, raise nose, fly.

Wouldn't work, they don't make belt fabric or bearings strong enough. And it would be too damned bumpy, like the main YYC runway times 1,000.

PaperTiger
17th Apr 2009, 16:30
PPRuNe has a gismo which replaces naughty words like **** with stars.

Might I humbly suggest that 'conveyor' be added to the list ?

Deja vu all over again.

SpannerInTheWerks
17th Apr 2009, 16:43
Roger Sofarover

My thoughts exactly.

The YouTube video is irrelevant as the aircraft is moving forward (against the direction of the conveyor) and is therefore carrying out a normal take-off irrespective of the speed of the conveyor (ground speed much greater than airspeed).

I think the original question assumed that the aircraft remained in a constant position, with simply the conveyor passing underneath it. The aircraft would then have groundspeed (the speed of the conveyor), but no airspeed and would stay firmly on the ground.

SITW :)

Storminnorm
17th Apr 2009, 16:56
I wish you'd all belt up, before you get carried away.

Roger Sofarover
17th Apr 2009, 20:51
Spanner agreed. Sorry I had a bit of finger trouble on an edit of the post and deleted it. The question relies on one fact only, will the aircraft/wings generate lift? The scenario was, run down the road at 12kph and hold up a piece of cardboard in the 'airflow' and see what happens, ie feel the effect. Now run on a running machine at 12kph and hold up your cardboard in the 'airflow' (sorry but there wont be one), what will happen to the card in terms of aerodynamic effect...nothing. The youtube vid is garbage as the aircraft is not running on a true conveyor belt.

eliptic
17th Apr 2009, 21:17
Tricky question,,depends how do you measure the speed? SOG, GPS, etc;)

SyllogismCheck
17th Apr 2009, 21:30
Listen very carefully, I shall say this only once.....



The point is NOT that an aeroplane not moving forward will take off. Obviously, it canít.

The point IS that a treadmill CAN NOT stop an aeroplane moving forward!

Thank you for your attention. :)

eliptic
17th Apr 2009, 22:08
You all wrong,, i can get a plane take of normally without the plane even moving on runway ,,guess how??? (and 0 zero wind )

G-CPTN
17th Apr 2009, 22:55
You all wrong,, i can get a plane take of normally without the plane even moving on runway ,,guess how??? (and 0 zero wind )
Helicopter?

chiglet
17th Apr 2009, 23:08
Inside another aeroplane?

rhythm method
17th Apr 2009, 23:11
A conveyor belt? :}

Jimmy Macintosh
17th Apr 2009, 23:14
You all wrong,, i can get a plane take of normally without the plane even moving on runway ,,guess how??? (and 0 zero wind )

Use a road?

By the way, thank you SyllogismCheck. I was about to start screaming that, glad you came in earlier. :)

mr fish
17th Apr 2009, 23:23
gerry anderson solved this one in the 60s,
thunderbirds, FIREFLASH episode.
mind you, the aircraft might have been on strings;)

Lightning6
17th Apr 2009, 23:31
Harrier by any chance?

bnt
18th Apr 2009, 00:00
Like, move the whole runway? This is what an aircraft carrier does, though its 40 knots is not enough permit jets to take off without engines. I wonder what would happen if you strapped a couple of Space Shuttle Solid Rocket Boosters to the sides of USS Nimitz? :ok:

PS: there are definitely previous threads on this topic. Use the search facility, but I don't advise doing it while sober. I tried to use physics and control system theory to explain why the conveyor belt can never do what you're asking it to do. It would need to have infinite acceleration, which means applying an infinite force to it (since we reasonably assume it has mass itself), and that would take an infinite amount of power.

You could build the thing of pure Unobtanium, and harness a black hole to it for power, and the plane would still take off, assuming its wheel bearings haven't annihilated the Earth in a cloud of anti-iron plasma.

hellsbrink
18th Apr 2009, 01:35
You all wrong,, i can get a plane take of normally without the plane even moving on runway ,,guess how??? (and 0 zero wind )

V-22 Osprey?

kiwi chick
18th Apr 2009, 02:30
He's not going to answer us cause he's busy in his back yard trying it out. :}

eliptic
18th Apr 2009, 06:57
BNT,,,

Correct answer!!!:D:ok:

Crank up the speed on a carrier

kiwi chick
18th Apr 2009, 08:40
Wow - when did they invent carriers that can travel at 80 knots? :hmm:

tony draper
18th Apr 2009, 08:50
I've seen a clip of a old Carrier with a biplane of some kind coming in and the crew had to run out and pull it down onto the deck, with the combination of the Carrier speed and windspeed across the deck the aircraft seemed to be hovering.
:uhoh:

eliptic
18th Apr 2009, 10:19
"!Wow - when did they invent carriers that can travel at 80 knots?"


P O C,,,a nuclear powered hovercraft air carrier,,,:rolleyes: