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Thread ID: 93430	2008-09-16 06:00:00	Aircraft Taking off problem	Thomas01 (317)	PC World Chat

Post ID	Timestamp	Content	User
705639	2008-09-17 08:40:00	But the wheels don't do anything!!! They don't provide the thrust, they're only there to lift the plane off the ground.	beeswax34 (63)
705640	2008-09-17 09:00:00	Ok, had a think about it while I was in the shower. I see now how the plane will indeed fly Was trying to overthink on an already tired brain... amazing what a shower will do to regenerate you :D	Myth (110)
705641	2008-09-17 09:11:00	Myth and Beeswax34, that ground has been over umpteen times :) :banana What has not yet been resolved is what the original question or 'postulate' actually means, or even what the questioner had in mind. In actual fact it can mean almost whatever anyone wants it to mean, because it is so imprecise. That is why both Billy and Erayd/Bletch can simultaneously be both right and wrong :lol: Original question for reference again: "Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation. There is no wind. Can the plane take off?" Speed of the wheels: could mean the velocity of the axle, a vector, ie speed and direction of travel of the axle, or could mean the rotational speed (angular velocity) of the wheel in which case we are talking of surface velocity of the tyres, and then we have the top and bottom of the tyres, same surface speed but opposite surface velocities . "The conveyor belt...moving in the opposite direction of rotation." The part of the conveyor belt of interest on which the plane is sitting is not rotating, it only has linear speed if it moves Thus that statement has no meaning. As Graham has said the question is silly nonsense.	Terry Porritt (14)
705642	2008-09-17 09:16:00	:D :thumbs:. Seems like TP is the most sensible one in this debate... but we all have great fun arguing about it regardless :rolleyes:.	Erayd (23)
705643	2008-09-17 20:09:00	If only WMC/VSX were here, then it would be a giant PF1 party. :D :D :D	pcuser42 (130)
705644	2008-09-17 23:46:00	Thanks Terry for your erudite and patient work. :punk It is a clumsy question and I suspect that most of the objections - mine included, turn upon the reading of it. My interpretation is that there can never be airspeed over the wings if the aeroplane remains on the same spot relative to the ground. Thus it can never takeoff - unless it is allowed to leave the conveyor a la VTL. I'm sure most people here understand airspeed and the concept of lift over aerodynamic surfaces. For the question to be accurately interpreted, the wheels can never advance from their point on the earth's surface. If they did then there is forward motion which contravenes the requirement that their speed (forward motion relative to the ground) is matched by a reverse speed. As Graham says, forget the wheels per se, think of the axles - and they do not move forward. If I'm wrong, lets think of a zero speed. Fire a jet out the back but don't allow the aircrafts wheels to move forward - will it take off?	Winston001 (3612)
705645	2008-09-17 23:56:00	The problem with that is the plane isn't locked to the surface, its just sitting on it, And no matter what speed the conveyer runs at the propeller can always still pull the plane forward and up. The plane will fly no matter how much you dissect the question.	Metla (12)
705646	2008-09-18 01:30:00	Ok Mets, if the speed is always matched - set the speed at zero. What happens? Incidentally there is no mention of a propellor in the original question.	Winston001 (3612)
705647	2008-09-18 01:43:00	i can't believe this argument still rages on, when common sense and a little thing called the law of physics says the plane will take off... but what if you put glue on the wheels and the treadmill is made of sandpaper and it's running at twice the speed and the plane is in fact a paperplane and the pilot isn't even in the plane?	Jan Birkeland (4741)
705648	2008-09-18 01:46:00	The real world gets in the way and the plane flys away.... The conveyor you require to keep the plane stationary does not exist, and you can't just imagine fantastical devices to suit your argument. as the conveyor sped up to compensate for the plane moving forward the rotation of the wheels would also speed up and the plane would still travel forward and take to the air. To infinity and beyond. If we can just imagine new devices then I suggest the plane is picked up and flung through the air by a giant chicken and the conveyor is then attacked by Ninjas. And yes, I can see the absurdity of what I just wrote, as a conveyor big enough to mount a plane on is also a fantastical imagining. But there ya go, that's all the apples in the barrel, pour a beer and look at the sunset. as I was saying.....the real world....	Metla (12)
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