powerhouse

yeah , raise them one notch and try it !!

Me Too !! I still don't want it to fly !! hahaha Jan 30

[ Home Page | Message Boards | News | Archive | Ask Cecil | Books | Buy Stuff | FAQs, etc. ] [ Previous Week | Recent Columns Index ] -------------------------------------------------------------------------------- An airplane taxies in one direction on a moving conveyor belt going the opposite direction. Can the plane take off? 03-Feb-2006 -------------------------------------------------------------------------------- Dear Cecil: Please, please, please settle this question. The discussion has been going on for ages, and any time someone mentions the words "airplane" or "conveyor belt" everyone starts right back up. Here's the original problem essentially as it was posed to us: "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 the opposite direction). Can the plane take off?" There are some difficulties with the wording of the problem, specifically regarding how we define speed, but the spirit of the situation is clear. The solution is also clear to me (and many others), but a staunch group of unbelievers won't accept it. My conclusion is that the plane does take off. Planes, whether jet or propeller, work by pulling themselves through the air. The rotation of their tires results from this forward movement, and has no bearing on the behavior of a plane during takeoff. I claim the only difference between a regular plane and one on a conveyor belt is that the conveyor belt plane's wheels will spin twice as fast during takeoff. Please, Cecil, show us that it's not only theoretically possible (with frictionless wheels) but it's actually possible too. --Berj A. Doudian, via e-mail Cecil replies: Excuse me--did I hear somebody say Monty Hall? On first encounter this question, which has been showing up all over the Net, seems inane because the answer seems so obvious. However, as with the infamous Monty-Hall-three-doors-and-one-prize-problem (see The Straight Dope: "On Let's Make a Deal" you pick Door #1, 02-Nov-1990), the obvious answer is wrong, and you, Berj, are right--the plane takes off normally, with no need to specify frictionless wheels or any other such foolishness. You're also right that the question is often worded badly, leading to confusion, arguments, etc. In short, we've got a topic screaming for the Straight Dope. First the obvious-but-wrong answer. The unwary tend to reason by analogy to a car on a conveyor belt--if the conveyor moves backward at the same rate that the car's wheels rotate forward, the net result is that the car remains stationary. An aircraft in the same situation, they figure, would stay planted on the ground, since there'd be no air rushing over the wings to give it lift. But of course cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly I WAS WRONG !!!

where do you have the clips on your needles ?? the jets are fine , look elseware!

How much was that tree ? haha and it last for ever !!

why don't you work on this ?>>>> <<<<<

I don't know ! take some down there ..

why don't you deliver my package !

why don't you take it to that guy in China town ??? I think he has a Dyno !!!

thank you Cole !! the plane has to have speed to get wind for the lift !! what arn't you guys catching here ??

NICE !!! get the Pro Design Pro Flo w/ k and n !!

aaahahahahahaha !!!!! good job Vic !!

what a cute dog !! too bad it has to ride in that darn ford !!! hahahaha !!!

how did I know your Dodge driving azz would get in this !! you pot stirring mofo !!

what ? my Helmet ,don't be

it's not a voyuer cam jeff !! wrong helmet !!

is that the mexican part of china ??

yeah-no ,they fit that turdbox like a glove !!

I do know that , but it just hits me wrong with whole import / buy American thing !!

So I'm driving to get lunch, and I pull behind this Nissan Sentra . I see the guy in the car next to me trying to look at the little nissan, so I try to look at what ever he is , then , there it is BAM !!!!!!!!! a fugging bumper sticker that says Got Patriotisim / Buy American ! so as my blood starts to boil , I look up at the car only to see a handycapped plate , as I pull around I see this is a older man 55-65 I couldn't even honk /say anything/beat azz !! I almost felt bad [ almost ] what the hell is wrong with people ??!!

Nice !! good job , many good times will be had with that !!

oh snap this you freak !! :xmas7: haha yeah you must have to much movement on it , I never broke a flag on my drag bike, I don't see you breaking one [ from speed ! ]

make sure you chain that thing to your hauler to !! they like to steal them !!

they are both good , check the prices and go for the deal !! make sure they are 3000 watts