Islander Posted January 7, 2011 Share Posted January 7, 2011 If the plane is moving north at 50mph, and the conveyor below it is moving south at 50mph, then, the plane is motionless relative to the eath and air. It takes air movement relative to the plane's wings to create lift. No motion relative to air; no workie. Not you, too! Okay, you say "If the plane is moving north,... ...then, the plane is motionless relative to the eath and air." Is the plane moving or not moving? In the original question, it's stated that the plane does move.If you think it's motionless, I have to point out that it's not so. The airplane is not a car. The speed at which a car's wheels turn determines the ground speed of the car (in the absence of wheelspin or skidding, of course). On a conveyor moving in the rearward direction, the car's wheels would have to turn faster than the conveyor is moving in order for the car to move forward. If the conveyor matches the wheel speed, the car does not move.However, with an airplane, the wheels' rotating speed is irrelevant. For example, if a plane is travelling in the air, its wheels are not turning at all, but the plane could be travelling as fast as multiples of the speed of sound.On the ground, once the pilot throttles up (assuming he has first released the brakes), the engine thrust will cause the plane to move relative to the ground and the air, regardless of what the wheels are doing. Keep in mind that a moving conveyor is not the stationary ground and does not affect the plane, since the plane is on free-spinning wheels.Once the plane attains sufficient airspeed for takeoff, it will lift off, no matter what the rotating speed of the wheels may be. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted January 7, 2011 Share Posted January 7, 2011 It appears that you may have mis-read the original statement. A number of people seem to overlook the ability of the plane to move, although it's clearly stated in the second sentence.From the first page, back in 2006, the original quote:a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.the question iswill the plane take off or not?Note where it says "as the plane moves". If the plane is moving north (for example) at 50mph, the conveyor will be moving south at 50mph. The plane's wheels will be spinning at 100mph. That does not matter, because the plane is not wheel-driven. The moving conveyor will not prevent the plane from moving or from taking off once it reaches takeoff speed.According to your premise, if the wheel drag was sufficient, when the conveyor reached a certain speed, it would begin to to slow the plane and eventually start to drag the plane backwards. However, the plane would take off long before that. If the plane is moving north at 50mph, and the conveyor below it is moving south at 50mph, then, the plane is motionless relative to the eath and air. It takes air movement relative to the plane's wings to create lift. No motion relative to air; no workie. No the wheel is now moving 100 mph now. Quote Link to comment Share on other sites More sharing options...
Jeff Matthews Posted January 7, 2011 Share Posted January 7, 2011 I saw this on another forum I frequent and found some of the commentary interesting. I don't know the answer although I've got an opinion. It WAS interesting seeing the answers/thoughts some people gave (2 pages worth). I'm copying it exactly like he had it there a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction. the question is will the plane take off or not? (ps its been debated to death on other forums, its always fun to see how people present the theory behind there answer) From the OP. The conveyor tracks the speed of the plane and matches that speed in the opposite direction. Thus, the plane is motionless relative to the earth and air. Quote Link to comment Share on other sites More sharing options...
Andy W Posted January 7, 2011 Share Posted January 7, 2011 The treadmill will only have slightly more effect on an airplane as is it would under Luke Skywalker's Land Speeder. If the wheel bearings were frictionless then it would be EXACTLY like Luke's Speeder. Take the wheels out of the equation - it's only there to confuse you. Quote Link to comment Share on other sites More sharing options...
Jeff Matthews Posted January 7, 2011 Share Posted January 7, 2011 The treadmill will only have slightly more effect on an airplane as is it would under Luke Skywalker's Land Speeder. If the wheel bearings were frictionless then it would be EXACTLY like Luke's Speeder. Take the wheels out of the equation - it's only there to confuse you. I think I understand the argument, but it seems incorrect. Let's assume the jet starts at rest. It fires the engines and commences forward. The speed at which it moves forward is represented - not by the wheels - but IN the wheels. The wheels are attached to the jet. Since the wheel speed REFLECTS the speed of forward thrust, any matching speed in the opposite direction of the conveyor displaces the thrust motion, rendering the jet motionless relative to the earth and air. No? Quote Link to comment Share on other sites More sharing options...
sputnik Posted January 7, 2011 Share Posted January 7, 2011 I think I understand the argument, but it seems incorrect. Let's assume the jet starts at rest. It fires the engines and commences forward. The speed at which it moves forward is represented - not by the wheels - but IN the wheels. The wheels are attached to the jet. Since the wheel speed REFLECTS the speed of forward thrust, any matching speed in the opposite direction of the conveyor displaces the thrust motion, rendering the jet motionless relative to the earth and air. No? Jeff, [:S] Do you have amnesia or are you really Jeff? The Jeff I know got this back on page 34. See link. http://community.klipsch.com/forums/t/82113.aspx?PageIndex=34 Quote Link to comment Share on other sites More sharing options...
Jeff Matthews Posted January 7, 2011 Share Posted January 7, 2011 Yeah, it's me, Sput. It never sunk-in intuitively. Now that I re-read the link to my own post quoting somebody else's explanation, it has stuck. I shall never visit this thread again. The treadmill with roller skates and a rope example realy helps. Quote Link to comment Share on other sites More sharing options...
sputnik Posted January 7, 2011 Share Posted January 7, 2011 Yeah, it's me, Sput. It never sunk-in intuitively. Now that I re-read the link to my own post quoting somebody else's explanation, it has stuck. I shall never visit this thread again. The treadmill with roller skates and a rope example realy helps. Whew, I was afraid you got hit on the head or something. Quote Link to comment Share on other sites More sharing options...
Islander Posted January 7, 2011 Share Posted January 7, 2011 I think I understand the argument, but it seems incorrect. Let's assume the jet starts at rest. It fires the engines and commences forward. The speed at which it moves forward is represented - not by the wheels - but IN the wheels. The wheels are attached to the jet. Since the wheel speed REFLECTS the speed of forward thrust, any matching speed in the opposite direction of the conveyor displaces the thrust motion, rendering the jet motionless relative to the earth and air. No? Well, it looks like you've got it now. Movement of the plane refers to movement of the airframe, not the wheels. Unlike a car, the jet has no speedometer driven by the wheels. The wheels are irrelevant. The airframe, or body, of the jet starts moving as soon as the throttle is moved past idle position. The wheels are put in the question to confuse the reader, but have no bearing on the outcome. Quote Link to comment Share on other sites More sharing options...
Saturn5 Posted January 8, 2011 Share Posted January 8, 2011 I have to admit when I first heard of this riddle, I fell for it and thought the plane wouldn't take off. Intuitively we think of it as a car example - where the car's forward momentum would be cancelled out by the conveyor belt's rearward speed. The disconnect comes in because the car is pushing against the conveyor belt through the wheels. The plane's thrust is against the air - which isn't affected by the conveyor belt, so the plane moves forward. Luke's landspeeder is a great example. Or even a modern hovercraft. Quote Link to comment Share on other sites More sharing options...
Islander Posted January 8, 2011 Share Posted January 8, 2011 Wow, if everyone here gets it now, that may put this speaker fan forum ahead of some engineer forums... [Y][8-|][] Quote Link to comment Share on other sites More sharing options...
BigStewMan Posted January 8, 2011 Share Posted January 8, 2011 you haven't given sufficient information to answer the question. What color is the plane and is it night or day? Quote Link to comment Share on other sites More sharing options...
DizRotus Posted December 24, 2011 Share Posted December 24, 2011 Q: "you haven't given sufficient information to answer the question. What color is the plane and is it night or day?" A: Silver and yes. Quote Link to comment Share on other sites More sharing options...
oldtimer Posted December 24, 2011 Share Posted December 24, 2011 . Quote Link to comment Share on other sites More sharing options...
Guest " " Posted December 24, 2011 Share Posted December 24, 2011 Which direction is the plane facing......in direction of the earths rotating or opposite of it. . The circumference of the Earth at the equator is 24900 miles and the residentsof the tropic areas travel that distance every 24 hours. They are traveling over a thousandmiles an hour. At 38° latitude we are traveling about 820 miles per hour. So in effect, the earth is another conveyer belt. Quote Link to comment Share on other sites More sharing options...
sheltie dave Posted December 24, 2011 Share Posted December 24, 2011 From the Boeing flight director at work... Plant a flag in the ground at the nose of the plane. Start the expirement. If the F18 does not move past the flag, the F18 will not generate enough lift for the plane to fly, no matter how much thrust is applied. Sustained laminar lift over a period of time over a given distance will enable the plane to fly. Quote Link to comment Share on other sites More sharing options...
Utard Posted December 24, 2011 Share Posted December 24, 2011 I do not understand how/why anyone would give this question half a thought? Anyone with a shred of intelligence knows the answer is no. I do not understand why this is such a hard concept for a lot of people to understand? They say humans are getting smarter in time but they are losing their common sense. Even the mythbusters debunked it. Quote Link to comment Share on other sites More sharing options...
DizRotus Posted December 24, 2011 Share Posted December 24, 2011 According to Mythbusters, it takes off. "1. Come ON! We put a gall-durned actual, honest-to-goodness plane on a bona fide conveyor belt and it TOOK OFF. What MORE do you people WANT?! If you're not satisfied by that, I doubt that anything we could do would help." http://dsc.discovery.com/fansites/mythbusters/top-ten/pocb/pocb.html Quote Link to comment Share on other sites More sharing options...
sheltie dave Posted December 25, 2011 Share Posted December 25, 2011 Neil, it all depends how you establish the paradigms for the question. If you bound the scenario by planting the flag in front of the plane, and the nose doesn't pass the flag, forget about it. If you do semantical tricks by towing the conveyor as they did in Mythbusters, or push the plane and conveyor off a cliff or put them in a freefall at 20,000 feet, then the plane will "take off." Quote Link to comment Share on other sites More sharing options...
sputnik Posted December 25, 2011 Share Posted December 25, 2011 . that ^ and..... There really should be an emoticon for beating your head against a dead horse. Quote Link to comment Share on other sites More sharing options...
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