Conundrum 1 #26 May 1, 2006 QuoteQuoteQuoteIf the plane is a Harrier, yes. Why's that? The Harrier vectors engine thrust downward and can take off like a rocket, or a hovercraft - it doesn't require aerodynamic lift over the wings. I know how Harriers take off, just wondering why you thought it would only take off if it was a Harrier, which is incorrect. Quote Share this post Link to post Share on other sites
JohnRich 4 #27 May 1, 2006 QuoteI know how Harriers take off, just wondering why you thought it would only take off if it was a Harrier, which is incorrect. Explain why you think the hypothetical plane will be able to take off. Quote Share this post Link to post Share on other sites
stitch 0 #28 May 1, 2006 QuoteQuoteHarrier is a VTOL fixed wing fighter.Meaning it takes off and lands like a helicopter. No kidding. Regardless if it was a Harrier or not, it would still take off.In therory yes.But the Harrier is built by Hawker-Siddley,a UK corp. so chances are no, it would not take-off."No cookies for you"- GFD "I don't think I like the sound of that" ~ MB65 Don't be a "Racer Hater" Quote Share this post Link to post Share on other sites
Icon134 0 #29 May 1, 2006 QuoteQuoteThink of it this way, if the wheels had zero friction and rotational inertia, Thats the problem tho. They have friction, both rolling resistance, and bearing friction. But, I'm cutting hairs in 4 here The amount of friction that is needed to overcome is not enough to prevent the plane from moving forward... Livin' on the Edge... sleeping with my rigger's wife... Quote Share this post Link to post Share on other sites
sundevil777 102 #30 May 1, 2006 QuoteI'm with mnealtx: the plane, by definition, is stationary relative to the air around it No, that is not the scenario. The conveyor simply makes the wheels spin twice as fast as normal. By definition, if the plane is stationary, the conveyor is stationary. That is the initial state of this scenario, from there the plane starts moving forward relative to the ground, with the wheels spinning twice as fast. I think this riddle is good at showing how easy it is to assume things not in the original problem statement.People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am Quote Share this post Link to post Share on other sites
Conundrum 1 #31 May 1, 2006 QuoteQuoteI know how Harriers take off, just wondering why you thought it would only take off if it was a Harrier, which is incorrect. Explain why you think the hypothetical plane will be able to take off. A plane's thrust is created not by the wheels but by the prop (or jet engine), and the friction of the wheels would not create enough drag to overcome that thrust, therefore, the plane will still pull itself forward, eventually creating enough lift to leave the ground. Now, how do you explain why you think it won't take off? Quote Share this post Link to post Share on other sites
mnealtx 0 #32 May 1, 2006 QuoteQuoteI'm with mnealtx: the plane, by definition, is stationary relative to the air around it No, that is not the scenario. The conveyor simply makes the wheels spin twice as fast as normal. By definition, if the plane is stationary, the conveyor is stationary. That is the initial state of this scenario, from there the plane starts moving forward relative to the ground, with the wheels spinning twice as fast. I think this riddle is good at showing how easy it is to assume things not in the original problem statement. With that clarification, that the conveyor belt is only running at the same (albeit reversed) speed as the plane's movement over the ground, then yes - the wheels will spin faster and the plane will still take off.Mike I love you, Shannon and Jim. POPS 9708 , SCR 14706 Quote Share this post Link to post Share on other sites
Conundrum 1 #33 May 1, 2006 QuoteQuoteQuoteI'm with mnealtx: the plane, by definition, is stationary relative to the air around it No, that is not the scenario. The conveyor simply makes the wheels spin twice as fast as normal. By definition, if the plane is stationary, the conveyor is stationary. That is the initial state of this scenario, from there the plane starts moving forward relative to the ground, with the wheels spinning twice as fast. I think this riddle is good at showing how easy it is to assume things not in the original problem statement. With that clarification, that the conveyor belt is only running at the same (albeit reversed) speed as the plane's movement over the ground, then yes - the wheels will spin faster and the plane will still take off. What part of the original question confused you to say it wouldn't take off? Quote Share this post Link to post Share on other sites
sundevil777 102 #34 May 1, 2006 Here's a physics forum thread, with exactly the same assumptions running rampant: http://forum.physorg.com/index.php?showtopic=2417&st=0 And a really rough attempt at an experiment to prove it: http://videos.streetfire.net/Comment.aspx?fileid=35E964D9-38DB-4EFD-BE8D-D6BA1A43A06BPeople are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am Quote Share this post Link to post Share on other sites
JohnRich 4 #35 May 1, 2006 QuoteBy definition, if the plane is stationary, the conveyor is stationary. That is the initial state of this scenario, from there the plane starts moving forward relative to the ground, with the wheels spinning twice as fast. I think this riddle is good at showing how easy it is to assume things not in the original problem statement."This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction)." From that description, I assume that the conveyor belt upon which the plane is standing is always exactly counteracting the forward movement of the plane from engine thrust. Thus, the plane never moves from it's spot on the ground. No air movement, no lift. I'm thinking of it like a car on a dynamometer machine, where the wheels are on rollers so that the engine can be run at speed, in gear, without the car actually moving. Quote Share this post Link to post Share on other sites
stitch 0 #36 May 1, 2006 Quote**I searched for this and found nothing, so forgive me if it was deleted or something** A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Will the plane be able to take off? Depends.Is Chuck Norris the pilot?"No cookies for you"- GFD "I don't think I like the sound of that" ~ MB65 Don't be a "Racer Hater" Quote Share this post Link to post Share on other sites
popsjumper 2 #37 May 1, 2006 Plane takes off with the wheels spining twice as fast as normal. It doesn't matter which way the conveyor is running...the plane would still take off. If it didn't, it's not a plane...it's a rock.My reality and yours are quite different. I think we're all Bozos on this bus. Falcon5232, SCS8170, SCSA353, POPS9398, DS239 Quote Share this post Link to post Share on other sites
sundevil777 102 #38 May 1, 2006 Quote"This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction)." From that description, I assume that the conveyor belt upon which the plane is standing is always exactly counteracting the forward movement of the plane from engine thrust. Thus, the plane never moves from it's spot on the ground. No air movement, no lift. I'm thinking of it like a car on a dynamometer machine, where the wheels are on rollers so that the engine can be run at speed, in gear, without the car actually moving. Nothing in that description says that the conveyor can counteract the movement of the plane to keep it stationary relative to the ground. Your scenario would have the plane's speed at zero, with the conveyor constantly moving faster, which does not agree with the problem statement. I wonder what the record time for a thread to get flaming is that doesn't involve sex?People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am Quote Share this post Link to post Share on other sites
mnealtx 0 #39 May 1, 2006 Quote What part of the original question confused you to say it wouldn't take off? I misunderstood the original premise, and thought that the conveyor would run at whatever speed it needed to to counteract any forward motion of the plane.Mike I love you, Shannon and Jim. POPS 9708 , SCR 14706 Quote Share this post Link to post Share on other sites
billvon 3,106 #40 May 1, 2006 As stated in the problem, the plane would remain stationary and not take off. In the real world, the conveyor system would rapidly exceed physical limits and either stop accelerating or destroy itself. If the aircraft survived this it would then take off normally. This is one of those "what happens when an unstoppable force meets an immovable object?" questions. Interesting in theory, perhaps, but not valid in the real world. Quote Share this post Link to post Share on other sites
sundevil777 102 #41 May 1, 2006 QuoteAs stated in the problem, the plane would remain stationary and not take off. That is not stated in the problem. Just that the conveyor would match the planes speed. If the plane was stationary, and the conveyor moving, they would not match.People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am Quote Share this post Link to post Share on other sites
billvon 3,106 #42 May 1, 2006 >I'm thinking of it like a car on a dynamometer machine . . . Here's the equivalent scenario: You put a car on a dynamometer with the transmission in neutral; no other attachement to the dynamometer other than the wheels resting on the rollers. The dynamometer has a control system that tracks the car's speed and tunes the speed of the dynamometer to be exactly the same (but in the opposite direction). Then you hook a cable up from the front bumper of the car, and attach the cable to a diesel tractor. Now you start the diesel tractor and start pulling. What happens? Quote Share this post Link to post Share on other sites
Icon134 0 #43 May 1, 2006 QuoteThe dynamometer has a control system that tracks the car's speed and tunes the speed of the dynamometer to be exactly the same (but in the opposite direction). Then you hook a cable up from the front bumper of the car, and attach the cable to a diesel tractor. Now you start the diesel tractor and start pulling. What happens? The car moves off the dynamometer when/if the chains securing the car break... or nothing happens as if the chains attaching car to the tractor break first... (i.e. the dynamometer doesn't counter any movement...) but that doesn't apply to this situation... the only way to keep the plane on the ground is to attach it firmly to the ground. (like in a wind tunnel) ScottLivin' on the Edge... sleeping with my rigger's wife... Quote Share this post Link to post Share on other sites
lawrocket 3 #44 May 1, 2006 Quotethe plane's speed That's the issue. Here in the US, if it tracks the speed of the plane in miles per hour, the plane will fly once it hits a certain speed. But, if it tracks the speed in kilometers per hour, then the American plane will not know how fast it's actually going, and will abort any planned takeoff. My wife is hotter than your wife. Quote Share this post Link to post Share on other sites
sundevil777 102 #45 May 1, 2006 That is a lousy analogy! People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am Quote Share this post Link to post Share on other sites
Icon134 0 #46 May 1, 2006 QuoteQuotethe plane's speed That's the issue. Here in the US, if it tracks the speed of the plane in miles per hour, the plane will fly once it hits a certain speed. But, if it tracks the speed in kilometers per hour, then the American plane will not know how fast it's actually going, and will abort any planned takeoff. good one.... Livin' on the Edge... sleeping with my rigger's wife... Quote Share this post Link to post Share on other sites
sundevil777 102 #47 May 1, 2006 QuoteQuotethe plane's speed That's the issue. Here in the US, if it tracks the speed of the plane in miles per hour, the plane will fly once it hits a certain speed. But, if it tracks the speed in kilometers per hour, then the American plane will not know how fast it's actually going, and will abort any planned takeoff. I have noticed that in Canada, the size of pizzas are still described in inches, as are TVs... The metric system just doesn't work for everything...People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am Quote Share this post Link to post Share on other sites
pop 0 #48 May 1, 2006 QuoteQuoteQuoteI know how Harriers take off, just wondering why you thought it would only take off if it was a Harrier, which is incorrect. Explain why you think the hypothetical plane will be able to take off. No matter how fast the wheels aer spinning the speed of the air over the wings is zero. Remerb the plane is still in place, onyl its wheels are spinning. In order to have lift off you need a certain speed of air to go over and under the wing, which is not created when the airplace is stationary. A plane's thrust is created not by the wheels but by the prop (or jet engine), and the friction of the wheels would not create enough drag to overcome that thrust, therefore, the plane will still pull itself forward, eventually creating enough lift to leave the ground. Now, how do you explain why you think it won't take off?7 ounce wonders, music and dogs that are not into beer Quote Share this post Link to post Share on other sites
jakee 1,593 #49 May 1, 2006 QuoteI'm thinking of it like a car on a dynamometer machine, where the wheels are on rollers so that the engine can be run at speed, in gear, without the car actually moving. And there in lies your fundamental, and rather glaring, error. You've been a skydiver (and I assume a driver) for quite some time so I'm sure you've noticed that there is a basic difference in the way cars and planes propel themselves. Cars have wheels that push against the road surface, aeroplanes have fans that push against the air. To counteract the thrust from a cars driving wheels you need a conveyor belt, to counteract the thrust from an aeroplane's fan you need a wind tunnel.Do you want to have an ideagasm? Quote Share this post Link to post Share on other sites
lawrocket 3 #50 May 1, 2006 There could be Martian gauges that measure in miles per hour. So long as it measures in a way Americans will understand, instead of the arbitrary metric system, then there would be no confusion. My wife is hotter than your wife. Quote Share this post Link to post Share on other sites
