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Guest mikevanisland

Conveyor belt controversy put to rest :-)

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I have trouble believing that the test holds sway over the debate. Why was the aircraft in the test moving forward (the camera had to pan) if the conveyor belt was "matching" the plane's speed? If it was matching the plane's speed, then the plane should not have moved, no matter how much it accelerated. Zero movement would have meant zero airflow over the wings, resulting in no takeoff.

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I have trouble believing that anyone would think the plane wouldn't take off. The only thing the conveyor did was make the planes wheels spin faster. The prop, corkscrewing through the air, is the only thing that maters to the planes forward momemtum. People keep thinking of it like a car, where the wheels are powering it. Rob

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Matching the plane's speed isn't enough. You have to match the plane's acceleration. If you have a conveyor belt that can accelerate as the plane does and keep it in one place, of course it can't take off.The question is more, can a plane still accelerate to takeoff speed when on a conveyor belt, and the answer is yet as a constant speed the conveyor belt has little effect on the plane's ability to accelerate.Imagine yourself being on a skateboard, holding on to a rope pulled by a car. It is quite easy to get closer to the car by pulling yourself forward along the rope, very little extra force is needed to get that acceleration despite the fact that you were already moving. The plane scenario is the same.

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On a cold, snowy day in St Louis, a ramper came over and curiously admired that big ol' 747 that was sitting in front of us. The ramp was snow covered. We noticed the catering truck had chains. He asked, "It's sure gettin' close to departure time. When you gonna put the chains on the airplane's tires?" "Chains?" I responded. Stepping back (for safety, I retrospect) he looked at me like I was nuts. "Well, if you don't put chains on that thing, it's Never gonna move."

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Lol!It might have an effect on braking (wheel braking only of course, not spoilers or reverse thrust) so the copilot has to climb into the gear housing and put the chains on before landing on a snowy runway. :(

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I guess some don't realize that no matter how fast the conveyor belt spins, the plane will take right off. Its not possible for a belt to act on the plane in any significant way, only wheel bearing friction.

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>Its not possible for a belt to act on the plane in any significant>way, only wheel bearing friction. Ooh...a dangerous statement. While I agree with your sentiment (and that the plane definately will take off), I would imagine that eventually the wheel bearings would seize given a fast enough speed. Then the conveyor would act on the plane in a significant way, because the wheels and landing gear assembly would probably get ripped off leaving the plane sitting on the conveyor belt with a busted prop!:-lolJeff HepburnKDEN

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I'm not sure I'm completely understanding this then... I thought that the conveyor belt was like a treadmill, and that it would match the aircraft's speed precisely. If the plane was going at 150 knots at it's undercarriage, the belt would be going at 150 knots in the opposite direction, resulting in zero forward motion on the part of the plane overall. Zero forward motion wound result in no air over the wings, and no liftoff.

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This test seemed flawed to me. The plane still had forward motion. With forward motion the wings developed lift.

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>I'm not sure I'm completely understanding this then... I>thought that the conveyor belt was like a treadmill, and that>it would match the aircraft's speed precisely. If the plane>was going at 150 knots at it's undercarriage, the belt would>be going at 150 knots in the opposite direction, resulting in>zero forward motion on the part of the plane overall. Zero>forward motion wound result in no air over the wings, and no>liftoff. What you are missing is that the rotation of the wheels (nearly) cancels out the effect of the moving conveyer belt. The extremely tiny fraction of energy transmitted due to wheel-bearing friction is irrelevant when compared against the force provided by the spinning prop.It's a complete non-sequitur.Tie a 'tow rope' to a flea and see if he can keep an aircraft from taking off by flying in the opposite direction! :)What I don't understand is that this isn't a terribly difficult physics problem! :-lol

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Bill I Agreethis is a "Duh" kinda question.Put a speedometer on the wheels of the plane then do a match of speed to the plane and the conveyor belt

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>What I don't understand is that this isn't a terribly>difficult physics problem! :-lol I do have to grin a bit, when I see so many references to a rather "simple" physics problem, as though much of the public are physics wizards.. :D However, being skeptical as I was (a year or so ago); I did tie a small airplane to a treadmill with rubber bands and noted very little pull on the bands. Meaning, the plane could easily takeoff.L.Adamson

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How about this explanation. If the plane had skis. The friction of the skis on the conveyor belt would pull the plane backwards - right? So the prop must overcome this friction to say keep the plane in one spot. Let the plane develop more power and it starts to move forward until it reaches take off speed. (apply some grease)The wheels just remove that initial friction and the plane moves right away. What they should have done was start the truck moving first - then the plane move backwards then apply power to the plane and watch it move forward and take off.But since the belt ripped when he stepped on it. That probably might have cause some damage.BTW you are standing on a conveyor belt right now - it's the earth. It rotates and the ground and you are already moving. Friction (and gravity) are keeping you in one spot. West moves to east. So a plane taking off facing west would never take off? A plane facing east would?Ron

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>>What I don't understand is that this isn't a terribly>difficult physics problem! :-lol Exactly, yet I have seen this debate reach 200 pages on some forums, where both sides think the other side is just plain ignorant.

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>I have trouble believing that the test holds sway over the>debate. Why was the aircraft in the test moving forward (the>camera had to pan) if the conveyor belt was "matching" the>plane's speed? If it was matching the plane's speed, then the>plane should not have moved, no matter how much it>accelerated. Zero movement would have meant zero airflow over>the wings, resulting in no takeoff. I agree!Either the conveyor belt was moving at less than the aircrafts speed and the net effect reached greater than stall speed and hence it lifted off.orThis is not a conveyor belt at all. Since the aircraft wheel was touching the ground. If it was a conveyor belt, there should have been a gap between the conveyor and the ground underneath. Because the aircraft wheel was moving forward due to the friction between the wheel and the ground. The cloth simply slid underneath. Manny

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Using this logic, if the plane landed on the conveyor rather than took off, the plane would come to a complete stop on the ground once the wheels would hit the conveyor. I think not.The wheels being on a conveyor have nothing to do with forward motion for a powered plane since the plane is not powered by the wheels but rather the propellers effect of pulling it through the air. The conveyor only makes the wheels spin faster.Rob

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I was back and forth on this one, probably overanalyzing it to death in my head but similar to the rubber band test, the simplest experiment solves this. They put a model car on a belt and had it at the same speed forward as the belt was going backwards, net speed was zero.Put the wheels in neutral the car moved backwards, but apply an external force unrelated to the treadmill such as a hand and they were able to push the car forward with very little resistance. Slap a plane on there and apply propeller force which has nothing to do with the treadmill but forces acting on external forces like air and the plane moves forward as long as the thrust from said propeller can overcome whatever resistance is created by the wheels, skis, undercarriage etc. influenced by the friction of the treadmill moving in the opposite direction.On wheels, the aircraft easily overcomes the resistance and takes off without a problem. Ski's present more resistance but with a powerful enough engine the aircraft will still manage to move forward and most likely take off.

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There is no point in over-analyzing.If you have a conveyor belt moving at 100kts, and a cessna facing the opposite direction powered up as it was placed on the conveyor belt, the friction of the wheels would be negligible and the cessna would accelerate as normal in the opposite direction and take off at around 55kts. The speed of the wheels on takeoff would be 155kts but that would be inconsequential to the end result.It really is that simple :)James

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>Using this logic, if the plane landed on the conveyor rather>than took off, the plane would come to a complete stop on the>ground once the wheels would hit the conveyor. I think not.>The wheels being on a conveyor have nothing to do with forward>motion for a powered plane since the plane is not powered by>the wheels but rather the propellers effect of pulling it>through the air. The conveyor only makes the wheels spin>faster.>>RobYes..the propeller effect moves the plane forward and the conveyor belt (if its a true conveyor belt) moves it backward. Net effect = 0

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>There is no point in over-analyzing.>>If you have a conveyor belt moving at 100kts, and a cessna>facing the opposite direction powered up as it was placed on>the conveyor belt, the friction of the wheels would be>negligible and the cessna would accelerate as normal in the>opposite direction and take off at around 55kts. The speed of>the wheels on takeoff would be 155kts but that would be>inconsequential to the end result.>>It really is that simple :)>>Jamesthats why you need to pay attention. The assumption was..They are at the same speed. Not asymmetric.

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>There is no point in over-analyzing.>>If you have a conveyor belt moving at 100kts, and a cessna>facing the opposite direction powered up as it was placed on>the conveyor belt, the friction of the wheels would be>negligible and the cessna would accelerate as normal in the>opposite direction and take off at around 55kts. The speed of>the wheels on takeoff would be 155kts but that would be>inconsequential to the end result.>>It really is that simple :)>>JamesHere's something even simpler - The Cessna will take off at 55kts regardless. The ONLY thing the conveyor belt is doing is making the wheels spin faster. As I watched that video I felt sorry for the pilot that doesn't understand what creates lift and makes his airplane fly. Airflow over the wings is the only thing that will produce lift. Now, if you want something to think about consider this. If you are taking off with a 55kt direct tailwind at which speed with the Cessna fly?55kt ground speed? or 55kt indicated speed?Have fun.ron

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>>There is no point in over-analyzing.>>>>If you have a conveyor belt moving at 100kts, and a cessna>>facing the opposite direction powered up as it was placed on>>the conveyor belt, the friction of the wheels would be>>negligible and the cessna would accelerate as normal in the>>opposite direction and take off at around 55kts. The speed>of>>the wheels on takeoff would be 155kts but that would be>>inconsequential to the end result.>>>>It really is that simple :)>>>>James>>>Here's something even simpler - >>The Cessna will take off at 55kts regardless. The ONLY thing>the conveyor belt is doing is making the wheels spin faster. >>As I watched that video I felt sorry for the pilot that>doesn't understand what creates lift and makes his airplane>fly. Airflow over the wings is the only thing that will>produce lift. >>Now, if you want something to think about consider this. If>you are taking off with a 55kt direct tailwind at which speed>with the Cessna fly?>>55kt ground speed? >or >55kt indicated speed?>>Have fun.>>ron>>>55k IAS. If you thought anything else.. I wouldn't want to fly with youThe tail wind comes into play the moment the wheel leaves the ground!:)

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Indicated. The Cessna doesn't care what speed its moving over the ground as long as the IAS shows the proper speed for flight. But in this case the answer is neither as you'd hit the pole at the end of the runway long before you took off :-lolRegards,Mike T.

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