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Airplane on a Conveyor Belt - Exclusive Photos!
Discussion: Plane on a Conveyor Belt
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PAFlyboy PAFlyboy |
Plane on a Conveyor Belt
Feb 4 2008, 2:17 PM EST As a pilot, I am not here to debate that the aircraft will take off, but the Mythbusters did not have an accurate test. As shown in the episode, the aircraft started moving foreward, before the belt was at the same speed, there by off setting the speed of the plane and the belt. The plane continued to accelerate faster than the belt and took off. The best way for this myth to be tested, would be to hold the plane in place, accelerate the belt to the takeoff speed, and then let the plane loose at full throttle.*****PLEASE MYTHBUSTERS, REVISIT THIS MYTH AND USE THIS RECOMMEND TEST FROM A RATED PILOT! Another way of looking at this myth would be a seaplane on a river. The seaplane will be carried with the flow downstream, until the engine can produce enough thrust to over come the pull, and it will sit there, and once it overcomes the flow, it will accelerate and take off. PLEASE REVISIT THIS MYTH. 45 out of 78 found this valuable. Do you? |
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EnderGT EnderGT |
RE: Plane on a Conveyor Belt
Feb 5 2008, 9:52 AM EST "As a pilot, I am not here to debate that the aircraft will take off, but the Mythbusters did not have an accurate test.You already saw that demonstrated with the model plane - the belt was moving full speed with Adam holding on to the plane, then they throttled the plane up and it moved forward. No need to revisit. 1 out of 2 found this valuable. Do you? |
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PAFlyboy PAFlyboy |
RE: Plane on a Conveyor Belt
Feb 6 2008, 7:43 PM EST "You already saw that demonstrated with the model plane - the belt was moving full speed with Adam holding on to the plane, then they throttled the plane up and it moved forward.With the model and treadmill, the mythbusters did what you explain, however, there is a big difference between a model and a full sized aircraft. The biggest problem with this myth, is that friction has not been addressed. The model weighted next to nothing, but a full sized aircraft will exert more downward force on the "belt" and will therefore give a more accurate test of the myth. In other words, I recommend a REVISIT please! Do you find this valuable? |
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EnderGT EnderGT |
RE: Plane on a Conveyor Belt
Feb 6 2008, 9:20 PM EST "With the model and treadmill, the mythbusters did what you explain, however, there is a big difference between a model and a full sized aircraft. The biggest problem with this myth, is that friction has not been addressed. The model weighted next to nothing, but a full sized aircraft will exert more downward force on the "belt" and will therefore give a more accurate test of the myth.Put a fully loaded 747-400 on a conveyor belt that is 4000 meters long (longer than max takeoff distance). Put the 747 on one end, with stops behind it to prevent it from being pulled backwards by the belt, and turn the belt on at 300 km/h. Then throttle up the plane and let it try to take off. If this were the experiment done, I would fully support it, IF AND ONLY IF you would all shut up and stop arguing once it took off! 0 out of 4 found this valuable. Do you? |
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madharv madharv |
RE: Plane on a Conveyor Belt
Feb 10 2008, 3:56 AM EST I am also a pilot, but all you have to know is a little physics. The only question that needs to be asked for the plane to take off, regardless of when the brakes are released or the conveyor belt starts, is can the wheels roll at the take-off speed plus the conveyor belt speed? That would be, in this case, twice the take off speed of 25 mph. No sweat. The propulsion generated by the propeller operates on the AIR, independently of the surface beneath the wheels, so the only way the airplane would not take off would be if the AIR speed relative to the wings was less than 25mph. As long as the brakes are off, the prop will accelerate the plane relative to the air, and it will take off. I can't believe the pilot in the show didn't believe the plane would take off. I hope somebody warned him to be ready. Here's a little puzzle: Would your airplane have trouble taking off going west? After all, we're on a planet where the surface is moving eastward, so isn't that the same thing as a conveyor belt, moving you constantly backward? Your reply would probably be "Of course it would take off going west, it's the airspeed that counts." and you'd be right. If the airspeed is sufficient and the wheels can roll fast enough over whatever surface you're on, you will take off. Do you find this valuable? |
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DesignerK DesignerK |
RE: Plane on a Conveyor Belt
Feb 11 2008, 4:52 PM EST I have several questions about this experiment; 1. if the planes engine were turned off and put on a conveyer moving 25 MPH, what would the plane do? (probably move backwards at 25 MPH eventually). 2. If you measured the RPMs of the planes engine required to get lift (without a treadmill) would it be the same number of RPMs as when it is on a treadmill? (I'm not so sure about that). 3. If the planes engine were running at the prescribed RPMs for lift and then released from a stationary position onto the moving treadmill, would it move. (probably, since it acts against air, not the ground). 4. If a car is pulling a glider, could you get lift? (I think probably yes). 5. If said car were on a tread mill pulling a glider and the treadmill was going the same speed as the car, would you get lift? (Absolutely not! The car requires ground friction for movement). I think the question is how much effort must the planes propulsion system exert to lift off from a treadmill. I don't think this myth can be busted without some major controlled environments. Anything that provides lift to the wings of a plane (natural winds, wind from a prop) can "blow" this experiment. Too many variables. Do you find this valuable? |
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DesignerK DesignerK |
RE: Plane on a Conveyor Belt
Feb 11 2008, 5:03 PM EST Another question; Is it possible to get a plane to remain stationary on a moving treadmill? (taxi speed?) I think finding out how many RPMs the planes engine needs to remain stationary on a treadmill as a baseline number would have been a good way to solve this myth without building a giant (sloppy) treadmill. Do you find this valuable? |
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madharv madharv |
RE: Plane on a Conveyor Belt
Feb 11 2008, 5:58 PM EST To your questions: 1. Yes, just like a car would. 2. At the same RPM as the normal take off RPM, the plane would probably take a bit longer to take off, because of the slight drag due to the wheels having to spin faster to achieve flight speed relative to the air. 3. Right again. As soon as the plane, which I assume was being held stationary relative to the surroundings, was dropped, it would start to accelerate, then hit the belt and be temporarily decelerated by the backward jolt of the belt, much like what happens when a plane lands. Then, as the engine continued pulling forward on the air, would accelerate as before, and take off. 4. Cars tow gliders into the air all the time. The wing doesn't care where the forward propolsion relative to the wind comes from. 5. Right again, but use precise terminology. The question should say speed RELATIVE TO THE BELT. Your final comment reveals that you still may be less than fully understanding. To try to summarize, the motion of the plane must be specified as relative. In the experiment, the wheels were turning at 50mph RELATIVE TO THE BELT when the plane took off. The plane's wing felt 25mph RELATIVE TO THE WIND when it took off. I'm trying to teach the point that the wheels on the plane are mostly irrelevant to the plane's ability to achieve airspeed. Consider the opposite of the experiment - a huge fan sitting in front of a plane on the runway, blowing at 25mph. Could the plane take off? Of course it could (until it tried to exit the fan's flow!), and the wheels would NOT move, because the only condition for flight would be present - airspeed. No conveyor belt, going any speed, can prevent an airplane from taking off, short of the tires flying apart at some ridiculously high speed. Just as the runway can't hold the plane back, neither can the belt. It just makes the wheels spin faster. 1 out of 1 found this valuable. Do you? |
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madharv madharv |
RE: Plane on a Conveyor Belt
Feb 11 2008, 6:11 PM EST There is little difference between taxiing a plane and taking off - just engine power setting. As long as the propeller is pulling the plane forward, and the brakes are off, the plane will move forward relative to the wind and surroundings. You must understand that the speed of the belt, no matter how fast, is irrelevant to the AIR speed of the plane. You are misunderstanding that the belt is somehow able to drag against the plane, and it can't, unless the brakes are applied. Think of the plane as being on ice skates and the belt being ice. That lack of friction is what the wheels and their bearings do - reduce friction. The example of the glider being towed by a car is a good analog to the propeller pulling against the air. Both the car and the air are independent, outside of, of the belt. The wheels simply spin as fast as they need to go, because they are lubricated like skates on ice. They do not act against the plane's motion. 0 out of 1 found this valuable. Do you? |
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DesignerK DesignerK |
RE: Plane on a Conveyor Belt
Feb 12 2008, 11:18 AM EST I understand airspeed and all that. My point is, the experiment would have been more convincing (perhaps not as fun) if there were more controlled elements (i.e.; baseline RPM for lift, controlled environment). People have had a hard time buying into the experiment with the relatively sloppy methods used here. Concerning my question about the plane staying stationary on a moving treadmill; Are you saying that no matter how low the engine is set, as long as it is enough to make the plane move, the plane will move? there must be a minimum setting that will provide just enough thrust to prevent the treadmill friction from dragging the plane away? I think that was the initial myth to be busted; with the wheels never exceding 25 MPH the plane would stay stationary (because there is SOME friction between the wheels and the treadmill). Of course, no treadmill will stop a plain when its engine reaches the proper RPMs for takeoff. Maybe a smaller engine with a lower minimum RPM would be required (though not powerful enough to actually fly the plane) Thanks for the reply Do you find this valuable? |
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EnderGT EnderGT |
RE: Plane on a Conveyor Belt
Feb 12 2008, 2:19 PM EST "Concerning my question about the plane staying stationary on a moving treadmill; Are you saying that no matter how low the engine is set, as long as it is enough to make the plane move, the plane will move? there must be a minimum setting that will provide just enough thrust to prevent the treadmill friction from dragging the plane away?"You're proposing that the plane not be allowed to throttle up to take-off speed. Well, of course it won't take off! Here's an alternate test for you, as suggested by someone on a different thread, that could provide an answer to your question: Attach the front of the plane plane to a fixed anchor via a force meter (a fish scale would be good for this - the kind that you hold up and hang the fish from). Leaving the plane off, start the treadmill underneath the plane. Measure how much force is exerted by the treadmill on the plane. You will see it start off somewhat high as the initial rolling resistance and friction in the tires and wheel bearings is overcome, and then drop to and stabilize at a very small amount, probably on the order of a few pounds, depending on the weight of the plane and the speed of the treadmill. Now attach the back of the plane to the fixed anchor via the same force meter, and start the engine. Measure the force generated at each throttle setting. If your engine has a throttle setting at which the amount of force generated equals the amount of force applied by the treadmill, then the answer to your question is "yes". Regarding this statement: "with the wheels never exceeding 25 MPH the plane would stay stationary" - are you claiming that this is true or that this was the myth that was proven untrue? 1 out of 1 found this valuable. Do you? |
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madharv madharv |
RE: Plane on a Conveyor Belt
Feb 12 2008, 6:55 PM EST This may be a duplicate posting, but I think my previous got wiped. I agree that the variables in the experiment were poorly communicated on the show. My understanding of the myth was not that the wheels were limited to 25mph. If that were the case, the plane would not have taken off, as the belt was moving at 25mph backward. The result of that would have been a plane that was stationary relative to the wind and the surroundings. My understanding was that the question was simply can a plane take off from a conveyor belt that is moving backwards relative to the surroundings, and going at the take off speed of the plane? Consider this: A pilot mistakenly takes off WITH the wind, which is going 25mph relative to the ground. With the brakes on, he has a 25mph tailwind. When his wheels are spinning at 25mph across the ground, the plane will not take off, because the airspeed would now be zero. Take off would occur later, when the prop had accelerated the plane to 25mph relative to the wind, at which time the wheels would be spinning at 50mph over the ground. Other than the inertia of accelerating the plane, this is an equivalent situation to the conveyor belt. Yes, there is probably some power setting low enough that the friction of the wheels would equal the thrust of the prop, and the plane would stand still relative to the surroundings. My plane will roll forward at almost any throttle setting when on a level surface. When I taxi, the only reason I nudge the throttle up a bit is to overcome the air resistance to get up to around 20-30mph. If you lived near Lubbock, TX I'd take you up and do some real physics! pics of my plane on my website at www.hmadison.com/sky.htm. 1 out of 1 found this valuable. Do you? |
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DesignerK DesignerK |
RE: Plane on a Conveyor Belt
Feb 13 2008, 10:00 AM EST Thanks for the good responses. I'm not an engineer, physicist nor pilot but I thought that this was not a difficult myth to understand. My goal with these questions was to get to the point of the things that seemed to confuse a few people in this forum. You guys confirmed what I suspected. Also thanks for clearing up the goals of the expiriment. Do you find this valuable? |
 HikingTony |
RE: Plane on a Conveyor Belt
Feb 14 2008, 7:07 AM EST I think the Mythbusters did a good job... they should have added one little item that might have made it clearer to those of us who didn't take physics. They should have added that the plane is able to take off... (for reasons explained by Mythbusters); however, the wheels of the plane we spinning at a rate greater than the speed of the conveyor belt. If the plane's engine was accelerated only to the speed where the plane's wheels were spinning at the same speed as that of the conveyor belt, the plane would have remained in position and would not have taken off because no lift could have been generated. 1 out of 1 found this valuable. Do you? |
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EnderGT EnderGT |
RE: Plane on a Conveyor Belt
Feb 14 2008, 12:21 PM EST "I think the Mythbusters did a good job... they should have added one little item that might have made it clearer to those of us who didn't take physics.While it is true that the wheels were spinning faster (relative to the belt) than the belt was moving (relative to the ground), it should be noted that the restriction that these speeds match was not in the original wording of the myth. Do you find this valuable? |
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hohon3 hohon3 |
RE: Plane on a Conveyor Belt
Feb 14 2008, 8:33 PM EST EnderGT, You need to give your ideas a rest and read some of the comments being posted. You have your mind closed to the idea that you just might be wrong. Try giving some of these other statements a chance and you just might see the error in your thinking. You continue to mix your apples with your oranges and have continued to combine the factors of the belt's speed, the wheel speed, and the wing's speed as having a direct link. The belt and wheels are linked and if there speed is equal and opposite, there is no relative motion on the plane with respect to the ground and therefore no relative motion of the wing with respect to the air. And with respect to the plane, the wheels are relative to their position with the ground. And with the wings, they're position is relative to the air. Apples and oranges. Now, if you can grasp that thought, it should be a very easy step to understanding that if the wing isn't moving through the air (because the plane isn't moving with respect to the ground), no lift will occur and the plane won't fly. The plane "flying" or taking off doesn't have anything to do with it's "ground speed" or wheel speed. Planes don't have speedometers in the cockpit, they use "air speed" in knots. They don't use miles per hour. A plane doesn't care how fast it's wheels are spinning, it cares how fast it's going through the air. As commercially rated pilot and as a registered engineer, I'm sure if you separate the factors applied in this myth to the areas where their relative impacts actually occur, you will see the error in your conclusions. No air speed, no lift, and therefore, no takeoff. It is as plain and simple as that, don't make it more complicated than it is. Check out pilot57's comments, they summed it up nicely. Do you find this valuable? |
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HikingTony |
RE: Plane on a Conveyor Belt
Feb 14 2008, 10:21 PM EST Thanks Hohon3, I did, in fact, "get it"! I do understand the difference between air speed and relative ground speed; however, was attempting to address the issue of the myth (obviously, I didn't do a very good job of that). Take care, HikingTony Do you find this valuable? |
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EnderGT EnderGT |
RE: Plane on a Conveyor Belt
Feb 15 2008, 4:57 PM EST "You need to give your ideas a rest and read some of the comments being posted. You have your mind closed to the idea that you just might be wrong. Try giving some of these other statements a chance and you just might see the error in your thinking.Right back at you. "The belt and wheels are linked and if there speed is equal and opposite, there is no relative motion on the plane with respect to the ground" Oh, wait, I think I understand your argument. Your argument is that the speed of the wheels, as measured from the conveyor frame of reference, must match the speed of the belt, as measured from the ground frame of reference. In this interpretation, the plane IS NOT ALLOWED to accelerate relative to the ground. In fact, as soon as the engine applies any thrust at all, the conditions of the myth (as per your interpretation) will be broken, since the speed of the wheels will no longer match the speed of the belt! Well, if you're not going to ALLOW the plane to TRY to take off, then OF COURSE it won't take off! I agree completely, no airspeed means no lift and thus no flight! But this is an incorrect interpretation of the myth based on a poor rewording. Here's my interpretation: "Can a treadmill prevent a plane from accelerating, gaining airspeed, and taking off?" The engine generates thrust via the acceleration of a mass of air and Newton's Third Law of Motion. The equal and opposite reaction accelerates the plane forwards. To counteract this thrust, the conveyor must exert an equal and opposite force on the plane. The wheels of the plane, due to their designed purpose of minimizing friction, make it impossible for the belt to apply enough force to overcome the thrust of the engine. The plane accelerates, easily overcoming the minimal additional drag generated by the wheels, and takes off. Different interpretations lead to different conclusions. Check the link I provided on the myth page to see the original wording - it does not specify that the wheel speed must match. Without the restriction, I hope you can see that the plane will indeed fly. Do you find this valuable? |
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paulckruger paulckruger |
RE: Plane on a Conveyor Belt
Feb 15 2008, 7:26 PM EST I first received my pilots license in 1969...been around awhile. This was a no-brainer for me from the start and was quite surprised that the gentleman who flew the plane in the test thought it would keep him from taking off. Being on a conveyor belt only means one thing to the plane. The tires are rotating faster. Since they do nothing but provide a means of support for the aircraft in the process of taking off, having a moving surface under them is no different than a plane taking off on a moving aircraft carrier. Thrust does not care about the wheels. Do you find this valuable? |
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hohon3 hohon3 |
RE: Plane on a Conveyor Belt
Feb 15 2008, 10:45 PM EST Granted . . . . how you view the stated myth will determine your final conclusion. For me, the speed of the conveyor belt was implied to be the "equal" to the ground speed of the plane. If the belt is slower, the plane moves forward and flies. If too fast, the plane moves backwards. The equal speed implication was reinforced by Jamie and Adam when they discussed the plane's needed speed for takeoff and what they would have to do to get their conveyor belt to match it. I believe the myth implied the conveyor belt would match the plane's ground speed. And if it does, there would be no forward motion relative to the ground nor the air. 1 out of 3 found this valuable. Do you? |