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Location: Airplane on a Conveyor Belt - Exclusive Photos!

Discussion: Plane on conveyor

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Dusty754 Dusty754	Plane on conveyor Apr 17 2008, 7:13 PM EDT I have questions regarding this test. First of all a car's indicated speed is produced by gears in the transmission. Thus if the car is moving forward at 25 MPH it is indicated because the speedometer is connected to the transmission. An airplane is different. Its airspeed indicator uses air flowing into the pitot tube. You could blow air into this pitot tube and get an indicated airspeed even without the engine running. If the plane got its speed indicated by the spinning of its wheels, the speed would show 0 once they stopped turning after it took off. So if the conveyor is moving at 25 MPH in order for the airplane to indicate 25 MPH it HAS to move faster than the conveyor. Perhaps they should have tried this test with a speedometer connected to the planes wheels. Post reply 8 out of 10 found this valuable. Do you find this valuable? Do you?
EnderGT EnderGT	RE: Plane on conveyor Apr 17 2008, 10:27 PM EDT You seem to have it and then you don't. A plane's ground speed doesn't matter to it's wings - only it's airspeed does. So why would you insist on measuring it's speed through the wheels, i.e. it's ground speed? Either way, lets pretend that you measure the plane's speed with a radar gun that is held by someone or something attached to the ground underneath or on either side of the treadmill, i.e. in a stationary frame of reference. Both the belt and the plane would be measured as having the same speed, and the plane would have airspeed and would take off. You can't have your cake and eat it too - you can't have the plane be moving and yet be motionless. Either the plane is moving past the cones (an argument used by other posters) and thus the belt is moving, or neither is moving past the cones and the plane is standing still. You can't have the belt be moving (again, past the cones) and the plane not, or vice versa, because then and only then would the speeds be not matched. It all comes down to force - can the conveyor apply a force on the plane that counteracts the thrust of the engine and thus prevents the plane from moving? The answer is, it can't. The plane will move, and will take off. Post reply 1 out of 3 found this valuable. Do you find this valuable? Do you?
Dusty754 Dusty754	RE: Plane on conveyor Apr 17 2008, 11:46 PM EDT Sorry but speed is speed and a planes ground speed is indicated on the same guage as its "air" speed. That guage gets its input from air flowing into a pitot tube. If the plane is facing into the wind and is tied down the airspeed guage will indicate a "speed" if the wind is sufficient and blowing into the pitot tube. Thus if the take off speed of the plane is 25, in order for the airspeed guage to indicate 25 the plane has to move at 25. SO in the test, if the pilot applied throttle to obtain 25 MPH the plane would have to be moving forward at 25, if the tarp was pulling the plane backward at 25 then the plane would have to be moving at 50, however the indicated airspeed would be 25 because that is what the relative wind would be indicating on the airspeed guage. Post reply 2 out of 2 found this valuable. Do you find this valuable? Do you?
miahal7 miahal7	RE: Plane on conveyor Apr 18 2008, 2:53 AM EDT Don't forget that negative 25 mph (conveyor) plus positive 25 mph (plane) equals 0. So while the plane's wheel speed was 50 mph, its air speed was still 0 mph (excluding wind). What happened in the myth is the plane's engine propelled it faster than the conveyor could pull it. This is why it moved forward and its wings were able to produce lift. Just so no one mistakes my stand on this myth, there is no way that plane takes off if the conveyor and the plane were at the same speed. Myth confirmed...imho. Post reply Do you find this valuable?
EnderGT EnderGT	RE: Plane on conveyor Apr 18 2008, 1:00 PM EDT "Don't forget that negative 25 mph (conveyor) plus positive 25 mph (plane) equals 0. " This is EXACTLY WRONG, and people continuing to think this is the reason this "myth" continues to be debated. Just because two things are moving the same speed in opposite directions DOESN'T MEAN their speeds cancel out! I can EASILY put a cube on a treadmill, start the treadmill moving at 5mph, then pull the cube backwards at 5mph. Same speeds, not canceling! "the plane's engine propelled it faster than the conveyor could pull it." Not faster - more forcefully. The propeller was able to apply more force to the plane than the conveyor was, and so the plane moved. You're also making the mistake of mixing your frames of reference. You're always measuring the speed of the belt from the ground frame of reference, which is fine, but then you're measuring the plane's speed from the belt's frame of reference in order to claim a 0 airspeed in the ground frame of reference, which is not fine. You have to measure both speeds, belt and plane, from the same frame of reference in order to make the comparison meaningful. Just to illustrate this point further: watch the video again. the belt is being dragged backwards past the cones AT THE SAME SPEED as the plane is moving forwards past the cones. You cannot allow the belt to move past the cones, yet claim that the plane isn't allowed to move past the cones, because in that case, the speeds are not matched! Again, just to be clear, no one is debating that 0 airspeed means 0 lift and thus no flight. Where your error comes in is when you insist that there must be 0 airspeed. There will only be 0 airspeed if the plane isn't TRYING to take off, in which case, why ask the question in the first place? Post reply 0 out of 1 found this valuable. Do you find this valuable? Do you?
miahal7 miahal7	RE: Plane on conveyor Apr 18 2008, 4:20 PM EDT "Just to illustrate this point further: watch the video again. the belt is being dragged backwards past the cones AT THE SAME SPEED as the plane is moving forwards past the cones. You cannot allow the belt to move past the cones, yet claim that the plane isn't allowed to move past the cones, because in that case, the speeds are not matched!" If the belt was being dragged backwards at the same speed as the plane then the plane would appear to remain stationary. The fact that the plane was moving forward when it took off means that the plane was going faster than the belt. Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
Dusty754 Dusty754	RE: Plane on conveyor Apr 18 2008, 6:17 PM EDT "You seem to have it and then you don't. A plane's ground speed doesn't matter to it's wings - only it's airspeed does. So why would you insist on measuring it's speed through the wheels, i.e. it's ground speed? Either way, lets pretend that you measure the plane's speed with a radar gun that is held by someone or something attached to the ground underneath or on either side of the treadmill, i.e. in a stationary frame of reference. Both the belt and the plane would be measured as having the same speed, and the plane would have airspeed and would take off. You can't have your cake and eat it too - you can't have the plane be moving and yet be motionless. Either the plane is moving past the cones (an argument used by other posters) and thus the belt is moving, or neither is moving past the cones and the plane is standing still. You can't have the belt be moving (again, past the cones) and the plane not, or vice versa, because then and only then would the speeds be not matched. It all comes down to force - can the conveyor apply a force on the plane that counteracts the thrust of the engine and thus prevents the plane from moving? The answer is, it can't. The plane will move, and will take off." So if this plane were places on a long freight train of flat cars and the cars were modified so there was no gaps between them and the train were traveling at 25 MPH southbound and the plane were facing north then the plane would take off when it was moving at 25 MPH indicated by its wheel spin? My whole problem with this myth is that an airplanes airspeed indicator, speedometer as you will does not get input from the ground as a car does. Thus if the plane has to be moving forward at 25 to get lift then its actual speed along the the flat cars would be greater than 25 MPH since it would have to overcome the southbound movement of the train. As for the ground speed not mattering. I have flown and know that the plane has to obtain rotation speed. This is the speed that the plane needs to get lift. Therefore that is the speed tha pmane has to travel along the ground. The bottom line is 25 MPH is 25 MPH whether you are traveling along the ground, in the air or under the surface of the water. But since the test was to measure a plane moving forward at 25 MPH as opposed to a belt moving backward at 25 MPH then the logical thing would have been to measure the planes speed through its tires and not through its pitot tube. Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
Dusty754 Dusty754	RE: Plane on conveyor Apr 18 2008, 6:31 PM EDT "If the belt was being dragged backwards at the same speed as the plane then the plane would appear to remain stationary. The fact that the plane was moving forward when it took off means that the plane was going faster than the belt. " Lat's look at the belt being dragged. If the Mythbusters could have made the "belt" a true belt the it would not have to have been dragged by the truck. However on the car experiment, if you paint white tick marks on the belt , they would indicate that the belt is moving in a reverse direction. I still believe that if a plane were put on a conveyor belt and the belt moved rin reverse at the same speed as the plane BASED on actual speed, not that indicated by the airspeed gauge, that the plane would remain stationary. I did not see anything in that whole experiment that measured the planes actual speed. This is why airplanes take off INTO the wind. If they were to take off with the wind they would use up more runway or even run out of runway. If the plane were being dragged backwards it would have to move forward faster than the speed it was being dragged in order to get lift. Thus the pilot in the test simply increased throttle until the airspeed gauge indicated 25 MPH and since the airspeed gauge does not get data from the planes actual speed then the test was flawed. The airspeed gauge uses air rammed into the pitot tube which usually sticks out a wing, thus the plane in the test was traveling faster than 25 MPH Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
Dusty754 Dusty754	RE: Plane on conveyor Apr 18 2008, 6:42 PM EDT "Don't forget that negative 25 mph (conveyor) plus positive 25 mph (plane) equals 0. So while the plane's wheel speed was 50 mph, its air speed was still 0 mph (excluding wind). What happened in the myth is the plane's engine propelled it faster than the conveyor could pull it. This is why it moved forward and its wings were able to produce lift. Just so no one mistakes my stand on this myth, there is no way that plane takes off if the conveyor and the plane were at the same speed. Myth confirmed...imho. " No. If the pilot used the airspeed indicator to achieve 25 MPH then the plane would have to actually be moving faster than the belts 25 MPH. The "speedometer" in an airplane is called airspeed indicator. It measures the planes forward momentum. It does this because air is forced into a pitot tube on the wing. Thus the planes actual speed was NOT 25 MPH but much greater. So the question of a plane on a conveyor traveling in reverse at let's say, 25MPH and a plane indicating a wheel speed of 25MPH forward, the plane would not take off. If they try that test again and use wheel speed to indicate the planes actual speed and it takes off then I will agree with the results. Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
EnderGT EnderGT	RE: Plane on conveyor Apr 21 2008, 10:53 AM EDT "If the belt was being dragged backwards at the same speed as the plane then the plane would appear to remain stationary. The fact that the plane was moving forward when it took off means that the plane was going faster than the belt. " I don't understand how you can quote my explanation of how you are wrong, just to make the same wrong claim yet again. You cannot mix frames of reference and then make a valid comparison! You CANNOT measure the belt speed from the ground frame of reference, and then measure the plane speed from the belt frame of reference (i.e. by measuring the rotational wheel speed), and then compare them and call them equal! To a stationary observer standing on the ground outside of the belt, i.e. the Mythbusters' cameras, or Adam, or you and I, the belt must move past the cones at the same speed as the plane moves past the cones, otherwise the speeds ARE NOT MATCHED! This all ignores the fact that the original riddle NEVER mentioned the wheels, or their speed. This also ignores the fact that a plane's wheel speed is irrelevant to it's ability to fly, so why would you claim that the wheel speed is the only appropriate way to measure the plane's speed? Do this for me. Ignore the riddle, and the wording. Answer this instead: Is a treadmill capable of preventing an airplane from accelerating? Can the treadmill apply enough drag on the plane to overcome the thrust of the plane's engine(s)? Post reply Do you find this valuable?
martiandrifter01	RE: Plane on conveyor Apr 22 2008, 1:18 AM EDT For Dusty754: A treadmill for a car is called a dynamometer. A treadmill for a boat is called a wave tank. A treadmill for an airplane is called a wind tunnel. Each was created to test a specific item in a specific environment, and it's done that way for a reason: a road is to a car as water is to a boat as air is to an airplane. ("Oh, you're wrong, because the wheels weren't purple!") WHATEVER. The airplane will fly because that's what they do when they reach airspeed, and they achieve that without serious hindrance from friction, conveyor belts, or engineering students' pranks. Post reply Do you find this valuable?
miahal7 miahal7	RE: Plane on conveyor May 16 2008, 6:07 PM EDT We both seem to have a firm grasp on the physics involved in this problem. Our debate is in what the myth was testing. I have always agreed with the Mythbuster's findings (for the most part); this myth seemed ambiguous at best, and most of the debate on this site stems from an unclear myth with an unclear result. Post reply Do you find this valuable?
EnderGT EnderGT	RE: Plane on conveyor May 16 2008, 6:58 PM EDT You and I and others may have a firm grasp on the physics involved, but you'd be surprised how many people don't seem to get it. If you interpret the question as "If the plane doesn't move, can it take off?" then no, the plane can't take off. If you interpret the question as "Can a conveyor keep a plane from moving?" then yes, the plane can take off. I'm continuously surprised by people showing up to debate the latter interpretation. Post reply Do you find this valuable?

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