ONE MORE TIME For those who think it won't fly (as I did) please explain why my "plane on a string analogy" doesn't help The wheels don't power the plane, they just keep it off the ground so it can take off...just as the string does. Unless I missed it, none in the "it won't fly" camp have told me where I am wrong.
Repeat after me: "It's an invalid question" "It's an invalid question" "It's an invalid question" "It's an invalid question" Oh, and one more thing; "It's an invalid question"
Everything has stopped. I have not done anything else on the internet for the last 3 or 4 days since I started reading this thread (apart from some of the links to other forums and sites debating it). It was like reading a good book and not really wanting it to end. If the question asked was:- On a day with absolutely calm wind, a plane is standing on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. The conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the airplane ever take off? Then the plane will of course fly without breaking any of the statements constraints. However as Alan's question stated:- Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation. There is no wind. Can the plane take off? The part I marked in bold actually (as has been said by a couple) prevents the airplane moving a thousanth of an inch forward as it would cause it's wheels to move faster than the conveyor and would break the constraints of the problem (of course this could physically occur). To throw a few more spanners into the conveyor belt problem. What is the "speed of the wheels", is it the point in contact with the conveyor or the axle. I think (though it was a few days ago now ) this has been mentioned. Oh an one other thing that has been mentioned. If you assume the wheel of the aircraft to be a pinion and the conveyor belt to be a rack (as in a rack and pinion steering), then IMHO the car R&P rack moves in the same direction as the pinion rotation else the gear teeth would break. This question says they are in the opposite direction of rotation which in the R&P steering would cause the gear teeth to shear. Does this mean the plane will travel at twice the expected speed or do the tyres break traction Brilliant thread. I think it made the engineer in me resurface as that is where all my qualifications are from, I moved to IT as a failed engineer which means all this post is probably a load of bolox!!!!! As just mentioned above, it is an invalid question in this instance.
Hi MalcQV, I'm glad you've enjoyed the thread so far. I don't agree that its an invalid question, though. With respect to those who think that it is an invalid question, I read it as saying that if the speed of the plane's wheels forward is 10mph, then the conveyor is doing 10mph backwards, in relation to the same reference point. There is no way the conveyor cam be allowed to spin up to an infinite speed within the contsraint of the problem (unless the plane does an infinite speed in the other direction, and it would take off well before that speed is reached). I feel the question is valid, and futhermore is valid if you consider both the translation speed of the wheels *and* the rotational speed. I made an argument for this a few times already, so I won't re-hash it here. Let the games begin!! (or rather, continue, endlessly... ) Best Regards, Rich.
The answer is NO. Flight is produced by wind moving over and under the wings producing lift. Even though the conveyor belt is moving it is not producing wind over the wing surface. Therefore not prducing lift. A plane can have the engine(s) running WOT with the brakes on and it will not lift off the ground.
Better late than never. My 2 cents is a good as anybody elses. Especially since I am a pilot and have read extensively on the principles of flight. Glad I can keep the discussion going.
Don't tell me you guys are STILL arguing over this... btw the noobs who jump in saying NO, you have a LOT of reading to do.
I used to fly too, sailplanes and power planes, but even if you were to be the world's foremost expert on flight it wouldn't change the fact that the question, as asked, has neither a yes or a no answer.
I've been deeply involved in a long disussion with my neighbors 3yr old son on the Einstins theory of relative time. Oddly enough that explination went over much easier than the better part of this thread. I've now developed my own theories on relativity, those that are based not on physical speed but the speed of brain function, thought processing, and deductive reasoning. Using this thread as my main source of study, I've proven that some people are so dense, and require such an extravogant effort only to never accept the fact that they are wrong, it's actually a contagious disease. Spending time reading the drivel that pours from their thoughts has reached such an exponential level of stupidity and ignorance, you can actually lower your intelligenc by further engaging in their pedantic bantering and fabricated excuses. I don't have the exact formula finished for just how many IQ points you will lose by further engaging in this thread, but it's definitely an exponential scale, to the point where you suffer a massive brain hemorage creating a black hole of sorts between your ears. There is such a vast lack of knowledge it pillages from others in an attempt to exist in a state of IQ larger than their shoe size. It's a very very dangerous condition and I highly recommend those of us with the knowledge and understanding to "get it" step back and just very carefully enjoy the entertainment. Be very careful not to get sucked into their trap tho. Shortly after this discovery Ben Stein called to let me know my Nobel Price in Medicine and Science should be delivered via fedex monday before 10am. It's the Buzz theory on relative stupidity, the dumber you are the dumber you make everyone else around you So what have I missed, other than a select few *****ing about it being an impossible scenario, blah blah blah.
Just because I'm tired of this going around and around I started a new theory discussion. This should further test my relative stupidity theory. My Hypothesis is that the truely intelligent people will drag this into a heated discussion and cause themselves great mental pain and anguish. Those of averate intelligence will simply say yes/no, and be done with it. Then others may go crosseyed, collapse onto the floor and die of a massive acute myocardial infarction after just beginning to ponder such an event. Now, if you dare, check into round 2 Here
Yes, late to the party, but here's my entry... The airplane takes off. The airplane's wheels do not turn. During the takeoff run, the treadmill simply travels at the same speed as the airplane.
The posed question is not invalid (sorry teak). The tyres do not break traction the aircraft is catapulted along the runway due to the opposite direction of rotation. I am posting on this no more. But I won't unsubscribe PS mxblue, your thread is too much for this IT guy
If you think about it more, you may be able to see that it is invalid. No matter which way the conveyor moves. The conveyor can NOT act as a catapult. It can only affect the rotation of the tires. In no way can it stop, or as in the case of a catapult, accelerate the plane. Again, the conveyor can affect ONLY the rotation of the tires, not the movement of the plane.
Damnit Teak, did you miss my whole disertation on the relative stupidity theory... your falling in.. NOOOOOOOOOOOOOOOO!! ! ! !
A lot of junk science on this thread. Only teak is close to being right. Except it's not really an invalid question. The tires accelerate, and the conveyor accelerates in the opposite direction. The tires' acceleration is angular, not linear. Net effect is that the plane does not move. Since it does not move, there is no airflow over the wings. So it doesn't get lift and it does not take off. Simple as that. Also, the tire speed does not zoom up to infinity. Assuming they can handle it, the max speed the tires reach is slightly faster than the speed of the plane if it had its wings removed. Basically, it's a jetcar (or propellor-driven) car. We have seen them go fast in the desert. If they were on a treadmill going the other way, they would not go forward. The reason I say it would go slightly faster than the max speed is that if the plane was moving on the ground, it would have drag. Since it's not moving, drag on the body of the plane is not a factor. Richrowe, you are right that there is no direct coupling to the tires. But there is an indirect coupling. It's called the landing gear. The axles of the landing gear act like thrust bearings on the wheels and tires. The engines thrust accelerates the planes body, which accelerates the landing gear, which accelerates the tires. It's that simple. Since the conveyor belt speeds up in the opposite direction and matches the speed at any given time, the tires and plane don't go anywhere. If the tires were ever able to go faster than the conveyor belt, the plane would accelerate forward. But the question says that the conveyor belt is matching the speed. So the tires rotate faster and faster but so does the conveyor belt in the opposite direction. Net result is that the tires and axles and landing gear and plane don't get moved horizontally. No horizontal movement, no horizontal acceleration, no lift, no flying plane Think of it this way. If you were running to stand still on a treadmill, and then you started running faster as someone sped up the treadmill, you wouldn't go anywhere, would you? No point debating which direction the conveyor belt is moving, it is obvious that there would be no issue whatsoever if the conveyor was moving in the same direction. The plane would get accelerated faster relative to the ground, and it would take off quicker. They use this in the form of a catapult on aircraft carriers. The question can only exist if the writer meant that the conveyor is moving in the opposite direction to the plane's take-off direction, just like a treadmill moves in the opposite direction to a runner. It is pointless to have a treadmill that moves in the same direction that you are running in, since you would get shot off the front in a second! It is also pointless to argue about which direction the wheels driving the conveyor are turning in. They are going in circles and change direction each and every moment. That's why they are going in a circle. Circular motion is specified as clockwise and anticlockwise. Saying left or right is meaningless, because each would be equally right at different points on the circle. Like I said, junk science.
Hey Art, ya gotta give props where props are due. Yin and I had the same answer pegged (with the same analogy) on posts #4 and #5. - It's been fun reading about the theories postulated by all them arm-chair scientists, though!
Art, Yin, Ghost, All you guys who think the wheels have to turn a certain direction for a plane to fly are killing me! I am getting sucked into this again! The wheels do not provide any propulsion or braking power. The direction they turn, and the direction of the conveyer are irrelevant for flight in this example! There is nothing stopping the airplane from moving forward under its own thrust and acheiving takeoff speed. Geez, float planes or ski planes don't even have wheels and yet they can takeoff. Go figure....... Rick
Art, one other thing, your treadmill analogy is not correct, since yur legs provide the thrust in contact with the treadmill. The wheels on the plane do NOT provide thrust! Rick
The wheels spinning does not create enough drag to counteract the thrust produced by the engine. The plane takes off. period.
