Quote:
Originally Posted by MuseChaser
In real world physics, there's probably a limit as to just how fast the wheels on a given plane COULD turn before creating enough heat to burn out the bearings and seize up. If you could somehow create an airplane-sized treadmill capable of whatever that speed is (so already we're leaving the real world again) and you could cause that condition before the airplane took off, then I guess you could win the argument. It would have to happen very quickly, because no matter how fast the treadmill was moving, the airplane WOULD start to move forward the instant the prop starting pushing air rearwards.
Barry
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I did this experiment for a grade 9 Science Fair. Using an gas powered string controlled Spitfire (was a great excuse to buy a flying model) and a belt sander hooked up to a rheostat I set out to prove or disprove the old wives tale that it would just sit there.
Now, that was 40 years ago so I do not recall all the numbers but the basic results were:
Plane at take off power + Sander with smooth belt at low speed = Normal take off
Plane at take off power + Sander with smooth belt at medium speed = Plane struggled and lost a bit of ground on sander but still managed to take off
Plane at take off speed + Sander with smooth belt at high speed = Plane could not overcome the belt and slowly fell of the back of the sander (where it promptly smacked the prop on the table and smashed it to pieces)
Plane at take off speed + sander with course belt at slow speed = Plane could barely get enough speed to take off
Plane at take off speed + sander with course belt at medium speed = Plane could not take off and slid off back again (and another prop bit the dust)
Didn't even bother to try high speed.
Oh, and I went through 4 sets of wheels during the process.
What was readily observable was that the friction between the belt and the wheels would eventual start to turn them backwards. Low friction and high speed or high friction at low speed would turn the wheels backwards enough to overpower the thrust of the engine and the wheels would stop turning and game over.
This is where what you said above comes in though. I did the math based on the HP of the model and the RPM speed of the sander and then took it up to full scale. Like I said I do not recall the real numbers but in order for the same results to happen with a real Spitfire the belt would have had to be going someplace in the neighborhood of 850 MPH. To the best of my knowledge even now there are no treadmills capable of hitting 850 MPH and if there was (like you said) the tires would blow well before the plane sat still. So could a plane on a treadmill just sit there? Sure, but there is not a hope in hell of having it happen in reality. Myth was BUSTED.