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  #58  
Old 03-04-2006, 08:38 PM
David Simmons David Simmons is offline
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Join Date: Nov 2001
Posts: 12,684
Quote:
Originally Posted by RM Mentock
Real-world or not, I don't think there is even an idealized version of this problem that would allow a treadmill to exert such a force (overcoming the jet engines) to the wheels of an airliner. bup's beltsander is a good illustration of this. Offhand, I'd say Cecil pooted this. Why didn't he at least vet it by Chronos?
Cecil said that the idea behind BR#2 is so elegant that we can forget about real world. Well, I suppose it is elegant. After all I forgot about the force required to accelerate the wheel . However I don't think it's elegant enough to overcome the sheer folly of the mechanics.

I assumed a light plane with an engine thrust of 500 lb. The wheel was 18" diameter with a tire weighing 15 lb. on a 6" dia. hub weiging 5 lb.

In order to accelerate the wheel enough to overcome a 500 lb. force the acceleration would be 1245 rad/sec2. In one second the wheel's periferal speed and thus the speed of the conveyer would be 636 mph.

Yes, a jumbo jet's wheels have a lot more inertia than do a Cessna's but the engines also put out a lot more thrust.