Thread: Idea B-24D Liberator
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Old Sep 06, 2011, 05:12 PM
Tom Arnold is offline
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Casper WY
Joined Dec 2005
4 Posts
Kevin, my best wishes for some successful flying. I tried what you are planning with a 48" span B-35 many years ago and let me pass on some hard learned lessons. I tried to turn all the corners with some neat bevel gears used in the model RR world (a good source of gadgets and gizmos). To make a long story short, they stripped with a scream at the first winding. The torque of a rubber motor was a LOT more than I had anticipated. In talking with Walt Mooney who was in our club, he said my failure was a blessing as bevel gears are very inefficient at transferring power---I think it was about a 75% efficiency. That meant that the power was reduced by 75% as it went through each gear. I would have had about 2 Butterfly Power at the props had it worked.

He also said a chain and sprocket affair would be much more efficient IF the chain has very little friction between the links. Using a belt and pully arrangement, the belt drive would have to "grab" the pulleys very tightly or the torque will cause them to slip and you then will have the loss of torque through each pulley as with the bevel gears.

As far as the torque goes, according to a chart I have that the competition guys say is pretty accurate, the breaking torque for 8 strands of 1/8th inch Tan Super Sport is 32 in-oz (which is the same as 2 loops of 1/4th).

Since whatever route you take, it is going to cost you some money you may want to reconsider the 3:1 gearing of the props. You mentioned "contest" in the first post and FAC rules disallow anything other than 1:1 gearing. It would be a bummer to get knocked out of a contest because of that. Actually, I think the 1:1 ratio will work just fine----look at Chris Starleaf's B-24 that flew 54 seconds at WestFAC III with just common direct drive rubber motors.

Good luck in any case---it will be a magnificent sight in the sky. (My B-35 uncompleted airframe ended its days as a wall hanging in my shop. sigh.)
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