Thread: Idea B-24D Liberator
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Old Sep 14, 2011, 01:00 PM
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The 'Wack, BC, Canada
Joined Oct 2002
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For the pulleys forget the spools. You need to make your own so they have a slight barrel shape to them. Having a slight crown in the middle will make the bands self center. It's the same reason why the drums and wheels on belt sanders and bandsaws are crowned in the middle. Using spools with angled sides will actually cause the bands to walk up the flanges and off the pulleys if they run over to the sides. I know it sounds counter to what you'd think but that's the way the physics of pulleys works. With flanged end spools your alignment would be critical. With non flanged "barrel" shaped pulleys you don't even need end flanges as long as the alignment is somewhere close.

And the best way to make such pulleys is with a Dremel moto tool used as a quick and dirtly wood lathe. The laminated balsa pulleys you can make with such a setup will be light and very effective.

As for the return run I'd use idler pulleys to "bend" the return run back up into the wing's thickness so the return run is up within about a 1/4 to 3/8 inch away from the tension side.

Speaking of wing thickness. No flat bottom skinny airfoils for THIS one. To produce the strength and rigidity (they are not the same thing) needed to adequitely support the prop drive nacelles and give you the room you need in the wing for all the drive stuff you're going to need to use a thicker airfoil. But if you make a thick airfoil with a flat bottom it'll have too much camber and not fly well. So you're stuck with using a "semi symetrical" airfoil so you get the right amount of airfoil camber and still have the thickness you want to install the drive stuff in the wing. But if things just get too crowded in there then running the return path along underneath the wing is still an option. Not the ideal one for sure. But better than trying to build the wing TOO thick.

You know..... a B17 with the wider and thicker "old school" wing would be a lot easier to do this. But if you've got a thing for the B24 then have at it.
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