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06-03-2004 10:37 AM  13 years agoPost 1
helicopter34

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New Jersey, exit 82

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Hey, I was just messing around with my tail boom, I am making a drive shaft because I don't have any carbon tube that is the right length to fill the whole tail boom (plug I use a longer home made aluminum boom) and I bought some K&S hollow alluminum tube to use as drive shaft. Its pretty light and since its tubular, it has a better resistance to wind up. I glue carbon rods into each end so that I can use the stock size bearings and gears.

But I just thought of another idea, for all you weight nazis, this probably isn't for you, but a cheap alternative to walts tail drive shaft to reduce windup, put a light coating of epoxy on your carbon drive shaft and then slide a clean tube from the inside of a pen. The reinforcement of the the tube will decrease tail drive shaft windup.

what do you guys think?

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06-03-2004 05:59 PM  13 years agoPost 2
hornet dave

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Cedar Rapids, IA USA

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I'll add my experience. I made some tubular aluminum tail driveshafts, with varying degrees of success. If you try to make a hollow shaft, with short lengths of carbon rod sticking out each end (which would go into the corresponding gears), I found that pressing the gears into place would cause the aluminum tube to bend, resulting in vibration problems. So, if you try this approach, learn from my mistakes and maybe sand down the carbon rods so that they slip into the gears with little force, then maybe use some CA or something to secure the gears onto the carbon shaft.

If you simply want to reduce the wind-up of the stock shaft, that's pretty easy to do. Just buy the smallest aluminum tube which fits over the tail driveshaft, and cut two lenghts of this tube so that they fit between the bearings on the carbon driveshaft. Then, use something round to roll down the diameter at the ends of the aluminum tube so that it fits snugly on the carbon rod. I used the handle of my exacto knife to do this, practice on some scrap material a few times first. Put the aluminum tubes in place on the driveshaft (make sure the center bearing is in place!), secure the tubes with a little CA, and assemble the shaft into the tail boom.

Of course, I didnt really notice any flight improvement from doing this, but the tail driveshaft is a lot stiffer as a result.

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06-05-2004 07:44 AM  13 years agoPost 3
helicopter34

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New Jersey, exit 82

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Yeah

Yeah I know what you mean, I didn't even bend the aluminum tube at all and it still caused some serious vibrations. The vibration strength would come in and out as you progress through the rpm range (must be hitting harmonics or somehting). It was bad. And I was up all night messing with it because it wasn't working, and I ran out of carbon fiber rod to do what you were suggesting (which I will do when my shippment of stuff comes in) so I tried making do with a wild concoction of leftover material. The consensus is that I wasted a lot of time and material and I'm mad and I hate helicopters.

Wind up is definitely a problem, as is unsupported sections of the tail being allowed to warp and vibrate. But I hate glueing tube over the CF rods with bearings in between because if for some reason I need to take the bearing off, I practically have to break everything to get to it. Ill try what you said, just put a little CA on the ends so that if I dunked the whole section in acetone, it was fall apart for dissambly.

Its basically a composite material (sandwich material). It always amazed me how by combining two materials, the strength of the material is greater than the sum of the strengths of an equal amounts (as the portion present in the composite) of each material. There is added strenght just from the combination (CF, FG, fiber injected plastics).

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