Rubber Band Maximum Winds

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Orion66
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Rubber Band Maximum Winds

Post by Orion66 »

Does anyone have figures about the maximum number of winds possible with certain widths of rubber? We're getting about 160 winds on a .095'' rubber band before breaking. If this number seems low, does anyone have any suggestions to increase the number? And, does there seem to be a number of winds above which the torque will be too great and cause damage to the helicopter? (Also, we are using a 1:10 ratio winder, stretching the rubber band to about 150% length for the first 80 or so turns)
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RJohnson
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Re: Rubber Band Maximum Winds

Post by RJohnson »

I'm assuming you mean 160 turns on the winder, not on the rubber band. If so, that number, 1600 , seems reasonable, but probably could be improved. One important thing to note is that the length of the band directly affects how many winds will go on. If you could provide the length of your band, maybe we could give you a more helpful answer. As for winding it, are you using lubricant? This will definitely help pack more turns in. As for stretch winding, I stretch out to 2x-2.5xthe resting length of the band and start walking in when the band feels tight when I push and pull it between my fingers. When it's tight, I take a step in, and wind until it's tight again and repeat until the band is about an inch longer than my motor sick.

Good luck!
calgoddard
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Re: Rubber Band Maximum Winds

Post by calgoddard »

Charts and graphs exist for flying outdoor model airplanes with rubber power that provide the flier with estimates of how many turns can be put into a rubber motor before it breaks.

One chart I sometimes use gives estimates of max turns per inch for a typical motor made of Tan II rubber (no longer manufactured). Data is given for motors such as 2 x 1/8, 4 x 1/8, 6 x 1/8, etc., where "1/8" inch is the standard rubber width. By way of example a 4 x 1/8 rubber motor would consist of four strands (two loops) of one eighth inch wide rubber.

One of the best resources for rubber powered airplane fliers are graphs published by Don DeLoach, a legendary outdoor free flight modeler. They show 75% breaking turns and 85% breaking turns versus motor length for motors made up of 2, 3, 4, 8 etc. strands of 1/8 inch Tan Super Sport (TSS) rubber.

When you get down to single loop motors made of fractions of the manufactured 1/8 inch width of TSS rubber, there are no charts or graphs available to my knowledge that show estimates of max turns. You have to collect your own data.

TSS rubber varies in density and thickness from batch to batch. While it is typically around .044" thick, that number varies in different batches and along the length of the rubber within a batch. Even when using a precision rubber stripper, such as that sold by Ray Harlan, it is not possible to strip rubber to a particular width with precision and uniformity. This is why world class indoor model airplane fliers use length and weight to measure the size of their rubber motors, and not thickness and width.

In the sport/hobby of indoor rubber powered aircraft, helicopters are rarely flown although there is an official indoor rubber powered helicopter class. I have never witnessed a rubber powered helicopter competition outside of Science Olympiad.
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