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Is there a torque/breaking turns chart that includes 3/32″ rubber?
I’ve just finished knocking out a batch of 4 strand 3/32″ P30 motors. They are about 18″ long. I don’t know how many turns they might be good for. There is a big contest coming uo and I’m trying to prepare!Dan — Torque, Torque, Torque.
I haven’t counted turns in years. If you want to, you can borrow my torquemeter. Made from an old arrow shaft, a Tee Nut fastner, some wire and bits of plywood.
See you at Muncie
Dan, here’s a link to a chart, does not have 3/32″ but has an equation for figuring turns per inch and breaking torque at the bottom of the page.
http://modelflight.com/rubber.html
EdDean,Dean,Dean.
I’m winding backwards. I even count down from my target!
I’m gonna try to calculate a target. Then maybe I’ll try the empirical method.
Well, you are welcome to use my torque meter, whatever empire or emporer you use, although I can’t recall any of them knowing anything about rubber motors. They would be better off if they did. 🙂
Tried that at the WC with one of our engines- didn’t have enough parts left in the engine to get it back the three turns….Thank God for Eugene and his batch of parts….
Dan, is the motor size you gave correct “I’ve just finished knocking out a batch of 4 strand 3/32″ P30 motors. They are about 18″ long.” or are you not using the full 10 grams allowed? My P30 motor is 3/32″ 6 strands 26″ long at 9.5 grams unlubed.
Ed8 strands-4 loops. About 18″ long. Some are strangely a bit light after tyung them. Haven’t flown any. I’ve been away working.
Hey John!
How many turns do those planes make in 5 secs? I always thought straight up was the objective.
Dan I realize the last post to your question was 2 and a half years ago, but I owe you for help in other forums…so here goes.
Dean and other are correct that using a torque meter is the way to go if you are after maximum and consistent performance. However, a torque meter and the desire to use it may not be with you at this moment. Here is an alternative. I make up 4” motors of the number of strands I would use in the motor of a different length. For instance, if I am interested in ten gram motors twenty inches in length and composed of 4 strands of 3/16th (I’m making these numbers up so don’t take them as a prescription for a 10 gram motor) I would make up a motor of 4 strands of 3/16th that is exactly 4 inches long. I then wind this motor up until it breaks and note the number of turns at the breaking point. Say the 4” motor breaks at 100 turns (again, I’m making up numbers). Dived 100 turns/4” and you find that the maximum number of turns for a motor of this number of strands of 3/16th rubber is 25 turns per inch or turns/inch. The maximum number of turns for a 20” motor of four strand of 3/16th rubber would be 20” X 25 turns/inch = 500 turns.Some details. I use this method to save rubber and gather data. With 4 stranded 20” motors there is not a lot of rubber involved, but the 16 strands in a 42” Mulvihill motor is a bunch and therefore I use the 4” proxy motors. There is nothing special about the four inch motor, it is just a length I picked that I thought would represent a larger motor but not so large as to waste rubber. When making up these motors I try to be very careful and mark the exact lengths on the rubber with a ballpoint pen. A four stranded 4’ motor would be 16” and I leave extra for the knot, which I trim after tying. Tie the knot right on the ballpoint pen ink marks. Now, the big advantage of using the shorter motors is that I make up multiple motors and break them all. I may use 5 to 10 motors to determine the characteristics of the rubber. I carefully record and date this information in a notebook for further use. Invariably, I misplace the notebook and am pleasantly surprised when I come across it at a later date. You, I’m sure are better organized than I. You shouldn’t have this problem.
So, now you know how many turns your motors can take before they fail. Different people use different percentages of available power depending upon the situation. BTW 90% turns does not equal 90% power available. Its’ more complicated than that and will be saved for a future discussion.
Remember this method is second best. If in rubber you want to be the Trophy eating machine you are in Power you are going to need torque meter. These can be bought but you can build one as good or better for little money. Try this web site: http://www.modelflight.com/torque.html
I have used the second torque meter by Jim O’Rielly and it works great. You will read torque in degrees of deflection rather than inche/onces and there ain’t nothing wrong with that as long as you aren’t trying to talk to another modeler about how many in/ozs of rubber was in your last purchase from FAI.If you go the torque meter route (using 4” or proxy motors) follow the same procedure you would counting turns, only record torque in degrees of deflection or inch/ounces an you will know where your end point is (motor failure).
I would like to know from anyone, if the above makes sense.Thanks,
Stardust
AKA Earl GriffithI wind the P30 to 1120 turns. If I launch into lift it maxes. Unless I short fuse it. Of course, THAT never happens.
Dan, Your 1120 turns sounds about right. Although not knowing what size rubber would help. In my P30’s I run 6 strands of 1/8″ and put in 1110 turns on a 22″ motor. I get about a 60-70 second motor run and the rest is glide. (Majestic plane) Great gliding plane for a P30.
Scott
Portland, TNI am building a P30 at the moment.In this discussion is the distance between prop and rear peg about an inch less than the rubber length
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