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cstatman
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Re: Rubber braiding and Hodes' Rubber Motor XL Sheet
Reply #4 - Jul 8th, 2020 at 2:25pm
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thank you SkyPilot -- you made my day

I also just try to get a circle overhead.   still learning to trim (after 40+ years of trying)

I'm happy if they don't beeline into the nearest airplane eating tree
  

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Sky9pilot
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Re: Rubber braiding and Hodes' Rubber Motor XL Sheet
Reply #3 - Jun 10th, 2020 at 12:58pm
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Matt,
I don't compete and fly just in small local area and I'm satisfied if I can muster a nice circle overhead with my models.  But some of our modelers are avid competitors and they will have more to share with you.  The old "KISS" moto for starting is good.  My wife reminds me of this often!  Roll Eyes Grin Wink
  

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Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Re: Rubber braiding and Hodes' Rubber Motor XL Sheet
Reply #2 - Jun 10th, 2020 at 12:38pm
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Sky9pilot- thanks for the thoughts!  Yep that all makes sense.  I'll definitely plan on starting simple with it, especially for trimming.  I'm going through all those numbers and the XL sheet to familiarize myself with the whole process, so I sort of know where I'm headed with the motor, and rubber cross section, and all that business for the future, and make sure that the components I'll be buying will actually do the job down the road.
  
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Re: Rubber braiding and Hodes' Rubber Motor XL Sheet
Reply #1 - Jun 10th, 2020 at 12:13pm
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Here's a link to the Hode's doc that Matt is referring to: Click Here

I would recommend to start with a non-competition motor to trim your Stinson.  Braiding can come at a later date.  Braiding is for getting the most out of your motor in competition. Often the length is determined by the contest requirements as a percentage of the weight of the model.   Also to keep tension on the prop hook so the free wheeler on the prop is free to operate and keep the motor from being as floppy with all the loose loops of rubber in the fuselage. You can braide a shorter motor for initial trimming.  Hopes this makes sense. 

How about some of our competing modelers giving us some input on this subject?

Here's the article on the "Rubber Motor Size Calculator"  for those interested from NFFS Tech Library, see attached.
  

Rubber_Motor_Size_Calculator.pdf ( 55 KB | 18 Downloads )

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Rubber braiding and Hodes' Rubber Motor XL Sheet
Jun 10th, 2020 at 11:18am
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Can someone clarify how the braiding step works into Hodes' Rubber Motor Excel Worksheet from freeflight.org Technical Library?  I'm trying to merge info from several articles and youtube videos, and just want to make sure I'm thinking correctly.  (I've worked through these calculations by hand, then discovered Hodes' worksheet, so I'm giving that a try now because I'm done thinking so hard, as I'm a "recovering engineer." Smiley)

I'm attempting to revive a 90% complete Comet Stinson SR-7 that I started in early 2000s, and recently found and pulled out of the basement.  I've been studying some of the info about braiding rubber motors, so I am familiar with the basic methods, advantages, etc.

I found the great intro articles at freeflight.org Technical Library for rubber motor sizing, braiding, number of windings, as well as Hodes' Rubber Motor Excel Worksheet for download.

Going through Hodes' worksheet, I plugged in what I know, and estimated the airplane weight (see attached- I hope it's viewable).  Some of my numbers might be off at this point (I don't have a scale), etc.

Hodes' worksheet tells me I need 122 inches total of 1/8" rubber strip.  Then, to get 1.75x the prop Hook-to-Peg distance (1.75 is just a whim based on what I've read, and to get the number of strands to be an even number), I'd need to use 6 strands of the 1/8" rubber, each at 20.1 inches long, BEFORE BRAIDING.

I now have 122 inches of 1/8" rubber, folded into 6 equal length strands (in theory, I don't have any rubber in-house yet).  Each strand is ~20.1 inches long.

My main question:
Based on the articles I've read, in order to braid it from this point, I think I would take those 6 strands at 20.1 inches long, unfold them into 3 strands at 40.2 inches long, then start the braiding process from there.  So I would next take the 3 strands, twist about 4-5 turns per inch into them, then fold the ends over to double them up to get the final 6 braided strands.  IS THIS CORRECT?

So, due to the braiding, the 6 strands will end up a bit shorter than the 1.75x the Hook-to-Peg length, which is nice because it takes up some slack I guess

Question 2:
How do I know that there will still be tension on the rubber once it unwinds after flight, and not be too long?  One of the advantages of braiding is that it is supposed to keep the prop pulled into the nose during flight after the rubber's energy is spent, as I understand.

Thanks for any thoughts.

Matt
  

( 158 KB | 24 Downloads )
Stinson_SR7_Hodes_xl_rubber_motor_-_Copy.png
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