At the Brodak FlyIn when we started allowing electric powered models we modified the line rule for 15’s. At that time 2.4Ghz was not legal so to have a two line electric throttle or electric motor insulated lines were needed. Commercial nylon coated lines were typically used although you could make your own and indeed that is what I did. The commercial lines were close to .015(not including the nylon insulation), but most measured at .0147 or so. With the help of Everett Shoemaker we did some stress analysis and determined that .014 was safe. Of course you can’t buy .014 stranded, they are .015, but the nylon insulated lines would then be legal.
To date, and we only have one more year, I am the only one to fly electric 15 at Brodak’s. I use .015 insulated lines. I don’t need the insulation today, but they are left over from before 2.4GHz was legalized. They were insulated by me so they aren’t as draggy as nylon lines.
These are also the lines I use at Muncie. Some day I’ll make new ones.
Here is the rule statement from the FlyIn web site.
All AMA Safety and general CL rules observed. Please note line lengths are specified differently than most other AMA events. Scale and AMA/Sportsman are 60ft. to 60 ft. 6 in. Not 60 ft. plus or minus 6 in. Similarly 15 profile is 52 ft. to 52 ft. 6 in. All are measured from the aircraft centerline to the handle grip center. (Where your palm rest on the handle.) Lines diameters (for three line systems) are .012 for 15, .015 for AMA/Sportsman and Class I, .018 for Class II. For 2 line systems line diameters are .014 for 15 Profile, and per AMA rules for AMA/Sportsman and Class I & II.