The AMA has allowed Spectra lines for combat contests, and sport flying. They are not yet legal for stunt contests. Spectra lines are commonly available through fishing tackle shops. Spectra is the trade name for Gel Spun Ultra High Molecular Weight Polyester (GSUMP), and the manufacturers trade name is Dyneema. The specific rule, included in the CL General category, is:
5.3.5.1 Spectra Lines.
Lines made of Spectra fiber, made of gel spun ultra high molecular weight polyethylene are permitted for sport flying and demonstration purposes. Spectra lines are not permitted in competition unless the specific rules for the event flown expressly permit such use. The use of high visibility yellow lines is recommended, but not required. For sport and demonstration flying with two lines, Spectra lines shall have the following strengths:
Aircraft Engine Watts Rated
Weight Displacement Spectra St.
24 oz .09 300 20lbs. .010”
40 oz .25 450 40lbs .013”
64 oz .40 600 60lbs .016”
75 oz .75 750 100lbs .018”
All lines shall be pull tested to 10 times the model weight. An aircraft must meet both the weight and power standards to qualify for the stated line size. Exceeding either standard places the aircraft in the next larger line size bracket. Aircraft shall be weighed with either a full fuel tank or battery on board.
Terminations shall be constructed using a 5 turn uni-knot, tied on a bight, or two strands of line looped back from the free end. An instruction film of the knot can be found at . The drawings below show a single strand for clarity, but should be tied on a bight. The knot is tied as follows:
1) Run at least six inches of line through the eye of the clip, and fold to make two parallel lines. Bring the tag end of the line back in a circle toward the clip.
2) Make six turns with the tag end around the double line and through the circle.
3) Hold the double line at the point where it passes through the eye, and pull the tag end to snug up the turns.
4) To create a loop connection: Adjust the loop size by sliding the knot up or down the standing line. Then pull the tag end with pliers to maximize tightness.