Figure 12-7.  Rope strengths.  Figure 12-9.  Tow ropes and cables are made of many different  reliable materials such as nylon, step-index fiber from Red Polyester,  Hollow Braid POLYPRO, Dacron, steel, and Polyethylene. Figure 12-8.  Safety link strength requirements. Diameter 3/16" 1/4" 5/16" Polyethylene Hollow braid 700 1,200 1,750 Polypropylene Monofilament 800 1,300 1,900 Polypropylene Multifilament 870 1,200 2,050 Nylon 960 1,500 2,400 Dacron 720 1,150 1,750 •  Safety link (weak link) at the glider end:  •  Minimum strength = eighty percent of the glider  maximum certificated operating weight.  •  Maximum strength = twice the maximum  certificated operating weight.  [Figure 12-8] •  Safety link (weak link) at the tow plane end:  •  Strength requirements = greater, but not more  than twenty five percent greater than that of the  safety link on the glider end, and not more than  twice the maximum certificated operating weight  of the glider. Tow ropes and cables are made of many different reliable  materials, such as nylon, step-index fiber from Red Polyester,  Hollow Braid POLYPRO, Dacron, steel, and Polyethylene.  [Figure 12-9] After all inspections are complete, compute the takeoff  performance for the tow plane using the approved POH. As  a rule of thumb, the tow plane is normally airborne in about  twice the computed distance. If your tow plane does not have  takeoff performance charts, make a normal takeoff without  the glider in tow and note the lift-off point. Use this physical  point in lieu of computed takeoff data. Pay particular attention  to your altitude over the departure end of the runway and the  clearance of any barriers. Using the computed takeoff data or actual takeoff point, choose a  physical abort point on the runway.  [Figure 12-10]  Thoroughly  brief the glider pilot on the abort point and abort procedures. If  the tow plane is not off the ground by the chosen abort point,  the glider should release, or be released, allowing the tow plane  to accomplish a normal takeoff.  Step-index fiber from Red Polyester Hollow Braid PolyPro Dacron Polyethylene Braids Take Off Planning Greater, but not more than 25 percent greater than  that of the safety link at the glider end, and not greater  than twice the glider max gross weight (MGW). RULE 1000 lbs. x 25% = 250 lbs. 1000 lbs. + 250 lbs. = 1250 lbs. 700 lbs. x 2 = 1400 lbs. 700 lbs. MGW Glider safety link  breaking strength  1,000 lbs. To meet the rule below, the tow plane safety  link strength requirement must be greater than  1,000 lbs. and not more than 1,250 lbs. The 1,400 lbs. strength requirement is not a player since 1,250 lbs. is the maximum. 12-5