Cable Tension Rigging Fixtures Tension Regulators Cable Connectors Turnbuckles Spring-Back 2-45 Figure 2-76.  Typical turnbuckle assembly. Figure 2-75.  Tensiometer. For the aircraft to operate as it was designed, the cable tension  for the flight controls must be correct. To determine the  amount of tension on a cable, a tensiometer is used. When  properly maintained, a tensiometer is 98 percent accurate.  Cable tension is determined by measuring the amount of force  needed to make an offset in the cable between two hardened  steel blocks called anvils. A riser or plunger is pressed against  the cable to form the offset. Several manufacturers make  a variety of tensiometers, each type designed for different  kinds of cable, cable sizes, and cable tensions.  [Figure 2-75] Rigging fixtures and templates are special tools (gauges)  designed by the manufacturer to measure control surface  travel. Markings on the fixture or template indicate desired  control surface travel. Cable tension regulators are used in some flight control  systems because there is considerable difference in  temperature expansion of the aluminum aircraft structure  and the steel control cables. Some large aircraft incorporate  tension regulators in the control cable systems to maintain  a given cable tension automatically. The unit consists of a  compression spring and a locking mechanism that allows the  spring to make correction in the system only when the cable  system is in neutral. A turnbuckle assembly is a mechanical screw device  consisting of two threaded terminals and a threaded barrel.  [Figure 2-76]  Turnbuckles are fitted in the cable assembly  for the purpose of making minor adjustments in cable length  and for adjusting cable tension. One of the terminals has  right-hand threads, and the other has left-hand threads. The  barrel has matching right- and left-hand internal threads. The  end of the barrel with the left-hand threads can usually be  identified by a groove or knurl around that end of the barrel.  When installing a turnbuckle in a control system, it is  With a control cable properly rigged, the flight control should  hit its stops at both extremes prior to the flight deck control.  In addition to turnbuckles, cable connectors are used in some  systems. These connectors enable a cable length to be quickly  connected or disconnected from a system.  Figure 2-78 illustrates one type of cable connector in use. Some turnbuckles are manufactured and designed to  accommodate special locking devices. A typical unit is shown  in  Figure 2-77 . necessary to screw both of the terminals an equal number of  turns into the barrel. It is also essential that all turnbuckle  terminals be screwed into the barrel until not more than three  threads are exposed on either side of the turnbuckle barrel.  After a turnbuckle is properly adjusted, it must be safetied.  There are a number of methods to safety a turnbuckle and/ or other types of swaged cable ends that are satisfactory. A  double-wrap safety wire method is preferred. 0 20 40 60 80 100 120 Trigger Pointer Lock Anvil Anvil Riser Length (threads flush with ends of barrel) Pin eye Barrel Swaged terminal