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Quick-disconnect procedures
RIGGING AND ADJUSTING TOOLS

Aviation Structural Mechanic (H&S) 3&2 - How airplanes are built and how to maintain them
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The eyes contain a pressed-in bearing. The rods are generally hollow and neck down to a smaller diameter at each end where the fittings are attached. One or both of the fittings are screwed into the necked portion of the rod, and are held in place by locknuts. When only one stem is adjustable, the stem of the other eye fitting is riveted into the neck at its end of the rod. A hole is drilled into the threaded neck of a push-pull rod for inspection to ensure that the stem has engaged a safe number of threads. The stem must be visible through the hole. Push-pull rods are generally made in short lengths to prevent bending under compression loads and vibration. Push-pull rod linkage must be inspected closely for dents, cracks, and bent tubing. Damaged tubes may have to be replaced. End fittings are checked for damage, wear, and security of attachment. Worn or loose fittings must be replaced. When you are replacing a damaged push-pull tube, the correct length of the new tube may be obtained by loosening the check nut and turning the end fitting in or out, as necessary. When the push-pull tube has been adjusted to its correct length, the check nut must be tightened against the shoulder of the end fitting. Normally, only one end of a push-pull rod is adjustable. The adjustable end has a hole (witness hole) drilled in the rod. The hole is located at the maximum distance the base of the end fitting is allowed to be extended. If the threads of the end fitting can be seen through this hole, the end fitting is within safe limits. When you are attaching push-pull rods with ball bearing end fittings, the attaching bolt and nut must tightly clamp the inner race of the bearing to the bell crank, idler arm, or other supporting structure. Nuts should be tightened to the torque values listed in the aircraft MIM. After installing a new push-pull rod in a flight control system, the control surface must be checked for correct travel. Procedures for accomplishing this are described later in this chapter. If the travel is incorrect, the length of the push-pull fod must be readjusted. BELL CRANKS AND WALKING BEAMS.— Bell cranks and walking beams are levers used in rigid control systems to gain mechanical advantage. They are also used to change the direction of motion in the system when parts of the airframe structure do not permit a straight run. They are often used in push-pull tube systems to decrease the length of the individual tubes, and thus add rigidity to the system. A bell crank has two arms that form an angle of less than 180 degrees, with a pivot point where the two arms meet. The walking beam is a straight beam with a pivot point in the center. Bell cranks and walking beams are mounted in the structure in much the same way as pulley assemblies. Brackets or the structure itself may be used as the point of attachment for the shaft or bolt on which the unit is mounted. Examples of a bell crank and a walking beam are shown in figure 9-22. The two are similar in con- struction and use. The names bell crank and walking beam are often used interchangeably. IDLER ARMS.—Idler arms are levers with one end attached to the aircraft structure so it will pivot and the other end attached to push-pull tubes. Idler arms are used to support push-pull tubes and guide them through holes in structural members. BUNGEE.—Bungees are tension devices used in some rigid systems that are subject to a degree of shock or overloading. They are similar to push-pull rods, and perform essentially the same function except that one of the fittings is spring-loaded in one or both directions. That is, a load may press so hard (compression) against the fittings that the bungee spring will yield and take up the load. This protects the rest of the rigid system against damage. The internal spring may also be mounted to resist tension rather than compression.    An internal double-spring arrangement will result in a bungee that protects against both overtension and overcompression. Figure 9-22.—Bell crank and walking beam. 9-28







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