Aircraft Rigging

Minimum Breaking Strength (Pounds) AllowableTolerance Nominal diameter increase ofConstruction on diameter MIL-W-83420 MIL-W-83420 MIL-C-18375 of wire rope cable diameter(plus only) COMP A COMP B (CRES) (CRES)at cut end INCHES INCHES INCHES POUNDS POUNDS POUNDS 1/32 3 x 7 0.006 0.006 110 110 3/64 7 x 7 0.008 0.008 270 270 1/16 7 x 7 0.010 0.009 480 480 360 1/16 7 x 19 0.010 0.009 480 480 3/32 7 x 7 0.012 0.010 920 920 700 3/32 7 x 19 0.012 0.010 1,000 920 1/8 7 x 19 0.014 0.011 2,000 1,760 1,300 5/32 7 x 19 0.016 0.017 2,800 2,400 2,000 3/16 7 x 19 0.018 0.019 4,200 3,700 2,900 7/32 7 x 19 0.018 0.020 5,000 5,000 3,800 1/4 7 x 19 0.018 0.021 6,400 6,400 4,900 9/32 7 x 19 0.020 0.023 7,800 7,800 6,100 5/16 7 x 19 0.022 0.024 9,800 9,000 7,600 11/32 7 x 19 0.024 0.025 12,500 3/8 7 x 19 0.026 0.027 14,400 12,000 11,000 7/16 6 x 19 IWRC 0.030 0.030 17,600 16,300 14,900 1/2 6 x 19 IWRC 0.033 0.033 22,800 22,800 19,300 9/16 6 x 19 IWRC 0.036 0.036 28,500 28,500 24,300 5/8 6 x 19 IWRC 0.039 0.039 35,000 35,000 30,100 3/4 6 x 19 IWRC 0.045 0.045 49,600 49,600 42,900 7/8 6 x 19 IWRC 0.048 0.048 66,500 66,500 58,000 1 6 x 19 IWRC 0.050 0.050 85,400 85,400 75,200 1 - 1/8 6 x 19 IWRC 0.054 0.054 106,400 106,400 1 - 1/4 6 x 19 IWRC 0.057 0.057 129,400 129,400 1 - 3/8 6 x 19 IWRC 0.060 0.060 153,600 153,600 1 - 1/2 6 x 19 IWRC 0.062 0.062 180,500 180,500 to prevent the cables from slipping off when they slacken abnormal cable wear patterns which can provide an indication due to temperature variations. Pulleys should be examined to of other problems in the cable system. [Figure 2-73] ensure proper lubrication; smooth rotation and freedom from Fairleads may be made from a nonmetallic material, such as phenolic, or a metallic material, such as soft aluminum. The fairlead completely encircles the cable where it passes through holes in bulkheads or other metal parts. Fairleads are used to guide cables in a straight line through or between structural members of the aircraft. Fairleads should never deflect the alignment of a cable more than 3° from a straight line.

Pressure seals are installed where cables (or rods) move through pressure bulkheads. The seal grips tightly enough to prevent excess air pressure loss but not enough to hinder movement of the cable. Pressure seals should be inspected at regular intervals to determine that the retaining rings are in place. If a retaining ring comes off, it may slide along the cable and cause jamming of a pulley. [Figure 2-74] 2-42 Unpressurized Pressurized Excessive cable tension Pully wear from misalignment Pully too large for cable Cable misalignment Frozen bearing Normal condition Travel Adjustment Control surfaces should move a certain distance in either direction from the neutral position. These movements must be synchronized with the movement of the flight deck controls. The flight control system must be adjusted (rigged) to obtain these requirements. The tools for measuring surface travel primarily include protractors, rigging fixtures, contour templates, and rulers. These tools are used when rigging flight control systems to assure that the desired travel has been obtained. Generally speaking, the rigging consists of Fairlead Split fairlead Retaining rings Control cable Bulkhead groove the following: 1. Positioning the flight control system in neutral and temporarily locking it there with rig pins or blocks; 2. Adjusting system cable tension and maintaining rudder, elevator, and ailerons in the neutral position; and 3. Adjusting the control stops to the aircraft manufacturer’s specifications.

Cable Tension 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 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.

Rubstrip Solid fairlead Guard pin Bracket Air seal Bulkhead Pulley 2-43 0 20 40 60 80 100 120 Trigger Pointer Lock Anvil AnvilRiser Tension Regulators 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.

Turnbuckles 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 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. Some turnbuckles are manufactured and designed to accommodate special locking devices. A typical unit is shown in Figure 2-77. Cable Connectors 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. Spring-Back With a control cable properly rigged, the flight control should hit its stops at both extremes prior to the flight deck control.

The spring-back is the small extra push that is needed for the flight deck control to hit its mechanical stop. Push Rods (Control Rods) Push rods are used as links in the flight control system to give push-pull motion. They may be adjusted at one or both ends. Figure 2-79 shows the parts of a push rod. Notice that it consists of a tube with threaded rod ends. An adjustable antifriction rod end, or rod end clevis, attaches at each end of the tube. The rod end, or clevis, permits attachment of the tube to flight control system parts. The checknut, when tightened, prevents the rod end or clevis from loosening.

They may have adjustments at one or both ends. The rods should be perfectly straight, unless designed to be otherwise. When installed as part of a control system, the assembly should be checked for correct alignment and free movement. Length (threads flush with ends of barrel) Pin eyeBarrelSwaged terminal 2-44 Locking-clipTurnbuckle body Spring connector Anchored end Peening Flange Flange ends It is possible for control rods fitted with bearings to become disconnected because of failure of the peening that retains the ball races in the rod end. This can be avoided by installing the control rods so that the flange of the rod end is interposed between the ball race and the anchored end of the attaching pin or bolt as shown in Figure 2-80.

Another alternative is to place a washer, having a larger diameter than the hole in the flange, under the retaining nut on the end of the attaching pin or bolt. This retains the rod on the bolt in the event of a bearing failure. Adjustable rod end clevis Tube Adjustable antifriction rod end Rivets Checknut Threaded rod end 2-45 Torque Tubes Where an angular or twisting motion is needed in a control system, a torque tube is installed. Figure 2-81 shows how a torque tube is used to transmit motion in opposite directions. Cable Drums Cable drums are used primarily in trim tab systems. As the trim tab control wheel is moved clockwise or counterclockwise, the cable drum winds or unwinds to actuate the trim tab cables.

[Figure 2-82] Rigging Checks All aircraft assembly and rigging must be performed in accordance with the requirements prescribed by the specific aircraft and/or aircraft component manufacturer. Correctly following the procedures provides for proper operation of the components in regard to their mechanical and aerodynamic function and ensures the structural integrity of the aircraft. Rigging procedures are detailed in the applicable manufacturer’s maintenance or service manuals and applicable structural repair manuals. Additionally, aircraft specification or TCDS also provide information regarding control surface movement and weight and balance limits.

The purpose of this section is to explain the methods of checking the relative alignment and adjustment of an aircraft’s Bearing Shaft Drum Quadrant Torque tube Horn Push-pull rod main structural components. It is not intended to imply that the procedures are exactly as they may be in a particular aircraft. When rigging an aircraft, always follow the procedures and methods specified by the aircraft manufacturer. Control wheel 2-46 Structural Alignment The position or angle of the main structural components is related to a longitudinal datum line parallel to the aircraft center line and a lateral datum line parallel to a line joining the wing tips. Before checking the position or angle of the main components, the aircraft must be jacked and leveled.

Small aircraft usually have fixed pegs or blocks attached to the fuselage parallel to or coincident with the datum lines. A spirit level and a straight edge are rested across the pegs or blocks to check the level of the aircraft. This method of checking aircraft level also applies to many of the larger types of aircraft. However, the grid method is sometimes used on large aircraft. The grid plate is a permanent fixture installed on the aircraft floor or supporting structure. [Figure 2-83] When the aircraft is to be leveled, a plumb bob is suspended from a predetermined position in the ceiling of the aircraft over the grid plate. The adjustments to the jacks necessary to level the aircraft are indicated on the grid scale. The aircraft is level when the plumb bob is suspended over the center point of the grid.

Certain precautions must be observed in all instances when jacking an aircraft. Normally, rigging and alignment checks should be performed in an enclosed hangar. If this cannot be accomplished, the aircraft should be positioned with the nose into the wind. 0 1 2 3 1 2 3 1 2 3 1 2 3 Nose up Nose down Pitch(deg) Right wing down Left wing down Roll (deg) AFT INBD AFT Plumb bob Plumb bob attachment Plumb bob stowage clip Right main wheel wall AFT bulkhead Grid plate 2-47