CIRRUS AIRPLANE MAINTENANCE MANUAL

Transcription

1 FASTENER AND HARDWARE GENERAL REQUIREMENTS 1. DESCRIPTION This section contains general requirements for common hardware installation. Covered are selection and installation of cotter pins, installation of turnbuckle locking clips, rod end inspection requirements, self-locking nut installation requirements, fastener length substitution requirements, fastener flushness requirements, and installation and usage requirements for washers and lockwashers. Page 1

2 2. MAINTENANCE PRACTICES A. Cotter Pins (See Figure 1) The preferred method to secure a pin or castellated nut is by the use of a cotter pin. Safety wiring is also an acceptable method to secure pins or castellated nuts. CAUTION: Cadium-plated cotter pins should not be used in applications bringing them in contact with fuel, hydraulic fluid, or synthetic lubricants. (1) Proper Usage of Cotter Pins (a) Select cotter pin material in accordance with temperature, atmosphere, and service limitations. (b) Cotter pins shall be new upon each application. (c) When nuts are to be secured to a fastener with cotter pins, tighten nut to low side (minimum) of applicable specified or selected torque range unless otherwise specified, and if necessary, continue tightening until slot aligns with hole. In no case shall the high side (maximum) torque range be exceeded. (d) If more than 50% of cotter pin diameter is above nut castellation, a washer should be used under nut or a shorter fastener should be used. A maximum of two washers may be permitted under a nut. (e) The largest diameter cotter pin which the hole and slot will accommodate should be used. In no application shall cotter pin size be less than size called out on the following table. (f) Install cotter pin with head firmly in slot of nut with axis of eye at right angles to bolt shank. Bend prongs so that head and upper prong are firmly seated against bolt. (g) In pin applications, install cotter pin with axis of eye parallel to shank of clevis pin or rod end. Bend prongs around shank of pin or rod end. Page 2

3 ALIGNMENT HOLE IN BOLT AND SLOT IN CASTELLATED NUT MUST BE ALIGNED WHEN COTTER PIN IS IN PLACE. PREFERRED MARGINALLY ACCEPTABLE UNACCEPTABLE TRIM PRONG TO FIT PREFERRED ALTERNATE METHOD COTTER PIN MUST BE TIGHT & LAY FLAT AGAINST PIN MAXIMUM COTTER PIN LENGTH C L MINIMUM COTTER PIN LENGTH SR22_MM20_1979 Figure 1 Cotter Pin Safetying Page 3

4 B. Locking Clip (See Figure 2) (1) Proper use of Locking Clips (a) Prior to safetying, both threaded terminals shall be screwed an equal distance into the turnbuckle body and shall be screwed in at least so that not more than three threads of any terminal are exposed outside of body. (b) After the turnbuckle has been adjusted to its locking position, (with slot indicator groove on terminals and slot indicator notch on body aligned) insert the end of locking clip into terminal and body until the U-curved end of locking clip is over the hole and in the center of the body. (c) Press locking clip into hole until it s fully seated (curved end of locking clip will expand and latch in body slot). (d) To check proper seating of locking clip, attempt to remove pressed U end from body with fingers only. Note: Both locking clips may be inserted in same hole of turnbuckle body or in opposite holes of turnbuckle body. Locking clips are for one time use only and shall not be re-used. Page 4

5 NOTE Locking clips can be used on safety turnbuckles if the barrel and terminal are notched to accept them. BARREL LOCKING CLIP LOCKING CLIP CABLE TERMINAL SR22_MM20_1980 Figure 2 Locking Clip Safetying Page 5

6 C. Rod Ends (See Figure 3) Rod end assemblies are subject to a variety of environmental conditions and forms of deterioration that ultimately may be easy to recognize such as a failed rod end. The not so readily visible types of deterioration include wear, corrosion and/or distortion. The critical area on a female rod end is the internal thread of the rod end. (1) Inspecting It will be necessary to remove the rod end from the corresponding control cable to properly inspect it for internal wear and corrosion as this condition is usually not evident on the outer surface of the rod end. Note: Before removing rod ends with inspection holes, ensure the rod ends are properly seated onto the control cable. The control cable must be installed beyond the inspection hole. When removing rod ends without inspection holes, leave the jam nut in its original position. Measure the distance from the face of the jam nut (side which was tightened against the rod end) to the end of the control cable. This distance is referred to as the thread engagement depth. Rod ends with a hole diameter of inch or inch must be threaded onto the control cable to a minimum thread engagement depth of inch. (a) (b) (c) (d) Examine all rod ends for proper depth installation and then remove the rod ends. Carefully examine the exterior of all rod ends for wear, corrosion, damage, and/or distortion. Replace all rod ends having signs of wear, corrosion, damage, and/or distortion. Carefully examine all rod ends for internal wear, corrosion, damage, and/or distortion. Replace all rod ends having signs of internal wear, corrosion, damage, and/or distortion. Carefully examine the threaded portion of rod end for damaged threads. Replace all rod ends having signs of damage to the threads. Note: If damaged threads or premature/excessive wear is found or suspected, replace the rod end. Page 6

7 JAM NUT THREADED CABLE END INSPECTION HOLE ROD END (WITH INSPECTION HOLE) JAM NUT THREADED CABLE END 0.312" MIN NOTE Threaded cable end must completely block inspection hole. ROD END (WITHOUT INSPECTION HOLE) Rod ends without inspection holes must be threaded onto 0.190" and 0.250" diameter threaded cable ends to a minimum thread engagement of 0.312". SR22_MM20_1981 Figure 3 Rod End Page 7

8 D. Self Locking Nuts (1) Restrictions (a) Do not use reworked or reprocessed self-locking nuts for any application. (b) Do not use at joints in a control system for singular attachment points. (c) Do not use on externally threaded parts that serve as an axle of rotation for another part where tensional (torque) loads can cause nut to loosen and/or become separated. Examples are pulleys, levers linkages, and cam followers. Note: Self-locking nuts can be used when threaded parts are held by a positive locking device that requires shearing or rupture before torsional loads can act on threaded parts. (d) Do not use where a loose nut, bolt, or screw, could fall or be drawn into an area that would impede or damage or otherwise distort operation. (e) Do not use for access panels, doors or to assemble components that are routinely disassembled or removed for access and servicing. (f) Do not use a self-locking nut where the loss of a bolt will affect the safety of flight. (g) Bolts, studs, or screws, excluding Hi-Locks, must extend 1/32-inch through self-locking nuts, for a length equivalent of approximately two threaded pitches. This length includes chamfer. (h) Self-locking nuts which are attached to the structure shall be attached in a positive manner to eliminate possibility of their rotation or misalignment when tightening is to be accomplished by rotating bolts to structure, and permit replacement of nuts. E. Threaded Fastener Length (See Figure 4) It is permissible to substitute a longer or shorter bolt or screw than specified provided the following requirements are met. (1) Substitution Requirements (a) In structural applications no threads shall be allowed in bearing in sheet material or fittings. If the joint is dimpled, threads are permitted in bearing in gages inch (2.5 mm) and under. Threads are permitted in bearing if the joint is countersunk to a "knife-edge" condition, or the sheet thickness minus the countersink depth is inch (0.50 mm) and under. (b) Bolts and screws with flat ends must extend through the nut or nutplate at least 1/32 inch. (c) Bolts and screws with round or chamfered ends must extend through the nut or nutplate the full round or chamfer. (d) Washers must be of the same type of material as the adjacent structure or compatible with the adjacent structure as defined in MIL-STD-889. For example, cad plated steel or aluminum washers to aluminum structure, steel washers to steel structure, etc. Page 8

9 F. Fastener Flushness (See Figure 4) (1) Flush Head Screws (a) The gap under the head of screws and bolts, and under nuts, shall be inch (0.05 mm) maximum for no more than 40% of the circumference. The heads of flush rivets, screws and Hi-Loks on the exterior of the airplane shall be flush with the local skin contour to within the tolerances specified. For fasteners installed in the exterior skin, head protrusion for flush head screws shall meet the following requirements. Heads shall not be shaved. Check gaps at the outer periphery of the intended bearing surfaces as indicated by the darkened areas. Gaps of any thickness shall not be continuous for more than 40% of the peripheral distance of the head or nut. (2) Driven Rivets (a) The aforementioned rivets should be flush with the exterior finish. Driven rivets must never protrude the surface more than inch (0.13 mm). (3) Blind Rivets, Screws and Hi-Loks (a) The aforementioned fasteners may be countersunk in the exterior finish no more than inch (0.13 mm). These fasteners must never protrude above the finish by more than inch (0.13 mm). (4) Camlocks (a) The aforementioned fasteners may be countersunk in the exterior finish no more than inch (0.5 mm). These fasteners must never protrude above the finish by more than inch (0.25 mm). Page 9

10 .032 Min. NOTE In structural applications no threads shall be allowed in bearing of sheet material or fittings. If the joint is dimpled, threads are permitted in bearing of gages and under. Threads are permitted in bearing if the joint is countersunk to a "knife-edge" condition, or the sheet thickness minus the countersink depth is and under. Bolts and screws with round or chamfered ends must extend through the nut the full round or chamfer. 40% Max. 40% Max..002 Max..002 Max..002 Max..002 Max. SR22_MM20_1748 Page 10 Figure 4 Fastener Length and Flushness

11 G. Washers (See Figure 5) Do not use washers under the head of flush screws unless specifically called out. When installing a countersunk MS20002 washer under the head of bolts, the washer shall be installed so that the countersunk side faces the bolt head. A maximum of two AN960 (thick or thin) washers may be used under a nut on all bolts, except when a AN 970 washer is specified; then a maximum of only one additional AN960 washer may be used between the nut and AN970 washer. A maximum of one AN960 (thick or thin) washer may be used under the head of a bolt, except when a countersunk MS20002 washer or a AN970 washer is specified, in which case no additional washers are allowed. H. Lockwashers (1) Lockwasher Usage (a) When loosening of threaded parts would not endanger safety of airplane or people. (b) When the self-locking feature cannot be provided in externally or internally threaded parts. (c) When safety wire cannot be used to prevent loosening of threaded parts. (d) When a cotter pin cannot be used to prevent rotation of internal threads with respect to external threads. (e) When fastening is not used for fabrication of primary structure. (f) When corrosion encouraged by gouging aluminum or magnesium alloys by edges of teeth on tooth-locked washers would not cause malfunctioning of parts being fastened together. Page 11

12 AN960 1 MAX AN970 AN960 2 MAX AN970 AN960 1 MAX SR22_MM20_1982 Page 12 Figure 5 Washer Placement