AC 43.13-1A 1972 FIGURE 4.19.-Corrosion.
WIRE SF
DIE MARKS FIGURE 4.20.--Manufacturer's wire splice.
visible after assembly of a finished cable length. In some instances, the process of twisting outer strands around the core strand may also slightly flatten individual outer wires, particularly in the area of a wire splice. This flattening is the result of die sizing the cable and does not affect the strength of the cable.
These conditions, as shown in figure 4.20, are normal and are not a cause for cable rejection.
c. Cable Maintenance. Frequent inspections and preservation measures such as rust prevention treatments for bare cable areas will help to extend cable service life. Where cables pass through fairleads, pressure seals, or over pulleys, remove accumulated heavy coatings of corrosion prevention compound. Provide corrosion protection for these cable sections by lubricating with a light coat of graphite grease or general purpose, low-temperature oil.
Chap 4 Page 109
CAUTION Avoid the use of vapor degreasing, steam cleaning, methylethylketone (MEK) or other solvents to remove corrosion-preventative compounds, as these methods will also remove the cable internal lubricant.
d. Routing. Examine cable runs for incorrect routing, fraying, twisting, or wear at fairleads, pulleys, anti-abrasion strips, and guards. Look for interference with adjacent structure, equipment, wiring, plumbing, and other controls. Inspect cable systems for binding, full travel, and security of attaching hardware.
Check for slack in the cable system by attempting to move the control column and/or pedals while the gust locks are installed on the control surfaces. With the gust locks removed, actuate the controls and check for friction or hard movement. These are indications that excessive cable tension exists.
NoTE: If the control movement is stiff after maintenance operations are performed on control surfaces, check for parallel cables twisted around each other or cables connected in reverse.
e. Cable Fittings. Check swaged treminal reference marks for an indication of cable slippage within the fitting. Inspect the fitting assembly for distortion and/or broken strands at the terminal. Assure that all bearings and swivel fittings (bolted or pinned) pivot freely to prevent binding and subsequent failure.
Check turnbuckles for proper thread exposure and broken or missing safety wires/clips.
f. Pulleys. Inspect pulleys for roughness, sharp edges, and presence of foreign material embedded in the grooves. Examine pulley bearings to assure proper lubrication, smooth rotation, freedom from flat spots, dirt, and paint spray. Periodically rotate pulleys, which turn through a small arc, to provide a new bearing surface for the cable. Maintain pulley alignment to prevent the cable from riding on the flanges and chafing against guards, covers, or adjacent structure. Check all pulley brackets and guards for damage, alignment, and security.
(1) Pulley Wear Patterns. Various cable system malfunctions may be detected by analyzing pulley conditions. These include such discrepan- Par 198
Page 110 AC 43,13-1/ 1971
EXCESSIVE CABLE TENSION PULLEY MISALIGNMENT
PULLEY TOO LARGE FOR CABLE CABLE MISALIGNMENT
FROZEN BEARING MORMAL CONDITION FIGURE 4.21.-Pulley wear patterns.
cies as too much tension, misalignment, pulley bearing problems, and size mismatches between cables and pulleys. Examples of these conditions are shown in figure 4.21.
g. Fairleads, Guides, Anti-Abrasion Strips. Inspect fairleads for wear, breakage, alignment, cleanness, and security. Examine cable routing at fairleads to assure that deflection angles are no greater than 3° maximum. Determine that all guides and anti-abrasion strips are secure and in good condition.
h. Pressure Seals and Seal Guards, Examine pressure seals for wear and/or material deterioration. Determine that the seal guards are positioned to prevent jamming of a pulley if a pressure seal fails and pieces slide along the
199. CABLE TENSION ADJUSTMENT. Carefully adjust control cable tension in accordance with the airframe manufacturer's recommendations.
Par 198 On large aircraft, take the temperature of the immediate area into consideration when using a tensiometer. For long cable sections, use the average of two or three temperature readings to obtain accurate tension values. If necessary, compensate for extreme surface temperature variations that may be encountered if the aircraft is operated primarily in unusual geographic or climatic conditions such as arctic, arid, or tropic locations.
Use rigging pins and gust locks as necessary to assure satsifactory results. At the completion of rigging operations, check turnbuckle adjustment and safetying in accordance with Section 2 of this chapter.
200. CORROSION AND RUST PREVENTION. To insure a satisfactory service life for aircraft control cables, use a cable lubricant to reduce internal friction and prevent corrosion. Loose rust and surface corrosion may be removed with a stainless steel brush, being careful not Chap &
AC 43.19-1А Page 111 1972 to damage the cable. Care should be taken to remove all residue from the cable strands prior to rust prevention treatment. If the cable is made from tinned steel, coat the cable with rust preventive oil and wipe off any excess. It should be noted that corrosion-resistant steel cable does not require this treatment for rust prevention.
201.-211. RESERVED.
Chap 4 Par 200
Page 112 AC 43.13-1A 1972 Section 2. SAFETY METHODS FOR TURNBUCKLES
212. GENERAL. Safety all turnbuckles with safety wire using either the double or single wrap method, or with any appropriately approved special safetying device complying with the requirements of FAA Technical Standard Order TSO-C21. The swaged and unswaged turnbuckle assemblies are covered by AN Standard Drawings. For safety wire sizes and materials, refer to figure 4.22. Do not reuse safety wire. Adjust the turnbuckle to the correct cable tension so that no more than three threads are exposed on either side of the turnbuckle barrel. Do not lubricate turnbuckles.
213. DOUBLE WRAP METHOD. O1 the methods using safety wire for safetying turnbuckles, the method described here is preferred, although either of the other methods described is satisfactory. The method of double wrap safetying is shown in figure 4.23(A). Use two separate lengths of the proper wire (see figure
4.22). Run one end of the wire through the hole in the barrel of the turnbuckle and bend the end of the wire towards opposite ends of the turnbuckle. Then pass the second length of the wire into the hole in the barrel and bend the ends along the barrel on the side opposite the first. Spiral the two wires in opposite directions around the barrel to cross each other twice between the center hole and the ends.
Then paas the wires at the end of the turnbuckle in opposite directions through the holes in the turnbuckle eyes or between the jaws of the turnbuckle fork, as applicable, laying one wire along the barrel and wrapping the other at least four times around the shank of the turnbuckle and binding the laid wires in place be fore cutting the wrapped wire off. Wrap th remaining length of safety wire at least for turns around the shank and cut it off. Repe.
the procedure at the opposite end of the turi buckle.
When a swaged terminal is being safetied, pass Cable size Type of wrap Diameter of safety wire Material (ennes ed condition) the ends of both wires, if possible, through the hole provided in the terminal for this purpose and wrap both ends around the shank as de- 710- - Single_ 0.040_. Copper, brass.' Single.. 0.040. Copper, brass.! scribed above. When the hole in the terminal is %- - Single.. 0.040_. Stainless steel, not large enough to accommodate the ends of Monel and both wires, the hole may be enlarged in accord- 'K" Monel. ance with note 2 of figure 4.22 and the safety- %- %- - Single. Double. 0.057 min 0.040- Copper, brass,! Copper, brass.! ing completed as described above. If the hole is %e and Double 0.040_ Stainless steel, not large enough to allow passage of both greater. Monel and wires, pass the wire through the hole and loop 'K" Monel,' it over the free end of the other wire, and then %% and Singie_. 0.057 min.. Stainless steel, wrap both ends around the shank as described.
greater. Monel or "K" Monel.' %% and Double_ 0.051 * Copper, braas. a. Another satisfactory double wrap method greater. is similar to the above, except that the spiraling of the wires is omitted as shown in figure I Galvanized or tinned steel, or soft tron wires are also acceptable. 4.28 (B).
• The safety wire holes in ⅜s-inch diameter and larger turnbuokle terminals for swaging may be drilled auficiently to accommodate the double 0.051-Inch b. The wrapping procedures described and dlameter copper or brass wires when used. shown on MS 38591 may be used in lieu of the FIGURE 4.22-Turnbuckle safetying guide. safetying method shown herein.
Par 212 Chap &
43.13-1A Page 113 71 4 TURN (MIN)
THIS APPLIES TO ALL
TURNBUCKLE WRAPPINGS (A) DOUBLE WRAP (SPIRAL) (B) DOUBLE WRAP SMENKE (C) SINGLE WRAP (SPIRAL) (D) SINGLE WRAP FIGURE 4.23.--Safetying turnbuckles.
Chap 4 Par 219
214. SINGLE WRAP METHOD, The single wrap methods described in the following paragraphs and as illustrated in figures 4.28 (C) and (D) are acceptable but are not the equal of the double wrap methods.
a. Pass a single length of wire through the cable eye or fork, or through the hole in the swaged terminal at either end of the turnbuckle assembly. Spiral each of the wire ends in opposite directions around the first half of the turnbuckle barrel so as to cross each other twice. Thread both wire ends through the hole in the middle of the barrel so that the third crossing of the wire ends is in the hole. Again, spiral the two wire ends in opposite directions around the remaining half of the turnbuckle, crossing them twice. Then, pass one wire end through the cable eye or fork or through the hole in the swaged terminals, in the manner described above, wrap both wire ends around the shank for at least four turns each, cutting off ====:
AC 43.13-1 197 excess wire. This method is shown in figure
4.28 (C).
b. Pass one length of wire through the center hole of the turnbuckle and bend the wire ends toward opposite ends of the turnbuckle. Then pass each wire end through the cable eye or fork, or through the hole in the swaged terminal and wrap each wire end around the shank for at least four turns, cutting off excess wire.
This method is shown in figure 4.23 (D). After safetying, no more than three threads of the turnbuckle threaded terminal should be exposed.
215. SPECIAL LOCKING DEVICES. Several turnbuckle locking devices are available for securing turnbuckle barrels. Persons intending to use a special device must assure the turnbuckle assembly has been designed to accommodate such device. A typical unit is shown in figure
4.24. When special locking devices are nof readily available, the use of safety wire is acceptable.
E==
TURNBUCKLE BODY -LOCKING CLIP MS21251 MS2I256
CLIP TYPE LOCKING DEVICE FIGURE 4.24.- Clip type locking device.
216.-226. RESERVED.
Par 214 Chap &
C 43.13-1A Page 115 972 Chapter 5. AIRCRAFT HARDWARE Section 1. IDENTIFICATION AND USE OF AIRCRAFT HARDWARE
27. BOLTS. Most bolts used in aircraft strucures are either general purpose AN bolts, or IAS (National Aircraft Standard) internal frenching or close-tolerance bolts. In certain ases, aircraft manufacturers make up special olts for a particular application and it is necesary to use them or their equivalent in relacement.
a. Identification. AN-type aircraft bolts can be dentified by the code markings on the bolteads. The markings generally denote the bolt nanufacturer, the material of which the bolt is nade, and whether the bolt is a standard AN- ype or a special purpose bolt. AN standard teel bolts are marked with either a raised ash or asterisk, corrosion-resistant steel is inlicated by a single raised dash, and AN alumium alloy bolts are marked with two raised ashes. The strength and dimensional details f AN bolts are specified on the Army/Navy Aeronautical Standard Drawings.
Special purpose bolts include the hightrength and low-strength types, close-tolerance ypes; such bolts are normally inspected y magnetic, fluorescent or equivalent inspecmethods, Typical markings include 'SPEC (usually highly heat treated), an ircraft manufacturer's part number stamped n the head, or plain heads (low strength).
Close-tolerance National Aircraft Standards (NAS) bolts are marked with either a raised r recessed triangle. The material markings or NAS bolts are the same as for AN bolts, xcept that they may be either raised or reessed. Bolts inspected magnetically (Magnalux) or by fluorescent means (Zyglo) are idenified by means of colored lacquer, or a head narking of a distinctive type. Figure 5.1 shows he typical coding used on aircraft boltheads.
b. Grip Length. In general, bolt-grip lengths should equal the material thickness. However, bolts of slightly greater grip length may be used provided washers are placed under the nut or the bolthead. In the case of plate nuts, add shims under the plate. For proper washers, refer to paragraph 231.
c. Locking or Safetying of Bolts. Lock or safety all bolts and/or nuts, except self-locking nuts.
Do not reuse cotter pins and safety wire.
d. Bolt Fit. Many boltholes, particularly those in primary connecting elements, have close tolerances. Generally, it is permissible to use the frst lettered drill size larger than the normal bolt diameter, except where the AN hexagon bolts are used in light-drive fit (reamed) applications and where NAS close-tolerance bolts or AN clevis bolts are used. Boltholes are to be normal to the surface involved to provide full bearing surface for the bolthead and nut, and not be oversized or elongated. In case of oversized or elongated holes in critical members, obtain advice from an FAA inspector or engineer, or the aircraft manufacturer before drilling or reaming the hole to take the next larger bolt, as usually, items such as edge distance, clearance, etc., must be considered.
e. Torques. The importance of correct applicacation can not be overemphasized. Undertorque can result in unnecessary wear of nuts and bolts as well as the parts they are holding together. When insufficient pressures are applied, uneven loads will be transmitted throughout the assembly which may result in excessive wear or premature failure due to fatigue. Overtorque can be equally damaging because of failure of a bolt or nut from overstressing the threaded areas. There are a few simple, but very important, procedures that should be followed to assure that correct torque is applied:
hap S Par 227
Page 116 AC 43.13- AIR E дО}> ~ M
•cIt
AN STANDARD AN STANDARD AN STANDARD AN STANDARD AN STANDARD
STEEL BOLT STEEL BOLT STEEL BOLT STEEL BOLT STEEL BOLT (CORROSION RESISTANT) SPEC
AN STANDARD AN STANDARD AN STANDARD AN STANDARD SPECIAL BOLT
STEEL BOLT STEEL BOLT STEEL BOLT STEEL BOLT 63-59131 SPECIAL BOLT DRILLED HEAD BOLT SPECIAL BOLT TOLERANCE NA S CLOSEOLT (2024) BOLT ALUMINUM ALLOY
MAGNETICALLY ORANGE- DYED CLEVIS BOLT REWORKED BOLT LOW STRENGTH INSPECTED MAGNETIC INS. MATERIAL BOLT FIGURE 5.1.-Bolt identification.
(1) Calibrate the torque wrench periodically to assure accuracy; and re-check frequently.
(2) Be sure that bolt and nut threads are clean and dry (unless otherwise specified by the manufacturer).
(8) Run nut down to near contact with the washer or bearing surface and check &friction drag torque" required to turn the nut.
(4) Add the friction drag torque to the desired torque recommended by the manufacturer, or obtain desired torque as shown in figure 5.2. This is referred to as final torque Par 227 which should register on the indicator or the setting for a snapover type wrench.
(b) Apply a smooth even pull when applying torque pressure. If chattering or a jerking motion occurs during final torque, back off and re-torque.
(6) When installing a castle nut, start alignment with the cotter pin hole at minimum recommended torque, plus friction drag torque, and do not exceed maximum plus friction drag.
If the hole and nut castellation do not align, change washers and try again. Exceeding the maximum recommended torque is not recommended.
Chap 5
- 43.13~1A 172
(7) If torque is applied to capscrews or theads, apply recommended torque plus fricon drag torque as determined in step (8).
(8) If special adapters are used which ill change the effective length of the torque rench, the final torque indication or wrench etting must be adjusted accordingly. Deterine the torque wrench indication or setting ith adapter installed as shown in figure 5.8.
igure 5.2 is a composite chart of recomended torque to be used when specific orque is not recommended by the manufacurer. The chart includes standard nut and bolt ombinations currently used in aviation main-
ex-head aircraft bolt is an all-purpose strucural bolt used for general applications involvug tension or shear loads. Alloy steel bolts maller than No. 10-32 and aluminum alloy olts smaller than 1/4-inch diameter are not to e used in primary structure. Do not use aluinum alloy bolts and nuts where they will be epeatedly removed for purposes of mainteance and inspection. Aluminum alloy nuts nay be used with cadmiumplated steel bolts oaded in shear on land airplanes, but are not o be used on seaplanes due to the possibility of lissimilar metals corrosion.
g. Close-Tolerance Bolts (AN-173 through AN- 86 (Hex-Head), NAS-80 through NAS-86 (100° countersunk)). Close-tolerance bolts are used in ugh-performance aircraft in applications here the bolted joint is subject to severe load eversals and vibration. The standard AN ex-head bolts may be used for the same appliations provided a light-drive fit is accomlished.
h. Internal Wrenching Bolts (MS-20004 through S-20024 or NAS-495). These bolts are suitable or use both in tension and shear applications.
n steel parts, countersink the bolthole to seat he large radius of the shank at the head or, as n aluminum alloys, use a special heat-treated vasher (NAS-143C) that fits the head to rovide adequate bearing area. A special heatreated plain washer (NAS-143) is used under he nut. Use special high-strength nuts on hap 5 Page 117 these bolts. (Refer to paragraph 280c(7).) Replace all internal wrenching bolts by another internal wrenching bolt. Standard AN hexhead bolts and washers cannot be substituted for them, as they do not have the required strength.
I. Drilled-Head Bolts (AN-73). The AN drilledhead bolt is similar to the standard hex-bolt, but has a deeper head which is drilled to receive wire for safetying. The AN-8 and the AN-78 series of bolts are interchangeable for all practical purposes from the standpoint of tension and shear strengths.
228. SCREWS. In general, screws differ from bolts by the following characteristics: Usually lower material strength, a looser thread fit (No. 2), head shapes formed to engage a screwdriver, and the shank threaded along its entire length without a clearly defined grip.
However, several types of structural screws are available that differ from the standard structural bolts only in the type of head.
The material is equivalent and a definite grip is provided. The AN-525 washerhead screws, the AN 509-100° countersunk structural screws, and the NAS-204 through NAS-235 are such parts. The material markings are the same as those used on AN standard bolts.
a. Structural Screws (NAS-204 through NAS- 235, AN-509 and AN-525). This type of screw, when made of alloy steel such as SAB-4180, ND-8680, or equivalent, and heat-treated from 125,000 p.s.i., may be used for structural assembly in shear applications similar to structural bolts.
b. Self-Tapping Screws. The AN-504 and AN- 506 screws are used for attaching minor removable parts such as nameplates and the like.
AN-580 and AN-581 are used in blind applications for the temporary attachment of sheet metal for riveting and the permanent assembly of nonstructural assemblies. AN-585 is a plain head self-tapping screw used in the attachment of nameplates or in sealing drainholes in corrosion-proofing tubular structures, and is not intended to be removed after installation. Never use self-tapping screws to replace standard Par 227
Page 118 AC 43.1 QuI Ble sion BOLT cel Tonsk tamina AN 3 thru AN 20 MB 20004 thru MB 20024 AN 3DD thru AN 20DD AN 42 thru AN 49 NAB 144 thru NAB 158 AN 173DD thru AN 186DD AN 78 thru AN 81 NAS 333 thru NAB 340 AN 509DD AN 173 thru AN 186 NAS 583 thru NAB 590 AN 525D M8 20033 thru M8 20046 NA8 624 thru NA8 644 MB 27039D MS 20073 NAB 1803 thru NAB 1320 M8 24694DD M8 20074 NAS 172 AN 500 NK9 NAS 174 M8 24694 NAS 517 AN 523 NK525 Steel shear boll M8 27030 NAH 106
NUTS NUTE NUTE Bleel Tension Steel Shear Steel Tenalon Steel Shear Aluminam Tension Aluminum Shear AN 310 AN 820 AN 810 AN 320 AN 365D AN 320D AN 315 AN 364 AN 315 AN 364 AN 310D AN 364D AN 363 NAS 1022 AN 383 NAS 1022 NA8 1021D NAS 1022D AN 365 MB 17826 AN 365 M8 17826 NAS 1021 MS 20384 M8 17825 M8 20364 MS 17825 M8 20365 MB 21045 M8 21045 MS 20365 NAS 1021 MB 20500 NA8 679 NAS 079 NAS 1291
FINE THREAD SERIES lorque Limit Torque Limit Torque Limita Torque Limits Forgus Limit Nat-bolt n.-lb in.-lbe fn.-Ibe in.-ibs sizo Min. Max. MiD. Mas. Min. Max. Min. MaI. Min. Max. Min. MAI.
8 -36 9 10-32 25 30 15 20 10 6-28 80 100 50 60 80 120 145 70 40 36-21 160 200 250 150 70 3r20 520 630 400 1-20 690 770 950 550 Kr-18 1, 000 1, 100 1, 300 800 % -18 1, 300 1, 250 1, 550 050 % -16 500 3, 650 3, 200 1, 900 76-14 3, 000 8, 550 4, 350 2, 600 1 -14 4, 500 4, 500 6, 500 3, 300 1% -12 7, 000 6, 000 7, 300 4, 400 1% -12 11, 000 11, 000 13, 400 8, 000
COARSE THREAD SERIES 8 -82 12 15 7 10 -24 20 12 15 * -20 40 25 80 ·-18 80 48 55 % -18 160 185 95 110 Kr14 285 255 140 155 ½ - 13 400 480 240 290 Kг12 500 700 300 420 % -11 700 900 420 540 4-10 1, 150 1, 600 700 950 36 - 9 2, 200 3, 000 1, 300 1, 800 1 - 8 8, 700 5, 000 2, 200 3, 000 1% - 8 5, 500 6, 500 8, 300 4,000 1¼ - 8 6, 500 8, 000 4, 000 5, 000 FIGURE 5.2.-Recommended torque values for nut-bolt combinations-- (without lubrication).
Par 228 Chay
43.13-1A Page 119
NOTE - LEGEND-
WHEN USING A TORQUE WRENCH ADAPTER WHICH T - ACTUAL (DESIREDI TORQUE CHANGES THE DISTANCE FROM THE TORQUE WRENCH Y= APPARENT (INDICATED) TORQUE DRIVE TO THE ADAPTER DRIVE, APPLY THE L. - EFFECTIVE LENOTH LEVER FOLLOWING FORMULAS TO OBTAIN THE CORRECTED = ENFECTIVE LENGTH OF EXTENSION TORQUE READING:
Hort Open End Open-End Wrench Adapter CENTERLINE ADAPTER DRIVE WRENCH TORQUE WRENCH DRIVE TORQUE WRENCH HANDGRIP CENTERLINE Adapter
WRENCH CENTERLINE ADAPTER (PREDETE MINED) DRIVE
CENTERLINE CENTERINE Set Screw Flare Nut Wrench Adapter Adapter EXAMPLE: (WITH "E" AS PLUS DIMENSIONI EXAMPLE: (ATTH "E" AS HINUS DUHENSION) T - 135 LE. IN. 8= 10715-18-11790 T - 135 LD. 04. r- 123-18 - 125-150.82 Hose Clamp Y - UNKNOWN Y - UNKNOWN Spanner Wrench Adapter L - 10.0 IN. 1 - 10.0 MN. Adapter € = 1.5 IN. Y - 117 LB. AN. 1 - 1.5 HN. Y - 159 18. 04.
FIGURE 5.3.-Torque wrench with various adapters.
crews, nuts, bolts, or rivets in the original pructure.
129. TAPER PINS (AN-385 AND AN-386), Plain und threaded taper pins are used in joints which carry shear loads and where absence of ›lay is essential. The plain taper pin is drilled and usually safetied with wire. The threaded aper pin is used with a taper-pin washer (AN-975) and shear nut (safetied with cotter ›in) or self-locking nut.
a. The Flathead Pin (MS-20392), Commonly 'alled a clevis pin, the flathead pin is used in conjunction with tie rod terminals and in sec- ›ndary controls which are not subject to coninuous operation. The pin is customarily intalled with the head up so that if the cotter ›in fails or works out, the pin will remain in lace.
b. The AN-380 Cotter Pin. This is used for safetying bolts, screws, nuts, other pins, and in arious applications where such safetying is recessary. Use AN-381 cotter pins in locations where nonmagnetic material is required or in ocations where resistance to corrosion is deired.
hap 3
230. NUTS.
a. Self-Locking Nuts. Self-locking nuts are acceptable for use on certificated aircraft subject to the restrictions on the pertinent manufacturer's recommended practice sheets. Selflocking nuts are used on aircraft to provide tight connections which will not shake loose under severe vibration. Two types of selflocking nuts are currently in use, the all-metal type and the fiber or nylon lock type. Do not use self-locking nuts at joints which subject either the nut or bolt to rotation. They may be used with antifriction bearings and control pulleys, provided the inner race of the bearing is clamped to the supporting structure by the nut and bolt. Attach nuts to the structure in a positive manner to eliminate rotation or misalignment when tightening the bolts or screws.
(1) All-metal locknuts are constructed with either the threads in the locking insert out-ofphase with the load-carrying section, or with a saw-cut insert with a pinched-in thread in the locking section. The locking action of the allmetal nut depends upon the resiliency of the metal when the locking section and loadcarrying section are engaged by screw threads.
Par 228
(2) Fiber or nylon locknuts are constructed with an unthreaded fiber-locking insert held securely in place. The fiber or nylon has a smaller diameter than the nut, and when a bolt or screw is entered, it taps into the insert, producing a locking action. After the nut has been tightened, make sure the rounded or chamfered end bolts, studs, or screws extend at least the full round or chamfer through the nut. Flat end bolts, studs, or screws should extend at least 1/32 inch through the nut. When fiber-type self-locking nuts are reused, check the fiber carefully to make sure it has not lost its locking friction or become brittle. Do not reuse locknuts if they can be run up fingertight. Bolts 5/16-inch diameter and over with cotter pinholes may be used with self-locking nuts but only if free from burrs around the holes. Bolts with damaged threads and rough ends are not acceptable. Do not tap the fiberlocking insert.
(3) Self-locking nut bases are made in a number of forms and materials for riveting and welding to aircraft structure or parts. Certain applications require the installation of self-locking nuts in channels, an arrangement which permits the attachment of many nuts with only a few rivets. These channels are track-like bases with regularly spaced nuts which are either removable or nonremovable.
The removable type carries a floating nut, which can be snapped in or out of the channel, thus making possible the ready removal of damaged nuts. Nuts such as the clinch-type and spline-type which depend on friction for their anchorage are not acceptable for use in aircraft structures.
(4) Self-locking nuts may be used on aircraft engines and accessories when their use is specified by the engine manufacturer in his bulletins or manuals.
b. Aircraft Castle Nut (AN-310). The castle nut is used with drilled-shank AN hex-head bolts, clevis bolts, eye bolts, drilled-head bolts or studs, and is designed to accommodate a cotter pin or lockwire as a means of safetying.
c. Miscellaneous Aircraft Nuts.
(1) The plain nut (AN-315 and AN-385) has limited use on aircraft structures and re- Par 230 AC 43.13 quires an auxiliary locking device such as checknut or lockwasher.
(2) Light hex-nuts (AN-840 and AN-345 are used in miscellaneous applications an must be locked by an auxiliary device.
(3) The checknut (AN-316) is used as locking device for plain nuts, screws, threade rod ends, and other devices.
(4) The castellated shear nut (AN-320) i designed for use with clevis bolts and threade taper pins, which are normally subjected t shearing stress only.
(5) Wing nuts (AN-350) are intended fo we were the desiren i battes is onditiont obtained by the use of the fingers or han tools.
(6) Sheet spring nuts, such as speed nuts are used with standard and sheet metal self tapping screws in nonstructural locations They find various uses in supporting lin clamps, conduit clamps, electrical equipment access doors, and the like, and are available i several types.
(7) Two commercial types of high-strengt internal or external wrenching nuts are availa ble, the internal and external wrenching elastic stop nut and the Unbrako internal and externa wrenching nut. Both are of the self-lockin type, are heat-treated, and are capable of carry ing the high-strength bolt-tension load.
231. WASHERS. The types of washers used i aircraft structure are: plain washers, lock washers, and special washers.
a. Plain washers (AN-960 and AN-970) ar widely used under hex nuts to provide smoothbearing surface, to act as a shim and t adjust holes in bolts. Use plain washers unde lockwashers to prevent damage to surfaces Cadmiumplated steel washers are recom mended for use under boltheads or nuts on alu minum alloy or magnesium structures wher corrosion, if it occurs, will then be between the washer and the steel. The AN-970 stee washer provides a greater bearing area than th plain type, and is used in wooden structure:
under both boltheads and nuts to prevent loca crushing of the surface.
Chap !