Aircraft Nuts, Washers, & Bolts (AVIA-1038 Week 2 Day 6) PDF

Learning Objectives- Week 2 Day 6 Aircraft Nuts- Continued Aircraft Washers Bolts- General Purpose, Drilled Head, Close Tolerance, Internal Wrenching Installation of Nuts, Washers, & Bolts 1  Ge...

Learning Objectives- Week 2 Day 6 Aircraft Nuts- Continued Aircraft Washers Bolts- General Purpose, Drilled Head, Close Tolerance, Internal Wrenching Installation of Nuts, Washers, & Bolts 1  General 7-46 Aircraft Nuts  After the nut has been tightened, make sure the rounded or chamfered end of the bolts, studs, or screws extends at least the full round or chamfer through the nut.  Normal standard is 1 to 3 threads showing above the nut  Flat end bolts, studs, or screws should extend at least 1⁄32 inch through the nut.  Bolts of 5⁄16 -inch diameter and over with cotter pin holes may be used with self-locking nuts, but only if free from burrs around the holes. 2  General 7-46 Aircraft Nuts  Bolts with damaged threads and rough ends are not acceptable.  Do not tap the nylon locking insert.  The self-locking action of the elastic stop nut is the result of having the bolt threads impress themselves into the untapped nylon.  Do not install elastic stop nuts in places where the temperature is higher than 250 °F (e.g. exhaust components), because the effectiveness of the self- locking action is reduced beyond this point. 3  General 7-46 Aircraft Nuts Self-locking nuts may be used on aircraft engines and accessories when the engine manufacturer specifies their use. Self-locking Nut Bases are made in a number of forms and materials for riveting and welding to aircraft structure or parts.[Figure 7-29] 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. 4  General 7-46 Aircraft Nuts  [Figure 7-29] self-locking nuts in channels, 5  General 7-46 Aircraft Nuts  These channels are track-like bases with regularly spaced nuts which are either removable or non- removable.  The removable type carries a floating nut, which can be snapped in or out of the channel, thus making possible the easy removal of damaged nuts.  Nuts, such as the clinch-type and splinetype, which depend on friction for their anchorage, are not acceptable for use in aircraft structures. 6  General 7-46 Aircraft Nuts Sheet Spring (Tinnerman) Nuts  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 line clamps, conduit clamps, electrical equipment, access doors, and the like, and are available in several types.  Speed nuts are made from spring steel and are arched prior to tightening. 7  General 7-46 Aircraft Nuts  This arched spring lock prevents the screw from working loose.  These nuts should be used only where originally used in the fabrication of the aircraft. 8  General 7-46 Aircraft Nuts Internal and External Wrenching Nuts  Two commercial types of high strength internal or external wrenching nuts are available; they are the internal and external wrenching elastic stop nut and the Unbrako internal and external wrenching nut.  Both are of the self-locking type, are heat treated, and are capable of carrying high strength bolt tension loads. 9  General 7-46 Aircraft Nuts 10  General 7-47 Aircraft Nuts Identification and Coding  Part numbers designate the type of nut. Refer to Fig 7-25  Non selflocking common types and their respective part numbers are:  Plain, AN315 (Fine) and AN335 (Coarse);  Castle AN310;  Plain check, AN316;  Light hex, AN340 (Fine) and AN345 (Coarse)  Castellated shear, AN320. 11  General 7-47 Aircraft Nuts The patented Self-locking types are assigned part numbers ranging from MS20363 through MS20367.  The Boots, the Flexloc, the fiber locknut, the elastic stop nut, and the self-locking nut belong to this group.  Part number AN350 is assigned to the wing nut. 12  General 7-44 Aircraft Nuts  Identification and Coding 13  General 7-47 Aircraft Nuts  Letters and digits following the part number indicate such items as material, size, threads per inch, and whether the thread is right or left hand.  The letter “B” following the part number indicates the nut material to be Brass, a “D” indicates 2017-T aluminum alloy, a “DD” indicates 2024-T aluminum alloy, a “C” indicates stainless steel, and a dash (-) in place of a letter indicates cadmium-plated carbon steel. (above info in chart form next slide) 14  General 7-47 Aircraft Nuts Material Identification Letter/Ident Material B Brass D 2017-T Alum. Alloy  DD 2024-T Alum. Alloy C Stainless Steel  “-” Cadmium plated Carbon Steel 15  General 7-47 Aircraft Nuts Size  The digit (or two digits) following the dash or the material code letter is the dash number of the nut, and it indicates the size of the shank and threads per inch of the bolt on which the nut will fit.  The dash number corresponds to the first figure appearing in the part number coding of general- purpose bolts. “AN315-3” “AN316-4”  A dash and the number 3, for example, indicates that the nut will fit an AN3 bolt (10-32); a dash and the number 4 means it will fit an AN4 bolt (1/4-28); a dash and the number 5, an AN5 bolt (5/16-24); and so on. 16  General 7-47 Aircraft Nuts  The code numbers for self-locking nuts end in three or four digit numbers.  The last two digits refer to threads per inch, and the one or two preceding digits stand for the nut size in 16ths of an inch. 17  General 7-47 Aircraft Nuts  Some other common nuts and their code numbers are: Code Number AN310D5R:  AN310 = aircraft castle nut  D = 2017-T aluminum alloy  5 = 5⁄16 inch diameter  R = right-hand thread (usually 24 threads per inch) 18  General 7-47 Aircraft Nuts Code Number AN320-10:  AN320 = aircraft castellated shear nut, cadmium plated carbon steel  10 = 5⁄8 inch diameter, 18 threads per inch (this nut is usually right-hand thread) 19  General 7-47 Aircraft Nuts Code Number AN350B1032:  AN350 = aircraft wing nut  B = brass  10 = number 10 bolt  32 = threads per inch 20  General 7-48 Aircraft Washers  Aircraft washers used in airframe repair are either plain, lock, or special type washers. Plain Washers  Plain washers, both the AN960 and AN970, are used under hex nuts. [Figure 7-30],  They provide a smooth bearing surface (for rotation of bolt only, install under head), and act as a shim in obtaining correct grip length for a bolt and nut assembly.  They are used to adjust the position of castellated nuts in respect to drilled cotter pin holes in bolts. 21  General 7-48 Aircraft Washers  [Figure 7-30]Plain washers, 22  General 7-48 Aircraft Washers  Use plain washers under lockwashers to prevent damage to the surface material.  Aluminum and aluminum alloy washers may be used under bolt heads or nuts on aluminum alloy or magnesium structures where corrosion caused by dissimilar metals is a factor.  When used in this manner, any electric current flow will be between the washer and the steel bolt.  However, it is common practice to use a cadmium plated steel washer under a nut bearing directly against a structure as this washer will resist the cutting action of a nut better than an aluminum alloy washer. 23  General 7-48 Aircraft Washers  The AN970 steel washer provides a greater bearing area than the AN960 washer and is used on wooden structures under both the head and the nut of a bolt to prevent crushing the surface.  The letter “L” in the AN960-416L for example, indicates a thin or light washer AN 960 AN 970 24  General 7-48 Aircraft Washers Lockwashers  Lockwashers, both the AN935 and AN936, are used with machine screws or bolts where the self-locking or castellated-type nut is not appropriate.  The spring action of the washer (AN935) provides enough friction to prevent loosening of the nut from vibration. [Figure 7-30] 25  General 7-48 Aircraft Washers  [Figure 7-30] Lockwashers 26  General 7-48 Aircraft Washers  Lockwashers should never be used under the following conditions:  With fasteners to primary or secondary structures  With fasteners on any part of the aircraft where failure might result in damage or danger to the aircraft or personnel  Where failure would permit the opening of a joint to the airflow  Where the screw is subject to frequent removal  Where the washers are exposed to the airflow 27  General 7-48 Aircraft Washers  Where the washers are subject to corrosive conditions  Where the washer is against soft material without a plain washer underneath to prevent gouging the surface 28  General 7-48 Aircraft Washers Shakeproof Lockwashers  Shakeproof lockwashers are round washers designed with tabs or lips that are bent upward across the sides of a hex nut or bolt to lock the nut in place.  There are various methods of securing the lockwasher to prevent it from turning, such as an external tab bent downward 90° into a small hole in the face of the unit, or an internal tab which fits a keyed bolt.  Shakeproof lockwashers can withstand higher heat than other methods of safetying and can be used under high vibration conditions safely. 29  General 7-48 Aircraft Washers  They should be used only once because the tabs tend to break when bent a second time. 30  General 7-48 Aircraft Washers Special Washers  The ball socket and seat washers, AC950 and AC955, are special washers used where a bolt is installed at an angle to a surface, or where perfect alignment with a surface is required.  These washers are used together. [Figure 7-30] 31  General 7-48 Aircraft Washers  The NAS143 and MS20002 washers are used for internal wrenching bolts of the NAS144 through NAS158 series.  This washer is either plain or countersunk.  The countersunk washer (designated as NAS143C and MS20002C) is used to clear the bolt head shank radius, and the plain washer is used under the nut. 32  General 7-48 Aircraft Washers  The NAS143C and MS20002C washers 33 AVIA-1038D6 34  Airframe 4-31 Intro to structural fasteners Structural fasteners a) used to join sheet metal structures securely b) available in thousands of shapes and sizes c) many specialized and specific to certain aircraft d) some structural fasteners are common to all aircraft 35  General 7-39 General Purpose Bolts  The Hex head aircraft bolt (AN-3 through AN-20) is an all-purpose structural bolt used for general applications involving tension or shear loads where a light drive fit is permissible (0.006-inch clearance for a 5⁄8-inch hole, and other sizes in proportion).  Alloy steel bolts smaller than No. 10-32 and aluminum alloy bolts smaller than 1⁄4 inch in diameter are not used in primary structures.  Aluminum alloy bolts and nuts are not used where they will be repeatedly removed for purposes of maintenance and inspection 36  General 7-39 General Purpose Bolts  Aluminum alloy nuts may be used with cadmium- plated steel bolts loaded in shear on land airplanes but are not used on seaplanes due to the increased possibility of dissimilar metal corrosion. 37  General 7-39 Drilled Head Bolt  The AN-73 drilled head bolt is similar to the standard hex bolt, but has a deeper head which is drilled to receive wire for safetying.  The AN-3 and the AN-73 series bolts are interchangeable, for all practical purposes, from the standpoint of tension and shear strengths. 38  General 7-39 Close Tolerance Bolts  Close tolerance bolts are machined more accurately than the general-purpose bolt.  Close tolerance bolts may be hex headed (AN-173 through AN-186) or have a 100° countersunk head (NAS-80 through NAS-86).  They are used in applications where a tight drive fit is required.  (The bolt will move into position only when struck with a 12- to 14-ounce hammer.)  Certain Close tolerance bolts are used in applications where two parts bolted together are subject to severe load reversals and vibration [AC43.13-1B Par 7-44]. 39  General 7-39 Internal Wrenching Bolts  Internal wrenching bolts, (MS-20004 through MS- 20024 or NAS- 495) are fabricated from high-strength steel and are suitable for use in both tension and shear applications.  When they are used in steel parts, the bolt hole must be slightly countersunk to clear the large corner radius of the shank at the head, which contributes to its strength.  In Dural material, a special heat-treated washer must be used to provide an adequate bearing surface for the head  (Dural is a high strength, low weight alloy made from Aluminum, Copper and Magnesium) 40  General 7-39 Internal Wrenching Bolts  The head of the internal wrenching bolt is recessed to allow the insertion of an internal wrench when installing or removing the bolt.  Special high-strength nuts are used on these bolts.  Replace an internal wrenching bolt with another internal wrenching bolt.  Standard AN hex head bolts and washers cannot be substituted for them as they do not have the required strength. 41 AVIA-1038D6 42  General 7-48 Installation of Nuts, Washers, and Bolts Bolt and Hole Sizes  Slight clearances in bolt holes are permissible wherever bolts are used in tension and are not subject to reversal of load.  A few of the applications in which clearance of holes may be permitted are in pulley brackets, conduit boxes, lining trim, and miscellaneous supports and brackets.  Bolt holes are to be normal to the surface involved, to provide full bearing surface for the bolt head and nut, and must not be oversized or elongated. 43  General 7-49 Installation of Nuts, Washers, and Bolts  A bolt in such a hole will carry none of its shear load until parts have yielded or deformed enough to allow the bearing surface of the oversized hole to contact the bolt.  In this respect, remember that bolts do not become swaged to fill up the holes as do rivets.  In cases of oversized or elongated holes in critical members, obtain advice from the aircraft or engine manufacturer before drilling or reaming the hole to take the next larger bolt. 44  General 7-49 Installation of Nuts, Washers, and Bolts  Usually, such factors as edge distance, clearance, or load factor must be considered.  Oversized or elongated holes in noncritical members can usually be drilled or reamed to the next larger size.  Many bolt holes, particularly those in primary connecting elements, have close tolerances.  Generally, it is permissible to use the first 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. 45  General 7-49 Installation of Nuts, Washers, and Bolts  Light drive fits for bolts (specified on the repair drawings as 0.0015 inch maximum clearance between bolt and hole) are required in places where bolts are used in repair, or where they are placed in the original structure.  The fit of holes and bolts cannot be defined in terms of shaft and hole diameters; it is defined in terms of the friction between bolt and hole when sliding the bolt into place. 46  General 7-49 Installation of Nuts, Washers, and Bolts  A tight drive fit, for example, is one in which a sharp blow of a 12- or 14-ounce hammer is required to move the bolt.  A bolt that requires a hard blow and sounds tight is considered to fit too tightly.  A light drive fit is one in which a bolt will move when a hammer handle is held against its head and pressed by the weight of the body. 47  General 7-49 Installation of Nuts, Washers, and Bolts Installation Practices  Examine the markings on the bolt head to determine that each bolt is of the correct material.  It is of extreme importance to use like bolts in replacement.  In every case, refer to the applicable Maintenance Instructions Manual and Illustrated Parts Breakdown.  Be sure that washers are used under both the heads of bolts and nuts unless their omission is specified. 48  General 7-49 Installation of Nuts, Washers, and Bolts  A washer guards against mechanical damage to the material being bolted and prevents corrosion of the structural members.  An aluminum alloy washer should be used under the head and nut of a steel bolt securing aluminum alloy or magnesium alloy members.  Any corrosion that occurs then attacks the washer rather than the members.  Steel washers should be used when joining steel members with steel bolts. 49  General 7-49 Installation of Nuts, Washers, and Bolts  Whenever possible, place the bolt with the head on top or in the forward position.  This positioning tends to prevent the bolt from slipping out if the nut is accidentally lost.  Be certain that the bolt grip length is correct.  Grip length is the length of the unthreaded portion of the bolt shank.  Generally speaking, the grip length should equal the thickness of the material being bolted together. 50  General 7-49 Installation of Nuts, Washers, and Bolts  However, bolts of slightly greater grip length may be used if washers are placed under the nut or the bolt head.  In the case of plate nuts, add shims under the plate. 51  AC43.13-1B Par 7-37 Installation of Nuts, Washers, and Bolts  From AC43.13-1B par 7-37 {In general, bolt grip lengths of a fastener is the thickness of the material the fastener is designed to hold when two or more parts are being assembled.  Bolts of slightly greater grip length may be used, provided washers are placed under the nut or bolthead.  The maximum combined height of washers that should be used is 1/8 inch.  This limits the use of washers necessary to compensate for grip, up to the next standard grip size.} 52  General 7-49 Installation of Nuts, Washers, and Bolts  Safetying of Bolts and Nuts  It is very important that all bolts or nuts, except the self-locking type, be safetied after installation.  This prevents them from loosening in flight due to vibration. 53