FANSHEW Aircraft Hardware Learning Objectives PDF

Learning Objectives- Week 2 Day 5 Aircraft hardware & their identification Threaded Fasteners & Thread classification British & Metric Screw threads Bolts Identification & Coding Aircraft Nuts 1 AVIA-1038D5 2 ...

Learning Objectives- Week 2 Day 5 Aircraft hardware & their identification Threaded Fasteners & Thread classification British & Metric Screw threads Bolts Identification & Coding Aircraft Nuts 1 AVIA-1038D5 2  General 7-37 Aircraft Hardware  Aircraft hardware is the term used to describe the various types of fasteners and miscellaneous small items used in the manufacture and repair of aircraft.  The importance of aircraft hardware is often overlooked because of its small size; however, the safe and efficient operation of any aircraft is greatly dependent upon the correct selection and use of aircraft hardware.  An aircraft, even though made of the best materials and strongest parts, would be of doubtful value unless those parts were firmly held together. 3  General 7-37 Aircraft Hardware  Several methods are used to hold metal parts together; they include riveting, bolting, brazing, and welding.  The process used must produce a union that will be as strong as the parts that are joined. 4  General 7-37 Identification  Most aircraft hardware items are identified by their specification number or trade name.  Threaded fasteners and rivets are usually identified by AN (Air Force-Navy), NAS (National Aircraft Standard), or MS (Military Standard) numbers.  Quick-release fasteners are usually identified by factory trade names and size designations.  Dzus, Camloc, and Airloc. 5  General 7-38 Threaded Fasteners  Various types of fastening devices allow quick dismantling or replacement of aircraft parts that must be taken apart and put back together at frequent intervals.  Riveting or welding these parts each time they are serviced would soon weaken or ruin the joint.  Furthermore, some joints require greater tensile strength and stiffness than rivets can provide.  Bolts and screws are two types of fastening devices which give the required security of attachment and rigidity. 6  General 7-38 Threaded Fasteners  Generally, bolts are used where great strength is required, and screws are used where strength is not the deciding factor.  Bolts and screws are similar in many ways.  They are both used for fastening or holding, and each has a head on one end and screw threads on the other.  Regardless of these similarities, there are several distinct differences between the two types of fasteners.  The threaded end of a bolt is always blunt while that of a screw may be either blunt or pointed. 7 Threaded Fasteners 8 Threaded Fasteners 9 Threaded Fasteners 10  Threaded Fasteners  11  General 7-38 Threaded Fasteners  The threaded end of a bolt usually has a nut screwed onto it to complete the assembly.  The threaded end of a screw may fit into a female receptacle, or it may fit directly into the material being secured.  A bolt has a fairly short threaded section and a comparatively long grip length or unthreaded portion; whereas a screw has a longer threaded section and may have no clearly defined grip length. 12  General 7-38 Threaded Fasteners  A bolt assembly is generally tightened by turning the nut on the bolt; the head of the bolt may or may not be designed for turning.  A screw is always tightened by turning its head.  When it becomes necessary to replace aircraft fasteners, a duplicate of the original fastener should be used if at all possible.  If duplicate fasteners are not available, extreme care and caution must be used in selecting substitutes. 13  General 7-38 Classification of Threads  Aircraft bolts, screws, and nuts are threaded in the NC (American National Coarse) thread series, the NF (American National Fine) thread series, the UNC (American Standard Unified Coarse) thread series, or the UNF (American Standard Unified Fine) thread series.  There is one difference between the American National series and the American Standard Unified series that should be pointed out. 14  General 7-38 Classification of Threads  In the 1-inch diameter size, the NF thread specifies14 threads per inch (1-14 NF), while the UNF thread specifies 12 threads per inch (1-12 UNF).  Both types of threads are designated by the number of times the incline (threads) rotates around a 1-inch length of a given diameter bolt or screw.  For example, a 4-28 thread indicates that a 1⁄4-inch (4⁄16 inch) diameter bolt has 28 threads in 1 inch of its threaded length. 15  General 7-39 Classification of Threads  Threads are also designated by Class of fit.  The Class of a thread indicates the tolerance allowed in manufacturing.  Class 1 is a loose fit  Class 2 is a free fit  Class 3 is a medium fit  Class 4 is a close fit  Aircraft bolts are almost always manufactured in the Class 3, medium fit. 16  General 7-39 Classification of Threads  A Class 4 fit requires a wrench to turn the nut onto a bolt, whereas a Class 1 fit can easily be turned with the fingers.  Generally, aircraft screws are manufactured with a Class 2, free fit for ease of assembly.  Bolts and nuts are also produced with right-hand and left-hand threads.  A right-hand thread tightens when turned clockwise; a left-hand thread tightens when turned counterclockwise. 17  http://en.wikipedia.org/wiki/British_Association_screw_th reads British Association screw threads From Wikipedia, the free encyclopedia  British Association or BA screw threads are a largely obsolete set of small screw threads, the largest being 0BA at 6 mm diameter.  They were, and to some extent still are, used for miniature instruments and modelling.  They are unusual in that they were probably the most "scientific" design of screw, with a basis in metric size (the 1 mm pitch and 6 mm diameter of 0BA) and with a mathematical relationship between the 'number' (e.g. 2BA with K=2) and the corresponding pitch, major diameter, and then spanner size. 18  http://en.wikipedia.org/wiki/British_Association_screw_th reads British Association screw threads  Though originally defined in terms of the imperial units then in use in the United Kingdom, this was deliberately set to be exact multiples of the metric system units, rounded to the nearest thousandth of an inch.  This anticipated worldwide metrication by about a century.  The design was first formulated in 1884, following a study of Swiss practice and was standardized in 1903. 19  http://en.wikipedia.org/wiki/British_Association_screw_th reads British Association screw threads  The British Standards Institution recommends the use of BA sizes in place of the smaller BSW (British Standard Whitworth), and BSF (British Standard Fine) screws (those below 1/4").  Generally, the 0BA size was dropped in place of 7/32" BSF in assemblies that included larger fasteners, however, in smaller equipment that was primarily electronic/electrical the 0BA size would typically be used in place of the BSF or BSW screw where it was the largest size required. 20  http://en.wikipedia.org/wiki/British_Association_screw_th reads British Association screw threads  BA threads are still used in some precision instruments, such as optics and moving-coil meters, relays etc. A 2BA thread is used to connect the head of a dart to its shaft — as such, it is one of the few common uses of this thread in North America.  2BA threads are commonly found in the old imperial BESA conduit boxes in the UK which are still in use (but not installed) today. 21  http://en.wikipedia.org/wiki/British_Association_screw_th reads British Association screw threads Requirements  The angle of the thread is 47.5°, and the depth of thread is 0.6 times the pitch with rounded tops and bottoms.  Thus, the shortening at the crest and root is given by 0.26817p with a radius of 0.18083p at both crest and root.  The thread angle is different from that used by Whitworth (55 degrees) and ISO Metric (60 degrees), so BA fasteners are never interchangeable with Whitworth/Metric ones even when the pitch and diameter seem similar (e.g. 0BA which appears similar to M6 x 1 mm). 22  http://en.wikipedia.org/wiki/British_Association_screw_th reads British Association screw threads  Standard BA sizes are defined between 0BA and 22BA. The even sizes are much more common, and the very small sizes are not used very often, and other standards tend to be used (e.g., NHS- Norman Hortogere Suisse). 23  http://en.wikipedia.org/wiki/ISO_metric_screw_thread ISO metric screw threads  The ISO metric screw threads are the world-wide most commonly used type of general-purpose screw thread.  They were one of the first international standards agreed when the International Organization for Standardization was set up in 1947.  The "M" designation for metric screws indicates the nominal outer diameter of the screw, in millimeters (e.g. an M6 screw has a nominal outer diameter of 6 millimeters). 24  http://en.wikipedia.org/wiki/ISO_metric_screw_thread ISO metric screw threads Basic profile of all ISO metric screw threads  The design principles of ISO general-purpose metric screw threads ("M" series threads) are defined in international standard ISO 68-1.  Each thread is characterized by its major diameter D and its pitch P.  ISO metric threads consist of a symmetric V-shaped thread.  In the plane of the thread axis, the flanks of the V have an angle of 60° to each other. 25  http://en.wikipedia.org/wiki/ISO_metric_screw_thread ISO metric screw threads  The outermost 1/8 and the innermost 1/4 of the height H of the V-shape are cut off from the profile.  In an external (male) thread (e.g., on a bolt), the major diameter Dmaj and the minor diameter Dmin define maximum dimensions of the thread.  This means that the external thread must end flat at Dmaj but can be rounded out below the minor diameter Dmin.  Conversely, in an internal (female) thread (e.g., in a nut), the major and minor diameters are minimum dimensions, therefore the thread profile must end flat at Dmin but may be rounded out beyond Dmaj. 26  http://en.wikipedia.org/wiki/ISO_metric_screw_thread ISO metric screw threads 27  http://en.wikipedia.org/wiki/ISO_metric_screw_thread ISO metric screw threads Designation  A metric ISO screw thread is designated by the letter M followed by the value of the nominal diameter D (Dmaj in the diagram above) and the pitch P, both expressed in millimetres and separated by the multiplication sign, × (e.g., M8×1.25).  If the pitch is the normally used "coarse" pitch listed in ISO 261 or ISO 262, it can be omitted (e.g., M8).  Tolerance classes defined in ISO 965-1 can be appended to these designations, if required (e.g., M500– 6g in external threads). 28  http://en.wikipedia.org/wiki/ISO_metric_screw_thread ISO metric screw threads  External threads are designated by lowercase letter, g or h. Internal threads are designated by upper case letters, G or H.  Preferred sizes  ISO 261 specifies a detailed list of preferred combinations of outer diameter D and pitch P for ISO metric screw threads.  ISO 262 specifies a shorter list of thread dimensions – a subset of ISO 261. 29  http://en.wikipedia.org/wiki/ISO_metric_screw_thread ISO metric screw threads 30  General 7-39 Aircraft Bolts  Aircraft bolts are fabricated from cadmium- or zinc plated corrosion resistant steel, un-plated corrosion resistant steel, or anodized aluminum alloys.  Most bolts used in aircraft structures are either general purpose, AN bolts, NAS internal wrenching or Close tolerance bolts, or MS bolts.  In certain cases, aircraft manufacturers make bolts of different dimensions or greater strength than the standard types. 31  General 7-39 Aircraft Bolts  Such bolts are made for a particular application, and it is of extreme importance to use like bolts in replacement.  The letter “S” stamped on the head usually identifies special bolts.  AN bolts come in three head styles—hex head, clevis, and eyebolt. [Figure 7-19]  NAS bolts are available in hex head, internal wrenching, and countersunk head styles.  MS bolts come in hex head and internal wrenching styles. 32  General 7-40 Aircraft Bolts  [Figure 7-19] 33  General 7-40 Aircraft Bolts  [Figure 7-19] 34  General 7-40 Aircraft Bolts  [Figure 7-19] 35  General 7-40 Aircraft Bolts  [Figure 7-19] 36  General 7-39 Identification and Coding  Bolts are manufactured in many shapes and varieties.  A clear-cut method of classification is difficult.  Bolts can be identified by the shape of the head, method of securing, material used in fabrication, or the expected usage.  AN-type aircraft bolts can be identified by the code markings on the bolt heads.  The markings generally denote the bolt manufacturer, the material of which the bolt is made, and whether the bolt is a standard AN-type or a special purpose bolt. 37  General 7-39 Identification and Coding  AN standard steel bolts are marked with either a raised “X” or asterisk; corrosion resistant steel is indicated by a single raised dash; and AN aluminum alloy bolts are marked with two raised dashes.  Additional information, such as bolt diameter, bolt length, and grip length may be obtained from the bolt part number. For example, in the bolt part number AN3DD5A,  the “AN” designates that it is an Air Force-Navy Standard bolt, 38  General 7-40 Identification and Coding  the “3” indicates the diameter in sixteenths of an inch (3⁄16),  the “DD” indicates the material is 2024 aluminum alloy. (Note: “D” indicates 2017 Alum Alloy)  The letter “C” in place of the “DD” would indicate corrosion resistant steel, and the absence of the letters (“-”)would indicate cadmium plated steel.  The “5” indicates the length in eighths of an inch (5⁄8), and the “A” indicates that the shank is undrilled.  If the letter “H” preceded the “5” in addition to the “A” following it, the head would be drilled for safetying. 39  General 7-41 Identification and Coding 40  General 7-40 Identification and Coding  Close tolerance NAS bolts are marked with either a raised or recessed triangle  The material markings for NAS bolts are the same as for AN bolts, except that they may be either raised or recessed.  Bolts inspected magnetically (Magnaflux) or by fluorescent means (Zyglo) are identified by means of colored lacquer, or a head marking of a distinctive type. 41  General 7-43 Aircraft Nuts  Aircraft nuts are made in a variety of shapes and sizes.  They are made of cadmium plated carbon steel, stainless steel, or anodized 2024T aluminum alloy, and may be obtained with either right- or left-hand threads.  No identifying marking or lettering appears on nuts.  They can be identified only by the characteristic metallic luster or color of the aluminum, brass, or the insert when the nut is of the self-locking type.  They can be further identified by their construction. 42  General 7-43 Aircraft Nuts  Aircraft nuts can be divided into two general groups: non-self-locking and self-locking nuts.  Non-self-locking nuts are those that must be safetied by external locking devices, such as cotter pins, safety wire, or locknuts.  Self-locking nuts contain the locking feature as an integral part. 43  General 7-44 Aircraft Nuts Non-Self-Locking Nuts  Most of the familiar types of nuts, including the plain nut, the castle nut, the castellated shear nut, the plain hex nut, the light hex nut, and the plain checknut are the non-self-locking type.[Figure 7-25]  The Castle nut, AN310, is used with drilled shank AN hex head bolts, clevis bolts, eyebolts, drilled head bolts, or studs.  It is rugged and can withstand large tensional loads.  Slots (called castellations) in the nut are designed to accommodate a cotter pin or lockwire for safety. 44  General 7-44 Aircraft Nuts  [Figure 7-25] The castle nut, AN310, 45  General 7-44 Aircraft Nuts  The Castellated shear nut, AN320, is designed for use with devices (such as drilled clevis bolts and threaded taper pins) which are normally subjected to shearing stress only.  Like the castle nut, it is castellated for safetying.  Note, however, that the nut is not as deep or as strong as the castle nut; also, that the castellations are not as deep as those in the castle nut. 46  General 7-44 Aircraft Nuts  The Plain hex nut, AN315 and AN335 (fine and coarse thread), is of rugged construction.  This makes it suitable for carrying large tensional loads.  However, since it requires an auxiliary locking device, such as a checknut or lockwasher, its use on aircraft structures is somewhat limited.  The Light hex nut, AN340 and AN345 (fine and coarse thread), is a much lighter nut than the plain hex nut and must be locked by an auxiliary device.  It is used for miscellaneous light tension requirements. 47  General 7-44 Aircraft Nuts  The plain checknut, AN316, is employed as a locking device for plain nuts, set screws, threaded rod ends, and other devices.  The wing nut, AN350, is intended for use where the desired tightness can be obtained with the fingers and where the assembly is frequently removed. 48  General 7-44 Aircraft Nuts Self-Locking Nuts  As their name implies, self-locking nuts need no auxiliary means of safetying but have a safetying feature included as an integral part of their construction.  Many types of self-locking nuts have been designed and their use has become quite widespread.  Common applications are: (1) attachment of antifriction bearings and control pulleys; (2) attachment of accessories, anchor nuts around inspection holes and small tank installation openings; and (3) attachment of exhaust stacks or pipes. 49  General 7-44 Aircraft Nuts  Self-locking nuts are acceptable for use on certificated aircraft subject to the restrictions of the manufacturer.  Self-locking nuts are used on aircraft to provide tight connections which will not shake loose under severe vibration.  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. 50  General 7-45 Aircraft Nuts  Plates must be attached to the structure in a positive manner to eliminate rotation or misalignment when tightening the bolts or screws.  The two general types of self-locking nuts currently in use are the all-metal type and the nylon lock type.  For the sake of simplicity, only three typical kinds of self-locking nuts are considered in this handbook: the Boots self-locking and the stainless steel self- locking nuts, representing the all-metal types; and the elastic stop nut, representing the nylon insert type. 51  General 7-45 Aircraft Nuts  Boots Self-Locking Nut  The Boots self-locking nut is of one-piece, all-metal construction, designed to hold tight in spite of severe vibration.  Note in Figure 7-26 that it has two sections and is essentially two nuts in one, a locking nut and a load- carrying nut.  The two sections are connected with a spring which is an integral part of the nut. 52  General 7-45 Aircraft Nuts  Figure 7-26 Boots Self-Locking Nut. 53 Aircraft Nuts- Boots Self-Locking Nut 54  General 7-45 Aircraft Nuts  The spring keeps the locking and load-carrying sections such a distance apart that the two sets of threads are out of phase; that is, so spaced that a bolt which has been screwed through the load carrying section must push the locking section outward against the force of the spring to engage the threads of the locking section properly.  Thus, the spring, through the medium of the locking section, exerts a constant locking force on the bolt in the same direction as a force that would tighten the nut. 55  General 7-45 Aircraft Nuts  In this nut, the load-carrying section has the thread strength of a standard nut of comparable size, while the locking section presses against the threads of the bolt and locks the nut firmly in position.  Only a wrench applied to the nut (Head?) will loosen it.  The nut can be removed and reused without impairing its efficiency.  Boots self-locking nuts are made with three different spring styles and in various shapes and sizes. 56  General 7-45 Aircraft Nuts  The Wing type, that is the most common ranges in size for No.6 up to 1⁄4 inch  The Rol-top ranges from 1⁄4 inch to 1⁄6 (1 1/16?)inch  The Bellows type ranges in size from No.8 up to 3⁄8 inch.  Wing-type nuts are made of anodized aluminum alloy, cadmium-plated carbon steel, or stainless steel. 57  General 7-45 Aircraft Nuts  The Rol-top nut is cadmium-plated steel  The Bellows type is made of aluminum alloy only. 58  General 7-45 Aircraft Nuts Stainless Steel Self-Locking Nut  The stainless steel self-locking nut may be spun on and off with the fingers, as its locking action takes place only when the nut is seated against a solid surface and tightened.  The nut consists of two parts: a case with a beveled locking shoulder and key, and a threaded insert with a locking shoulder and slotted keyway. 59  General 7-45 Aircraft Nuts  Until the nut is tightened, it spins on the bolt easily because the threaded insert is the proper size for the bolt.  However, when the nut is seated against a solid surface and tightened, the locking shoulder of the insert is pulled downward and wedged against the locking shoulder of the case.  This action compresses the threaded insert and causes it to clench the bolt tightly. 60  General 7-45 Aircraft Nuts  The cross-sectional view in Figure 7-27 shows how the key of the case fits into the slotted keyway of the insert so that when the case is turned, the threaded insert is turned with it.  Note that the slot is wider than the key.  This permits the slot to be narrowed and the insert to be compressed when the nut is tightened. 61  General 7-45 Aircraft Nuts  The cross-sectional view in Figure 7-27 62  General 7-45 Aircraft Nuts Elastic Stop Nut  The Elastic stop nut is a standard nut with the height increased to accommodate a nylon locking collar.  This nylon collar is very tough and durable and unaffected by immersion in hot or cold water or ordinary solvents, such as ether, carbon tetrachloride, oils, and gasoline.  It will not damage bolt threads or plating. 63  General 7-46 Aircraft Nuts  As shown in Figure 7-28, a nylon locking collar is not threaded, and its inside diameter is smaller than the largest diameter of the threaded portion or the outside diameter of a corresponding bolt.  When the nut is screwed onto a bolt, it acts as an ordinary nut until the bolt reaches the nylon collar.  When the bolt is screwed into the nylon collar, however, friction (or drag) causes the nylon to be pushed upward. 64  General 7-46 Aircraft Nuts  Figure 7-28, a nylon locking collar 65  General 7-46 Aircraft Nuts  This creates a heavy downward pressure on the load carrying part and automatically throws the load carrying sides of the nut and bolt threads into positive contact.  After the bolt has been forced all the way through the nylon collar, the downward pressure remains constant.  This pressure locks and holds the nut securely in place even under severe vibration.  Nearly all elastic stop nuts are steel or aluminum alloy.  However, such nuts are available in practically any kind of metal. 66  General 7-45 Aircraft Nuts  Aluminum alloy elastic stop nuts are supplied with an anodized finish.  Steel nuts are cadmium plated.  Normally, elastic stop nuts can be used many times with complete safety and without detriment to their locking efficiency.  When reusing elastic stop nuts, be sure the fibre has not lost its locking friction or become brittle.  If a nut can be turned with the fingers, replace it.  Some shops have a standing policy to discard all stop nuts after their first use. 67  General 7-45 Aircraft Nuts  Self-locking Nuts- NTSB  P51 2011 Reno Air race crash- Trim tab screws Viewer Discretion Advised-MSNBC report  End of Day 5 68