Special Fasteners, Screws, and Hole Repair

7-60 C A B A = Thickness of material (grip range) B = 3/64 – 1/8" C = Total rivet shank length (Minimum grip illustrated) Before installation After installation Many special fasteners produce high strength with lightweight and can be used in place of conventional AN bolts and nuts. When AN bolts are tightened with the nut, the bolt stretches, narrowing the diameter and then the bolt is no longer tight in the hole. Special fasteners eliminate this loose fit, because they are held in place by a collar that is squeezed into position. These fasteners are not under the same tensile loads as a bolt during installation. Special fasteners are also used extensively for light sport aircraft (LSA). Always follow the aircraft manufacturer’s recommendations.

Pin Rivets Pin (Hi-Shear) rivets are classified as special rivets but are not of the blind type. Access to both sides of the material is required to install this type of rivet. Pin rivets have the same shear strength as bolts of equal diameters, are about 40 percent of the weight of a bolt, and require only about one- fifth as much time for installation as a bolt, nut, and washer combination. They are approximately three times as strong as solid shank rivets. Pin rivets are essentially threadless bolts. The pin is headed at one end and is grooved about the circumference at the other. A metal collar is swaged onto the grooved end effecting a firm, tight fit. [Figure 7-55] Pin rivets are fabricated in a variety of materials but should be used only in shear applications.

They should never be used where the grip length is less than the shank diameter. Part numbers for pin rivets can be interpreted to give the diameter and grip length of the individual rivets. A typical part number breakdown would be: NAS177-14-17 7-61 Before pulling begins1 Stem is pulled into rivet sleeve and starts to form bulbed blind head. 2 Formation of blind head and hole filling are completed. Shear ring now begins to shear from stem cone to allow stem to pull further into rivet. 4 Completely installed bulbed CherryLOCK® rivet6 Clamp-up completed as stem continues to bulb out blind head.

3 Shear ring has moved down stem cone until pulling head automatically stops stem break notch flush with top of rivet head. Pulling head has inserted locking collar, and stem has fractured flush with rivet head. 5 Sheet gap Stem Rivet sleeve Locking collar Rivet head Shear ring Shear ring guarantees blind side bulbed head Clamp-up and hole fill action begin. Locking collar is now ready to be inserted. (Maximum grip illustrated) Rivet head firmly seated Blind side bulb head is formed below minimum grip. Blind side bulbed head (In minimum grip, shear ring may not shear) NAS = National Aircraft Standard 177 = 100° countersunk head rivet OR 178 = flathead rivet 14 = Nominal diameter in 32nds of an inch 17 = Maximum grip length in 16ths of an inch Taper-Lok Taper-Loks are the strongest special fasteners used in aircraft construction. The Taper-Lok exerts a force on the walls of the hole because of its tapered shape. The Taper-Lok is designed to completely fill the hole, but unlike the rivet, it fills the hole without deforming the shank. Instead, the washer head nut squeezes the metal with tremendous force against the tapered walls of the hole. This creates radial compression around the shank and vertical compression lines as the metals are squeezed together. The combination of these forces generates strength unequaled by any other fastener. [Figure 7-56] HI-LOK™ Fastening System The threaded end of the HI-LOK™ two-piece fastener contains a hexagonal shaped recess. The hex tip of an Allen wrench engages the recess to prevent rotation of the pin while the collar is being installed. The pin is designed in two basic head styles. For shear applications, the pin is made in countersunk style and in a compact protruding head style. For tension applications, the MS24694 countersunk and regular protruding head styles are available.

The self-locking, threaded HI-LOK™ collar has an internal counterbore at the base to accommodate variations in material thickness. At the opposite end of the collar is a wrenching device that is torqued by the driving tool until it shears off during installation, leaving the lower portion of the collar seated with the proper torque without additional torque inspection. This shear-off point occurs when a predetermined preload or clamp-up is attained in the fastener during installation. Note: For these fasteners, “Preload” is defined as the maximum tensile load experienced by a fastener in a joint during the fastener installation sequence. Consequently, the 7-62 100° Countersunk (MS20426) For countersunk applications 100° Countersunk NAS 1097 For thin top sheet machine countersunk applications Universal (MS20470) For protruding head applications Unisink A combination of flush and protruding head for use in very thin top sheets. Eliminates need for double-dimpling. Not covered by NAS Standard.

156° Countersunk NAS 1097 A large diameter, shallow countersunk head providing wide area for honeycomb applications. Not covered by NAS Standard. term “Residual Tension” is defined as the remaining tensile load experienced by a fastener in a joint after the fastener installation sequence is complete, and after any residual relaxation of the joint assembly. The advantages of HI-LOK™ two-piece fastener include its lightweight, high fatigue resistance, high strength, and its inability to be over-torqued. The pins, made from alloy steel, corrosion-resistant steel, nickel, or titanium alloy, come in many standard and oversized shank diameters. The collars are made of aluminum alloy, corrosion-resistant steel, titanium, or alloy steel. The collars have wrenching flats, fracture point, threads, and a recess. The wrenching flats are used to install the collar. The fracture point has been designed to allow the wrenching flats to shear when the proper torque has been reached. The threads match the threads of the pins and have been formed into an ellipse that is distorted to provide the locking action. The recess serves as a built-in washer. This area contains a portion of the shank and the transition area of the fastener.

The hole shall typically be prepared so that the maximum interference fit does not exceed 0.002-inch. This avoids build up of excessive internal stresses in the work adjacent 7-63 ¼" Grip Min. grip Max. grip 4 4 4 Diameter 3/16 " Rivet grip number to be used: −04 Read 2 4 6 8 Read 269C3 Gauge C A B A = Thickness of material (grip range) B = 3/64 – 1/8" C = Total rivet shank length 9SP-B Head Style 9SP-B = brazier or universal head 9SP-100 = 100º countersunk head Material composition of shank A = 2017 aluminum alloy B = 5056 aluminum alloy R = mild steel Shank diameter in 32nds of an inch: 4 = 1⁄8" 6 = 3⁄16" 5 = 5⁄32" 8 = ¼" Grip range (material thickness) in 16ths of an inch A 6 3 Huck Manufacturing Company 9S P-B A 6 3 RV Manufacturer Olympic Screw and Rivet Corporation Rivet type 2 = self plugging (friction lock) 5 = hollow pull through Material composition of shank 0 = 2017 aluminum alloy 5 = 5056 aluminum alloy 7 = mild steel Head style 0 = universal head 1 = 100° countersunk Shank diameter in 32nds of an inch: 4 = 1⁄8" 6 = 3⁄16" 5 = 5⁄32" 8 = ¼" Grip range in 16ths of an inch 2 0 4 2 Olympic Screw and Rivet Corporation RV 2 0 0 4 2 CR Cherry rivet Series number Designates rivet material, type of rivet, and head style (163 = 2117 aluminum alloy, self-plugging (friction lock) rivet, protruding head) Shank diameter in 32nds of an inch: 4 = 1⁄8" 6 = 3⁄16" 5 = 5⁄32" 8 = ¼" Grip range (material thickness): Knob stem in 32nds of an inch; serrated stem in 16ths of an inch 163 6 Townsend Company, Cherry Rivet Division CR 163 6 6 to the hole. The HI-LOK™ pin has a slight radius under its head to increase fatigue life. After drilling, deburr the edge of the hole to allow the head to seat fully in the hole. The HI-LOK™ is typically installed in interference fit holes for aluminum structure and a clearance fit for steel, titanium, and composite materials.

HI-TIGUE™ Fastening System The HI-TIGUE™ fastener offers all the benefits of the HI-LOK™ fastening system along with a unique radius contour on the thread lead-in, or a raised bead design that enhances the fatigue performance of the structure making it ideal for situations that require a controlled interference fit. The HI-TIGUE™ fastener assembly consists of a pin and 7-64 Preload Manufacturing head Washer nut Radial compression Lines of force Pin Driven collar Collar Military Standard Type of rivet and head style: 20600 = self-plugging (friction lock) protruding head 20600 = self-plugging (friction lock) 100º countersunk head Material composition of sleeve: AD = 2117 aluminum alloy B = 5056 aluminum alloy Shank diameter in 32nds of an inch: Type of stem: K = knot head stem W = serrated stem Grip range (material thickness) in 16ths of an inch Military Standard Number MS 20600 B 4 K 2 MS 20600 B 4 K 2 collar. These pin rivets have a radius at the transition area.

During installation in an interference fit hole, the radius area will “cold-work” the hole. These fastening systems can be easily confused, and visual reference should not be used for identification. Use part numbers to identify these fasteners. [Figure 7-57] HI-LITE™ Fastening System The HI-LITE™ fastener is similar in design and principle to the HI-LOK™ fastener, has the controlled radius from full diameter section to the threaded area of the HI-TIGUE™ fastener, and has a shorter transition area between the shank and the first load-bearing thread. HI-LITE™ fasteners have approximately one less thread. These differences reduce the weight of the HI-LITE™ fastener without lessening the shear strength. HI-LITE™ fasteners are available in the same materials and head configurations as the HI-LOK™ system, and can also be installed in high interference like the HI-TIGUE™ fastener. HI-LITE™ collars are also different and thus are not interchangeable with HI-LOK™ collars or HI-TIGUE™ collars.

Captive Fasteners Captive fasteners are used for quick removal of engine nacelles, inspection panels, and areas where fast and easy access is important. A captive fastener can turn in the body in which it is mounted, but will not drop out when it is unscrewed from the part it is holding. Some of the most commonly used are the Dzus, Camloc, and Airloc. Turn Lock Fasteners Turn lock fasteners are used to secure inspection plates, doors, and other removable panels on aircraft. Turn lock fasteners are also referred to by such terms as quick opening, quick action, and stressed panel fasteners. The most desirable feature of these fasteners is that they permit quick and easy removal of access panels for inspection and servicing purposes. Turn lock fasteners are manufactured and supplied by several manufacturers under various trade names.

Dzus Fasteners The Dzus turn lock fastener consists of a stud, grommet, and receptacle. Figure 7-58 illustrates an installed Dzus fastener and the various parts. The grommet is made of aluminum or aluminum alloy material. It acts as a holding device for the stud. Grommets can be fabricated from 1100 aluminum tubing, if none are available from normal sources. 4 = 1⁄8" 6 = 3⁄16" 5 = 5⁄32" 8 = 1⁄4" 7-65 Collar The hex portion breaks away once the correct seating torque is reached Pin Stud Detachable part Grommet Cut-away view of complete Dzus assembly Fixed part Spring and rivets Stud assembly Spring assembly The spring is made of steel, which is cadmium plated to prevent corrosion. The spring supplies the force that locks or secures the stud in place when two assemblies are joined.

The studs are fabricated from steel and are cadmium plated. They are available in three head styles: wing, flush, and oval. Body diameter, length, and head type may be identified or determined by the markings found on the head of the stud. [Figure 7-59] The diameter is always measured in sixteenths of an inch. Stud length is measured in hundredths of an inch and is the distance from the head of the stud to the bottom of the spring hole. A quarter of a turn of the stud (clockwise) locks the fastener. The fastener may be unlocked only by turning the stud counterclockwise. A Dzus key or a specially ground screwdriver locks or unlocks the fastener.

Camloc Fasteners Camloc fasteners are made in a variety of styles and designs. Included among the most commonly used are the 2600, 2700, 40S51, and 4002 series in the regular line, and the stressed panel fastener in the heavy-duty line. The latter is used in stressed panels, which carry structural loads. The Camloc fastener is used to secure aircraft cowlings and fairings. It consists of three parts: a stud assembly, a grommet, and a receptacle. Two types of receptacles are available: rigid and floating. [Figure 7-60] The stud and grommet are installed in the removable portion; the receptacle is riveted to the structure of the aircraft. The stud and grommet are installed in either a plain, dimpled, countersunk, or counter bored hole, depending upon the location and thickness of the material involved.

A quarter turn (clockwise) of the stud locks the fastener. The fastener can be unlocked only by turning the stud 7-66 DZUS 6½ F 0.50 F = flush head 61/2= body diameter in 16ths of an inch 0.50 = length (50⁄100 of an inch) Stud assembly Grommet Receptacle counterclockwise. Airloc Fasteners The Airloc fastener consists of three parts: a stud, a cross pin, and a stud receptacle. [Figure 7-61] The studs are manufactured from steel and case hardened to prevent excessive wear. The stud hole is reamed for a press fit of the cross pin. The total amount of material thickness to be secured with the Airloc fastener must be known before the correct length of stud can be selected for installation. The total thickness of material that each stud satisfactorily locks together is stamped on the head of the stud in thousandths of an inch (0.040, 0.070, 0.190, and so forth). Studs are manufactured in three head styles: flush, oval, and wing.

The cross pin is manufactured from chrome-vanadium steel and heat-treated to provide maximum strength, wear, and holding power. [Figure 7-61] It should never be used the second time; once removed from the stud, replace it with a new pin. Receptacles for Airloc fasteners are manufactured in two types: rigid and floating. Number—No. 2, No. 5, and No. 7, classifies sizes. They are also classified by the center-to- center distance between the rivet holes of the receptacle: No. 2 is 3⁄4 inch; No. 5 is 1 inch; and No. 7 is 13⁄8 inch. Receptacles are fabricated from high-carbon, heat-treated steel. An upper wing assures ejection of the stud when unlocked and enables the cross pin to be held in a locked position between the upper wing, cam, stop, and wing detent, regardless of the tension to which the receptacle is subjected.

Screws

Screws are the most commonly used threaded fastening devices on aircraft. They differ from bolts because as they are generally made of lower strength materials. They can be installed with a loose-fitting thread, and the head shapes are made to engage a screwdriver or wrench. Some screws have a clearly defined grip or unthreaded portion, while others are threaded along their entire length. Several types of structural screws differ from the standard structural bolts only in head style. The material in them is the same, and a definite grip length is provided. The AN525 washer head screw and the NAS220 through NAS227 series are such screws.

Commonly used screws are classified in four groups: 1. Structural screws, which have the same strength as equal size bolts. 2. Machine screws, which include most types used for general repair. 3. Se lf-tapping screws, which are used for attaching lighter parts. 4. Drive screws, which are not actually screws but nails. They are driven into metal parts with a mallet or hammer and their heads are not slotted or recessed. Structural Screws Structural screws are made of alloy steel, are properly heat- treated, and can be used as structural bolts. These screws 7-67 Studs Installed fastener Stud receptacles Airloc cross pin Cross pinReceptacle Panel Stud are found in the NAS204 through NAS235 and AN509 and AN525 series. They have a definite grip and the same shear strength as a bolt of the same size. Shank tolerances are similar to AN hex head bolts, and the threads are National Fine. Structural screws are available with round, brazier, or countersunk heads. Either a Phillips or a Reed & Prince screwdriver drives the recessed head screws.

The AN509 (100°) flathead screw is used in countersunk holes where a flush surface is necessary. The AN525 washer head structural screw is used where raised heads are not objectionable. The washer head screw provides a large contact area. Machine Screws Machine screws are usually of the flathead (countersunk), roundhead, or washer head types. These are general purpose screws and are available in low-carbon steel, brass, corrosion- resistant steel, and aluminum alloy. Roundhead screws, AN515 and AN520, have either slotted or recessed heads. The AN515 screw has coarse threads, and the AN520 has fine threads.

Countersunk machine screws are listed as AN505 and AN510 for 82° and AN507 for 100°. The AN505 and AN510 correspond to the AN515 and AN520 roundhead in material and usage. The fillister head screw, AN500 through AN503, is a general purpose screw and is used as a cap screw in light mechanisms. This could include attachments of cast aluminum parts, such as gearbox cover plates. The AN500 and AN501 screws are available in low-carbon steel, corrosion-resistant steel, and brass. The AN500 has coarse threads, while the AN501 has fine threads. They have no clearly defined grip length. Screws larger than No. 6 have a hole drilled through the head for safetying purposes.

The AN502 and AN503 fillister head screws are made of heat-treated alloy steel, have a small grip, and are available in fine and coarse threads. These screws are used as cap screws where great strength is required. The coarse threaded screws are commonly used as cap screws in tapped aluminum alloy and magnesium castings because of the softness of the metal. Self-Tapping Screws Machine self-tapping screws are listed as AN504 and AN506. The AN504 screw has a roundhead, and the AN506 is 82° countersunk. These screws are used for attaching removable parts, such as nameplates, to castings and parts in which the screw cuts its own threads.

AN530 and AN531 self-tapping sheet metal screws, such as the Parker-Kalon Z-type sheet metal screw, are blunt on the end. They are used in the temporary attachment of metal for riveting, and in the permanent assembly of nonstructural assemblies. Self-tapping screws should not be used to replace standard screws, nuts, bolts, or rivets. Drive Screws Drive screws, AN535, correspond to the Parker-Kalon U-type. They are plain head self-tapping screws used as cap screws for attaching nameplates in castings and for sealing drain holes in corrosion proofing tubular structures. They are not intended to be removed after installation.

Identification & Coding for Screws The coding system used to identify screws is similar to that used for bolts. There are AN and NAS screws. NAS screws 7-68 are structural screws. Part numbers 510, 515, 550, and so on, catalog screws into classes, such as roundhead, flathead, washer head, and so forth. Letters and digits indicate their material composition, length, and thickness. Examples of AN and NAS code numbers follow. AN501B-416-7 AN = Air Force-Navy standard 501 = fillister head, fine thread B = brass 416 = 4⁄16-inch diameter 7 = 7⁄16-inch length The letter “D” in place of the “B” would indicate that the material is 2017-T aluminum alloy. The letter “C” would designate corrosion resistant steel. An “A” placed before the material code letter would indicate that the head is drilled for safetying.

NAS144DH-22 NAS = National Aircraft Standard 144 = head style; diameter and thread—1⁄4-28 bolt, internal wrenching DH = drilled head 22 = screw length in 16ths of an inch—13⁄8 inches long The basic NAS number identifies the part. The suffix letters and dash numbers separate different sizes, plating material, drilling specifications, and so forth. The dash numbers and suffix letters do not have standard meanings. It is necessary to refer to a specific NAS page in the Standards book for the legend.

Riveted & Rivetless Nut Plates

When access to the back of a screw or bolt installation is impractical, riveted or rivetless nut plates are used to secure the connection of panels. One example in aircraft this technique is especially useful is to secure the floorboards to the stringers and to each other. Nut Plates Nuts that are made to be riveted in place in aircraft are called nut plates. Their purpose is to allow bolts and screws to be inserted without having to hold the nut. They are permanently mounted to enable inspection panels and access doors to be easily removed and installed. When many screws are used on a panel, to make installation easier, normally floating anchor nuts are used. The floating anchor nut fits into a small bracket, which is riveted to the aircraft skin. The nut is free to move, which makes it much easier to align it with the screw. For production ease, sometimes ganged anchor nuts are used for inspection panels. Ganged anchor nuts allow the nuts to float in a channel, making alignment with the screw easy.

Self-locking nut plates are made under several standards and come in several shapes and sizes. Figure 7-62 shows an MS21078 two-lug nut plate with a nonmetallic insert and an MS21047 lightweight, all-metal, 450 °F (232 °C) nut plate. Nut plates can also have three riveting points if the added strength is required. Rivnuts This is the trade name of a hollow, blind rivet made of 6053 aluminum alloy, counter bored and threaded on the inside. One person using a special tool, which heads the rivet on the blind side of the material, can install Rivnuts. The Rivnut is threaded on the mandrel of the heading tool and inserted in the rivet hole. The heading tool is held at right angles to the material, the handle is squeezed, and the mandrel crank is turned clockwise after each stroke. Continue squeezing the handle and turning the mandrel crank of the heading tool until a solid resistance is felt, which indicates that the rivet is set.

The Rivnut is used primarily as a nut plate and in the attachment of deicer boots to the leading edges of wings. It may be used as a rivet in secondary structures or for the attachment of accessories, such as brackets, fairings, instruments, or soundproofing materials. Rivnuts are manufactured in two head types, each with two ends: the flathead with open or closed end and the countersunk head with open or closed end. All Rivnuts, except the thin head countersunk type, are available with or without small projections (keys) attached to the head to keep the Rivnut from turning. Keyed Rivnuts are used as a nut plate, while those without keys are used for straight blind riveting repairs where no torque loads are imposed. A keyway cutter is needed when installing Rivnuts that have keys.

The countersunk style Rivnut is made with two different head angles: the 100° with 0.048 and 0.063 inch head thickness and the 115° with 0.063 inch head thickness. Each of these head styles is made in three sizes: 6-32, 8-32, and 10-32. These numbers represent the machine screw size of the threads on the inside of the Rivnut. The actual outside diameters of the shanks are 3⁄16 inch for the 6-32 size, 7⁄32 inch for the 8-32 size, and 1⁄4 inch for the 10-32 size. Open-end Rivnuts are the most widely used and are recommended in preference to the closed end type wherever possible. However, closed-end Rivnuts must be used in pressurized compartments.

Rivnuts are manufactured in six grip ranges. The minimum 7-69 Two-lug anchor nut MS21078 MS21051 MS21055 NAS444 or A6195NAS680A A1777, A1789, or A1794 MS21047 MS21059 One-lug anchor nut Corner anchor nut Right-angle anchor nut Ganged anchor nuts U-type tinnerman nuts provide convenient anchor points for cowlings, fairings, and panels. High-temperature two-lug anchor nut Two-lug floating anchor nut Anchor type tinnerman nuts are suitable for nonstructural applications MS33737 Instrument nut To reduce magnetic influences in the flightdeck, nonmagnetic mounting nuts secure instruments in a control panel.

grip length is indicated by a plain head and the next higher grip length by one radial dash mark on the head. Each succeeding grip range is indicated by an additional radial dash mark until five marks indicate the maximum range. Notice in Figure 7-63 that some part number codes consist of a “6,” an “8,” or a “10,” a “dash,” and two or three more numbers. In some, the letters “K” or “KB” replaces the dash. The first number indicates the machine screw size of the thread, and the last two or three numbers indicate the maximum grip length in thousandths of an inch. A dash between the figures indicates that the Rivnut has an open end and is keyless; a “B” in place of the dash means it has a closed end and is keyless; a “K” means it has an open end and has a key; and a “KB” indicates that it has a closed end and a key. If the last two or three numbers are divisible by five, the Rivnut has a flathead; if they are not divisible by five, the Rivnut has a countersunk head.

An example of a part number code is: 10KB106 10 = Grip length KB = Closed end and key 106 = Screw and thread size Dill Lok-Skrus and Dill Lok-Rivets Dill “Lok-Skru” and “Lok-Rivet” are trade names for internally-threaded rivets. They are used for blind attachment of accessories, such as fairings, fillets, access door covers, door and window frames, floor panels, and the like. Lok- Skrus and Lok-Rivets are like the Rivnut in appearance and application; however, they come in two parts and require more clearance on the blind side than the Rivnut to accommodate the barrel. [Figure 7-64] The Lok-Rivet and the Lok-Skru are alike in construction, except the Lok-Skru is tapped internally for fastening an accessory by using an attaching screw, whereas the Lok-Rivet is not tapped and can be used only as a rivet. Since both Lok-Skrus and Lok-Rivets are installed in the same manner, the following discussion for the Lok-Skru also applies to the Lok-Rivet.

The main parts of a Lok-Skru are the barrel, the head, and an attachment screw. The barrel is made of aluminum alloy 7-70 6-45 8-45 10-45 6B45 8B45 10B45 6K45 8K45 10K45 6KB45 8KB45 10KB45 6-75 8-75 10-75 6B75 8B75 10B75 6K75 8K75 10K75 6KB75 8KB75 10KB75 6-100 8-100 10-100 6B100 8B100 10B100 6K100 8K100 10K100 6KB100 8KB100 10KB100 6-91 8-91 10-91 6B91 8B91 10B91 6-121 8-121 10-121 6B121 8B121 10B121 6-146 8-146 10-146 6B146 8B146 10B146 6-106 8-106 10-106 6B106 8B106 10B106 6K106 8K106 10K106 6KB106 8KB106 10KB106 6-136 8-136 10-136 6B136 8B136 10B136 6K136 8K136 10K136 6KB136 8KB136 10KB136 6-161 8-161 10-161 6B161 8B161 10B161 6K161 8K161 10K161 6KB161 8KB161 10KB161 Flat—0.32 H ead Thickness 100°— 0.48 Head Thickness 100°— 0.63 Head Thickness and comes in either closed or open ends. The head is either aluminum alloy or steel, and the attachment screw is made of steel. All the steel parts are cadmium plated, and all of aluminum parts are anodized to resist corrosion. When installed, the barrel screws up over the head and grips the metal on the blind side. The attaching screw is then inserted if needed. There are two head types: the flathead and the countersunk head. The Lok-Skru is tapped for 7-32, 8-32, 10-32, or 10-24 screws, and the diameters vary from 0.230 inch for 6-32 screws, to 0.292 inch for 10-32 screws. Grip ranges vary from 0.010 inch to 0.225 inch.

Deutsch Rivets This rivet is a high-strength blind rivet used on late model aircraft. It has a minimum shear strength of 75,000 psi and can be installed by one person. The Deutsch rivet consists of two parts: the stainless-steel sleeve and the hardened steel drive pin. [Figure 7-65] The pin and sleeve are coated with a lubricant and a corrosion inhibitor. The Deutsch rivet is available in diameters of 3⁄16, 1⁄4, or 3⁄8 inch. Grip lengths for this rivet range from 3⁄16 to 1 inch. Some variation is allowed in grip length when installing the rivet. For example, a rivet with a grip length of 3⁄16 inch can be used where the total thickness of materials is between 0.198 and 0.228 inch.

When driving a Deutsch rivet, an ordinary hammer or a pneumatic rivet gun and a flathead set are used. The rivet is seated in the previously drilled hole, and then the pin is driven into the sleeve. The driving action causes the pin to exert pressure against the sleeve and forces the sides of the sleeve out. This stretching forms a shop head on the end of the rivet and provides positive fastening. The ridge on the top of the rivet head locks the pin into the rivet as the last few blows are struck. Sealing Nut Plates When securing nut plates in pressurized aircraft and in fuel cells, a sealing nut plate is used instead of the open-ended variety previously described. Care must be taken to use exactly the correct length of bolt or screw. If a bolt or screw is too short, there is not enough threads to hold the device in place. If the bolt or screw is too long, it penetrates the back side of the nut plate and compromises the seal. Normally, a sealant is also used to ensure complete sealing of the nut plate.

Check the manufacturer’s specifications for the acceptable sealant to be used for sealing nut plates. Hole Repair & Hole Repair Hardware Many of the blind fasteners are manufactured in oversized diameters to accommodate slightly enlarged holes resulting from drilling out the original fastener. When using rivets 7-71 or even bolts, care must be taken to ensure the hole is not elongated or slanted. To reduce the chances of an incorrectly drilled rivet or bolt hole, use a slightly smaller drill bit first, then enlarge to the correct diameter. The last step to prepare the hole for the fastener is to deburr the hole using either a very large drill bit or a special deburring tool. This practice also works well when drilling out a previously attached fastener. If the drill bit does not exactly find the center of the rivet, bolt, or screw, the hole can easily be elongated, but when using a smaller drill bit, drill the head only off the fastener. Then the ring and stem that is left can be pushed out with a pin punch of the appropriate diameter. If an incorrectly drilled hole is found, the options are to re-drill the hole to the next larger diameter for an acceptable fastener or repair the hole using an Acres fastener sleeve.

Repair of Damaged Holes with Acres Fastener Sleeves Acres fastener sleeves are thin-wall tubular elements with a flared end. The sleeves are installed in holes to accept standard bolts and rivet-type fasteners. The existing fastener holes are drilled 1⁄64 inch oversize for installation of the sleeves. The sleeves are manufactured in 1-inch increments. Along their length, grooves provide a place to break or cut off excess length to match fastener grip range. The grooves also provide a place to hold adhesive or sealing agents when bonding the sleeve into the hole. Advantages & Limitations The sleeves are used in holes that must be drilled 1⁄64 inch oversize to clean up corrosion or other damage. The oversize hole with the sleeve installed allows the use of the original diameter fastener in the repaired hole. The sleeves can be used in areas of high galvanic corrosion where the corrosion must be confined to a readily replaceable part. Oversizing of holes reduces the net cross-sectional area of a part and should not be done unless absolutely required.

Consult the manufacturer of the aircraft, aircraft engine, or aircraft component prior to repair have damaged holes with Acres sleeves. Identification The sleeve is identified by a standard code number that represents the type and style of sleeve, a material code, the fastener shank diameter, and surface finish code letter, and grip tang for the sleeve. [Figure 7-66] The basic code number represents the type and material of the sleeve. The first dash number represents the diameter of the sleeve for the fastener installed, and the second dash represents the grip length of the sleeve. The required length of the sleeve is determined on installation and the excess is broken off the sleeve. A JK5512A-05N-10 is a 100° low profile head sleeve of aluminum alloy. The diameter is for a 5⁄32-inch fastener with no surface finish and is 5⁄8 inch in length.

Hole Preparation Refer to Figure 7-67 for drill number for standard or close fit holes. Inspect hole after drilling to assure all corrosion is removed before installing the sleeve. The hole must also be the correct shape and free from burrs. The countersink must be enlarged to receive the flare of the sleeve, so the sleeve is flush with the surrounding surface. Installation After selecting the correct type and diameter sleeve, use the 6501 sleeve breakoff tool for final installation length. Refer to Figure 7-67 for the sleeve breakoff procedure. The sleeve may be installed with or without being bonded in the hole.

When bonding the sleeve in a hole, use MIL-S-8802A 1⁄2 sealant. Reinstall original size fastener and torque as required. Sleeve Removal Sleeves not bonded in the hole may be removed by either 7-72 driving them out with a drift pin of the same diameter as the outside diameter of the sleeve, or they may be deformed and removed with a pointed tool. Bonded sleeves may be removed by this method, but care should be used not to damage the structure hole. If this method cannot be used, drill the sleeves out with a drill 0.004 to 0.008 inch smaller than the installation drill size. The remaining portion of the sleeve after drilling can be removed using a pointed tool and applying an adhesive solvent to the sealant.

Control Cables & Terminals

Cables are the most widely used linkage in primary flight control systems. Cable-type linkage is also used in engine controls, emergency extension systems for the landing gear, and various other systems throughout the aircraft. Cable-type linkage has several advantages over the other types. It is strong and lightweight, and its flexibility makes it easy to route through the aircraft. An aircraft cable has a high mechanical efficiency and can be set up without backlash, which is very important for precise control. Cable linkage also has some disadvantages. Tension must be adjusted frequently due to stretching and temperature changes.

Aircraft control cables are fabricated from carbon steel or stainless steel. Cable Construction The basic component of a cable is a wire. The diameter of the wire determines the total diameter of the cable. Several wires are preformed into a helical or spiral shape and then formed into a strand. These preformed strands are laid around a straight center strand to form a cable. Cable designations are based on the number of strands and the number of wires in each strand. The most common aircraft cables are the 7 × 7 and 7 × 19. The 7 × 7 cable consists of seven strands of seven wires each. Six of these strands are laid around the center strand.

[Figure 7-68] This is a cable of medium flexibility and is used for trim tab controls, engine controls, and indicator controls. The 7 × 19 cable is made up of seven strands of 19 wires each. Six of these strands are laid around the center strand. [Figure 7-68] This cable is extra flexible and is used in primary control systems and in other places where operation over pulleys is frequent. Aircraft control cables vary in diameter, ranging from 1⁄16 to 3⁄8 inch. The diameter is measured as shown in Figure 7-68. Cable Fittings Cables may be equipped with several different types of fittings, such as terminals, thimbles, bushings, and shackles.

Terminal fittings are generally of the swaged type. They are available in the threaded end, fork end, eye end, single shank ball end, and double shank ball end. The threaded end, fork end, and eye end terminals are used to connect the cable to a turnbuckle, bell crank, or other linkage in the system. The ball end terminals are used for attaching cables to quadrants and special connections where space is limited. Figure 7-69 illustrates the various types of terminal fittings. The thimble, bushing, and shackle fittings may be used in place of some types of terminal fittings when facilities and supplies are limited and immediate replacement of the cable is necessary.

Turnbuckles A turnbuckle assembly is a mechanical screw device consisting of two threaded terminals and a threaded barrel. [Figure 7-70] Turnbuckles are fitted in the cable assembly for 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 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. The methods of safetying turnbuckles are discussed later in this chapter. Push-Pull Tube Linkage Push-pull tubes are used as linkage in various types of mechanically-operated systems. This type linkage eliminates the problem of varying tension and permits the transfer of either compression or tension stress through a single tube. A push-pull tube assembly consists of a hollow aluminum alloy or steel tube with an adjustable end fitting and a check nut at either end. [Figure 7-71] The check nuts secure the end fittings after the tube assembly has been adjusted to its correct length. Push-pull tubes are generally made in short lengths to prevent vibration and bending under compression loads.