Clamps 1/4" Min.
Ref.
Nut Socket Fitting Hose Tubing Nipple 3° Max.
Angular deviation 1/16" Max offset Minimum gap "G" shall be 1/2" or Tube OD/4, whichever is greater.
Maximum gap "G" is not limited except on suction lines using other than self-sealing hose. On such suction lines, maximum G shall be 1-1/2 inch or one tube diameter, whichever is greater.
FIGURE 5-16. Flexible fluid connection assembly.
in the tubing. A tube cannot be cut or flared accurately enough so that it can be installed without bending and still be free from mechanical strain. Bends are also necessary to permit the tubing to expand or contract under temperature changes and to absorb vibration. If the tube is small (under one-fourth inch) and can be hand formed, casual bends may be made to allow for this. If the tube must be machine formed, definite bends must be made to avoid a straight assembly.
Start all bends a reasonable distance from the fittings, because the sleeves and nuts must be slipped back during the fabrication of flares and during inspections. In all cases the new tube assembly should be so formed prior to installation that it will not be necessary to pull or deflect the assembly into alignment by means of the coupling nuts.
FABRICATION AND REPLACEMENT OF
FLEXIBLE HOSE Hose and hose assemblies should be checked for deterioration at each inspection period. Leakage, separation of the cover or braid from the inner tube, cracks, hardening, lack of flexibility, and FIGURE 5-17. Sleeve-type fittings.
excessive "cold flow" are apparent signs of deterioration and reason for replacement. The term "cold flow" describes the deep, permanent impressions in the hose produced by the pressure of hose clamps or supports.
When failure occurs in a flexible hose equipped with swaged end fittings, the entire assembly must be replaced. Obtain a new hose assembly of the correct size and length, complete with factoryinstalled end fittings.
When failure occurs in hose equipped with reusable end fittings, a replacement line can be fabricated with the use of such tooling as may be necessary to comply with the assembly instructions of the manufacturer.
Assembly of Sleeve-Type Fittings Sleeve-type end fittings for flexible hose are detachable and may be reused if determined to be serviceable. The inside diameter of the fitting is the same as the inside diameter of the hose to which it is attached. Common sleeve-type fittings are shown in figure 5-17.
To make a hose assembly, select the proper size hose and end fittings. Cut the hose to the correct length using a fine-tooth hacksaw. Place the socket in a vise. Screw the hose into the socket counterclockwise until the hose bottoms on the shoulder of the socket (figure 5-18); then back off one-quarter turn. Lubricate inside of hose and nipple threads liberally. Mark the hose position 114
assembly prior to tightening the cap or plug.
Hose tests, using a gas, are conducted underwater.
In all cases follow the hose manufacturer's instructions for proof-test pressure and fluid to be used when testing a specific hose assembly.
Place the hose assembly in a horizontal position and observe for leakage while maintaining the test pressure. Proof-test pressures should be maintained for at least 30 seconds.
<I T FIGURE 5-18. Assembly of MS fitting to flexible hose.
around the hose at the rear of the socket using a grease pencil or painted line. Insert the nipple into the nut and tighten the nipple and nut on the assembly tool. If an assembly tool is not available, a mating AN815 adapter may be used.
Using a wrench on the assembly tool, screw the nipple into the socket and hose. A ½2- to %-inch clearance between the nut and sleeve is required so that the nut will swivel freely when the assembly tool is removed. After assembly, always make sure all foreign matter is removed from inside the hose by blowing out with compressed air.
Proof-test After Assembly All flexible hose must be proof-tested after assembly by plugging or capping one end of the hose and applying pressure to the inside of the hose assembly. The proof-test medium may be a liquid or a gas. For example, hydraulic, fuel, and oil lines are generally tested using hydraulic oil or water, whereas air or instrument lines are tested with dry, oil-free air or nitrogen. When testing with a liquid, all trapped air is bled from the Instaliation of Flexible Hose Assemblies Flexible hose must not be twisted on installation, since this reduces the life of the hose considerably and may also loosen the fittings. Twisting of the hose can be determined from the identification stripe running along its length. This stripe should not spiral around the hose.
Flexible hose should be protected from chafing by wrapping it with tape, but only where necessary.
The minimum bend radius for flexible hose varies according to size and construction of the hose and the pressure under which the hose is to operate. Bends that are too sharp will reduce the bursting pressure of flexible hose considerably below its rated value (figure 5-19).
Flexible hose should be installed so that it will be subject to a minimum of flexing during operation. Although hose must be supported at least every 24 inches, closer supports are desirable. A flexible hose must never be stretched tightly between two fittings. From 5 percent to 8 percent of its total length must be allowed for freedom of movement under pressure. When under pressure, flexible hose contracts in length and expands in diameter.
Protect all flexible hose from excessive temperatures, either by locating the lines so they will not be affected or by installing shrouds around them.
INSTALLATION OF RIGID TUBING Before installing a line assembly in an aircraft, inspect the line carefully. Remove dents and scratches, and be sure all nuts and sleeves are snugly mated and securely fitted by proper flaring of the tubing. The line assembly should be clean and free of all foreign matter.
Connection and Torque Never apply compound to the faces of the fitting or the flare, for it will destroy the metal-to-metal contact between the fitting and fare, a contact 115
PLANNING HOSE LINE INSTALLATIONS WRONG
WRONG RIGHT
2... observe linear stripe. The hose must not be twisted. High pressures applied to a twisted hose may cause failure or loosen the nut.
RIGHT
1... provide slack or bend in the hose line to provide for changes in length that will occur when pressure is applied.
WRONG
WRONG RIGHT RIGHT
3.., relieve sharp bends, avoid strain or hose collapse nd make cleaner installations by using Aeroquir elbows or other adapter fittings. Provide as large a bend radius as possible. Never use less than the recommended minimum bend radius specified for the hose.
4... provide additional bend radius when lines are subject to flexing and remember that the metal end fittings are not flexible. Place line support clamps so as not to restrict hose flexing.
FrcURE 5-19. Flexible hose installation.
which is necessary to produce the seal. Be sure Do not deflect into place that the line assembly is properly aligned before Replace tube assembly tightening the fittings. Do not pull the installation into place with torque on the nut. Correct and Incorrect - Will damage flare or threads, or cause sleeve to incorrect methods of installing flared-tube assemcrack under vibration if tight- blies are illustrated in figure 5-20. Proper torque ened values are given in figure 5-21. It must be remembered that these torque values are for flared- Incorrect - May pull off or type fittings only. Always tighten fittings to the distort flare if tightened correct torque value when installing a tube assembly. Overtightening a fitting may badly damage Correctly fitted or completely cut off the tube flare, or it may ruin and tightened the sleeve or fitting nut. Failure to tighten suf- .025 clearance between Flare and shoulder allow the line to blow out of the assembly or to ficiently also can be serious, as this condition may before tightening leak under system pressure.
The use of torque wrenches and the prescribed torque values prevents overtightening or under- FIGURE 5-20. Correct and incorrect methods of tightening. If a tube fitting assembly is tightened properly, it can be removed and retightened many tightening flared fittings. times before re-flaring is necessary.
Hose End Fittings Minimum bend and Hose Assemblies radii (inches) Aluminum Alloy Tubing, Bolt, Steel Tubing, Bolt MS28740 or Equivalent Alum.
Fitting or Nut Fitting or Nut End Fitting alloy Tubing Fitting Bolt Torque Torque 1100-H14 O.D. or Nut Size inch-Ibs. inch--Ibs. Minimum Maximum 5052-0 Steel 1/8 -2 3/8 20 - 30 3/16 -3 30 - 40 90 - 100 70 120 7/16 21/32 1/4 40 - 65 135 - 150 100 250 9/16 7/8 5/16 60 85 180 - 200 210 420 3/4 1 1/8 3/8 75 - 125 270 - 300 300 480 15/16 1 5/16 1/2 150 - 250 450 - 500 500 850 1 1/4 1 3/4 5/8 --10 200 - 350 650 - 700 700 1150 1 1/2 2 3/16 3/4 - 12 300 - 500 900 - 1000 1 3/4 2 5/8 7/8 -14 500 - 600 1000 - 1100
- 16 500 - 700 1200 - 1400 3 3 1/2 1-1/4 -20 600 - 900 1200 - 1400 3 3/4 4 3/8 1-1/2 -24 600-- 900 1500 - 1800 5 5 1/4 I -3/4 -28 850 - 1050 7 6 1/8 -32 950 - 1150 7 FIGURE 5-21. Flared fitting data.
Flareless Tube Installation Tighten the nut by hand until an incrcase in resistance to turning is encountered. Should it be impossible to run the nut down with the fingers, use a wrench, but be alert for the first signs of bottoming. It is important that the final tightening commence at the point where the nut just begins to bottom.
With a wrench, turn the nut % turn (one flat on a hex nut). Use a wrench on the connector to prevent it from turning while tightening the nut.
After the tube assembly is installed, the system should be pressure tested. Should a connection leak, it is permissible to tighten the nut an additional % turn (making a total of ⅓ turn). If, after tightening the nut a total of ½ turn, leakage still exists, the assembly should be removed and the components of the assembly inspected for scores, cracks, presence of foreign material, or damage from overtightening.
NOTE: Overtightening a flareless-tube nut drives the cutting edge of the sleeve deeply into the tube, causing the tube to be weakened to the point where normal in-flight vibration could cause the tube to shear. After inspection (if no discrepancies are found), reassemble the connections and repeat the pressure test procedures.
CAUTION: Do not in any case tighten the nut beyond ⅓ turn (two flats on the hex nut) ; this is the maximum the fitting may be tightened without the possibility of permanently damaging the sleeve and nut.
Common faults are:
1. Flare distorted into nut threads.
2. Sleeve cracked.
3. Flare cracked or split.
4. Flare out of round.
5. Inside of flare rough or scratched.
6. Fitting cone rough or scratched.
7. Threads of nut or union dirty, damaged or broken.
Some manufacturers service instructions will specify wrench torque values for flareless tubing installations (e.g., see figure 5-22).
PLUMBING ASSEMBLY PRECAUTIONS Make certain that the material in the fittings used is similar to that of the tubing; for example, use steel fittings with steel tubing and aluminum alloy fittings with aluminum alloy tubing. Brass fittings plated with cadmium may be used with aluminum alloy tubing.
For corrosion prevention, aluminum alloy lines and fittings are usually anodized. Steel lines and fittings, if not stainless steel, are plated to prevent rusting or corroding. Brass and steel fittings are usually cadmium plated, although some may come plated with nickel, chromium, or tin.
To ensure proper sealing of hose connections and to prevent breaking hose clamps or damaging the hose, follow the hose clamp tightening instructions carefully. When available, use the hose clamp torque-limiting wrench. These wrenches are available in calibrations of 15 and 25 inch-pounds. In the absence of torque-limiting wrenches, the fingertight-plus-turns method should be followed. Be- 117
WRENCH TORQUE FOR 304 1/8 H STEEL TUBES Tube Wrench Torque Outside Diameter Wall Thickness Inch-Pounds 3/16 0.016 90 - 110 3/16 0.020 90 - 110 1/4 0.016 110 - 140 1/½ 0.020 110 - 140 5/16 0.020 100 - 120 3/8 0.020 170 - 230 3/8 0.028 200-250 1/2 0.020 300 - 400 1/2 0.028 400 - 500 1/2 0.035 500 - 600 5/8 0.020 300 - 400
0.035 600 - 700 5/8 0.042 700 - 850 3/4 0.028 650 - 800 3/4 0.049 800 - 960
0.020 800 - 950
0.065 1600 - 1750 WRENCH TORQUE FOR 304-1A or 3471A STEEL T IBES 3/8 0.042 145 - 175 1/2 0.028 300 - 400 1/2 0.049 500 - 600
0.035 750 - 900 WRENCH TORQUE FOR 6061-T6 OR T4 TUBES 1/4 0.035 110 - 140 3/8 0.035 145 - 175 1/2 0.035 270 - 330 1/2 0.049 320 - 380 5/8 0.035 360 - 440 5/8 0.049 425 -- 525 3/4 0.035 380 - 470
0.035 750 - 900 1 1/4 0.035 900 - 1100 FIGURE 5-22. Torque values for flareless fittings.
Hose clamp tightening, finger-tight-plus turns method cause of the variations in hose clamp design and Initial installation Worm screw type Clamps-radiat and hose structure, the values given in figure 5-23 are only per inch lamp 10 threads other type-28 threads per inch approximate. Therefore, use good judgment when Self sealing hose approximately 15 Finger-tight-plus 2 complete turns 2-1/2 complete turns Finger-tight-plus connections are subject to "cold flow" or a setting tightening hose clamps by this method. Since hose inch-pounds process, a followup tightening check should be All other aircraft Finger-tight Finger-tight made for several days after installation.
hose approximately 25 Plus 1¼ complete Plus 2 complete turns inch-pounds turns Retightening of Hose Clamps If Clamps do not seal at specified tightening, examine hose connections and replace parts as necessary The above is for initial installation and should not be used for loose clamps For re-tightening loose hose clamps in service proceed as follows:
Non-self-scaling hose - If the clamp screw cannot be tightened with the fingers do not disturb unless leakage is evident. If leakage is present tighten 1/4 turn.
2. Self-sealing hose - If looser than finger-tight, tighten to finger tight and add 1/4 turn.
FIGURE 5-23. Hose clamp tightening.
SUPPORT CLAMPS Support clamps are used to secure the various lines to the airframe or powerplant assemblies.
Several types of support clamps are used for this purpose. The rubber-cushioned and plain are the most commonly used clamps. The rubber-cushioned clamp is used to secure lines subject to vibration;
the cushioning prevents chafing of the tubing. The plain clamp is used to secure lines in areas not subject to vibration.
A Teflon-cushioned clamp is used in areas where the deteriorating effect of Skydrol ® 500, hydraulic fluid (MIL-0-5606), or fuel is expected. However, because it is less resilient, it does not provide as 118
good a vibration-damping effect as other cushion materials. Tube OD (in.) Distance between supports (in.)
Use bonded clamps to secure metal hydraulic, Aluminum Alloy Steel fuel, and oil lines in place. Unbonded clamps 9½ 11½ should be used only for securing wiring. Remove 12 13½ 14 16 any paint or anodizing from the portion of the tube 15 18 at the bonding clamp location. Make certain that 16½ 19 23 20 clamps are of the correct size. Clamps or support- 22 25% ing clips smaller than the outside diameter of the hose may restrict the flow of fluid through the hose. 1 26% 24 30 27½ All plumbing lines must be secured at specified intervals. The maximum distance between sup- FIGURE 5-24. Maximum distance between ports for rigid fluid tubing is shown in figure 5-24. supports for fluid tubing.
119 ......
CHAPTER 6
AIRCRAFT HARDWARE, MATERIALS, AND PROCESSES
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.
Identification Most items of aircraft hardware 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.
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. 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.
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 deñned grip length. 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.
Classification of Threads Aircraft bolts, screws, and nuts are threaded in either 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. In the 1-inch-diameter size, the NF thread specified 14 threads per inch (1-14NF), while the UNF thread specifies 12 threads per inch (1-12UNF). Both type 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 4-inch-diameter bolt has 28 threads in 1 inch of its threaded length.
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, and Class 4 is a close fit. Aircraft bolts are almost always manufactured in the Class 3, medium fit.
* Standard head bolt Drilled hey head bolt ank head bolt Internal hex head bolt Evebolt Clevis bolt 4037
SOCIA M COOPER
AN STANDARD AN STANDARD AN STANDARD AN STANDARD AN STANDARD STEEL BOLT STEEL BOLT STEEL BOLT STEFI. BOLT STEEL BOLT (CORROSION RESISTANT) SPEC
AN STANDARD AN STANDARI AN STANDARD AN STANDARD SPECIAL BOLT
STEEL BOLT STEEL BOUT STEEL BOLT STEEL BOLT (63-59131
SPECIAL BOLT DRILLED HEAD SPECIAL BOLT NAS CLOSE ALUMINUM
BOLT TOLERANCE BOLT ALLOY (2021) BOLT
MAGNETICALLY ORANCE-DYED CLEVIS BOLT REWORKED BOLT LOW STRENCTH INSPECTED MAGNETIC INS. MATERIAL BOLT FIGURE 6-1. Aircraft bolt identification.
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 thread fit for ease of assembly.
Bolts and nuts are also produced with righthand and left-hand threads. A right-hand thread tightens when turned clockwise; a left-hand thread tightens when turned counterclockwise.
AIRCRAFT BOLTS Aircraft bolts are fabricated from cadmium- or zinc-plated corrosion-resistant steel, unplated corrosion-resistant steel, and anodized aluminum alloys. Most bolts used in aircraft structures are either general-purpose, AN bolts, or NAS internalwrenching or close-tolerance bolts, or MS bolts.
In certain cases, aircraft manufacturers make bolts of different dimensions or greater strength than the standard types. Such bolts are made for a particular application, and it is of extreme importance to use like bolts in replacement.
Special bolts are usually identified by the letter "S" stamped on the head.
AN bolts come in three head styles-hex-head, clevis, and eyebolt (see figure 6-1). NAS bolts are available in hex-head, internal-wrenching, and countersunk head styles. MS bolts come in hexhead and internal-wrenching styles.
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 (.006- inch clearance for a ⅛-inch hole, and other sizes in proportion).
Alloy steel bolts smaller than No. 10-32 and 122
aluminum alloy bolts smaller than ¼-inch 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. Aluminum alloy nuts may No leaded 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.
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.
Close-Tolerance Bolts This type of bolt is 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).
Internal-Wrenching Bolts AN-type aircraft bolts can be identified by the code markings on the boltheads. 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. AN standard steel bolts are marked with either a raised dash 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 ANDDSA, the "AN" designates that it is an Air Force-Navy Standard bolt, the "3' indicates the diameter in sixteenths of an inch (6), the "DD" indicates the material is 2024 aluminum 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 (g), 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.
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 These 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 bolthole must be slightly countersunk to seat the large corner radius of the shank at the head.
In Dural material, a special heat-treated washer must be used to provide an adequate bearing surface for the head. The head of the internalwrenching 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.
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.
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.
SPECIAL-PURPOSE BOLTS Bolts designed for a particular application or use are classified as special-purpose bolts. Clevis bolts, eyebolts, Jo-bolts, and lock bolts are specialpurpose bolts.
Clevis Bolts The head of a clevis bolt is round and is either slotted to receive a common screwdriver or recessed to receive a crosspoint screwdriver. This type of bolt is used only where shear loads occur and never in tension. It is often inserted as a mechanical pin in a control system.
Eyebolt This type of special-purpose bolt is used where external tension loads are to be applied. The eye 123
is designed for the attachment of such devices as the fork of a turnbuckle, a clevis, or a cable shackle. The threaded end may or may not be drilled for safetying.
Jo-Bolt Jo-bolt is a trade name for an internally threaded three-piece rivet. The Jo-bolt consists of three parts-a threaded steel alloy bolt, a threaded steel nut, and an expandable stainless steel sleeve. The parts are factory preassembled.
As the Jo-bolt is installed, the bolt is turned while the nut is held. This causes the sleeve to expand over the end of the nut, forming the blind head and clamping against the work. When driving is complete, a portion of the bolt breaks off. The high-shear and tensile strength of the Jo-bolt makes it suitable for use in cases of high stresses where some of the other blind fasteners would not be practical. Jo-bolts are often a part of the permanent structure of late-model aircraft. They are used in areas which are not often subjected to replacement or servicing. (Because it is a threepart fastener, it should not be used where any part, in becoming loose, could be drawn into the engine air intake.) Other advantages of using Jo-bolts are their excellent resistance to vibration, weight saving, and fast installation by one person.
Presently, Jo-bolts are available in four diameters: The 200 series, approximately 16-inch in diameter; the 260 series, approximately ¼-inch in diameter; the 312 series, approximately 6-inch in diameter; and the 375 series, approximately 3 g-inch in diameter. Jo-bolts are available in three head styles which are: F(flush), P(hex-head), and FA (flush millable).
Lockbolts The lockbolt combines the features of a highstrength bolt and rivet, but it has advantages over both. The lockbolt is generally used in wing-splice fittings, landing-gear fittings, fuel-cell fittings, longerons, beams, skin-splice plates, and other major structural attachments. It is more easily and quickly installed than the conventional rivet or bolt and eliminates the use of lockwashers, cotter pins, and special nuts. Like the rivet, the lockbolt requires a pneumatic hammer or "pull gun" for installation; when installed, it is rigidly and permanently locked in place. Three types of lockbolts are commonly used, the pull type, the stump type, and the blind type. (See figure 6-2.)
Pull type. Pull-type lockbolts are used mainly in aircraft primary and secondary structures. They Pull type stump type Blind type FIGURE 6-2. Lockbolt types.
are installed very rapidly and have approximately one-half the weight of equivalent AN steel bolts and nuts. A special pneumatic "pull gun" is required to install this type of lockbolt. Installation can be accomplished by one person since bucking is not required.
Stump type. Stump-type lockbolts, although they do not have the extended stem with pull grooves, are companion fasteners to pull-type lockbolts. They are used primarily where clearance will not permit installation of the pull-type lockbolt. A standard pneumatic riveting hammer (with a hammer set attached for swaging the collar into the pin-locking say tor grooves) and a bucking bar are tools necessary for the installation of stump-type lockbolts.
Blind type. Blind-type lockbolts come as complete units or assemblies. They have exceptional strength and sheet pull-together characteristics.
Blind lockbolts are used where only one side of the work is accessible and, generally, where it is difficult to drive a conventional rivet. This type of lockbolt is installed in the same manner as the pulltype lockbolt.
Common features. Common features of the three types of lockbolts are the annular locking grooves on the pin and the locking collar which is swaged into the pin's lock grooves to lock the pin in tension. The pins of the pull- and blind-type lockbolts are extended for pull installation. The extension is provided with pulling grooves and a tension breakoff groove.
Composition. The pins of pull- and stump-type GRIP GRIP RANGE GRIP GRIP BANGE lockbolts are made of heat-treated alloy steel or NO. NO.
high-strength aluminum alloy. Companion collars Min. Max. Min. Max.
are made of aluminum alloy or mild steel. The .031 .094 17 1.031 1.094 blind lockbolt consists of a heat-treated alloy steel -094 . 156 18 1.094 1.156 pin, blind sleeve and filler sleeve, mild steel collar, 3 4 . 156 .219 . 219 281 19 20 1.156 1.219 1.219 281 and carbon steel washer. 5 .281 - 344 21 1.281 Substitution. Alloy steel lockbolts may be used 6 7 .406 .344 .469 406 22 23 1.406 1.344 ..469 to replace steel hi-shear rivets, solid steel rivets, or 8 -469 .531 24 1.469 1.531 AN bolts of the same diameter and head type. Aluminum alloy lockbolts may be used to replace 10 9 .594 .656 .531 .594 - 656 718 26 25 27 1.531 1.594 1.656 1.594 1.656 1.718 solid aluminum alloy rivets of the same diameter 12 .718 . 781 28 1.718 1.781 and head type. Steel and aluminum alloy lock- 13 14 843 781 .906 .843 29 30 1.781 1.843 1.843 1.906 bolts may also be used to replace steel and 20241 15 .906 _968 31 1.906 1.968 aluminum alloy bolts, respectively, of the same 16 .968 1.031 32 33 2.031 1.968 2.094 2.031 diameter. Blind lockbolts may be used to replace solid aluminum alloy rivets, stainless steel rivets, or all blind rivets of the same diameter. FIGURE 6-3. Pull- and stump-type lockbolt grip ranges.
Numbering system. The numbering systems tor the various types of lockbolts are explained by the following breakouts (see figure 6-4).
Pull-type Jockbolt- Lockbolt collar- ALPP HT 8 8 LC C 8 Grip length in 16ths of an inch. Diameter of pin in 32nds of an inch. *Material-- C = 24ST aluminum alloy (green color).
F = 61ST aluminum alloy (plain color).
-Body diameter in 32nds of an K = mild steel (cadmium plated).
inch. -Lockbolt collar.
Pin materials-- K = 75S-T6 aluminum alloy.
T = heat-treated alloy steel.
* Use 255T aluminum alloy with heat-treated alloy lockbolts only.
Use 61ST aluminum alloy with 75ST aluminum alloy lockbolts only.
Use mild steel with heat-treated alloy steel lockbolts for high temperature applications ouly.
Class fit- II = hole filling (interference fit).
N = non-hole filling (clearance fit).
-Head type- ACT 509 = close tolerance AN 509 C-sink head.
ALPP = pan head.
ALPB = brazier head.
ALP509 = standard AN-509 C-sink head.
ALP426 = standard AN-426 C-sink head.
Blind-type lockbolt- BL 8 [Grip length in 16ths of an inch, 132 inch.
-Diameter in 32nds of an inch.
Stump-type lockbolt- ALSE E 8 8
- Grip length in 16ths of an inch.
-Body diameter in 32nds of an inch.
-Pin material- E = 75S-T6 aluminum alloy.
T = heat-treated alloy steel.
Head type- ASCT509 = close tolerance AN-509 C-sink head.
ALSE = flat head type.
ALS509 = standard AN-509 C-sink head.
ALS126 = standard AN-426 C-sink head.
-Blind lockbolt.
FIGURE 6-4. Lockbolt numbering system.
¼-inch Diameter 6-inch Diameter mended: The pin may then be driver out with a drift punch.
GRIP GRIP RANGE GRIP GRIP RANGE NO. NO.
Min. Max. Min. Max. AIRCRAFT NUTS .031 .094 . 156 . 094 . 156 .094 . 156 .219 and sizes. They are made of cadmium-plated Aircraft nuts are made in a variety of shapes . 156 219 .219 .281 .219 281 .281 344 carbon steel, stainless steel, or anodized 2024T .281 .344. 344 .406 aluminum alloy, and may be obtained with either
- 344 406 .406 .469 .406 469 .469 531 right- or left-hand threads. No identifying marking .469 531 9 531 .594 or lettering appears on nuts. They can be identified 531 594 .. 656 594 10 11 .656 .594 .718 656 only by the characteristic metallic luster or color 11 . 656 718 12 718 .781 of the aluminum, brass, or the insert when the 12 718 781 13 .781 .843 nut is of the self-locking type. They can be further 13 .781 - 843 14 .843 .906 14 .843 15 .906 968 identified by their construction.
15 16 968 .906 1.031 16 1.031 - 968 1.094 1. 05 Aircraft nuts can be divided into two general 17 1.031 094. 1.094 1.156 groups: Non-self-locking and self-locking nuts.
18 1.094 1.156 . 156 .219 Non-self-locking nuts are those that must be 19 20 1.156 1.219 1.219 1 .281 . 219 .281 281 .343 safetied by external locking devices, such as
1.281 1.343 _343 .406 .343 406 .406 469 cotter pins, safety wire, or locknuts. Self-locking 23 1.406 1.469 24 1.460 1.531 nuts contain the locking feature as an integral 24 25 1.469 1.531 1.531 1.594 part.
FicURE 6-5. Blind-type lockbolt grip ranges.
Grip Range. The bolt grip range required for any application should be determined by measuring the thickness of the material with a hook scale inserted through the hole. Once this measurement is determined the correct grip range can be selected by referring to the charts provided by the rivet manufacturer. Examples of grip-range charts are shown in figures 6-3 and 6-5.
When installed, the lockbolt collar should be swaged substantially throughout the complete length of the collar. The tolerance of the broken end of the pin relative to the top of the collar must be within the following dimensions:
Pin Tolerance diameter Below Above 16 - 079 . 032 .079 . 050
- 079 - 050
- 079 - 060 When removal of a lockbolt becomes necessary, remove the collar by splitting it axially with a sharp, cold chisel. Be careful not to break out or deform the hole. The use of a backup bar on the opposite side of the collar being split is recom- 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 check nut are the non-self-locking type.
(See figure 6-6.)
The castle nut, AN310, is used with drilledshank AN hex head bolts, clevis bolts, eyebolts, drilled head bolts, or studs. It is fairly rugged and can withstand large tensional loads. Slots (called castellations) in the nut are designed to accommodate a cotter pin or lock wire for safety.
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.
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 check nut 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 126