CHAPTER 4. AIRCRAFT PAINTING AND FINISHING-(Cont.)
Common Paint Troubles Painting Trim and Identification Numbers Decalcomanias (Decals) CHAPTER 5. AIRCRAFT STRUCTURAL REPAIRS Basic Principles of Sheet Metal Repair General Structural Repair Inspection of Damage Classification of Damage Stresses in Structural Members 131 Special Tools and Devices for Sheet Metal Metalworking Machines Forming Machines Forming Operations and Terms Making Straight Line Bends Setback Making Layouts Hand Forming Rivet Layout Rivet Installation Preparation of Rivet Holes Driving Rivets ..
Rivet Failures Removing Rivets Special Rivets - Self-Plugging (Friction Lock) Rivets Self-Plugging (Mechanical Lock) Rivets Pull-Thru Rivets Rivnuts Dill Lok-Skrus and Lok-Rivets Deutsch Rivets Hi-Shear Rivets Specific Repair Types Structural Sealing Metal Bonded Honeycomb Construction Features Damage - Repairs Repair Materials Potted Compound Repair Glass Fabric Cloth Overlay Repairs One Skin and Core Repair Procedures Plastics - Transparent Plastics - Storage and Protection Forming Plastics ---- Installation Procedures Laminated Plastics - Fiber Glass Components Radomes Wooden Aircraft Structures _- Inspection of Wooden Structures - Service and Repair of Wooden Structures Glues Gluing vii
CHAPTER 5. AIRCRAFT STRUCTURAL REPAIRS-(Cont.)
Spliced Joints -- 234 Plywood Skin Repairs --. 235 Spar and Rib Repair -- 242 Bolt and Bushing Holes 244 Rib Repairs ------ 245 CHAPTER 6. AIRCRAFT WELDING General _ 247 Oxyacetylene Welding Equipment 248 Welding Positions ----- 255 Welded Joints --- 255 Expansion and Contraction of Metals 257 Correct Forming of a Weld 258 Oxyacetylene Welding of Ferrous Metals 258 Welding Nonferrous Metals Using Oxyacetylene 260 Titanium 262 Cutting Metal Using Oxyacetylene 263 Brazing Methods -- 264 Soft Soldering 265 Electric Arc Welding --. 266 Welding Procedures and Techniques Welding of Aircraft Steel Structures 276 CHAPTER 7. ICE AND RAIN PROTECTION General Pneumatic Deicing Systems Deicer Boot Construction Deicing System Components Pneumatic Deicing System Maintenance 291 Thermal Anti-Icing Systems 293 Pneumatic System Ducting 296 Ground Deicing of Aircraft Windshield Icing Control Systems 300 Water and Toilet Drain Heaters Rain Eliminating Systems Maintenance of Rain Eliminating Systems CHAPTER 8. HYDRAULIC AND PNEUMATIC POWER SYSTEMS Aircraft Hydraulic Systems Hydraulic Fluid ----. 309 Types of Hydraulic Fluids 310 Phosphate Ester Base Fluids 311 Filters 313 Basic Hydraulic System - 315 Reservoirs --------- 316 Pressure Regulation - 323 Actuating Cylinders -- 328 Selector Valves 329 Aircraft Pneumatic Systems 331 Pneumatic System Components 334 Typical Pneumatic Power System 338 CHAPTER 9. LANDING GEAR SYSTEMS General _. 341 Main Landing Gear Alignment, Support, Retraction 348 vili
CHAPTER 9. LANDING GEAR SYSTEMS-(Cont.)
Emergency Extension Systems -- Landing Gear Safety Devices Nosewheel Steering System .
Shimmy Dampers Brake Systems Brake Assemblies Inspection and Maintenance of Brake Systems Aircraft Landing Wheels -- Aircraft Tires - 377 Aircraft Tire Maintenance 379 Tire Inspection-Mounted On Wheel 381 Tire Inspection-Tire Demounted 382 Tube Inspection Mounting and Demounting Causes of Air Pressure Loss in Tubeless Aircraft Tires The Wheel Good Pressure Gage Practice - Repairing Operating and Handling Tips.
Tube Repair 396 Sidewall-Inflated Aircraft Tires 396 Tire Inspection Summary Antiskid System Landing Gear System Maintenance 400 CHAPTER 10. FIRE PROTECTION SYSTEMS General Fire Detection Systems Types of Fires - Fire Zone Classification 412 Extinguishing Agent Characteristics Fire Extinguishing Systems 417 Reciprocating Engine Conventional CO2 System 417 Turbojet Fire Protection System - 419 Turbine Engine Fire Extinguishing System 420 Turbine Engine Ground Fire Protection Fire Detection System Maintenance Practices Fire Detection System Troubleshooting Fire Extinguisher System Maintenance Practices Fire Prevention and Protection -.
Cockpit and Cabin Interiors -.
Smoke Detection Systems - CHAPTER 11. AIRCRAFT ELECTRICAL SYSTEMS General -.
Lacing and Tying Wire Bundles - Cutting Wire and Cable Emergency Splicing Repairs Connecting Terminal Lugs to Terminal Blocks Bonding and Grounding Connectors Conduit -- Electrical Equipment Installation Aircraft Lighting Systems ------ Maintenance and Inspection of Lighting Systems ix
CHAPTER 12. AIRCRAFT INSTRUMENT SYSTEMS General --. 469 Instrument Cases 469 Dials -- 469 Range Markings 470 Instrument Panels ------ 470 Repair of Aircraft Instruments 471 Aircraft Pressure Gages - 471 Pitot-Static System ----- 474 Maintenance of Pitot-Static Systems 481 Turn-and-Bank Indicator 482 Synchro-Type Remote Indicating Instruments 483 Remote-Indicating Fuel and Oil Pressure Gages 485 Capacitor-Type Fuel Quanity System 485 Angle-of-Attack Indicator 487 Tachometers -- 488 Synchroscope 491 Temperature Indicators 491 Ratiometer Electrical Resistance Thermometer 497 Fuel Flowmeter Systems - 497 Gyroscopic Instruments - 499 Sources of Power for Gyro Operation 501 Vacuum-Driven Attitude Gyros 504 Pressure-Operated Gyros 506 Vacuum System Maintenance Practices 506 Electric Attitude Indicator 507 Autopilot System 511 Basic Autopilot Components 513 Flight Director Systems - 518 Autopilot System Maintenance . 516 CHAPTER 13. COMMUNICATIONS AND NAVIGATION SYSTEMS General - 519 Basic Radio Principles -- 519 Basic Equipment Components 520 Power Supply --- 522 Communication Systems - 522 Airborne Navigation Equipment 524 VHF Omnirange System 524 Instrument Landing System 525 Distance-Measuring Equipment 528 Automatic Direction Finders 529 Radar Beacon Transponder 530 Doppler Navigation Systems 530 Inertial Navigation System 531 Airborne Weather Radar System 532 Radio Altimeter -- 533 Emergency Locator Transmitter (ELT) 533 Installation of Communication and Navigation Equipment 534 Reducing Radio Interference 536 Installatoin of Aircraft Antenna Systems 537 CHAPTER 14. CABIN ATMOSPHERE CONTROL SYSTEM Need for Oxygen 539 Compusition of the Atmosphere 539 Pressurization 541 Air Conditioning and Pressurization Systems 543
CHAPTER 14. CABIN ATMOSPHERE CONTROL SYSTEM—(Cont.)
Basic Requirements Sources of Cabin Pressure Supercharger Instruments Pressurization Valves Cabin Pressure Control System - 551 Air Distribution 556 Air Conditioning System Heating Systems Combustion Heaters Maintenance of Combustion Heater Systems 564 Cooling Systems -- Air Cycle Cooling System Air Cycle System Component Operation 568 Electronic Cabin Temperature Control System 574 Electronic Temperature Control Regulator Vapor Cycle System (Freon) --- 576 Freon System Components _----- 577 Description of a Typical System 580 Air Conditioning and Pressurization System Maintenance 583 Cabin Pressurization Operational Checks 585 Cabin Pressurization Troubleshooting 586 Oxygen Systems General ---- 587 Portable Oxygen Equipment 587 Smoke Protection Equipment 588 Oxygen Cylinders _------ 588 Solid State Oxygen Systems 589 Oxygen Plumbing -. 591 Oxygen Valves - 592 Regulators --- 594 Oxygen System Flow Indicators -- •597 Pressure Gages -- 597 Oygen Masks --- 597 Servicing Gaseous Oxygen Systems 598 Prevention of Oxygen Fires or Explosions 600
GENERAL The airframe of a fixed-wing aircraft is generally considered to consist of five principal units, the fuselage, wings, stabilizers, fright control surfaces, and landing gear. Helicopter airframes consist of the fuselage, main rotor and related gearbox, tail rotor (on helicopters with a single main rotor), and the landing gear.
The airframe components are constructed from a wide variety of materials and are joined by rivets, bolts, screws, and welding or adhesives. The aircraft components are composed of various parts called structural members (i.e., stringers, longerons, ribs, bulkheads, etc.). Aircraft structural members are designed to carry a load or to resist stress. A single member of the structure may be subjected to a combination of stresses. In most cases the structural members are designed to carry end loads rather than side loads: that is, to be subjected to tension or compression rather than bending.
Strength may be the principal requirement in certain structures, while others need entirely different qualities. For example, cowling, fairing, and similar parts usually are not required to carry the stresses imposed by flight or the landing loads.
However, these parts must have such properties as neat appearance and streamlined shapes.
MAJOR STRUCTURAL STRESSES In designing an aircraft, every square inch of wing and fuselage, every rib, spar, and even each metal fitting must be considered in relation to the physical characteristics of the metal of which it is made. Every part of the aircraft must be planned to carry the load to be imposed upon it. The determination of such loads is called stress analysis. Although planning the design is not the function of the aviation mechanic, it is, nevertheless, important that he understand and appreciate the stresses involved in order to avoid changes in the original design through improper repairs.
There are five major stresses to which all aircraft are subjected (figure 1-1) :
CHAPTER 1
AIRCRAFT STRUCTURES
(1) Tension.
(2) Compression.
(3) Torsion.
(4) Shear.
(5) Bending.
The term "streas" is often used interchangeably with the word "strain." Stress is an internal force of a substance which opposes or resiste deformation. Strain is the deformation of a material or substance. Stress, the internal force, can cause Tension (figure l-la) is the stress that resists a force that tenda to pull apart. The engine pulls the aircraft forward, but air resistance tries to hold it back. The result is tension, which tries to stretch the aircraft. The tensile strength of a material is measured in p.s.i. (pounds per square inch) and is calculated by dividing the load (in pounds) required to pull the material apart by its cross-sectional area (in square inches).
Compression (figure 1-1b) is the stress that resists a crushing force. The compressive strength of a material is also measured in p.s.i. Compression is the stress that tends to shorten or squeeze aircraft Torsion is the stress that produces twisting (figure 1-1c). While moving the aircraft forward, the engine also tends to twist it to one side, but other aircraft components hold it on course. Thus, torsion is created. The torsional strength of a material is ite resistance to twisting or torque.
Shear is the stress that resists the force tending to cause one layer of a material to slide over an adjacent layer. Two riveted plates in tension (figure 1-1d) subject the rivets to a shearing force.
Usually, the shearing strength of a material is either equal to or less than its tensile or compressive strength. Aircraft parts, especially screws, bolts, and rivets, are often subject to a shearing force.
Bending stress is a combination of compression and tension. The rod in figure I-le has been shortened (compressed) on the inside of the bend and stretched on the outside of the bend.
(a) Tension
(b) Compression
(c) Torsional (d) Shear Tension outside of bond Bent structural memb Shear along imaginary line (dotted) Compression inside of bend
(e) Bending (the combiuation stress) FIGURE 1-1. Five stresses acting on an aircraft.
FIXED-WING AIRCRAFT The principal components of a single-engine, propeller-driven aircraft are shown in figure 1-2.
Figure 1-3 illustrates the structural components of a typical turbine powered aircraft. One wing and the empennage assemblies are shown exploded into the many components which, when assembled, form major structural units.
FUSELAGE The fuselage is the main structure or body of the aircraft. It provides space for cargo, controls, accessories, passengers, and other equipment. In singleengine aircraft, it also houses the powerplant. In multi-engine aircraft the engines may either be in the fuselage, attached to the fuselage, or suspended from the wing structure. They vary principally in size and arrangement of the different compartments.
There are two general types of fuselage construction, the truss type, and the monocoque type. A truss is a rigid framework made up of members such as beams, struts, and bars to resist deformation by applied loads. The truss-framed fuselage is generally covered with fabric.
Truss Type The truss type fuselage frame (figure 1-4) is usually constructed of steel tubing welded together in such a manner that all members of the truss can carry both tension and compression loads. In some 2
Vertical stabilizer Horizontal Wing stabilizer -Rudder Right aileron Elevator Empennage Nacelle Fuselage Left aileron Landing gear
- Propeller Wing FIGURE 1-2. Aircraft structural componenta, aircraft, principally the light, single-engine models, truss fuselage frames are constructed of aluminum alloy and may be riveted or bolted into one piece, with cross-bracing achieved by using solid rods or tubes.
Monocoque Type The monocoque (single shell) fuselage relies largely on the strength of the skin or covering to carry the primary stresses. The design may be divided into three classes: (1) Monocoque, (2) semimonocoque, or (3) reinforced shell. The true monocoque construction (figure 1-5) uses formers, frame assemblies, and bulkheads to give shape to the fuselage, but the skin carries the primary streases. Since no bracing members are present, the skin must be strong enough to keep the fuselage rigid. Thus, the biggest problem involved in monocoque construction is maintaining enough strength while keeping the weight within allowable limits.
To overcome the strength/weight problem of monocoque construction, a modification called semimonocoque construction (figure 1-6) was developed.
In addition to formers, frame assemblies, and bulkheads, the semimonocoque construction has the skin reinforced by longitudinal members. The reinforced shell has the skin reinforced by a complete framework of structural members. Different portions of the same fuselage may belong to any one of the three classes, but most aircraft are considered to be of semimonocoque type construction.
Semimonocoque Type The semimonocoque fuselage is constructed primarily of the alloys of aluminum and magnesium, although steel and titanium are found in areas of high temperatures. Primary bending loads are taken by the longerons, which usually extend across several points of support. The longerons are supplemented by other longitudinal members, called stringers. Stringers are more numerous and lighter in weight than longerons. The vertical structural members are referred to as bulkheads, frames, and formers. The heaviest of these vertical members are located at intervals to carry concentrated loads and at points where fittings are used to attach other units, such as the wings, powerplants, and stabiliz-
Vertical stabilizer Rudder Fuselage section Tail cone Elevator Horizontal stabilizer /Ventral fin Wing flap Inboard aileron Spoiler
•Outboard aileron Nose Wing tip Nose gear Main landing gear Pylon Wing leading Wing section Wing center section or. strut edge Powerplant FreuRE 1-3. Typical structural components of a turbine powered aircraft.
Longeron (tubular steel) rons and serve as fill-ins. They have some rigidity, Diagonal web members but are chiefly used for giving shape and for attach- (tubular steel) ment of the skin. The strong, heavy longerons hold the bulkheads and formers, and these, in turn, hold the stringers. All of these joined together form a rigid fuselage framework.
There is often little difference between some rings, frames, and formers. One manufacturer may call a brace a former, whereas another may call the same type of brace a ring or frame. Manufacturers' Vertical instructions and specifications for a specific aircraft members web are the best guides.
Stringers and longerons prevent tension and com- FIGURE 1-4. Warren truss of welded tubular steel, pression from bending the fuselage. Stringers are ers. Figure 1-7 shows one form of the semimonocoque design now in use.
The stringers are smaller and lighter than longeusually of a one-piece aluminum alloy construction, and are manufactured in a variety of shapes by casting, extrusion, or forming. Longerons, like stringers, are usually made of aluminum alloy; how.
Pormer Longeron- Gussets Bulkhead Frame FICURE 1-5. Monocoque construction.
FIGURE 1-7. Fuselage structural members.
Skin Formers Stringers Bulkhead FIGURE 1-6. Semimonocoque construction.
ever, they may be of either a one-piece or a built-up construction.
By themselves, the structural members discussed do not give strength to a fuselage. They must first be joined together by such connective devices as gussets, rivets, nuts and bolts, or metal screws. A gusset (figure 1-7) is a type of connecting bracket.
The bracing between longerons is often referred to as web members. They may be installed vertically or diagonally.
The metal skin or covering is riveted to the longerons, bulkheads, and other structural members and carries part of the load. The fuselage skin thickness will vary with the load carried and the stresses sustained at a particular location.
There are a number of advantages in the use of the semimonocoque fuselage. The bulkheads, frames, stringers, and longerons facilitate the design and construction of a streamlined fuselage, and add to the strength and rigidity of the structure.
The main advantage, however, lies in the fact that it does not depend on a few members for strength and rigidity. This means that a semimonocoque fuselage, because of its stressed-skin construction, may withstand considerable damage and still be strong enough to hold together.
Fuselages are generally constructed in two or more sections. On small aircraft, they are generally made in two or three sections, while larger aircraft may be made up of as many as six sections.
Quick access to the accessories and other equipment carried in the fuselage is provided for by numerous access doors, inspection plates, landing wheel wells, and other openings. Servicing diagrams showing the arrangement of equipment and location of accees doors are supplied by the manufacturer in the aircraft maintenance manual.
Location Numbering Systems There are various numbering systems in use to facilitate location of specific wing frames, fuselage bulkheads, or any other structural members on an aircraft. Most manufacturers use some system of station marking; for example, the nose of the aircraft may be designated zero station, and all other stations are located at measured distances in inches behind the zero station. Thus, when a blueprint reads "fuselage frame station 137," that particular frame station can be located 137 in. behind the nose of the aircraft. A typical station diagram is shown in figure 1-8.
To locate structures to the right or left of the center line of an aircraft, many manufacturers consider the center line as a zero station for structural member location to its right or left. With such a 5
008 Fuselage WL = Waterline stations FICURE 1-8. Fuselage stations.
system the stabilizer frames can be designated as being so many inches right or left of the aircraft center line.
The applicable manufacturer's numbering system and abbreviated designations or symbols should always be reviewed before attempting to locate a structural member. The following list includes location designations typical of those used by many manufacturers.
(1) Fuselage stations (Fus, Sta, or 1.S.) are numbered in inches from a reference or zero point known as the reference datum.
The reference datum is an imaginary vertical plane at or near the nose of the aircraft from which all horizontal distances are measured. The distance to a given point is measured in inches parallel to a center line extending throngh the aircraft from the nose through the center of the tail cone. Some manufacturers may call the fuselage station a body station, abbreviated B.S.
(2) Buttock line or butt line (B.L.) is a width measurement left or right of, and parallel to, the vertical center line.
(3) Water line (W.L.) is the measurement of height in inches perpendicular from a horizontal plane located a fixed number of inches below the bottom of the aircraft fuselage.
(4) Aileron station (A.S.) is measured outboard from, and parallel to, the inboard edge of the aileron, perpendicular to the rear beam of the wing.
(5) Flap station (F.S.) is measured perpendicular to the rear beam of the wing and parallel to, and outboard from, the inboard edge of the flap.
(6) Nacelle station (N.C. or Nac. Sta.) is measured either forward of or behind the front spar of the wing and perpendicular to a designated water line.
In addition to the location stations listed above, other measurements are used, especially on large aircraft. Thus, there may be horizontal stabilizer stations (H.S.S.), vertical stabilizer stations (V.S.S.) or powerplant stations (P.P.S.). In every case the manufacturer's terminology and station location system should be consulted before locating a point on a particular aircraft.
WING STRUCTURE The wings of an aircraft are surfaces which are designed to produce lift when moved rapidly through the air. The particular design for any given aircraft depends on a number of factors, such as size, weight, use of the aircraft, desired speed in flight and at landing, and desired rate of climb. The wings of a fixed-wing aircraft are designated left and right, corresponding to the left and right sides of the operator when seated in the cockpit.
The wings of some aircraft are of cantilever design; that is, they are built so that no external bracing is needed. The skin is part of the wing structure and carries part of the wing stresses.
Other aircraft wings use external bracings (struts, wires, etc.) to assist in supporting the wing and carrying the aerodynamic and landing loads. Both aluminum alloy and magnesium alloy are used in wing construction. The internal structure is made up of spars and stringers running spanwise, and
ribs and formers running chordwise (leading edge to trailing edge). The spars are the principal structural members of the wing. The skin is attached to the internal members and may carry part of the wing stresses. During flight, applied loads which are imposed on the wing structure are primarily on the skin. From the skin they are transmitted to the ribs and from the ribs to the spars. The spars support all distributed loads as well as concentrated weights, such as fuselage, landing gear, and, on multi-engine aircraft, the nacelles or pylons.
The wing, like the fuselage, may be constructed in sections. One commonly used type is made up of a center section with outer panels and wing tips.
Another arrangement may have wing stubs as an integral part of the fuselage in place of the center section.
Inspection openings and access doors are provided, usually on the lower surfaces of the wing.
Drain holes are also placed in the lower surface to provide for drainage of accumulated moisture or fluids. On some aircraft built-in walkways are provided on the areas where it is safe to walk or step.
On some aircraft jacking points are provided on the underside of each wing.
Various points on the wing are located by station number. Wing station 0 (zero) is located at the center line of the fuselage, and all wing stations are measured outboard from that point, in inches.
In general, wing construction is based on one of three fundamental designs: (1) Monospar, (2) multi-spar; or (3) box beam. Modifications of these basic designs may be adopted by various manufacturers.
The monospar wing incorporates only one main longitudinal member in its construction. Ribs or bulkheads supply the necessary contour or shape to the airfoil. Although the strict monospar wing is not common, this type of design, modified by the addition of false spars or light shear webs along the trailing edge as support for the control surfaces, is sometimes used.
The multi-spar wing incorporates more than one main longitudinal member in its construction. To give the wing contour, ribs or bulkheads are often included.
The box beam type of wing construction uses two main longitudinal members with connecting bulkheads to furnish additional strength and to give contour to the wing. A corrugated sheet may be Tapered leading edge, Tapered leading straight trailing edge and trailing edges Delta wing Sweptback Straight leading and Straight leading edge, wings trailing edges tapered trailing edge FIcURE 1-9. Typical wing leading and trailing edge ahapes.