Aircraft Wood and Structural Repair .................6-1 Aircraft Wood and Structural Repair.............................6-1 Wood Aircraft Construction and Repairs ......................6-2 Inspection of Wood Structures ..................................6-3 External and Internal Inspection.............................6-3 Glued Joint Inspection ............................................6-4 Wood Condition .....................................................6-5 Repair of Wood Aircraft Structures...............................6-7 Materials.....................................................................6-7 Suitable Wood ............................................................6-7 Defects Permitted ...................................................6-9 Defects Not Permitted.............................................6-9 Glues (Adhesives).................................................6-10 Definition of Terms Used in the Glue Process .....6-10 Preparation of Wood for Gluing...............................6-11 Preparing Glues for Use........................................6-11 Applying the Glue/Adhesive ................................6-11 Pressure on the Joint .............................................6-12 Testing Glued Joints .............................................6-13 Repair of Wood Aircraft Components .....................6-13 Wing Rib Repairs .................................................6-13 Wing Spar Repairs ...............................................6-15 Bolt and Bushing Holes ........................................6-19 Plywood Skin Repairs ..............................................6-20 Fabric Patch ..........................................................6-20 Splayed Patch........................................................6-20 Surface Patch ........................................................6-20 Plug Patch .............................................................6-21 Scarf Patch ............................................................6-24 The Back of the Skin is Accessible for Repair .....6-24 The Back of the Skin Is Not Accessible for  Repair....................................................................6-26 Advanced Composite Materials .........................7-1 Description of Composite Structures .............................7-1 Introduction ................................................................7-1 Laminated Structures..................................................7-2 Major Components of a Laminate ..........................7-2 Strength Characteristics ..........................................7-2 Fiber Orientation.....................................................7-2 Warp Clock.............................................................7-3 Fiber Forms ................................................................7-3 Roving.....................................................................7-3 Chapter 6 Chapter 7 Unidirectional (Tape)..............................................7-3 Bidirectional (Fabric)..............................................7-3 Nonwoven (Knitted or Stitched).............................7-4 Types of Fiber ............................................................7-4 Fiberglass................................................................7-4 Kevlar ®...................................................................................................7-4 Carbon/Graphite .....................................................7-5 Boron ......................................................................7-6 Ceramic Fibers........................................................7-6 Lightning Protection Fibers ....................................7-6 Matrix Materials .........................................................7-6 Thermosetting Resins .............................................7-6 Thermoplastic Resins..............................................7-8 Curing Stages of Resins .............................................7-8 Pre-Impregnated Products (Prepregs) ........................7-8 Dry Fiber Material......................................................7-8 Thixotropic Agents.....................................................7-9 Adhesives ...................................................................7-9 Film Adhesives .......................................................7-9 Paste Adhesives ......................................................7-9 Foaming Adhesives ..............................................7-10 Description of Sandwich Structures.............................7-10 Properties..................................................................7-11 Facing Materials .......................................................7-11 Core Materials ..........................................................7-11 Honeycomb...........................................................7-11 Foam .....................................................................7-12 Balsa Wood...........................................................7-13 Manufacturing and In-Service Damage .......................7-13 Manufacturing Defects .............................................7-13 Fiber Breakage......................................................7-13 Matrix Imperfections ............................................7-13 Delamination and Debonds...................................7-14 Combinations of Damages....................................7-14 Flawed Fastener Holes..........................................7-14 In-Service Defects ....................................................7-14 Corrosion ..................................................................7-15 Nondestructive Inspection (NDI) of Composites ........7-15 Visual Inspection......................................................7-15 Audible Sonic Testing (Coin Tapping) ....................7-16 Automated Tap Test .............................................7-16 Ultrasonic Inspection................................................7-17 Through Transmission Ultrasonic Inspection.......7-17 Pulse Echo Ultrasonic Inspection .........................7-17 Ultrasonic Bondtester Inspection..........................7-18 Phased Array Inspection .......................................7-18 Radiography .............................................................7-18 XXI Landing Gear Repairs...............................................5-34 Engine Mount Repairs..............................................5-36 Rosette Welding .......................................................5-36