AIRCRAFT FABRIC COVERING, & FINISHING MATERIALAFC-2

COURSE OBJECTIVEBy the end of this course you will be able to describeCommon types of fabric used & their characteristicsCommon types of chords, tapes & threads used for attaching fabric to aircraft structureDifferent chemicals used with fabric coveringDifferent method of securing a fabric to an aircraft structureVarious defects associated with fabric & means of eliminating them

CONTENTIntroductionTypes of aircraft fabricBasis for aircraft fabric re-coveringAircraft fabric testingAircraft fabric covering preparationInstalling aircraft fabricFinishing aircraft fabric covering

REFERENCESAircraft Maintenance Technician Series Volume 1 StructuresChapter 3 Non-Metallic StructureAC65-9A Airframe HandbookChapter 3 Fabric Covering

INTRODUCTION

INTRODUCTIONHistorical BackgroundMost popular few years backCurrently replaced by all metal constructionBut still found on special purpose aircraft Agricultural aircraftAmateur built aircraftNewly introduced light sport aircraft (LSA)Antique/old aircraft that need restoration

INTRODUCTION CONTDDefinitionFabric Covering cloth/textile made from interwoven fibers after undergoing thru careful manufacturing processFibers/yarnsSmall fine filaments made from various materials and used to make threads.Cotton, linen, glass, cellulose or polyester

INTRODUCTION CONTDFabric TermsWarpDirection along length of fabric (Threads running lengthwise are termed the warp) Filling, Woof or Weft:Direction across length of fabric ( Threads running crosswise are termed the weft or woof or fill in the United States).Count (Thread count):Number of threads per inch

INTRODUCTION CONTDFabric Terms cont.Ply/layer/thickness Number of yarns/fibers making up threadBiasCut, fold, or seam made diagonally (45 degree) to the warp/fill threadCalenderingProcess of ironing fabric by threading the fabric between serious cold and hot rollers to produce smooth finish

INTRODUCTION CONTDFabric Terms cont.MercerizationDipping yarn/fabric in a hot solution of caustic soda to shrink fabric & acquire great strength & luster/shine. Is a chemical process which increases the tensile strength of the fibre and its absorption characteristicsSizingMaterial/lubrication such as starch used to stiffen yarns for ease in weaving/interlacing

INTRODUCTION CONTDFabric Terms cont.Pinked edgeEdge cut by machine or shears in a continuous series of V to prevent raveling/knotting or twistingSelvage edgeThe edge of the cloth woven to prevent raveling BleachingChemical process used to whiten cotton fabric

ContdGreige condition of polyester fabric upon completion of the production process before being heat shrunk.Cross coatbrushing or spraying where the second coat is applied 90 to the direction the first coat was applied. The two coats together make a single cross coat.

INTRODUCTION CONTDFabric Terms contd

TYPES OF FABRIC

TYPES OF AIRCRAFT FABRIC

TYPES OF AIRCRAFT FABRICThere are basically two FAA approved fabric types Organic FabricsInorganic/Synthetic Fabrics

TYPES OF AIRCRAFT FABRIC CONTDOrganic Fabric is made from plant material Cotton and Linen are popular natural fabricGrade A cotton - standard for many years.Weight 4.5 ounce per square yard1ounce = 28.35gram, & 1yard = 0.91metersThread count - 80-84 threads per inch (tpi) in wrap & fill directionMinimum tensile strength80psi of width in both warp & fill direction

TYPES OF AIRCRAFT FABRIC CONTDOrganic Fabric Cont.Tensile StrengthCustomary determinant for the strength of fabricAmount of pull needed to break strips of fabric one inch wide both in wrap and fill directionExpressed in pounds per square inch or psi

TYPES OF AIRCRAFT FABRIC CONTDGrade A CottonManufactured under Technical Standard Order TSO-C15 Meets Aeronautical Material Specification AMS 3806Meets Military Specification MIL-C-5646Approved for use on aircraft having:Never exceed speed (VNE) in excess of 160 mphWing loading greater than 9 psf.

TYPES OF AIRCRAFT FABRIC CONTDVNE Never Exceed SpeedMax speed aircraft is allowed to attain in any condition of flightWing LoadingRatio of max. allowable gross wt. to wing planform area in square feetSelection of aircraft fabric and related hardware is determined by: VNE and Wing loading

DISADVANTAGES OF ORGANIC FABRICBeing organic, both cotton and linen fabrics have a tendency to absorb moisture and are prone to damage from fungal attack such as mildew/decay and rot. They are a tempting food source for insects and vermin and they also deteriorate when exposed to ultra-violet radiation. They are flammable and combustion is accelerated by certain types of dope. It is, therefore, vital that protective finishes such as dope and paint are kept in good condition and the aircraft is stored in a safe and suitable environment.

TYPES OF AIRCRAFT FABRIC CONTDInorganic/Synthetic FabricsRequire chemical processing to create the fiber.Advantages: Resist Deterioration by ultraviolet rays and Attack by microorganismsDisadvantages:Require care for proper bonding.Two types used to cover an FAA certificated aircraftPolyester fiber fabricsGlass fiber fabrics

POLYSTER FABRICPolyester fabric is a durable man made polymer (synthetic fiber) which is resistant to moisture, acids, alkalis, fuel and oils. It is susceptible to deterioration when exposed to ultraviolet radiation for a long time and must therefore be completely covered by protective coatings in service.The material is produced by polymerization of selected hydrocarbon materials, extruded in its molten state to form filaments. The filaments are then heat stretched to the desired denier (or diameter) of fibre prior to weaving.

TYPES OF AIRCRAFT FABRIC CONTDPolyester Fibers cont.Polyester fabric, come under trade nameDacron, Fortrel, and KodelDacron is a commonly used polyester fabric Weight 3.7oz/square yardTensile strength = 148 psiPolyester fibers/fillaments come under trade nameCeconite, Superflite and Poly-Fiber

TYPES OF AIRCRAFT FABRIC CONTDPolyester Fibers cont.Polyester fabric is currently most widely used covering material Advantage over linen and cottonLower costAdditional strengthWeight savingIncreased service life

TYPES OF AIRCRAFT FABRIC CONTDGlass FibersGlass Fibre is produced as a monofilament and its fabrics are generally stronger than cotton or polyester.Made from fine spun/twisted/rotated glass filaments woven into a cloth.Glass fibre fabric has a loose weave of glass filament which makes it more difficult to dope.

ContdAdvantageNot affected by moisture, mildew/fungus/decay/rot, chemical & acids and fire resistantDisadvantageAdds significant weight compared to linen, & cotton

BASIS FOR AIRCRAFT FABRIC RE-COVERING

BASIS FOR AIRCRAFT FABRIC RE-COVERINGRecovering Need Re-covering is expensive & time consumingDo not undertake till definitely necessaryRequired only when original fabric covers deteriorate to 70% of its strengthWhat does this mean?

BASIS AIRCRAFT FABRIC RE-COVERING CONTDExample 1New Grade A cotton has tensile strength 80psiUsed on aircraft withVNE > 160mphWing loading > 9psfAllowed to deteriorate to tensile strength of 56psiBelow 56 psi requires replacement/re-covering

BASIS AIRCRAFT FABRIC RE-COVERING CONTDExample 2If aircraft VNE < 160mps and Wing loading < 9psfIntermediate fabrics could be usedNew strength 65 psiAllowed to deteriorate to 46psi

NOTE: Dried & cracked dopes dont need fabric replacement

A/C DOPEDope is primarily used to protect the fabric covering of an aircraft from damage by environmental factors such as moisture, sunlight and pollution. It also prevents the passage of air through the fabric and reduces friction, which improves the efficiency of the airframe. Certain dopes have the property that they shrink when drying and tighten the fabric (used to tauten). Most dopes can be used to stick/attach fabric patches onto the covering for repairs and access holes and, sometimes, the fabric to stick to the structure.

BASIS AIRCRAFT FABRIC RE-COVERING CONTDDried and cracked dopes occur whenPlasticizers dried out and dope becomes brittlePlasticizer give a dope flexibility & resilience If fabric is still good, finish can be rejuvenatedIf fabric is good and the dope is cracked, it may be treated with rejuvenator, a mixture of very potent solvents and plasticizers, to restore its resilience. Rejuvenation restores condition of dope coatingIt does nothing to improve strength of fabricQuestion: How do we determine strength of fabric?

FABRICS, TAPES, SEWING THREADS AND CORDS

Materials used to attach fabric to the a/c structure

FABRICS

Inorganic Commercial Names:Polyester Fabrics . DACRON BaseFiberglass Extremely resistant to deterioration from heat and chemicals

SURFACE TAPE

Doped over each seam or rib to cover the stitching.Provides a smooth appearance.Can be: Serrated/ragged or PinkedStraight edge impregnated with a compoundFor better adhesion and to prevent raveling/twisting Same material as the original fabricShould be placed over all lacings, seams, corners, edges and places where wear is expected.Applied after the second wet coat of dope

SURFACE TAPE

SURFACE TAPE CONT Specification MIL-T-5083Size2 in. for use over seams, edges, corners and lacings/fastenings.3 in. for application over the trailing edges of airfoils.

REINFORCING TAPEMuch larger Warp thread than Fill ThreadUsed over ribs between the fabric and lacing chord. To prevent lacing cord from cutting through the fabricUse: - Inter rib bracing (under fabric cover) & Over fabric on ribsSize: - Must be slightly larger than the member it coversMaterial :- Cotton, Linen, Fiberglass, DacronStrength :- 150lbs/half inchSpecification:- MIL-T-5661

ANTI TEAR STRIPSIf VNE is > 250 MPH Bonded to fabric with dopeSame material as the coveringUnder reinforcing tape on entire top of the wingFrom trailing edge around to behind sparUnder slipstream components on bottom of wingFrom trailing edge around leading edge and back to trailing edge

SEWING THREADS AND CORDSUsed to join two fabric edges together during installation.Cords are used when significant strength is required.Attaching a fabric covering to wing or fuselage.TypesMachine thread (5lb/strand)Hand sewing thread (14lb/strand)Lacing/fastening chordTensile strength, weight & specification varies with type threads

LACING CORDTensile Strength Must be strong enough to transmit the force on the upper surface of the wing 40 lb for single or 80 lb. for doubleShould be waxed before use to lubricate it.Can be done by hand SpecificationMIL-C -5649, MIL-C -5648, MIL-T -6779, MIL-T-5660

SPECIAL FASTENERSOriginal fastening device must be duplicated.Wire clipsSelf tapping screwsAt least two threads of the screw must extend beyond the rib cap stripA washer should be used under the head of the screwA pinked edge tape should be doped over the head of the screw.

SEAMS/JOINTSA series of stitches used to join two or more pieces of material.CharacteristicsStrengthMust have sufficient strength to carry the stresses to which it will be subjected.ElasticityDurabilityTightly woven stitches are more durable.Appearance

SEAM-TYPES1. Sewed seams Machine sewed seamsHand sewed seams - To close final openings - A inch hem/edge should be turned under all seams - Should be locked at 6 intervals.2. Doped seams*

MACHINE SEWED SEAMSTypes of machine sewed seamsFolded fellFrench fellModified Folded fellPlain overlapFor selvage and pinked edgesShould have two rows of stitches with 8 to 10 stitches per inch.Distance from the edge: - 1/16 in.Distance between stitches :- -3/8*

SEAMS CONT.*

SEAMS CONTDFAA approved machine seams

SURFACE TAPE APPLICATIONFor double stitched lap jointPinked edge surface tape 4 wideFor span wise seamPinked edge surface tape 3 wideFor span wise seams on trailing edgePinked edge surface tape notched 1deep and 1wide.For lapped and doped span wise seamsLap 4 and cover with surface tape 4 wide for metal or wood covered leading edge and 3 wide for trailing edge.

AIRCRAFT FABRIC TESTING

AIRCRAFT FABRIC TESTINGQuestion: How do we determine the strength of a fabric?FABRIC TESTINGRequired on 100hr or annual inspection programTwo commonly used methods Manual TestSeyboth Test

AIRCRAFT FABRIC TESTING CONTDManual TestPrecession spring loaded instrumentWith blunt pin on its end and Scale calibrated in pounds per inchHold test squarely against the fabricPress until scale reads min strengthIf test penetrates fabric strength below min.If only small depression fabric good

AIRCRAFT FABRIC TESTING CONTDSeyboth TestSpecially shaped spring loaded sharp point with indicator pin marked with green, yellow and red colored bands

AIRCRAFT FABRIC TESTING CONTDSeyboth Test Cont.Hold straight against fabric & press till fabric is penetrated & shoulder rests on fabric Red band shows Weak fabricYellow band marginal strengthGreen band airworthy fabricPlace small circular patch on hole

AIRCRAFT FABRIC TESTING CONTDFabric Testing cont.Both tests performed on fabric covered by a dopeAdequate to identify good fabric but dont show actual strength of un-doped fabricIf fabric strength is marginal - further test neededRemove 1-1/4 by 6 inches long fabric from wing or fuselage darker fabrics preferable Soak it in thinner & pull threads till 1inch leftPull test to determine actual tensile strength

AIRCRAFT FABRIC RE-COVERING PREPARATION

AIRCRAFT FABRIC RE-COVERING PREPARATIONTypical preparation steps1. Removing wing and tail surfaces2. Remove old fabric3. Inspecting the structure4. Preparing the structure 5. Selecting approved fabric & material6. Preparing the chemical

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTD1. Removing wing & tail surfacesAccording to mfg. instruction & place them on cradles/supports2. Remove old fabricRoll up old fabric & store it till new recovering completeIf dope/oil soaked, store away from ignition3. Inspecting the structureFuselage tail section for corrosion and rustControl cables for wear and damageHinges for damage & lubrication

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTDInspecting structure contdInspect wings providing at most attentionCheck spars for crack & other damageLeading & trailing edge for crack & corrosionCheck control cables and pulleys

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTDInspecting the structure contdCheck wing truss for squareness using trammel barTrammel bar wood/metal bar with sharp pointed pinsCompare distance A and B with trammel barIf not equal adjust drag and anti-drag wires

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTD4. Prepare the structureRemove old dope & apply primerCover metal surfaces (L.E) with tape dope proofingAluminum foil or cellulose tape or zinc chromate paintBrace/support all the ribs with reinforcing tape for stability

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTD5. Selecting approved fabric & MaterialsGrade A cotton fabric stamped TSO-C15, or AMS3806Waxed linen rip lacing chord meet MIL-T-6779Long needle for sewing the fabric meet VT-276 specReinforcing tape narrow tape of heavy cotton threadsProvide additional strength for fabric cover Surface tape - grade A cotton with pinked/notched edge doped over all rib, L.E, T.E, & all tips after lacingProvide additional wear resistance on the edges.

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTD6. Chemical preparationDope:A chemical used to tauten fabric covering and to make it air & water tightConsists of :A film base cellulose fiber Solvent - acid for dissolving the film basePlasticizer & Thinner

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTDChemical preparation contdFilm base dissolved in acidShrinks and tautens the fabric after dryingPlasticizer Improves resilience/flexibility & prevent dope crack after dryingThinners adjust viscosity of the dopeConsistency when brushing and spraying

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTDChemical preparation cont.Two basic types of dopes used on aircraft fabric coveringNitrate dopeButyrate dopeNitrate DopeExcellent encapsulating/capturing propertyBest material for attaching fabric to structure for initial coats of dopeDisadvantage Highly flammable serious drawback

BUTYRATE DOPEBetter tautening characteristics than nitrate dopeBurn but not as easily as nitrate dopeDisadvantageDoes not encapsulate the fiber as well as nitrate dopeClear dope/butyrate dope is weakened by ultra violate raysPrevention methodTiny aluminum flake/powder is mixed with clear dope and sprayed over coats of clear dopeForm light tight covering preventing UV from reaching the fabric

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTDChemical preparation contdColored dopes given an aircraft attractive finishLight colored dope last longer absorbs least amount of heat from sunSome pigments red bleed thru finishing coat and are called bleeding dopesBleeding dopes must be applied last

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTDChemical preparation contdDopes dries out when thinners & solvents evaporateRapid evaporation of solvents leads to moisture absorptionThis allows the moisture in the atmosphere to condense and deposit on wet dopeMoisture causes cellulose to precipitate from dope film & form white porous deposit called BlushBlushed doped surface is weak, porous & unattractive

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTDChemical preparation cont.High Humidity in a paint room also cause blushing of dopesPrevention method Use retarders in place of thinnersRetarders are thinners with certain additives to slow its rate of evaporation

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTDChemical preparation contdCotton & linen fabrics are susceptible to destruction by mildew/yeast and fungusWeakens fabric in short timePrevention method:Fungicidal dope with the first coatThorough penetration of dope into fabric is required for fungicide to be effective

AIRCRAFT FABRIC RE-COVERING PREPARATION CONTDChemical preparation cont.Dope proofingAll parts of the aircraft that come in contact with doped fabric must be treated with a protective coating by using:-Dope proof paint (zinc chromate paint)Aluminum foilCellulose tape

AIRCRAFT FABRIC INSTALLATION

GENERALAll covering must be tauten and smooth for the best appearance and performance of the aircraft.Storage - Materials must be stored in a cool, dry place.Hence therefore the fabric shop must be:CleanWell lighted andWell ventilated

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FACILITIES , TOOLS AND EQUIPMENTTOOLS AND EQUIPMENTSupports - Easels - To support a wing vertically - Trestles (saw horses) - To support a wing horizontallyNeedlesShearsSewing thimble/capsewing machine

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AIRCRAFT FABRIC INSTALLATIONRecall thatWings removedFabric removedStructures Inspected and repairedFabric & hardware selectedChemicals preparedInstallation will be the next step

AIRCRAFT FABRIC INSTALLATIONInstalling a fabric involves1. Selection of installation method2. Removing Wrinkles3. Applying first coat of dope4. Attaching Fabric5. Opening drain grommets/eyelets & inspection rings6. Application of Surface Tape 7. Installing drain grommets & inspection rings

AIRCRAFT FABRIC INSTALLATION CONTD1. Selection of installation methodTwo basic methods areThe Envelope MethodThe Blanket Method

AIRCRAFT FABRIC INSTALLATION CONTDThe Envelope MethodMethod of installing pre-sewn fabric to form envelope/coverBegin with simplest structure & to complex onesGeneral recommended orderFlapsAileronsTail surfacesWings and then fuselages

AIRCRAFT FABRIC INSTALLATION CONTDTHERE ARE DETAIL PROCEDURES FOR:Covering small componentsCovering the wingCovering the fuselage

Refer the respective maintenance manual for detailed procedures.

AIRCRAFT FABRIC INSTALLATION CONTDThe Blanket MethodA method when pre-sewn envelope not availableSew the blanket using one of FAA approved machine sewing threads & seam methodsFour basic FAA approved machine seam/joint stylesPlain overlapFrench fellFolded fellModified folded fell

AIRCRAFT FABRIC INSTALLATION CONTDFAA approved machine seams

AIRCRAFT FABRIC INSTALLATION CONTD2. Removing the WrinklesUse distilled or demineralized water and wet fabric thoroughly Some tightness will be lost but wrinkles will be removedCaution:Water must not run into the structureDo not cut fabric around fitting while wetFabric shortens while shrinking

AIRCRAFT FABRIC INSTALLATION CONTD3. Applying the First coat of DopeAllow water to dry completely for a maximum of 48hrsApply fungicidal dope If more than 48hrs is elapsed airborne fungus will settle on surfaceHow is fungicidal dope prepared and applied?

AIRCRAFT FABRIC INSTALLATION CONTDPreparation and application of fungicidal dopePour unthinned nitrate dope into fungicidal pasteRatio one gallon of nitrate dope to four ounce of fungicidal paste one ounce = 28.35gramsStir till paste is mixed thoroughlyThin the dope with equal amount nitrate dopeApply with animal-bristle brushBrush till fungicidal dope completely surrounds the fabricNone of the dope should run down inside the fabric

AIRCRAFT FABRIC INSTALLATION CONTD4. Attaching the FabricBoth cotton and linen fabric are normally attached to the airframe by stringing or stitching and tensioned using nitrate or butyrate dope.Fabric must be attached to wing ribs in such a way thatAerodynamic forces will be transmitted to the structure and lifting the entire aircraftThree methods of attaching fabric to aircraft structureA. Lacing (lacing cord)B. Clipping (wire clips) C. Screwing (self tapping screws)

AIRCRAFT FABRIC INSTALLATION CONTDA. LacingUses waxed/polished linen cord & long lacing needleLabor intensive and time consuming operationFabric must be attached by methods approved by mfg.Mark each rib with lead pencil for stitch placementMake holes on each side of the ribUsing stitching needleAs close to rib caps as possible

AIRCRAFT FABRIC INSTALLATION CONTDLacing cont.Stitch spacing b/n 1st & last stitch = all other spacingStitch spacing is based on VNECopy of spacing used by mfg. needed or Use stitch spacing chart

AIRCRAFT FABRIC INSTALLATION CONTDLacing cont.Stitch spacing chart (spacing vs. VNE )Slip stream = dia. of propeller + additional ribs

AIRCRAFT FABRIC INSTALLATION CONTDLacing contdKnots will be placed where they are least visiblePlace knots on top - high wing aircraftPlace knots on bottom low wing aircraftException1st knot always placedopposite regular knots

AIRCRAFT FABRIC INSTALLATION CONTDLacing cont.Tie a square knot on the side opposite of regular knot at center of reinforcing tape

AIRCRAFT FABRIC INSTALLATION CONTDLacing contd

AIRCRAFT FABRIC INSTALLATION CONTDLacing cont.If come short of lacing cordDo not use square knot it will slipUse splice knot shown below

TYPES OF STITCHES

FABRIC COVERING

AIRCRAFT FABRIC INSTALLATION CONTDB. ClippingRib stitching is labor intensive operationOther methods of attachmentClippingScrewing

AIRCRAFT FABRIC INSTALLATION CONTDClipping Two basic types of clipping are usedMartin Clip & Cessna Clip methods: Approval by FAA required FAA form 337 must be filled

AIRCRAFT FABRIC INSTALLATION CONTDC. Screwing Before drilling holes for metal screw in wing ribs originally stitched Approval by FAA requiredFAA form 337 must be filledMetal screws & plastic/aluminum washer

AIRCRAFT FABRIC INSTALLATION CONTD5. Opening Drain Grommets/eyeletsSmall doughnut shaped pieces of acetate plasticO.D. = and ID. = 5/16 Attached to fabric at all low point of the structureTo ventilate the aircraft To prevent condensed moisture from rotting/decay fabricAfter completing recoveringOpen drain grommet by cutting fabric from inside of grommet by a sharp pointed knife blade

AIRCRAFT FABRIC INSTALLATION CONTDOpening Inspection ringsMade of acetate plasticO.D = 4-5/8 and ID = 3-1/2 Installed at location chosen by mfgAllow access to inside of the structureFor inspection and servicingAfter re-covering, cut the center from inspection rings where access is required

AIRCRAFT FABRIC INSTALLATION CONTD6. Application of Surface TapeSurface tape:Strips of aircraft fabric doped over all seams & places where fabric is attached to aircraft structureIts also doped over wing L.E where abrasive wear occursProvide additional wear resistance on the edgesFor application of surface tape follow the detail procedures outlined in applicable manual

FABRIC REPAIR METHODS

REPAIR METHOSIf the fabric has been damaged extensively, it is usually impractical and uneconomical to make satisfactory repairs by sewing and patching. Cuts and tears in fabric are sometimes caused by stones thrown up by the slipstream or wheels, from accidental damage during ground movement or servicing. Damage may also be caused by bird strikes.METHODS:Repair of tearsSewed - In repairDoped - On repairDoped In panel repair

REPAIR OF TEARSTearsRemove all dope approximately 2 past damage.Baseball stitch.Apply surface tape over repair.Finish with original dope to original levels.V & L shaped TearsSame but start at apex (bottom of v) to ensure all is in place.Baseball stitch

DOPED-ON REPAIRUsed: When VNE < 150 MPHAnd damage is < 16Remove damaged areaRemove the finish back from the edge of the cutout for about 2. Dope on patch (up to 16 in any direction)Up to 8 hole needs 2 overlap12 hole = 3 overlap

REPAIR BY DARNING/RENOVATION.

SEWED-IN REPAIRWhen damage area exceeds 16 inches and the never exceed speed is greater than 150 MPH.The damage is removed and a rectangular or square patch is sewed to the edges of the cutout.A patch is applied over the seams

DOPED IN PANEL REPAIRS

If the damage is extensive to be repaired by the doped-on or sewed-in methodCan be repaired by removing and replacing the entire panelRemove surface tape from the ribsCutout damage leaving 1 of fabric adjacent to the ribsCut a patch large enough to extend 3 beyond the rib.Remove finish down to the clear dopeInstall patch and dope it downPlace new reinforcing tape and stitchApply surface tape and finish

AIRCRAFT FABRIC FINISHING

AIRCRAFT PAINTING, FINISHING & MARKING*

INTRODUCTIONPaintA colored liquid applied to a surface in order to decorate it or to protect it, or to create a painting/image/picture/work of art. FinishTo treat something, especially wood or metal, in order to achieve a desired surface effect Purpose of finishes:Protection from deteriorationPleasing appearance (desired appearance)

CLASSIFICATION OF FINISHES/PAINTSProtectiveFor interior and exterior surfacesAppearanceFor exterior surfacesDecorativeEmblems (logo) - symbolsDecals (stickers) - signsIdentification numbers and letters

FINISHING MATERIALSCleaning agentsDopeThinnersPrimersPaintsAdditives Rejuvenators Masking materials

CLEANING AGENTSAre used to clean: Surfaces to be paintedPainting equipmentExamples:AcetoneRemoving grease from fabricCleaning spray paint gunsBenzeneCleaning equipment

CLEANING AGENTS CONT..Acrylic nitrocellulose lacquer thinnerWiping areas prior to paintingImproved adhesionVolatile mineral spiritsCleaning striped/uncovered surfaces prior to the application of paint

THINNERSTo thin dopes, enamels and paints for spraying and brushing consistency.Use correct thinner:Toluene - for zinc chromate primerTurpentine - for varnish, enamels and other oil base paints.

PRIMERSZinc chromate PrimerFor corrosion protectionAs a base for protective topcoats Is also a good dope proof paintStandard wash primerUsed with some paints that require an under coat (a metal pre treatment coating compound)Leaves a very thin layerContains phosphoric acid as one of its component at the time of application.Acrylic cellulose nitrate modified primerUsed between wash primer and nitrocellulose topcoat

PRIMERS CONTRed iron oxideGray enamel undercoatUnder top coatsSuitable for sanding to create a perfectly smooth base for paint.PolyurethaneEpoxy

PAINTS

Types of paintsLacquer /varnishEasy to applyEasy to repairCan be fuel or chemical resistantMay need to be buffed/polished to reach maximum glossiness/smoothnessAcrylic nitrocellulose and nitrocellulose

PAINTS CONT

EnamelAcrylic enamels provide a glossy/shine/smooth surface which is very resistant to scratching due to its hardnessMore care is needed during applicationDrying time is longerHarder to repair

PAINTS CONT

PolyurethaneExcellent durabilityExcellent weather resistanceExcellent chemical resistanceUsed in areas exposed to chemical attack such as Skydrol.Should not be waxed/polishedHard to strip/cut up

CONTENTS OF PAINTPigmentProvides color and durability.Also improves the strength and adhesion of the paint.BinderHolds the pigment in liquid form.When applied it gives the paint the ability to adhere to the surface.Backbone of the paint

CONTENTS OF PAINT CONT.SolventEffectively thins the paintIt carries the pigment and binderUsed to regulate how much a paint flowsCalled a thinner when used with lacquerCalled a reducer when used with enamel

CONTENTS OF PAINT CONT.AdditivesCompose only a small percentage of the paint.Used to alter the physical and chemical properties of the paint.Provide a more glossy appearanceSpeed drying timeImprove chemical resistanceImprove strengthImprove corrosion resistanceImprove the appearance of the paint - Metal flakeImprove weather resistance

ADDITIVES CONT.EXAMPLES:

Butyl AlcoholMixed with dope to retard dryingTurpentine As a quick drier for enamelsPaint drierTo improve drying properties

REJUVENATION OF THE DOPE FILM

If fabric loses its strength, there is nothing to do but remove it and recover the aircraft. But if the fabric is good and the dope is cracked, it may be treated with rejuvenator, a mixture of very potent/strong solvents and plasticizers, to restore its resilience/flexibility. The surface of the fabric is cleaned and the rejuvenator sprayed on in a wet coat. The solvents soften the old finish so the plasticizers can become part of the film.

REJUVENATOR CONTCan extend life of cover, but must check the underneath material. When the rejuvenator dries, the surface should be sprayed with two coats of aluminium pigmented dope, then sanded and a third coat of pigmented dope applied, followed with the coloured dope finish. RETARDERS: Used to slow the drying time of the dope and to prevent blushing.Used when HUMIDITY IS HIGH

MASKING MATERIALTo exclude areas not to be paintedMetalHeld in place by weightsFiberboard (compressed wood)Held in place by weightsPaperHeld in place by masking tapeMasking tape

METHODS OF APPLYING FINISHESThe most common methods are:-DippingFor factories and large repair stationsInvolves the dipping of the part in a tank filled with the finishing material.BrushingFor small repair work and when it is impractical to spray paint.Paint should be thinned to the proper consistency for brushingSpray paintingAtomized finishing material is sprayed on the surface of the part

SPRAY PAINTINGRequires:Source of compressed airA reservoir or feed tankTo hold supply of the finishing materialDevice for controlling the combination of air and finishing material (spray gun)

AIRCRAFT FABRIC FINISHINGFinishing system of fabric covered aircraft consists of: Hand brush first coat of fabricWait 30 minutes drying periodApply surface tape prior to second coat of dopeApply second coat of dopeThird and fourth coats could be applied to provide tight and rigid surfaceApply two or more coat of properly pigmented dope

REGISTRATION MARKS FOR A/CAll a/c a/c registered must be marked with nationality and registration marks for easy identificationThe marks must be painted on the a/c or otherwise affixed/fastened so they are as permanent as the finishThe registration and nationality markings shall consist the roman capital letter N followed by the registration number of the a/cThe height of letters and numbers for fixed wing a/c must be at least 12 inchesThe width of the characters in the markings must be two thirds the height of the character

ASSINMENTS1. Discuss about the different varieties of a/c finishing materials2. Discuss and characterize the different types of fabric materials commonly used for wooden a/c cover3. Explain about a/c fabric installation procedures (the seven steps)4. Discus about on how we determine the strength of a fabric material

THE ENDTHANK YOU