Dope_and_Fabric

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					Dope & Fabric
  Refresher

   Presented by:
 Prof. Tim LeBaron
Vincennes University
IA Renewal Seminar
   February 1999
Nomenclature
 Bias
 Bleaching
 Calendaring
 Fill (Woof)
 Mercerizing
 Selvage
 Sizing
 Thread count
 Warp
 Weight
Material Selection
 Marked along the selvage edge
 Minimum requirements
       Must meet or exceed TCDS
            Vne < 160 MPH, AND
            Wing loading < 9 lb/ft2
            MUST USE GRADE A OR BETTER
   STC
       Stits Poly Fiber
       Ceconite
   Razorback
       No STC, uses AC 20-44!!!
Covering Methods
 Envelope
   Already sewn for your aircraft
   Slide on like a sock, attach to frame.

 Blanket
   Individualstrips are sewn together and
   cover is then attached to frame
Covering Methods
 Should not have any seams where rib
 stitching may occur
Fabrics
 Organic
   Grade   A Mercerized
   80 lb/in
       Means a 1” strip must be able to support 80
        pounds in tension without breaking
   Deterioration
       FAA says 70% strength for airworthy
            80 * .7 = 56 lb/in
Fabrics
 Organic
   Intermediate      grade
     Wing loading no more than 9 lb/ft AND
     Speed less than 160 MPH

   65 lb/in test strength new
   No Longer Available, the data may be
    necessary for determining the original
    strength for recovering.
        Linen fits in this category
Fabrics
 Inorganic
   Advantages
     Resist deterioration by ultraviolet rays
     Resist microorganism attack better

   Disadvantage
       More careful following of process is required to
        ensure correct final product
Fabrics
 Inorganic Common Names
 Polyester Fabrics (DACRON Base)
        Poly Fiber
   Stits

   Ceconite

 Fiberglass
   Razorback
        Extremely resistant to attack
Tapes
 Surface   Tape
   AKA finishing tape
   Same material, usually “pinked” for better
    adhesion qualities
   Used for:
     Opening reinforcement
     Rib attach cover

     steamlining

 Reinforcing
Tapes
 Surface   Tape
   AKA finishing tape
   Same material, usually “pinked” for better
    adhesion qualities
   Can get separate rolls
   Used for:
     Opening reinforcement
     Rib attach cover

     streamlining
Tapes
 Reinforcing
   Much  larger Warp thread than Fill Thread
   Synthetic – must check to see if there is
    special tape to be used
   Use:
     Inter rib bracing (under fabric cover)
     Over fabric on ribs to prevent lacing cord from
      cutting through
Tapes
   Anti Tear Strips
       If Vne is > 250 MPH
       Bonded to fabric
       Under reinforcing tape on entire top of the wing
            From trailing edge around to behind spar
       Under slipstream components on bottom of wing
            Slipstream = one propeller width plus one rib
            From trailing edge around leading edge and back to
             training edge
Threads
 Thread – you know
 Cord – heaver than thread. Used for
  more strength (Rib stitching).

NOTE: When using inorganic fabrics, use
  the same material as is being installed
              on aircraft.
Threads
 Machine     thread – obvious
   Tensile  strength = 5 lb per strand
   “White, silk-finish, no. 16, four cord cotton
    thread with a Z twist” (Z twist signifies a left
    twist)
   1 lb for 5000 yards
Threads
   Hand sewing thread
       Tensile strength = 14 lb per single strand
       “unbleached, cotton, silk finished, no. 8, four cord
        thread”
       1 lb for 1650 yards
   Twist
       Z = left twist
       S = right twist
       Importance?
             Right handed should stitch from right to left, using left
             twist, so thread will not untwist
            Left handed is all opposite should use right twist thread
Threads
 silk   finished
   Has  been “sized” to produce a hard, glazed
    surface to prevent threat form fraying or
    weakening
Lacing Cord
 AKA   rib-stitching cord or rib lacing cord
 Tensile Strength = 40 lb for single or 80
  lb for double
 Should be waxed before use to
  “lubricate” it
   Can   be done by hand
Waxed cords
 Used   for attaching Chafing Strips
  4 – 5 ply, double twisted and waxed.
   Chafing Strips
     Leather, neoprene, Teflon, polyethylene
     Used where a cable or control passes through

      the fabric.
RIB Stitching
 Determined  from old cover
 Or Figure 2-12, p. 2-21 in AC 34-13.1B

   NOTE: Different spacing for in the slipstream
             and out of the slipstream

      and last stitches have ½ stitch
 First
  spacing
               NOTE
When using any “system”you must use all
   the components of the system for
           correct installation.

   DONOT MIX AND MATCH THE
   SYSTEMS!!
Dope
 Function: Seals, tautens, and protects the
  airplane fabric covering.
 A colloidal solution of cellulose acetate
  butyrate or cellulose nitrates;
 Other solutions have been developed for
  inorganic fabrics

    NOTE: If using on inorganic, use NON-
               Tautening dopes!
Dope
 Nitrate
   Nitrocellulose   combined with plasticizers
    and thinners.
   HIGHLY FLAMMABLE in both liquid and
    dry states!
 Advantage  – lower cost, easier to apply,
  better adhesion.
Dope
 Butyrate
   Cellulose  acetate butyrate with plasticizers
    and thinners.
   More fire resistant

   Provides greater shrinkage of the fabric.

   Care must be taken not to warp the
    structure of the aircraft
Dope
 Synthetic
   Proprietary names (Poly-Fill, Poly- Spray,
    etc) are being used on trade name fabrics.
   Must be followed exactly for correct
    protection and strength.
Dope Additives
 Fungicidal
   Prevents   microbes from weakening the
    fabric
      Zinc dimethyldithiocarbonate (white powder)
      Copper naphthonate (bleeds some on light
       colors)
      VERY THIN FIRST COAT to ensure the fabric

       is encapsulated
Dope Additives
 Aluminum    Powders (silver dope)
   After all the tapes, inspection rings, etc.
    have been added
   Aluminum oxide settles to form an
    aluminum layer to reflect ultraviolet rays.
   Different from pigmented silver dope!
Rejuvenator
 Thin dopelike finish with powerful solvents.
 Softens and penetrates the old dope and tries
  to replace some of the placticizers and
  solvents that have evaporated and oxidized.
 Should use the special stuff, but THINNED
  BUTYATE can do the job.
 Can extend life of cover, but must check the
  underneath material.
Solvents
 Nitrate
   Nitrate   Dope or Lacquer thinner
 Butyrate
   Cellulose   butyrate dope thinner
 Acetone
   Should not be used as a thinner, but can
    be cleaner for brushes and guns.
Solvents
 Blushing
   Weakens   and “fades” the applied dope,
    making the finish weak and useless.
   Caused by solvents evaporating too fast
    and introducing moisture into the materials.
Retarders
 Slowdrying thinner used to slow the
 drying time of the dope.
   Used   when HUMIDITY IS HIGH
Process
 Table   4-1, P. 96 Maintenance & Repair
Testing & Inspection
   Based on tensile strength
       Seyboth Tested
            Penetrates the fabric
            ALL HOLES MUST BE REPAIRED!
       Maule Tester
            Normally does not penetrate the fabric
 With these testers, the fabric is tested on the
  airframe
 Tested perpendicular to the fabric being
  tested
Testing and Inspection
 Most   accurate test
   Actual   removal of a strip and destructively
   tested.
     From weakest area
     1” wide and several inches long

     Put in tester and pull until tears

   Must   meet the 70% rule
Repairs
 Tears
   Remove   all dope appx 2” past damage
   Baseball stitch
   Apply surface tape over repair
   Finish with original dope to original levels

 “V”   Tear
   Same  but start at apex (bottom of v) to
    ensure all is in place
Repairs
 Doped
   Vne < 150 MPH
   Remove damaged area

   Dope on patch (up to 16” in any direction)

   Up to 8” hole needs 2” overlap, 8-16” hole
    needs ¼ the longest distance of damage
       12” hole = 3” overlap
Repairs
   Sewn- in
     Vne > 150 MPH and less than 16” damage
     Damage removed, patch cut to fill the hole,
      and sewn in using baseball stitch.
     Surface patch now cut to cover the sewn in
      one
        If within 1” of a structure member (rib, stringer,
         etc.) must extend 3” beyond
        Reinforcing tape, Rib stitched, surface tape and
         then refinished to original
Repairs
 Doped   on panel

				
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