Dope And Fabric

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Dope And Fabric

  1. 1. Dope & Fabric Refresher Presented by: Prof. Tim LeBaron Vincennes University IA Renewal Seminar February 1999
  2. 2. Nomenclature <ul><li>Bias </li></ul><ul><li>Bleaching </li></ul><ul><li>Calendaring </li></ul><ul><li>Fill (Woof) </li></ul><ul><li>Mercerizing </li></ul><ul><li>Selvage </li></ul><ul><li>Sizing </li></ul><ul><li>Thread count </li></ul><ul><li>Warp </li></ul><ul><li>Weight </li></ul>
  3. 3. Material Selection <ul><li>Marked along the selvage edge </li></ul><ul><li>Minimum requirements </li></ul><ul><ul><li>Must meet or exceed TCDS </li></ul></ul><ul><ul><ul><li>V ne < 160 MPH, AND </li></ul></ul></ul><ul><ul><ul><li>Wing loading < 9 lb/ft 2 </li></ul></ul></ul><ul><ul><ul><li>MUST USE GRADE A OR BETTER </li></ul></ul></ul><ul><li>STC </li></ul><ul><ul><li>Stits Poly Fiber </li></ul></ul><ul><ul><li>Ceconite </li></ul></ul><ul><li>Razorback </li></ul><ul><ul><li>No STC, uses AC 20-44!!! </li></ul></ul>
  4. 4. Covering Methods <ul><li>Envelope </li></ul><ul><ul><li>Already sewn for your aircraft </li></ul></ul><ul><ul><li>Slide on like a sock, attach to frame. </li></ul></ul><ul><li>Blanket </li></ul><ul><ul><li>Individual strips are sewn together and cover is then attached to frame </li></ul></ul>
  5. 5. Covering Methods <ul><li>Should not have any seams where rib stitching may occur </li></ul>
  6. 6. Fabrics <ul><li>Organic </li></ul><ul><ul><li>Grade A Mercerized </li></ul></ul><ul><ul><li>80 lb/in </li></ul></ul><ul><ul><ul><li>Means a 1” strip must be able to support 80 pounds in tension without breaking </li></ul></ul></ul><ul><ul><li>Deterioration </li></ul></ul><ul><ul><ul><li>FAA says 70% strength for airworthy </li></ul></ul></ul><ul><ul><ul><ul><li>80 * .7 = 56 lb/in </li></ul></ul></ul></ul>
  7. 7. Fabrics <ul><li>Organic </li></ul><ul><ul><li>Intermediate grade </li></ul></ul><ul><ul><ul><li>Wing loading no more than 9 lb/ft AND </li></ul></ul></ul><ul><ul><ul><li>Speed less than 160 MPH </li></ul></ul></ul><ul><ul><li>65 lb/in test strength new </li></ul></ul><ul><ul><li>No Longer Available, the data may be necessary for determining the original strength for recovering. </li></ul></ul><ul><ul><ul><li>Linen fits in this category </li></ul></ul></ul>
  8. 8. Fabrics <ul><li>Inorganic </li></ul><ul><ul><li>Advantages </li></ul></ul><ul><ul><ul><li>Resist deterioration by ultraviolet rays </li></ul></ul></ul><ul><ul><ul><li>Resist microorganism attack better </li></ul></ul></ul><ul><ul><li>Disadvantage </li></ul></ul><ul><ul><ul><li>More careful following of process is required to ensure correct final product </li></ul></ul></ul>
  9. 9. Fabrics <ul><li>Inorganic Common Names </li></ul><ul><li>Polyester Fabrics (DACRON Base) </li></ul><ul><ul><li>Stits Poly Fiber </li></ul></ul><ul><ul><li>Ceconite </li></ul></ul><ul><li>Fiberglass </li></ul><ul><ul><li>Razorback </li></ul></ul><ul><ul><ul><li>Extremely resistant to attack </li></ul></ul></ul>
  10. 10. Tapes <ul><li>Surface Tape </li></ul><ul><ul><li>AKA finishing tape </li></ul></ul><ul><ul><li>Same material, usually “pinked” for better adhesion qualities </li></ul></ul><ul><ul><li>Used for: </li></ul></ul><ul><ul><ul><li>Opening reinforcement </li></ul></ul></ul><ul><ul><ul><li>Rib attach cover </li></ul></ul></ul><ul><ul><ul><li>steamlining </li></ul></ul></ul><ul><li>Reinforcing </li></ul>
  11. 11. Tapes <ul><li>Surface Tape </li></ul><ul><ul><li>AKA finishing tape </li></ul></ul><ul><ul><li>Same material, usually “pinked” for better adhesion qualities </li></ul></ul><ul><ul><li>Can get separate rolls </li></ul></ul><ul><ul><li>Used for: </li></ul></ul><ul><ul><ul><li>Opening reinforcement </li></ul></ul></ul><ul><ul><ul><li>Rib attach cover </li></ul></ul></ul><ul><ul><ul><li>streamlining </li></ul></ul></ul>
  12. 12. Tapes <ul><li>Reinforcing </li></ul><ul><ul><li>Much larger Warp thread than Fill Thread </li></ul></ul><ul><ul><li>Synthetic – must check to see if there is special tape to be used </li></ul></ul><ul><ul><li>Use: </li></ul></ul><ul><ul><ul><li>Inter rib bracing (under fabric cover) </li></ul></ul></ul><ul><ul><ul><li>Over fabric on ribs to prevent lacing cord from cutting through </li></ul></ul></ul>
  13. 13. Tapes <ul><li>Anti Tear Strips </li></ul><ul><ul><li>If V ne is > 250 MPH </li></ul></ul><ul><ul><li>Bonded to fabric </li></ul></ul><ul><ul><li>Under reinforcing tape on entire top of the wing </li></ul></ul><ul><ul><ul><li>From trailing edge around to behind spar </li></ul></ul></ul><ul><ul><li>Under slipstream components on bottom of wing </li></ul></ul><ul><ul><ul><li>Slipstream = one propeller width plus one rib </li></ul></ul></ul><ul><ul><ul><li>From trailing edge around leading edge and back to training edge </li></ul></ul></ul>
  14. 14. Threads <ul><li>Thread – you know </li></ul><ul><li>Cord – heaver than thread. Used for more strength (Rib stitching). </li></ul><ul><li>NOTE: When using inorganic fabrics, use the same material as is being installed on aircraft. </li></ul>
  15. 15. Threads <ul><li>Machine thread – obvious </li></ul><ul><ul><li>Tensile strength = 5 lb per strand </li></ul></ul><ul><ul><li>“White, silk-finish, no. 16, four cord cotton thread with a Z twist” (Z twist signifies a left twist) </li></ul></ul><ul><ul><li>1 lb for 5000 yards </li></ul></ul>
  16. 16. Threads <ul><li>Hand sewing thread </li></ul><ul><ul><li>Tensile strength = 14 lb per single strand </li></ul></ul><ul><ul><li>“ unbleached, cotton, silk finished, no. 8, four cord thread” </li></ul></ul><ul><ul><li>1 lb for 1650 yards </li></ul></ul><ul><li>Twist </li></ul><ul><ul><li>Z = left twist </li></ul></ul><ul><ul><li>S = right twist </li></ul></ul><ul><ul><li>Importance? </li></ul></ul><ul><ul><ul><li>Right handed should stitch from right to left, using left twist, so thread will not untwist </li></ul></ul></ul><ul><ul><ul><li>Left handed is all opposite should use right twist thread </li></ul></ul></ul>
  17. 17. Threads <ul><li>silk finished </li></ul><ul><ul><li>Has been “sized” to produce a hard, glazed surface to prevent threat form fraying or weakening </li></ul></ul>
  18. 18. Lacing Cord <ul><li>AKA rib-stitching cord or rib lacing cord </li></ul><ul><li>Tensile Strength = 40 lb for single or 80 lb for double </li></ul><ul><li>Should be waxed before use to “lubricate” it </li></ul><ul><ul><li>Can be done by hand </li></ul></ul>
  19. 19. Waxed cords <ul><li>Used for attaching Chafing Strips </li></ul><ul><ul><li>4 – 5 ply, double twisted and waxed. </li></ul></ul><ul><ul><li>Chafing Strips </li></ul></ul><ul><ul><ul><li>Leather, neoprene, Teflon, polyethylene </li></ul></ul></ul><ul><ul><ul><li>Used where a cable or control passes through the fabric. </li></ul></ul></ul>
  20. 20. RIB Stitching <ul><li>Determined from old cover </li></ul><ul><li>Or Figure 2-12, p. 2-21 in AC 34-13.1B </li></ul><ul><ul><li>NOTE: Different spacing for in the slipstream and out of the slipstream </li></ul></ul><ul><li>First and last stitches have ½ stitch spacing </li></ul>
  21. 21. NOTE <ul><li>When using any “system”you must use all the components of the system for correct installation. </li></ul><ul><ul><li>DO NOT MIX AND MATCH THE SYSTEMS!! </li></ul></ul>
  22. 22. Dope <ul><li>Function: Seals, tautens, and protects the airplane fabric covering. </li></ul><ul><li>A colloidal solution of cellulose acetate butyrate or cellulose nitrates; </li></ul><ul><li>Other solutions have been developed for inorganic fabrics </li></ul><ul><li>NOTE: If using on inorganic, use NON-Tautening dopes! </li></ul>
  23. 23. Dope <ul><li>Nitrate </li></ul><ul><ul><li>Nitrocellulose combined with plasticizers and thinners. </li></ul></ul><ul><ul><li>HIGHLY FLAMMABLE in both liquid and dry states! </li></ul></ul><ul><li>Advantage – lower cost, easier to apply, better adhesion. </li></ul>
  24. 24. Dope <ul><li>Butyrate </li></ul><ul><ul><li>Cellulose acetate butyrate with plasticizers and thinners. </li></ul></ul><ul><ul><li>More fire resistant </li></ul></ul><ul><ul><li>Provides greater shrinkage of the fabric. </li></ul></ul><ul><ul><li>Care must be taken not to warp the structure of the aircraft </li></ul></ul>
  25. 25. Dope <ul><li>Synthetic </li></ul><ul><ul><li>Proprietary names (Poly-Fill, Poly- Spray, etc) are being used on trade name fabrics. </li></ul></ul><ul><ul><li>Must be followed exactly for correct protection and strength. </li></ul></ul>
  26. 26. Dope Additives <ul><li>Fungicidal </li></ul><ul><ul><li>Prevents microbes from weakening the fabric </li></ul></ul><ul><ul><ul><li>Zinc dimethyldithiocarbonate (white powder) </li></ul></ul></ul><ul><ul><ul><li>Copper naphthonate (bleeds some on light colors) </li></ul></ul></ul><ul><ul><ul><li>VERY THIN FIRST COAT to ensure the fabric is encapsulated </li></ul></ul></ul>
  27. 27. Dope Additives <ul><li>Aluminum Powders (silver dope) </li></ul><ul><ul><li>After all the tapes, inspection rings, etc. have been added </li></ul></ul><ul><ul><li>Aluminum oxide settles to form an aluminum layer to reflect ultraviolet rays. </li></ul></ul><ul><ul><li>Different from pigmented silver dope! </li></ul></ul>
  28. 28. Rejuvenator <ul><li>Thin dopelike finish with powerful solvents. </li></ul><ul><li>Softens and penetrates the old dope and tries to replace some of the placticizers and solvents that have evaporated and oxidized. </li></ul><ul><li>Should use the special stuff, but THINNED BUTYATE can do the job. </li></ul><ul><li>Can extend life of cover, but must check the underneath material. </li></ul>
  29. 29. Solvents <ul><li>Nitrate </li></ul><ul><ul><li>Nitrate Dope or Lacquer thinner </li></ul></ul><ul><li>Butyrate </li></ul><ul><ul><li>Cellulose butyrate dope thinner </li></ul></ul><ul><li>Acetone </li></ul><ul><ul><li>Should not be used as a thinner, but can be cleaner for brushes and guns. </li></ul></ul>
  30. 30. Solvents <ul><li>Blushing </li></ul><ul><ul><li>Weakens and “fades” the applied dope, making the finish weak and useless. </li></ul></ul><ul><ul><li>Caused by solvents evaporating too fast and introducing moisture into the materials. </li></ul></ul>
  31. 31. Retarders <ul><li>Slow drying thinner used to slow the drying time of the dope. </li></ul><ul><ul><li>Used when HUMIDITY IS HIGH </li></ul></ul>
  32. 32. Process <ul><li>Table 4-1, P. 96 Maintenance & Repair </li></ul>
  33. 33. Testing & Inspection <ul><li>Based on tensile strength </li></ul><ul><ul><li>Seyboth Tested </li></ul></ul><ul><ul><ul><li>Penetrates the fabric </li></ul></ul></ul><ul><ul><ul><li>ALL HOLES MUST BE REPAIRED! </li></ul></ul></ul><ul><ul><li>Maule Tester </li></ul></ul><ul><ul><ul><li>Normally does not penetrate the fabric </li></ul></ul></ul><ul><li>With these testers, the fabric is tested on the airframe </li></ul><ul><li>Tested perpendicular to the fabric being tested </li></ul>
  34. 34. Testing and Inspection <ul><li>Most accurate test </li></ul><ul><ul><li>Actual removal of a strip and destructively tested. </li></ul></ul><ul><ul><ul><li>From weakest area </li></ul></ul></ul><ul><ul><ul><li>1” wide and several inches long </li></ul></ul></ul><ul><ul><ul><li>Put in tester and pull until tears </li></ul></ul></ul><ul><ul><li>Must meet the 70% rule </li></ul></ul>
  35. 35. Repairs <ul><li>Tears </li></ul><ul><ul><li>Remove all dope appx 2” past damage </li></ul></ul><ul><ul><li>Baseball stitch </li></ul></ul><ul><ul><li>Apply surface tape over repair </li></ul></ul><ul><ul><li>Finish with original dope to original levels </li></ul></ul><ul><li>“ V” Tear </li></ul><ul><ul><li>Same but start at apex (bottom of v) to ensure all is in place </li></ul></ul>
  36. 36. Repairs <ul><li>Doped </li></ul><ul><ul><li>Vne < 150 MPH </li></ul></ul><ul><ul><li>Remove damaged area </li></ul></ul><ul><ul><li>Dope on patch (up to 16” in any direction) </li></ul></ul><ul><ul><li>Up to 8” hole needs 2” overlap, 8-16” hole needs ¼ the longest distance of damage </li></ul></ul><ul><ul><ul><li>12” hole = 3” overlap </li></ul></ul></ul>
  37. 37. Repairs <ul><li>Sewn- in </li></ul><ul><ul><li>V ne > 150 MPH and less than 16” damage </li></ul></ul><ul><ul><li>Damage removed, patch cut to fill the hole, and sewn in using baseball stitch. </li></ul></ul><ul><ul><li>Surface patch now cut to cover the sewn in one </li></ul></ul><ul><ul><ul><li>If within 1” of a structure member (rib, stringer, etc.) must extend 3” beyond </li></ul></ul></ul><ul><ul><ul><li>Reinforcing tape, Rib stitched, surface tape and then refinished to original </li></ul></ul></ul>
  38. 38. Repairs <ul><li>Doped on panel </li></ul>

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