13-1A Page 81 Chapter 3. FABRIC COVERING Section 1. PRACTICES AND PRECAUTIONS TEXTILE MATERIALS. All fabric, surface reinforcing tape, machine thread, lacing etc., used for re-covering or repairing an sit structure must be high-grade aircraft e material of at least as good quality and alent strength as those described in subcraphs a through g.
Aircraft Fabric. Acceptable fabrics such as and linen for covering wings, control yes, and fuselages are listed in figure 3.1.
es conforming to the Aeronautical Mate- 'pecifications incorporate a continuous ung showing the specification number to it identification of the fabric in the field.
Re-covering Alrcraft. Re-cover or repair airwith fabric of at least as good quality equivalent strength as that originally used he aircraft. However, in re-covering air- : which were originally covered with low igth or so-called "glider cloth," it is coned more desirable to use Grade A or "inediate fabric conforming to AMS 3806 or , as amended, respectively. Certain sync and fiberglass fabrics have been develthat are acceptable alternates to AMS or AMS 8804 fabric, providing the Supental Type Certificate (STC) installation uctions furnished with the material are wed. Specification MIL-C-9084, MIL-Y- C, and MIL-G-1140 materials in the uned condition have equivalent strength char-
•istics to TSO-C15 material specifications.
Reinforcing Tope. Acceptable reinforcing is listed in figure 8.2. Use reinforcing tape imilar quality as the fabric and at least alf the strength of that conforming to :fication MIL-T-5661.
Surface Tape. Use surface tape (also finishape) having approximately the same props as the fabric used. See figure 8.2.
•. Lacing Cord. Use lacing cord having a strength of at least 80 pounds double or 40 pounds single strand. See figure 8.2.
f. Machine Thread. Use machine thread having a strength of at least 5 pounds single strand (figure 8.2).
g. Hand-Sowing Thread. Use hand-sewing thread having a strength of at least 14 pounds single strand (figure 8.2).
128. COVERING PRACTICES, The method of fabric attachment should be identical, as far as strength and reliability are concerned, to the method used by the manufacturer of the airplane to be re-covered or repaired. Fabric may be applied so that either the warp or fillthreads are parallel to the line of flight. Either the envelope method or blanket method of covering is acceptable.
a. Flutter Precautions. When re-covering or repairing control surfaces, especially on high performance airplanes, make sure that dynamic and static balances are not adversely affected. Weight distribution and mass balance must be considered to preclude the possibility of induced flutter.
129. PREPARATION OF THE STRUCTURE FOR COVERING. One of the most important items in covering aircraft is proper preparation of the structure. Dopeproofing, covering edges which are likely to wear the fabric, preparation of plywood surfaces, and similar operations, if properly done, will do much toward insuring an attractive and long-lasting job.
o. Dopeproofing. Treat all parts of the structure which come in contact with doped fabric with a protective coating such as aluminum foil, dopeproof paint or cellulose tape. Clad aluminum and stainless steel parts need not be dopeproofed.
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b. Chafe Points. Cover all points of the structure, such as sharp edges, boltheads, etc., which are likely to chafe or wear the covering with doped-on fabric strips or cover with an adhesive tape. After the cover has been installed, reinforce the chafe points of the fabric by doping on fabric patches. Where a stronger reinforcement is required, apply a cotton duck or leather patch sewed to a fabric patch and then dope in place. Reinforce all portions of the fabric pierced by wires, bolts, or other projections.
c. Inter-Rib Bracing. Conventional wing ribs, which do not have permanent inter-rib bracing should be bound in position by means of cotton tape running parallel to the beams. Apply the tape diagonally between the top and bottom capstrips of each successive rib approximately halfway between the front and rear beams.
Apply the tape continuously from the butt rib to the tip rib with one turn of tape around each intermediate rib capstrip.
d. Preparation of Plywood Surfaces for Covering.
Prior to covering plywood surfaces with fabric, prepare the surface by cleaning and applying sealer and dope.
(1) Cleaning. Sand all surface areas which have been smeared with glue in order to expose a clean wood surface. Remove loose deposits such as woodchips and sawdust. Remove oil or grease spots by carefully washing with naphtha.
(2) Application of Sealer and Dope, Apply one brush coat or two dip coats (wiped) of a dopeproof sealer such as that conforming to Specification MIL-V-6894 thinned to 80 percent nonvolatile content and allow to dry 2 to 4 hours. Finally, before covering, apply two ng thy hat brush coats of clear dope allowing the first coat of dope to dry approximately 45 minutes before applying the second coat.
130. FABRIC SEAMS. Seams parallel to the line of flight are preferable; however, spanwise seams are acceptable.
a. Sewed Seams.
(1) Machine-sewn seama (parts D, E, and F of figure 8.8) should be of the folded fell or French fell types. Where selvage edges or Par 129 AC 4 pinked edges are joined, a plain lap se satisfactory.
(2) Begin hand sewing or tacking :
point where machine sewing or uncut fal again reached. Lock hand sewing at int of 6 inches, and finish the seam with ;
stitch and a knot (figure 8.4). At the where the hand sewing or permanent to is necessary, cut the fabric so that it c doubled under before sewing or permanent ing is performed (figure 3.8 (C)). After sewing has been completed, remove the t rary tacks. In hand sewing, use a minim four stitches per inch.
(3) Cover a sewed spanwise seam metal- or wood-covered leading edge pinked-edge surface tape at least 4 wide.
(4) Cover a sewed spanwise seam trailing edge with pinked-edge surface u least 3 inches wide. For aircraft with 1 exceed speeds in excess of 200 m.p.h notches at least 1 inch in depth and 1 ir width in both edges of the surface tape used to cover spanwise seams on trailing ‹ especially the trailing edges of control sur Space notches at intervals not exceedin inches. On tape less than 8 inches wid notches should be 1/3 the tape width. I event that the surface tape begins to ser because of poor adhesion or other cause tape will tear at a notched section, thus venting progressive loosening of the length of the tape which could seriously the controlling of the aircraft.
(5) Cover a double-stiched lap joint pinked-edge surface tape at least 4 i wide.
(6) Make sewed spanwise seams or upper or lower surface in a manner tha amount of protuberance is minimum, Cove seam with pinked-edge tape at least 3 i wide.
(7) Sewed seams parallel to the lir flight (chordwise) may be located over however, place the seam on the rib so tha lacing will not penetrate through the seam.
13.13-1A Page 63 Minimum Minimum Minimum ten- Materials Specification tensile tearing sile strength Thread count Use and remarks atrength new strength new deter lorated per inch (undoped) (undoned) (undoped) ›lane cloth Society Auto- 80 pounda 5 pounds 56 pounds 80 mini- For use on all aircraft.
ercerized motive En- per inch warp and per inch. mum, 84 Required on aircraft ›tton gineera AMB warp fll. maxi- with wing loadings Brade "A"). 3806 (T80- and fill. mum greater than 9 p.s.f.
Oló refer- warp Required on aircraft ences thia and fill. with placarded neverspec.). exceed speed greater than 160 m.p.h.
MIL-C-5646 Alternate to AMB 8806.
›lane cloth MIL-C-5013 Alternate to MIL-C-5646 allulose or AM8 3806 (unitrate pre- doped). Finish with oped. cellulose nitrate dope.
›lane cloth MIL-C-5642. Alternate to MIL-C-5646 ellulose or AM8 8806 (unmetate doped). Finish with utyrate, cellulose acetate redoped. butyrate dope.
plane cloth Society Auto- 65 pounds 4 pounds 48 pounds 80 mini- For use on aircraft with tercerized motive En- per inoh warp per inoh. mum, 04 wing loadings of 9 p.s.f.
ston. gineera AMS warp and fill. maxi- or less, provided never- 8804 (T80- and fill. mum exceed speed is 160 C14 refer- warp m.p.h. or less.
ences this and fill.
врес.).
›lane cloth Society Auto- 50 pounds 8 pounde 35 pounde 110 maxi- For use on gliders with Lercerized motive En- per inch warp per inch. mum wing loading of 8 p.s.f.
itton. gineers AM8 warp and fill. warp or less, provided the 3802. and fll. and fill. placarded neverexceed speed is 185
m.p.h. or less.
bric A. A. F. No. 55 pounds 4 pounds 30 pounds 80 mini- Alternate to AMS 8802- 16128. per inch warp per inch. mum A.
AMB 3802. warp and fill. warp and fill. and fill.
British 7F1_- This material meets the minimum strength requirements of TSO- C15.
FIGURE 8.1.-Textile fabric used in aircraft covering.
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Page 84 AC 4 Materiala Specification Yarn alse Minimum ten- aile strength Yarda per pound Use and remarks Reinforcing tape, MII-1-6661 150 pounda Used as reinforcing tape on cotton. per one- and under rib lacing half-inch Strength of other widths a width. in proportion.
Lacing cord, pre- MII-0-5649 80 pounds 810 mini- Lacing fabric to structure waxed braided double. mum. less already waxed, mu cotton. lightly waxed before and Lacing cord, special U.8. Army No. 20/8/8/8 -- 85 pounde cotton. 8-27. double.
Lacing cord, braided MIL-C-5648 80 pounda 170 minicotton. single. mum.
Lacing cord thread; MIL-T-6779 a ply 59 pounds 820 minilinen and linen- single. mum.
hemp. 11 ply 70 pounds 510 mininingie. mtim.
Lacing cord thread; MIL-T-5060 Ticket No. 62 pounds 480 minihigh-tenacity cot- 10 single. mum.
ton.
Machine thread cot- Federal V-T- 20/4 ply - pounds 5,000 nor- Use for all machine sewing ton. 278b. singie. mal.
Hand sewing thread V-T-278b. 8/4 ply 14 pounds 1,650 nor- Use for all hand sewing. Use cotton. single. mal. waxed thread.
Burface tape cotton MIL-1-5083 80 1bs/in. - Use over seams, leading (made from AN- trailing edges, outer edge 0-121). ribs, pinked, scalloped or st edges.
Surface tape cotton. Same as fabric Same as Alternate to MIL-T-5088.
used. fabric used.
FIGURE 8.2.-Miscellaneous textile materials.
b. Doped Seams.
(1) For a lapped and doped spanwise seam on a metal- or wood-covered leading edge, lap the fabric at least 4 inches and cover with pinked-edge surface tape at least 4 inches
(2) For a lapped and doped spanwise seam at the trailing edge, lap the fabric at least 4 Par 130 inches and cover with pinked-edge sur at least 3 inches wide.
131. COVERING METHODS.
a. The Envelope Method. The enve of covering is accomplished by sewin widths of fabric cut to specified and machine sewn to form an envel
PIN & TEMPORARY WRAPPING•
TO HOLD TENSION GIVEN TO
TOP COVER
TOP COVER (D) PLAIN OVERLAP SEAM.
FORMER (A) ATTACHING FABRIC AT AILERON CUTOUT.
(E) FRENCH FELL SEAM. (F) FOLDED FELL SEAM.
TOP COVER FINISH TOP COVER
WITH TAPE
SPA CANE CLOSER (B) ATTACHING FABRIC AT METAL WING BUTT. (C) ATTACHING FABRIC AT WOODEN WING BUTT.
TACKS SHOULD BE
TINNED IRON OR BRASS, STAINLESS STEEL NO.18 B. W. G.
FIGURE 8.3.-Typical methods of attaching fabric.
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PULL NO. 2-
COMPLETED KNOT
TO TIGHTEN KNOT IO LB STITCH AFTER PULL NO.I- HOLD STITCH TENSION*
BY PRESSING HERE DURING PULL NO.2 OPERATION NO. 2 -EDGE OF CAPSTRIP
DIRECTION OF LACING OPERATION NO. I FIGURE 3.4.-Standard knot for rib laring and terminating a sewed seam (modified spine knot).
can be drawn over the frame. The trailing and outer edges of the covering should be machine sewn unless the component is not favorably shaped for sewing, in which case, the fabric should be joined by hand sewing.
b. The Blanket Method. The blanket method of covering is accomplished by swing together widths of fabric of sufficient lengths to form a blanket over the surfaces of the frame. Join the trailing and outer edges of the covering by a plain overthrow or baseball stitch. For airplanes with placard never-exceed speed of 150 miles per hour or less, the blanket may be lapped at least 1 inch and doped to the frame or the blanket, lapped at least 4 inches at the nose of metal- or wood-covered leading edges, doped, and finished with pinked-edge surface tape at least 4 inches wide. When fabricating both the envelope and blanket coverings, cut the fabric in lengths sufficient to pass com- Par 131 pletely around the frame, starting at the t ing edge and returning to the trailing edge.
132. REINFORCING TAPE. Place reinforcing ;
of at least the width of the capstrips unde lacing. In the case of wings with plywoo metal leading edge covering, the reinfor tape need be brought only to the front spa the upper and lower surfaces.
a. Use of Antitear Strips. On aircraft never-exceed speed in excess of 250 mile hour, antitear strips are recommended the reinforcing tape on the upper surfa wings, and the bottom surface of that pa the wing in the slipstream. Where the anti strip is used on both the top and bottom faces, pass it continuously up to and aro the leading edges and back to the trailing e Where the strip is used only on the top i face, carry it up to and around the leac edge and back on the lower surface as far as the front beam. For this purpose the s stream should be considered as being eque the propeller diameter plus one extra rib si on each side.
Cut antitear strips from the same materia used for covering and wide enough to ext beyond the reinforcing tape on each side to engage the lacing cord. Attach the str applying dope to that part of the fabric covered by the strip, and apply dope f over the strip.
133. LACING.
a. Securely fasten both surfaces of fa covering on wings and control surfaces t ribs by lacing cord or any other metho nally approved for the aircraft. Care sho taken to insure that all sharp edges a which the lacing cord may bear are pr by tape in order to prevent abrasion cord. Join separate lengths of lacing the splice knot shown in figure 3.5.
the common square knot for this p ercise the utmost care to assure sion and security of all stitches.
or starting stitch use a double li trated in figure 3.6. Make all stitches using a single loop tied o standard knot for rib lacing (mor
1.13-1A shown in figure 8.4). The spacing between starting stitch and the next stitch should ne-half the normal stitch spacing. Final loon of the knot depends upon the original tion selected by the manufacturer. If such rmation is not available, consider positionthe knot where it will have the least effect he aerodynamics of the airfoil. The seine t admits a possibility of improper tightenresulting in a false (slip) form with tly reduced efficiency and must not be used stitch tie-offs. Lock the tie-off knot for the stitch by an additional half-hitch. Where ning ends, as at the rear beam and at the ling edge, space the last two stitches at half normal spacing. Under no circumaces pull tie-off knots back through the lacholes.
. The double-loop lacing illustrated in figure represents a method for obtaining higher ngths than possible with the standard sinlacing, When using the double-loop lacing, the tie-off knot shown in figure 3.8.
. Fuselage Lacing. Fabric lacing is also necesy in the case of deep fuselages, and on fuseas where former strips and ribs shape the ric to a curvature. In the latter case, lace fabric at intervals to the formers. Attachof the fabric to fuselages must be so acplished as to be at least the equivalent in ength and reliability to that used by the ufacturer of the airplane.
• STITCH SPACING. The stitch spacing should
ILL TO TIGHTEN PULL TO TIGHTEN
KNOT FORMED BUT NOT TIGHTENED
• LOAD
KNOT COMPLETED FIGURE 8.5.-Splice knot.
Page 87 not exceed the spacing approved on the original aircraft. In case the spacing cannot be ascertained due to destruction of the covering, acceptable rib-stitch spacing is specified in figure 8.9. Place the lacing holes as near to the capstrip as possible in order to minimize the tendency of the cord to tear the fabric. Lightly wax all lacing cords with beeswax for protection. In case waxed-braided cord is used, this procedure is unnecessary. (See figure 3.2 for acceptable lacing cords.)
135. SURFACE TAPE (FINISHING TAPE). Cover all lacing with tape of at least the quality and width used on the original airplane. This tape should not be applied until the first coat of dope has dried. Replace all inspection openings in the covering, and reinforce the fabric around them and along leading edges with tape. Wear or friction, induced by moving parts or fittings, can be repaired by sewing a leather patch on a fabric patch and doping in place. Pinked surface tape is sometimes applied over the trailing edges of control surfaces and airfoils. For sure application, the tape must be at least 3 inches in width, and if the aircraft never-exceed speed is greater than 200 miles per hour, notch the tape at intervals not exceeding 18 inches. If separation of the tape from the trailing edge begins, it will tear at a notched section and thereby prevent loosening of the entire strip which could seriously affect the controllability of the aircraft.
136. SPECIAL FASTENERS. When repairs are made to fabric surfaces attached by special mechanical methods, duplicate the original type of fastener. When self-tapping screws are used for the attachment of fabric to the rib structure, observe the following procedure:
a. Redrill the holes where necessary due to wear, distortion, etc., and in such cases, use a screw one size larger as a replacement.
b. Extend the length of the screw beyond the rib capstrip at least two threads of the grip (threaded part).
c. Install a thin washer, preferably celluloid, under the heads of screws and dope pinkededge tape over each screw head.
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Pae 68 AC 4:
STANDARD RIB LACING KNOT LEAD "A" HOOPS HITON A LEAD STITON WITH LEAD
BEFORE PROGEEDING TO SECOND STITCH.
LOCK SQUARE KNOT WITH / HALF HITCH AROUND STITCH LOOPS C WITH END "B" CUT OFF SURPLUS OF END "B"
- CAPSTRIP -LEAD "A" END "8"
TIE SQUARE KNOT ON CENTER OF CAPSTRIP.
STITON LOOPS "O"
SATIN AH FOR
CAPSTRIP -
TIE SQUARE KNOT ON CENTER OF CAPSTRIP.
151 8190
TARTING STITCI FIGURE 8.6.-Starting stitch for rib stitching.
Par 136
3.13-1A Page 89
DOUBLE LOOP LACING, SEE FIG. 3.8 FOR DETAILS OF KNOT.
— CAPSTRIP
CAPSTRIP
STARTING STITCH, SEE FIG. 3.6 FOR DETAILS.
9* NORMAL STITCH SPACING FIGURE 3.7.-Standard double loop lacing.
пр 3 Par 136
Page 90 AC •
- PULL NO.4 PULL NO. 4- 10 L8.
TO COMPLETE KNOT.
EDGE OF
CAPSTRIP
DIRECTION OF LACING PULL NO. 2 - 6 6B
TO TIGHTEN STITCH
COMPLETED KNOT
EDGE OF CAPSTRIP PULL NO.3
PULL SNUG OPERATION NO. 2 -STITCH LOOPS
AROUND CAPSTRIP PULL NO. 1 - 10 LB. FROM PREGEEDING
TO TIGHTEN LOOPS STITCH OPERATION NO. I FIGURE 8.8.-Standard knot for double loop lacing.
Par 136
43.13~1A MAXIMUM SPACING OF RIB LACING - INCHES I. IF ORIGINAL RIB STITCH SPACING CANNOT BE DETERMINED, NOTES USE SPACING INDICATED IN THESE CURVES.
2. LACING TO BE CARRIED TO LEADING EDGE WHEN VELOCITY EXCEEDS 275 M.P.H.
• SPACING OTHER THAN IN SLIPSTREAM-
SPACING IN SLIPSTREAM- PLACARD NEVER EXCEEDS SPEEDS-M.P.H. (INDICATED) (CURVES PRESUME LEADING EDGE SUPPORT REINFORCEMENT
SUCH AS PLYWOOD, METAL) FIGURE 8.9.-Fabric attachment spacing.
37.-147. RESERVED.
1г 136 Chap 3
Page 92 AC 43,13 Section 2. DOPING
148. APPLICATION OF AIRCRAFT DOPE, EPOXY, it be done properly. Since local atmosphe AND RESINS. Determine that dope and fabric conditions affect the doping process, determ materials are compatible by consulting the the amount of thinner necessary at the ti product manufacturer's instructions before the finishing material is to be applied by fi applying finish to aircraft surfaces. Compati- using it on experimental panels.
bility of products may also be determined by wetting samples of the fabric with the impreg- 149. BLUSHING AND USE OF BLUSH-RETARDI nating materials and thorough examination of THINNER. Blushing of dopes is very comm the material after it has dried. The following when doping is accomplished under humid c military specifications, or later revisions ditions. The condition is caused by the ral thereof, apply to aircraft dope, epoxy, and poly- evaporation of thinners and solvents, wh ester resins: lowers the témperature on the surface, causi MIL-D-5549A-1 condensation of moisture and producing 1 white appearance known as "blush. Blushi MIL-D-7850 tendencies are also increased, if strong ci rents of air flow over the surface when app MIL-D-6550A-1 ing dope or immediately thereafter.
MIL-D-5551A-2 A blushed finish has very little protective tautening value. When the relative humidity MIL-D-5558A-2 such that only a small amount of blushing MIL~D-5552A-1 encountered, the condition may be eliminat MIL-D-5554A-1 by thinning the dope with a blush-retardi MIL-D-5555-1 MIL-R-9800A thinner and slightly increasing the room te perature. If it is not possible to correct humi MIL-R-25042A ity conditions in the dope room, suspend dopi operations until more favorable atmosphe MIL-R-7575B conditions prevail. The use of large amounts blush-retarding thinner is not advisable 1 cause of the undesirable drying properties ¿ companying the use of this material.
150. NUMBER OF COATS. Apply as many coats dope as are necessary to result in a taut al well-filled finish job. A guide for finishing fa ric-covered aircraft follows:
a. Two coats of clear dope, brushed on al sanded after the second coat,
b. One coat of clear dope, either brushed sprayed, and sanded.
c. Two coats of aluminum pigmented dop sanded after each coat.
Par 148 Chap