• Standard rib lacing knot Half hitch around stitch loops C with lead A before proceeding to second stitch.
Lead A Lock square knot with half hitch around stitch loops C with end B. Cut off surplus of end B.
Finished first knot First stitch of Capstrip standard lacing 2 - l'ie square knot on capstrip with lead A and end B Lead A End B Stitch loops C Capstrip Start of first knot S/ 2 Refer to 3-5 Details of seine knot S = Normal stitch spacing lacing around entire rib Schematic represents starting stitch First step of Tie square knot on center of capstrip FicURE 3-9. Starting stitch for rib lacing.
Seine Knot Double loop lacing (See Fig. 3-6 for details of knot.)
— Capstrip Capstrip 5/2 lacing around entire rib Starting stitch.
(See Fig. 3-9 for details.)
S = Normal stitch spacing FIGURE 3-10. Standard double-loop lacing.
- NEEDLE
- LACING CORD
CAP STRIP OF RIB
- FABRIC 2 - CROSS OVER UNDER RIB CAP 1 - START NEEDLE THROUGH FABRIC STRIP AND THROUGH FABRIC
CLOSE TO SIDE OF RIB CAP STRIP 3 - PULL EYE END OF NEEDLE
THROUGH THE FIRST HOLE IN FABRIC 4 ~ BRING EYE END OF NEEDLE UP
THROUGH FABRIC OPPOSITE FIRST
HOLE AND FORM CORD ON END OF
NEEDLE, AS SHOWN, TO MAKE HALF HITCH 5 - PULL NEEDLE COMPLETELY OUT 6 - PUT NEEDLE UNDER HALF HITCH AND TIGHTEN HALF HITCH AS SHOWN. AND THROUGH LOOP "K" AS SHOWN -
THEN PULL NEEDLE THROUGH AND
TIGHTEN HALF HITCH - THEN HOLD THUMB AT "I" TO KEEP HALF HITCH TIGHT, AND TIGHTEN LOOP "K", BACK
OF HALF HITCH TO FORM A SEINE KNOT.
FIGURE 3-11. Rib lacing around capstrip.
surfaces wherever moisture may be trapped. It is customary to place one of these grommets on each side of a rib on the underside at the trailing edge.
The grommets are also placed at the lowest drainage points of wings, ailerons, fuselage, and empennage components to provide complete drainage.
Cover Cover Plastic grommets (figure 3-12) are either in the shape of a thin, circular washer or are streamlined.
Plastic grommets are doped to the fabric cover immediately after the surface tape is applied. Streamlined grommets usually are installed with the opening located toward the trailing edge of the surface.
Cover Opening Patch Grommet
- Grommet ~ Grommet Plastic grommet Streamlined Metal grommet plastic grommet FIGURE 3-12. Typical grommets.
Brass and aluminum grommets, also shown in figure 3-12, are mounted on either circular or square fabric patches. The edges of the patch are pinked to provide better adhesion. The patch assembly is doped to the cover after the surface tape is applied.
Inspection doors and access holes are provided in all surfaces, whether fabric or metal covered. One way to provide these openings on fabric-covered surfaces is to dope a zipper-equipped patch in the desired place. Another inspection method for cloth or metal surfaces is to install a framework inside the wing to which a cover plate can be attached by screws. These frameworks are built into the structure wherever access or inspection holes are necessary.
REPAIR OF FABRIC COVERS General Repair fabric-covered surfaces so that the original strength and tautness are returned to the fabric.
Repair all tears or punctures immediately to prevent the entry of moisture or foreign objects into the interior of the structure. Sewn and unsewn repairs are permitted. The type of repair technique to be used depends on the size and location of the damage as well as the never-exceed speed of the aircraft.
When re-covering or repairing control surface fabric, especially on high-performance airplanes, the repairs must not involve the addition of weight aft of the hinge line. The addition of weight disturbs the dynamic and static balance of the surface to a degree that will induce flutter.
Repair of Tears Small cuts or tears are repaired by sewing the edges together and doping a pinked- or frayed-edge patch over the area. The baseball stitch is used in repairing tears. The type illustrated in figure 3-13 enables the damaged edges to be drawn to their original location, thus permitting a tighter repair to be made. The first stitch is started by inserting the needle from the underneath side. All remaining stitches are made by inserting the needle from the top instead of from the bottom so that the points for making the stitch can be more accurately located. The edges are sewn together using the proper thread, The last stitch is anchored with a modified seine knot. Stitches should not be more than 1/4 in.
apart and should extend 1/4 in. into the untorn cover.
Cut two patches of sufficient size to cover the tear and extend at least 1-1/2 in. beyond the tear in all directions (figure 3-14). The fabric used should be at least as good as the original fabric. The edges of the patch should be either pinked or frayed about 1/4 in. on all sides. One patch is saturated with nitrate thinner or acetone and laid over the sewn tear to remove the old finish. The patch is occasionally moistened with a brush until all but the clear 99
1/4" min.
Baseball stitch Start sewing at the point Lock stitching every 8 or 10 stitches, and at ends with SAARA modified seine knot FICURE 3-13. Repair of tears in fabric.
undercoats are soft enough to be removed with a putty knife. Since only the finish under the patch is removed, a neat, smooth repair can be made. A coat of clear tautening dope is applied to the second patch and to the area of the cover from which the finish has been removed. While still wet, this patch is applied to the cover and rubbed so it is smooth and free of air bubbles. Successive coats of clear, pigmented dope are applied until the patched surface has attained the same tension and appearance as the original surrounding surface.
Sewed Patch Repair Damage to covers where the edges oi the tear are tattered beyond joining or where a piece has been completely torn away is repaired by sewing a fabric patch into the damaged area and doping a surface patch over the sewed insert. A sewed-in repair patch may be used if the damage is not longer than 16 in. in any one direction.
The damaged area is trimmed in the form of a circle (figure 3-15) or oval-shaped opening.
fabric insert is cut large enough to extend 1/2 in.
beyond the diameter of the opening. The 1/2-in.
allowance is folded under as reinforcement. Before sewing, fasten the patch at several points with a few temporary stitches to aid in sewing the seams. The edges of the insert are sewed with a baseball stitch.
After the sewing is completed, clean the area of the old fabric to be doped as indicated for repair of tears and then dope the patch in the regular manner. Apply surface tape over any seams that have a second coat of dope. If the opening extends over or closer than 1 in. to a rib or other laced member, the patch should be cut to extend 3 in. beyond the member. After sewing has been completed, the patch should be laced to the rib over a new section of reinforcing tape. The old rib lacing and reinforcing tape should not be removed.
If the fabric covering is damaged at the trailing edge or part of it is torn away as shown in figure 3-16A, it can be repaired as follows. The damaged portion of the panel is removed, and a rectangularor square-shaped opening is made as shown in figure 3-16B. A patch is cut of sufficient size to extend 3/4 in. beyond both sides and the bottom edge of the opening, and 1/2 in. beyond the top.
The edges of the patch are reinforced by being folded under 1/2 in. before being sewed, and each corner is stretched and temporarily held in place with T-pins. Two sides and the trailing edge, as shown in figure 3-16C, are sewed to the old cover with the folded edge extending 1/4 in. beyond both 100
1.5 15
1.5" 1.5" .5". _L -1.5"
•1.5- FIGURE 3-14. Patching over tears. Dash line represents a stitched tear.
ribs. The top of the opening is then sewed. Taping and doping, as shown in figure 3-16D, completes the repair.
Sewed-In Panel Repair When the damaged area exceeds 16 in. in any direction, a new panel should be installed. Remove the surface tape from the ribs adjacent to the damaged area and from the trailing and leading edges of the section being repaired. Leave the old reinforcing tape in place.
Cut the old fabric along a line approximately 1 in. from the center of the ribs on the sides nearest to the damage, and continue the cuts to remove the damaged section completely. The old fabric should not be removed from the leading and trailing edges unless both upper and lower surfaces are being re-covered. Do not remove the reinforcing tape and lacing at the ribs.
Cut a patch to extend from the trailing edge up to and around the leading edge and back approximately to the front beam. The patch should extend (C) (D) approximately 3 in. beyond the ribs adjacent to the damage. FIGURE 3-15. Sewed patch repair.
-Surface tape Rib
•Damaged panel -Trailing edge Opening in panel (A) (B) Side tape Tape end under Hidden stitch ends pinked side tape Baseball stitch - each side and trailing edge before doping New fabric patch • Surface tape All edges of patch folded under 1/2 inch (C) (D) FIGURE 3-16. Repair of panel at trailing edge.
Clean the area of the old fabric to be covered by the patch, put the patch in place, stretch taut and pin. After the patch is pinned in place, fold under the trailing and leading edges of the patch 1/2 in. and sew to the old fabric. Fold the side edges under 1/2 in. and sew to the old cover. After completing the sewing, place reinforcing tape over the ribs under moderate tension and lace down (rib lace or stitch) to the ribs. Remove the temporary pinning.
Give the panel a coat of clear dope and allow to dry. Apply surface tape with the second coat of dope over the reinforcing tape and over the edges of the panel. Finish the doping using regular doping procedures.
This type of repair may be extended to cover both the upper and lower surfaces and to cover several rib bays if necessary. The panel must be laced to all ribs covered.
Unsewed (Doped-On) Fabric Repairs Unsewed (doped-on) repairs may be made on all aircraft fabric-covered surfaces, provided the aircraft never-exceed speed is not greater than 150
m.p.h. A doped-on patch repair may be used if the damage does not exceed 16 in. in any direction. Cut out the damaged section, making a round or ovalshaped opening trimmed to a smooth contour. Use a grease solvent to clean the edges of the opening to be covered by the patch. Sand off the dope from the area around the patch or wash it off with a dope thinner. Support the fabric from underneath while sanding.
For holes up to 8 in. in size, make the fabric patch of sufficient size to provide a lap of at least 2 in. around the hole. For holes over 8 in. in size, make the overlap of the fabric around the hole at least one-fourth the hole diameter with a maximum lap limit of 4 in. If the hole extends over a rib or closer than the required overlap to a rib or other laced member, the patch should be extended at least 3 in. beyond the rib. In this case, after the edges of the patch have been doped in place and the dope has dried, the patch should be laced to the rib over 102
a new section of reinforcing tape in the usual manner. The old rib lacing and reinforcing should not be removed. All patches should have pinked edges or, if smooth, should be finished with pinked-edge surface tape.
as taut as possible, and apply a coat of dope to the portion of the panel that overlaps the old fabric.
After this coat has dried, apply a second coat of dope to the overlapped area and allow to dry.
Place reinforcing tape, under moderate tension, over the ribs and lace the fabric to the ribs.
Doped-In Panel Repair make the repair by doping in a new panel. This type of repair may be extended to cover both the When the damage exceeds 16 in. in any direction, dry. Apply surface tape with the second coat of dope over the reinforcing tape and over the edges Give the panel a coat of clear dope and allow to upper and lower surfaces and to cover several rib of the panel. Finish the doping process using the bays if necessary. The panel should be laced to all regular doping procedure.
ribs covered, and it should be doped or sewed as in REPLACING PANELS IN WING COVERS the blanket method. Repairs to structural parts require opening of the Remove the surface tape from the ribs adjacent fabric. The surface tape is removed from the damto the damaged area and from the trailing and aged rib, the ribs on either side of the damaged rib, leading, edges of the section being repaired. Leave and along the leading and trailing edges where the the old reinforcing tape and lacing in place. Next fabric is to be cut. The rib lacing is removed from cut the fabric along a line approximately 1 in. from the damaged rib. The cover is cut along the top of the ribs on the sides nearest to the damage and the damaged rib and along the leading and trailing continue cutting to remove the damaged section edges as shown in figure 3-17.
completely. The old fabric should not be removed To close an opening of this size, the cut edges are from the leading and trailing edges unless both joined over the rib, the leading edge, and the trailupper and lower surfaces are being re-covered. ing edge with the baseball stitch and a new fabric Cut a patch to run around the trailing edge 1 in. panel is sewn over all the repaired area. The new and to extend from the trailing edge up to and panel extends between the adjacent ribs and from around the leading edge and back approximately to the trailing edge to the leading edge (figure 3-18).
the front beam. The patch should extend approxi- The new fabric is cut so that it can be folded under mately 3 in. beyond the ribs adjacent to the dam- 1/2 in. ard carried 1/4 in. beyond the adjacent age. As an alternative attachment on metal or ribs where it is sewed. The leading and trailing wood-covered leading edges, the patch may be edges are folded and sewed in the same manner.
lapped over the old fabric at least 4 in. at the nose After the panel has been sewed in place, new reinof the leading edge, doped, and finished with at forcing tape is laced over the repaired rib. The new least 8 in. of pinked-edge surface tape. fabric is laced at each of the adjacent ribs without Clean the area of the old fabric that is to be using any additional reinforcing tape. Finally, all covered by the patch and apply a generous coat of surface tapes are replaced, and the new surface is dope to this area. Put the new panel in place, pull finished to correspond to the original covering.
Do not remove reinforcing tape and rib lacing.
Repaired rib Trailing edge Damaged fabric cut tomake needed repairs Leading edge FICURE 3-17. Opening cover for internal structural repair.
RE-COVERING AIRCRAFT SURFACE WITH GLASS CLOTH Fiber glass fabrics are acceptable for re-covering or reinforcing an aircraft surface, provided the material meets the requirements of Military Specifications MIL-C-9084, MIL-Y-1140, and. MIL-G- 1140. The tensile strength of the glass cloth should be at least equivalent to the tensile strength of the fabric originally installed on the aircraft. The chemical finish of the glaas cloth should be chemically compatible with the dope or resin to be used.
Lither the blanket or envelope method of reinforcement should be used on treated fabrics that can be sewn. Untreated fabric that cannot be sewn may be applied in overlapping sections. The practices recommended for doped seams should be used.
Where the glass cloth is applied only to the upper surface of the wings for hail protection, it should wrap around the trailing edge at least 1 in. and extend from the trailing edge up to and around the leading edge and back approximately to the front spar. Before starting the work, make certain that the bonding agents used will be satisfactory. Blistering or poor adhesion can occur when using bond ing agents which are not chemically compatible with the present finish on the aircraft, or which have already deteriorated because of age. A simple means of determining this is to apply a small piece of the reinforcement cloth to the original cover, using the proposed finishing process. The test sample should be visually checked the next day for blistering or poor adhesion.
When butyrate dope is used to bond glass cloth, the finishing can be accomplished in the following manner:
(3) Install reinforcing tape and structural attachments (Class B) and dope on finishing tape (cotton is recommended); then brush in one coat of 50% thinner and 50% butyrate dope.
(4) Follow by conventional finishing schedules, which call for application of one or more coats of full-bodied clear butyrate dope, two spray coats of aluminum pigmented butyrate dope, light surface sand ing, and two spray coats of pigmented butyrate dope.
When resin is used to bond the glass cloth, after surface cleaning, the finishing may be done in the following manner:
(1) Rejuvenate the doped surface. After placing the glass cloth on the surface, brush in thoroughly a coat of resin. Saturate overlapped areas thoroughly and allow to cure.
(2) Brush in a second coat of resin smoothly and evenly and allow to cure. The finished surface should not be considered completed until all the holes between the weave of the cloth are filled flush with resin.
(3) After water sanding, paint the surface with one coat of primer surfacer and finish as desired.
(1) Thoroughly clean the surface and allow to dry. If the surface has been waxed or previously covered with other protective coatings, thoroughly remove at least the top finish coat. After placing the glass cloth on the surface, brush out smoothly and thoroughly with butyrate dope thinner and 10% (by volume) retarder.
(2) Apply a heavy coat of butyrate dope between all glass cloth overlaps. When dry, brush in butyrate rejuvenator and allow to set until the surface has again drawn tight.
Install drain grommets and inspection holes as provided in the original cover.
When using glass fabric to reinforce movable control surfaces, check to ascertain that no change has been made in their static and dynamic balance.
CAUSES OF FABRIC DETERIORATION Aircraft fabrics deteriorate more rapidly in areas of heavy industrialization than in areas that have cleaner air. The greatest single cause of aircraft fabric deterioration is sulfur dioxide. This toxic compound is present in variable amounts in the 104
New fabric patch may go entirely around 1/2 inch new airfoil if damaged on bottom surface.
fabric folded under- Trailing edge New reinforcing Rib lace folded tape on top of patch edge of patch after hand sewing.
- Rib lacing All edges folded and hand-sewn as 1/4 inch past rib y New fabric extends /Old doped stitch Detail of shown at detail cover Old doped cover Original baseball-stitched - Rib reinforcing tape back in place and rib lacing under patch
• Leading edge 1/2 inch folded under - FIGURE 3-18. Method of replacing cover.
atmosphere. It occurs in large concentrations in industrial areas. Sulfur dioxide combines with oxygen, sunlight, and moisture to form sulfuric acid, which, readily attacks cotton fabrics. Linen fabrics are also affected, but to a lesser degree than cotton.
Dacron fabric is far more resistant to sulfur dioxide and other chemicals than any other fabric except fiber glass fabric. Fiber glass fabric is not affected by moisture, mildew, chemicals, or most acids.
Mildew Mildew spores attack fabrics when they are damp. All natural cellulose fibers provide nourishment for mildew growth when conditions are right.
Mildew spores, also known as fungus or mold, can be controlled by using a fungus inhibitor. The inhibitor is usually mixed with dope and applied with the first coat of dope. Dope containing fungicides should not be sprayed because they contain poisons.
Re-covering should be done in dry, clean buildings. Damp, dirty buildings encourage mildew growth. The spores grow on damp rags, paper, etc., and are deposited directly on the fabric surfaces by any movement which stirs the air in the area.
Spores are always present in the atmosphere in varying degrees and are induced into the airframe enclosures by air movement. An aircraft should be flown frequently to circulate dry air into the wings and fuselage so that moisture, which supports mildew, will not accumulate.
Acid Dopes and Thinners The use of dopes or thinners whose acidity has increased beyond safe limits can cause rapid deterioration of aircraft fabrics. When dope is stored under extremes of heat or cold, chemical reactions increase the acidity beyond safe limits.
Stocks of Military dope compound are sold as surplus when periodic tests indicate that the dope has developed an acid content in excess of a safe value. Using surplus dope can lead to early fabric deterioration.
General-purpose thinners should not be used to thin aircraft dope. Such thinners are usually acidic and are not formulated for use with dope.
Insufficient Dope Film A thin dope film does not provide sufficient protection of the fabric from the elements, and early deterioration of the fabric may result. Ultraviolet light, which is invisible, combines with oxygen to form an oxidizing agent that attacks organic materials. The ultraviolet rays can be screened by adding pigments to the dope film and by adequately covering the fabric with the dope. Aluminum powder usually is added to two of the dope coats to stop any ultraviolet light from reaching the fabric. Undoped fabric or fabric covering that is not protected by coats of aluminum-pigmented dope should not be exposed to sunlight for long periods.
Adequate protection of the fabric usually is achieved if the dope film hides the weave of the fabric, leaving a smooth surface. This cannot be determined by the number of coats of dope applied, but rather by the dope film thickness. This varies with application technique, temperature, dope consistency, and equipment.
Cracks in the dope film admit moisture and light, causing localized deterioration of the fabric.
Storage Conditions It is generally assumed that a hangared aircraft is protected from fabric deterioration. However, premature deterioration can occur, especially on aircraft stored in an unheated hangar that has a dirt foor. During the day, sun shining on the roof raises the air temperature in the hangar. This warm air absorbs moisture from the ground. When the air cools, the absorbed moisture condenses and settles on the aircraft. Atmospheric pressure changes draw the damp air into the airframe enclosures. These conditions provide an ideal situation for promoting mildew growth.
When storing fabric-covered aircraft, all openings large enough for rodents to enter should be taped. Uric acid from mice can rot fabric. It can also corrode metal parts, such as ribs, spars, and
CHECKING CONDITION OF DOPED FABRIC The condition of doped fabric should be checked at intervals sufficient to determine that the strength of the fabric has not deteriorated to the point where airworthiness of the aircraft is affected.
The areas selected for test should be those known to deteriorate most rapidly. The top surfaces generally deteriorate more rapidly than the side or bottom surfaces. When contrasting colors are used on an aircraft, the fabric will deteriorate more rapidly under the darker colors. The dark colors absorb more heat than the lighter colors. The warmer inner surface of the fabric under the dark color absorbs more moisture from the air inside the wing or fuselage. When the surface cools, this moisture condenses and the fabric under the dark area becomes moist and promotes mildew growth in a localized area. When checking cloth fabric that has been reinforced by applying fiber glass, peel back the glass cloth in the areas to be tested. Test the underlying cloth in the conventional manner.
Checking fabric surfaces is made easier by using a fabric punch tester. There are several acceptable fabric punch testers on the market; one such tester incorporates a penetrating cone (figure 3-19).
Fabric punch testers are designed for use on the dope-finished-fabric surface of the aircraft and provide only a general indication of the degree of deterioration in the strength of the fabric covering.
Their advantage is that they may be used easily and quickly to test the fabric surfaces without cutting samples from the airplane's fabric. If a fabric punch tester indicates that the aircraft fabric strength is marginal, a laboratory test should be performed to determine the actual fabric strength.
Colored band indicator Fabric FIGURE 3-19. Fabric punch tester.
When using a punch tester similar to the one illustrated in figure 3-19, place the tip on the doped fabric. With the tester held perpendicular to the surface, apply pressure with a slight rotary action until the flange of the tester contacts the fabric. The condition of the fabric is indicated by a colorbanded plunger that projects from the top of the tester. The last exposed band is compared to a chart supplied by the manufacturer of the tester to determine fabric condition.
The test should be repeated at various positions on the fabric. The lowest reading obtained, other than on an isolated reparable area, should be considered representative of the fabric condition as a whole. Fabrics that test just within the acceptable range should be checked frequently thereafter to ensure continued serviceability.
The punch tester makes only a small hole (approximately 1/2-in. diameter) or a depression in the fabric that can be repaired quickly by doping.
on a 2-in. or 3-in. patch.
TESTING FABRIC COVERING Tensile Testing of Undoped Fabric Tensile testing of fabric is a practical means of 106
Spring-loaded scale Jackscrew and crank Fabric strip Pounds Fixed base FIGURE 3-20. Fabric tensile tester.
determining whether a fabric covering has deteriorated to the point where re-covering is necessary.
Figure 3-20 illustrates a typical fabric tensile tester.
A sample of the undoped fabric to be tested is cut to exactly 1-1/2-in. wide and to a sufficient length (usually 6 in.) to allow insertion in the fabric tester. Usually, each edge of the strip is frayed 1/4 in., reducing the woven width to 1 in. The ends of the fabric strip are fastened securely in the clamps of the tester. As the crank of the tester is turned, the threaded jackscrew is backed out, thus gradually increasing the tension (pull) on the fabric against the resistance of the spring-loaded scale until the fabric strip breaks. The scale reading, taken at the moment the fabric strip breaks, indicates the strength of the fabric in pounds per inch.
Fabric specimens must be tensile tested in the undoped condition. Use acetone dope thinner or other appropriate thinning agents to remove the finishing materials from the test specimen.
STRENGTH CRITERIA FOR AIRCRAFT FABRIC Present minimum strength values for new aircraft fabric covering are provided in figure 3-1.
The maximum permissible deterioration for used aircraft fabric, based on a large number of tests, is 30%. Fabric that has less than 70% of the origi nally required tensile strength is not considered airworthy. Figure 3-1 contains the minimum tensile strength values for deteriorated fabric tested in the undoped condition.
Some light aircraft operators use the Grade A type fabric, but are only required to use intermediate grade fabric. In this case, the Grade A material is still considered airworthy, provided it has not deteriorated, as tested in the undoped condition, below 46 pounds, i.e., 70% of the originally required tensile strength value for new intermediate fabric.
DOPES AND DOPING To tighten fabric covering and to make it airtight and watertight, brush or spray the cloth with dope.
A tight fabric cover is essential to securing and holding the cross-sectional shape of the airfoil to the form given it by the ribs. This dope also protects the fabric from deterioration by weather or sunlight and, when polished, imparts a smooth surface to the fabric and reduces skin friction. Dopes must be applied under ideal conditions to obtain satisfactory and consistent results. A clean, fresh, dry atmosphere with a temperature above 70° F.
and a relative humidity below 60%, combined with good ventilation, is necessary in the dope room. The dope must be of the proper consistency and be applied uniformly over the entire surface.
Dopes will deteriorate seriously if stored in too warm a place for a long period. The temperature should not exceed 60° F. for long-time storage and must not exceed 80° F. for periods up to 4 months.
Precautions against fire should be taken wherever dope is stored or used because of its flammable nature. Dope and paint rooms that are not located in a separate building should be isolated from the rest of the building by metal partitions and fireproof doors.
As stated previously, the most desirable condition in a dope room is a temperature above 70° F. and a relative humidity below 60%. At lower tempera tures the dope will not flow freely without the addition of excessive thinners. The relative humidity can be lowered by raising the temperature if the dope shop is not equipped with humidity control.
To condition fabric surfaces to the desired temperature and moisture conditions, allow them to stand about 4 hrs. in the dope room after covering and prior to doping.
The number of coats of dope applied to a fabric surface depends on the finish desired. It is customary to apply two to four coats of clear dope, fol- 107