43.12-1A CHG 1 highly stressed main fittings, as set forth in apter 7, and if necessary, take corrosion vention measures as recommended in Chap-
(3) Replace torn, kinked, or cracked fittings.
(4) Elongated or worn boltholes in fittings ich were designed without bushings are not be reamed oversize. Replace such fittings, ess the method of repair is approved by a resentative of the FAA. Do not fill holes h welding rod. Acceptable methods of rering elongated or worn boltholes in landing r, stabilizer, interplane, or cabane-strut ends y, not originally equipped with pin plates, are wn in figure 2.36. (Also see figure 2.11 on geron repair at fitting.)
. Aluminum and Aluminum Alloy Fittings.
(1) Replace damaged fittings with new parts, ring the same material specifications.
(2) Repairs may be made in accordance with a furnished by the aircraft manufacturer or a substantiating the method of repair may be mitted to the FAA for review.
1. CASTINGS. Damaged castings are to be reced and not repaired unless the method of air is specifically approved by the aircraft nufacturer or substantiating data for the rer has been reviewed by the FAA.
I. SELECTIVE PLATING IN AIRCRAFT MAINTE- NCE. Selective plating is a method of depositmetal from an electrolyte to the selected The electrolyte is held in an absorbent terial attached to an inert anode. Plating tact is made by brushing or swabbing the * (cathode) with the electrolyte-bearing Selective Plating Uses. This process can be I for any of the following reasons:
Co prevent or minimize disassembly, reor masking costs.
sizing worn components (plate to size).
ing in damaged or corroded areas.
plate small areas of extremely large plate electrical contacts.
plate parts too large for existing Page 73
(7) To supplement conventional plating.
(8) To plate components which become contaminated if immersed in a plating bath.
(9) To cadmium-plate ultra high strength steels without hydrogen embrittlement.
(10) On-site plating.
(11) Reverse current applications (e.g., stain removal, deburring, etching, dynamic balancing).
b. Specifications. Selective plating (electrodeposition), when properly applied, will meet the following specifications and standards:
2Q-C-320 Chromium Plating QQ-N-290 Nickel Plating QQ-P-416 Plating, Cadmium QQ-5-865 Silver Plating QQ-Z-325 Zinc Plating MIL-T-10727 Tin Plating MIL-C-14550 Copper Plating MII-G-45204 Gold Plating
c. General Requirements.
(1) Areas to be repaired by this process should be limited to reasonably small areas of large parts, although it may be desirable to plate small parts, particularly electrical or electronic parts, in their entirety.
(2) All solutions should be kept clean and free from contamination. Care should be taken to insure that the solutions are not contaminated by used anodes or other plating solutions. Brush plating solutions are not designed to remove large amounts of scale, oil, or grease. Mechanical or chemical methods should be used to remove large amounts of scale or oxide. Use solvents to remove grease or oil.
(3) Brush plating solutions are five to fifty times as concentrated as tank solutions. The current densities used range from 500 to 4,000 amps/feet?. The voltages listed on the solution bottles have been precalculated to give proper current densities. Too high a current density burns the plating, while too low a current density produces stressed deposits and low efficiencies.
Agitation is provided by anode/cathode motion.
Too fast a motion results in low efficiencies and stressed deposits; too slow a motion causes burning. A dry tool results in burnt plate, coarse grain structure, and unsound deposits. The tool* Par 102
* cannot be too wet. Solution temperatures of 110° to 120° F. are reached during operation.
(4) Materials such as stainless steel, aluminum, chromium, and nickel, which have a passive surface, will require an activating operation to remove the passive surface. During the activating process, do not use solutions that have been previously used with reverse current because of solution contamination.
d. Equipment. The power source should operate on either 110 or 220 volt alternating current (AC), 60 Hertz, single phase input. It should have a capability to produce direct current having smooth characteristics with controlled ripple and be able to output a current of at least 25 amperes at 0 to 25 volts. Minimum instrumentation of the power source should include a voltmeter, ammeter, and ampere-hour meter.
(1) The ammeter should provide a full scale reading equal to the maximum capacity of the power source with an accuracy of +5 percent of the current being measured.
(2) The voltmeter should have sufficient capacity to provide a full scale reading equal to the maximum capacity of the power source and an accuracy of +1.0 volt.
(3) An ampere-hour meter should be readable to 0.001 ampere-hour and have an accuracy of 10.01 ampers-hour.
(4) The stylus should be designed for rapid cooling and to hold anodes of various sizes and configurations. For safety, the anode holder should be insulated.
(5) The containers for holding and catching runoff solutions should be designed to the proper configuration and be inert to the specific solution.
(6) The mechanical cleaning equipment and materials should be designed and selected to prevent contamination of the parts to be cleaned.
e. Materials. The anodes should be of highpurity dense graphite or platinum-iridium alloys.
Do not mix solutions from different suppliers.
This could result in contamination.
f. Detail Requirements. On large parts, no area greater than approximately 10 percent of the total area of the part should be plated by this process. Small parts may be partially or completely plated. Special cases exceeding these Par 104 AC 43.13-1A CI limitations should be coordinated with the ma facturer of the plating equipment being used :
his recommendations should be followed.
g. Anode Selection. As a general guide, contact area of the anode should be appr mately one-third the size of the area to be plat When selecting the anode, the configuration the part will dictate the shape of the anode,
h. Required Ampere-Hour Calculation.
selected plating solution has a factor which equal to the ampere-hours required to dep
0.0001 inch on one square inch of surface. :
termine the thickness of plating desired or certain area and multiply the solution fac times the plating thickness times the area square inches to determine the ampere-hours quired. This factor may vary because of te I. Cleaning. Remove corrosion, scale, oxi and unacceptable plating prior to processi Use a suitable solvent or cleaner to remove gre or oil.
I. Plating on Aluminum and Aluminum Bi Alloys.
(1) Electroclean the area using forw (direct) current until water does not break the surface. This electroclean process should accomplished at 10 to 15 volts, using the app priate electroclean solution.
(2) Rinse the area in cold clean tap water.
(3) Activate the area with reverse curre 7 to 10 volts, in conjunction with the proj activating solution until a uniform gray to bla surface is obtained.
(4) Rinse thoroughly in cold, clean tap wat
(5) Immediately electroplate to color wh the area is still wet, using the appropriate nic solution.
(6) Rinse thoroughly.
(7) Immediately continue plating other solution to desired thickness.
(8) Rinse and dry.
k. Plating on Copper and Copper i
(1) Electroclean the area usin (direct) current until water does no the surface. The electroclean process accomplished at 8 to 12 volts using t.
priate electroclean solution.
43.13-1A CHG 1
(2) Rinse the area in cold, clean tap water.
(3) Immediately electroplate the area with y of the plating solutions except silver. Silver quires an undercoat.
(4) Rinse and dry.
I. Plating on 300 and 400 Series Stainless Steels, ckel Base Alloys, Chrome Base Alloys, High ckel Ferrous Alloys, Cobalt Base Alloys, Nickel ate, and Chrome Plate.
(1) Electroclean the area using forward irect) current until water does not break on e surface. This electroclean process should be complished at 12 to 20 volts using the approiate electrocleaning solution.
(2) Rinse the area in cold, clean tap water.
(3) Activate the surface using forward lirect) current for 1 to 2 minutes using the tivating solution and accomplish at 6 to 20 Its.
(4) Do not rinse.
(5) Immediately nickel flash the surface to thickness of 0.00005 to 0.0001 inch using the propriate nickel solution.
(6) Rinse thoroughly.
(7) Immediately continue plating with any her solution to desired thickness.
(8) Rinse and dry.
m. Plating on Low-Carbon Steels (Heat Treated 180,000 psi).
(1) Electroclean the area using forward irect) current until water does not break on e surface. This electroclean process should be complished at 12 to 20 volts using the approiate electrocleaning solution.
(2) Rinse the aren in cold, clean tap water.
(3) Reverse current etch at & to 10 volts, the appropriate activating solution, until form gray surface is obtained.
Rinse thoroughly.
mediately electroplate the part using ns except copper acid or silver. Both re undercoats.
se and dry.
ig on Cast Iron and High-Carbon Steels at Treated to 180,000 psi).
flectroclean the area using forward current until water does not break on Page 73-2 the surface. This electroclean process should be accomplished at 12 to 20 volts using the appropriate electrocleaning solution.
(2) Rinse the area thoroughly in cold, clean tap water.
(3) Reverse current etch at & to 10 volts, using the appropriate etching solution, until a uniform gray is obtained.
(4) Rinse thoroughly.
(5) Remove surface smut with 15 to 25 volts using the appropriate activating solution.
(6) Rinse thoroughly.
(7) Electroplate immediately using any of the solutions except copper or silver (both these require undercoats).
(8) Rinse and dry,
o. Plating on Ultra High Strength Steels (Heat Treated Above 180,000 psi).
(1) Electroclean the area using REVERSE current until water does not break on the surface.
This electroclean process should be accomplished at 8 to 12 volts using the appropriate electroclean solution.
(2) Rinse the area thoroughly in cold, clean tap water.
(3) Immediately electroplate the part, using either nickel, chromium, gold, or cadmium. Other metals require an undercoat of one of the above.
Plate initially at the highest voltage recommended for the solution so as to develop an initial barrier layer. Then reduce to standard voltage.
(4) Rinse and dry.
(5) Bake the part for 4 hours at 375° +25° F.
NoTF 1: Where the solution vendor provides sub stantiating data that hydrogen embrittlement will not result from plating with a particular solution, then a post bake Is not required. This substantlating data can be in the form of aircraft Industry manufacturers' process specifications, military specifications, or other suitable data.
NoTE 2: Acid etching should be avoided, if pos sible. Where etching is absolutely necessary, It should always be done with reverse current. Use alkaline solutions for initial deposita.
p. Dissimilar Metals and Changing Base.
a general rule, when plating two dissimilar metals, follow the plating procedure for the one with the most steps or activation. If activating* Par 104
* steps have to be mixed, use reverse current activation steps prior to forward (direct) current.
activation steps.
q. Plating Solution Selection.
(1) Alkaline and neutral solutions are to be used on porous base metals, white metals, highstrength steel, and for improved coating ability.
Acid solutions are to be used for rapid buildup and as a laminating structure material in conjunotion with alkaline type solutions.
(2) Chrome brush plating solutions do not yield as hard a deposit as bath plating solutions.
The hardness is about 600 Brinell as compared to 1,000 Brinell for hard chrome deposited from a tank.
(3) Silver immersion deposits will form with no current flowing on most base metals from the silver brush plating solutions; such deposits have poor adhesion to the base metal. Consequently, a flash or a more noble metal should be deposited prior to silver plating to develop a good bond.
(4) In general, brush plating gives less hydrogen embrittlement and a lower fatigue strength loss than does equivalent tank deposits.
However, all brush-plated, ultra high strength steel parts (heat treated above 180,000 psi) Par 104 AC 43.13-1A CI should be baked as mentioned in paragr
104.0.(5), unless it is specifically known t embrittlement is not a factor.
r. Qualification Tests. All brush plated t faces shall be tested for adhesion of the elec deposit. Apply a 1-inch wide strip of Minnes Mining and Manufacturing tape code 250, or approved equal, with the adhesive side to freshly plated surface. Apply the tape v heavy hand pressure and remove it with quick motion perpendicular to the plated t face. Any plating adhering to the tape shall cause for rejection.
s. Personnel Training for Quality Cont Manufacturers of selective plating equipm provide training in application techniques their facilities. Personnel performing select plating must have adequate knowledge of methods, techniques, and practices invol These personnel should be products of th training programs and certified as qualified erators by the manufacturers of the prod used, as well as by local quality control deps
105.-114. RESERVED.
Page 74 AC 43.13 Section 4. REPAIR OF LAMINATE STRUCTURES
115. GENERAL. There is a wide variation in the composition and structural application of laminates, and it is essential that these factors be given major consideration when any restoration activities are undertaken. To a similar extent, there also exist many types of laminate structure repairs that may or may not be suitable for a given condition. For this reason, it is important that the aircraft or component manufacturer's repair data be reviewed when determining what specific type of repair is permissible and appropriate for the damage at The materials used in the repair of laminate structures must preserve the strength, weight, aerodynamic characteristics, or electrical properties of the original part or assembly. This . can best be accomplished by replacing damaged material with material of identical chemical composition or a substitute approved by the manufacturer.
In order to eliminate dangerous stress concentrations, avoid abrupt changes in cross-sectional areas. Whenever possible, for scari joints and jacings, make small patches round or oval-shaped, and round the corners of large repairs. Smooth and properly contour aerodynamic surfaces.
It is recommended that test specimens be prepared at the same time that the actual repair is accomplished. These can then be subjected to a destructive test to establish the quality of the adhesive bond in the repaired part. To make this determination valid, the specimens must be assembled with the same adhesive batch mixture and subjected to curing pressure, temperature, and time identical with those in the actual repair.
a. Fiberglass Laminate Repairs. The following repairs are applicable to fiberglass laminate used for fairings, covers, cowlings, honeycomb panel facings, etc. Prior to undertaking the re- Par 115 pair, clean the repair area thoroughly with castile soap and warm water. Remove a paint by wet or dry sanding methods. Se blasting may be used but caution must be ex cised to not abrade the surfaces excessively.
Superficial scars, scratches, surface abi sion, or rain erosion can generally be repair by applying one or more coats of a suital resin, catalyzed to cure at room temperatu to the abraded surface. The number of co required will depend upon the type of re and severity of the damage.
Damage not exceeding the first layer or of fiberglass laminate can be repaired by fil with a putty consisting of a compatible ro temperature-setting resin and clean short gl fibers. Before the resin sets, apply a sheet cellophane over the repair area and work c any bubbles and excess resin. After the res has cured, sand off any excess and prepare t area for refinishing.
Damage deep enough to seriously affect t strength of the laminate (usually more th the first ply or layer of fabric) may be 1 paired as illustrated in figure 2.87. Coat t
DAMAGE TO FACING
DAMAGED MATERIAL /REMOVED BY SANDIN . REPLACED LAMINATIONS
SANDED TO CONTOUR FIGURE 2.37.-Typical laminate (facing) repair.
Chaj
I-IA Page 75 I area with room-temperature-setting DAMAGE TO FACHG ANO COME and apply contoured pieces of glass fabaked in resin. Apply a cellophane sheet he repair and work out any bubbles and resin. After the resin has cured, scrape excess resin and sand the surface of the to the original contour. OOT DAMASED COME MACHO' SCAMPED POR MATC
REMOVEU, nage that extends completely through cing and into the core requires the rerent of the damaged core and facing. A d for accomplishing this type of repair is in figure 2.88. An alternate method for ling the facing is shown in figure 2.89.
imaged portion is carefully trimmed out rcular or oval shape and the core matemoved completely to the opposite facing.
se caution so as not to damage the oppoeing or to start delamination between ngs and the core around the damage.
FIGURE 2.88.-Typical core and facing repair.
CAUTION iding fiberglass laminates gives off a fne dust it may cause skin and/or respiratory irritation less suitable skin and respiration protection is ed.
› replacement core stock of the same maand density as the original (or an acceptsubstitute) and cut it to fit snugly in the ned hole. When all pieces of replacement YOLE TRIMMED, "STEP-PEELED COME NEMOVEL r laminations are cut and soaked in resin, AND FACING all surfaces of the hole and the scarfed with resin. Then coat all surfaces of the replacement with resin and insert it into ole. After all of the pieces of resin-imated glass-fabric facing are in place, WET-LAMINATED PATCH WITH the entire area with a piece of cellophane EXTRA LAYER OF THIN CLOTH 'arefully work down the layers of fabric move any air bubbles and excess resin.
y light pressure by means of sand bags or cuum blanket. When the resin has cured, the repair to match the original contour efinish the surface. TEMPORARY BLOCK OR MOLO 'TEMPORARY SHIM mage that is completely through a lamisandwich structure may be repaired as ilated in either figure 2.39 or 2.40. The ed joint method, figure 2.40, is normally on small punctures up to 8 or 4 inches in mum dimension and in facings which are e of thin fabric that is difficult to peel. The ›ed joint, figure 2.39, is most often used on
COMPLETE BY STEP-PEELING AND WET-LAMINATING OPPOSITE
FACING IN A SIMILAR OPERATION FIGURE 2.88.-Typical stepped Joint repair.
larger repairs to facings composed of thick fabrics.
When access for repair is possible from only one side, blind repair procedures are employed.
Per 116
Page 76 АС • OLE Repairs of this type have been made by t glass-fiber-reinforced plastic backing pli proximately 0.060-inch thick. The b plate can be fabricated from layers of fabric and room-temperature-curing re sandwiching the resin-impregnated lay‹
- 100т-. HOLE AND TRIMMED, CORE REMOVED, FACING SCARFED tween two sheets of cellophane. Work t cess resin out and allow the plate to cur flat surface or a cellophane-covered sur!
the proper curvature near the damaged or at the same location on a comparable u aged part. The technique for bondir backing plate in place is similar to tha WET-LAMINATED PATCH trated in figure 2.41 for metal-faced la repairs. After the backing plate is bor place with resin, complete the repair as in figure 2.88.
b. Metal-Faced Laminate Repairs. Rel TEMPORARY MOLDLOCK TEMPORARY SHIM laminate with magnesium, titanium, o OR less steel facings require procedures w COMPLETE BY SCARFING AND WET-LAMINATING OPPOSITE specially devised and not included in
FACING IN A SIMILAR OPERATION lowing methods of repair. Aluminum FIGURE 2.40.-Typical scarfed joint repair. such as 7075-T6, 2024-T8, and 2014-1
WOOD OR SELF-TAPPING
METAL SCREWS STEP 1- PLYWOOD CAUL
BACKING PLATE --CELLOPHANE
ANO COPE
BEING GLUED
IN PLACE
OLUE SOUEEZE-OUT
REPLACE PLAT 10064"
PLYWODO CAUL
CUSHION TAPERED COVER STEP 8- -CELLOPHANE
PLATE BEING
GLUED IN PLACE
JAPERED COVER PLATE (SAME THICKNESS AS FACING)
FILLED SCREW HOLES -OVEALAP 125T-
COMPLETED REPAIR FIGURE 2.41.-Typical one side blind repair.
Par 115
13-1A only used for the repair of facings for ated structural parts having aluminum gs. For maximum corrosion resistance, nly clad aluminum for repairs to clad alum alloy facings.
hts, scratches, or fractures, not exceeding ourth inch in largest dimension, in alumifacings may be repaired with a suitable such as viscous epoxy resin. Thoroughly the repair area with fine sandpaper and he before applying the filler. After the has partially cured, remove any excess with a sharp scraper or chisel. When stely cured, sand to original contour. If amage included a fracture, reclean the round the filled hole and apply a surface as shown in figure 2.42, by means of resin and a similar curing cycle.
tures or punctures in one facing and damage to the core of an aluminumaminate may be repaired by several difmethods. The technique used will deupon the size of the damage and the igth, aerodynamic, and sonic fatigue rence requirements of the area involved. If repair requires aerodynamic smoothness, 'acing surrounding the repair core cavity -DAMAGE TO METAL FACING
HONEYCOMB CORE 1 CELLOPHANE
PLYWOOD PRESSURE PLATE CUSHION:
ELWOOD OR SELF-TAPPING SCREWS.
OVERLAP TAPERED COVER PLATE
•FILLER FIGURE 2.42.- -Typical metal facing patch.
Page 77 may have to be step cut to one-half its thickness. This can be done by using a router with an end mill bit and a template.
Damage that extends completely through the core and both facings may be repaired using the same general techniques as those used for repairing fiberglass laminates when both facings are accessible (see figures 2.39 and 2.40).
When the inner facing is not accessible, a procedure such as that shown in figure 2.41 may be used. The outer surface patch could then be installed in a manner similar to the repair shown in figure 2.42.
After locating the extent of the total damaged area by tapping or other nondestructive test methods, remove the damaged facing and that portion of the core material which is also affected. The depth to which the core must be removed will depend upon the type of core material and method of repair. If the replacement core material is the same as the original, fabricate it to shape keeping the same core ribbon or grain direction. When a substitution is permissible, wood or glass-fabric honeycomb cores are sometimes used in the repair of aluminum honeycomb cores as they are generally easier to shape. Typical types of core replacementa are shown in figure 2.43. Resin fills can be used to replace the core and facing where smaller core damage exists. Phenolic microballoons, low-density insulating materials and/or other ingredients, are added to lower the density and give greater flexibility, thus lowering stress concentrations in the repair area.
For the repair of larger holes in which it is inconvenient to use a face patch because of aerodynamic smoothness requirements in that area, both the core and facing are sometimes replaced with glass-fiber fabric discs and resin.
Undercut the core, as shown in figure 2.44, in order to obtain a better bonding of the fill with the facing. Fill the core cavity with accurately shaped resin-saturated glass cloth discs, and press each ply down to remove any air bubbles.
Special care should be taken that the final plies fit well against the underside of the top facing.
When the core cavity is filled, close the cutout in the facing with resin-impregnated glassfiber fabric discs that have been precut to size.
There are five general types of facing Par 115
Page 78 AC 4 A. REPLACEMENT WITH CORE PLUG OF SAME OR OTHER TYPES OF CORE MATERIAL patches used after replacement of the cor been completed and they are described k COME PLUG Each of these patches meet certain servi COME IEYCOMB. AOUTED AREA ¡ EPOXY-RESIN quirements that must be considered bef ADHE SIVE decision can be reached as to which is a priate for a specific application.
(1) A Small, Flush Plug-type. A plug ( same material and thickness as the faci B. RESIN FILL bonded in place after the core has bee EPOXY-RESIN 'FILL. ORIGINAL ROUTED AREA- placed. This type of patch gives aerody smoothness but does not replace any o HONEYCOMB. COME PARTIAL ON COMPLETE DEPTH OF CORE strength initially lost in the damaged facin
12) An Overlap Type Metal Facing Patc overlap surface patch is bonded in place the facing and replaced core. With this t patch, and good bonding techniques, i C. RESIN FILL, UNDERCUT CORE cally full strength of the facing is reg EPOSY-RESIN FILL. MOUTED AREA Overlaps of less than 125 times the thi HONEYCOMB ORIGINAL DEPTH OF COME ATIAL OR COMPLETE of the facing can be used in repairs wh COME CORE UNDERCUT skins are not highly stressed.
(3) A Step-type Facing Patch. The ste facing patch retains aerodynamic smoot but has only a maximum of 50 percent c D. GLASS-CLOTH-RESIN LAMINATE, UNDERCUT CORE original facing tensile strength.
(4) A Scarf-type Facing Patch. This is a OUTED AREA bination of the overlap and the ster CORE which results in the same aerody!
smoothness as the step-type but gr strength efficiency.
(5) An Overlap Type Resin-glass Facing E. REPLACEMENT WITH CORE PLUG OF SAME An overlap patch of glass-fiber fabric TYPE OF SANDWICH CONSTRUCTION resin has fair aerodynamic smoothness a SANDWICH HOUTED AREA easy to fabricate with a minimum of e
ORIGIMAL МОЖЕУСОНА EPOXY-RESIN ment. It fits easily in transition curvature
CORE ADHESIVE results in a lower facing strength thai original skin.
c. Finishing. The type of finish coating al FIGURE 2.43.-Typical types of core replacement. to a laminate repair will normally be
CORE ORIGINAL CORE TO SKIN ADHESIVE
- JAGGED EDGES
SECTION SHOWING UNDERCUT
• FINISHED UNDERCUT AREA FIGURE 2.44.-Typical undercut core material cavity.
Par 115
„13-1A d by the facing material and the applicaof the part or assembly. Rain erosion of ic parts, the need for electrical or dielecproperties and/or the necessity for anticorn coatings must be considered when the e of finish is made. Plastic-faced parts as radomes are finished primarily for rain on while aluminum- or other metal-faced nates are finished for corrosion protection.
coatings to perform their function prop- Page 79 erly, it is essential that they be applied to surfaces that are clean, free of voids, and exceedingly smooth.
The edges of all parts not protected by a bonding of aluminum or glass-fabric laminate must be sealed to reduce the rate of moisture absorption. The wood-bonded edges of plywood, mahogany, spruce, or balsa may be given two coats of aluminized spar varnish.
116.-126. RESERVED.
Par 115
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.
Par 127
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.