43.13-1A Page 119
NOTE - LEGEND-
WHEN USING A TORQUE WRENCH ADAPTER WHICH T - ACTUAL (DESIREDI TORQUE CHANGES THE DISTANCE FROM THE TORQUE WRENCH Y= APPARENT (INDICATED) TORQUE DRIVE TO THE ADAPTER DRIVE, APPLY THE L. - EFFECTIVE LENOTH LEVER FOLLOWING FORMULAS TO OBTAIN THE CORRECTED = ENFECTIVE LENGTH OF EXTENSION TORQUE READING:
Hort Open End Open-End Wrench Adapter CENTERLINE ADAPTER DRIVE WRENCH TORQUE WRENCH DRIVE TORQUE WRENCH HANDGRIP CENTERLINE Adapter
WRENCH CENTERLINE ADAPTER (PREDETE MINED) DRIVE
CENTERLINE CENTERINE Set Screw Flare Nut Wrench Adapter Adapter EXAMPLE: (WITH "E" AS PLUS DIMENSIONI EXAMPLE: (ATTH "E" AS HINUS DUHENSION) T - 135 LE. IN. 8= 10715-18-11790 T - 135 LD. 04. r- 123-18 - 125-150.82 Hose Clamp Y - UNKNOWN Y - UNKNOWN Spanner Wrench Adapter L - 10.0 IN. 1 - 10.0 MN. Adapter € = 1.5 IN. Y - 117 LB. AN. 1 - 1.5 HN. Y - 159 18. 04.
FIGURE 5.3.-Torque wrench with various adapters.
crews, nuts, bolts, or rivets in the original pructure.
129. TAPER PINS (AN-385 AND AN-386), Plain und threaded taper pins are used in joints which carry shear loads and where absence of ›lay is essential. The plain taper pin is drilled and usually safetied with wire. The threaded aper pin is used with a taper-pin washer (AN-975) and shear nut (safetied with cotter ›in) or self-locking nut.
a. The Flathead Pin (MS-20392), Commonly 'alled a clevis pin, the flathead pin is used in conjunction with tie rod terminals and in sec- ›ndary controls which are not subject to coninuous operation. The pin is customarily intalled with the head up so that if the cotter ›in fails or works out, the pin will remain in lace.
b. The AN-380 Cotter Pin. This is used for safetying bolts, screws, nuts, other pins, and in arious applications where such safetying is recessary. Use AN-381 cotter pins in locations where nonmagnetic material is required or in ocations where resistance to corrosion is deired.
hap 3
230. NUTS.
a. Self-Locking Nuts. Self-locking nuts are acceptable for use on certificated aircraft subject to the restrictions on the pertinent manufacturer's recommended practice sheets. Selflocking nuts are used on aircraft to provide tight connections which will not shake loose under severe vibration. Two types of selflocking nuts are currently in use, the all-metal type and the fiber or nylon lock type. Do not use self-locking nuts at joints which subject either the nut or bolt to rotation. They may be used with antifriction bearings and control pulleys, provided the inner race of the bearing is clamped to the supporting structure by the nut and bolt. Attach nuts to the structure in a positive manner to eliminate rotation or misalignment when tightening the bolts or screws.
(1) All-metal locknuts are constructed with either the threads in the locking insert out-ofphase with the load-carrying section, or with a saw-cut insert with a pinched-in thread in the locking section. The locking action of the allmetal nut depends upon the resiliency of the metal when the locking section and loadcarrying section are engaged by screw threads.
Par 228
(2) Fiber or nylon locknuts are constructed with an unthreaded fiber-locking insert held securely in place. The fiber or nylon has a smaller diameter than the nut, and when a bolt or screw is entered, it taps into the insert, producing a locking action. After the nut has been tightened, make sure the rounded or chamfered end bolts, studs, or screws extend at least the full round or chamfer through the nut. Flat end bolts, studs, or screws should extend at least 1/32 inch through the nut. When fiber-type self-locking nuts are reused, check the fiber carefully to make sure it has not lost its locking friction or become brittle. Do not reuse locknuts if they can be run up fingertight. Bolts 5/16-inch diameter and over with cotter pinholes may be used with self-locking nuts but only if free from burrs around the holes. Bolts with damaged threads and rough ends are not acceptable. Do not tap the fiberlocking insert.
(3) Self-locking nut bases are made in a number of forms and materials for riveting and welding to aircraft structure or parts. Certain applications require the installation of self-locking nuts in channels, an arrangement which permits the attachment of many nuts with only a few rivets. These channels are track-like bases with regularly spaced nuts which are either removable or nonremovable.
The removable type carries a floating nut, which can be snapped in or out of the channel, thus making possible the ready removal of damaged nuts. Nuts such as the clinch-type and spline-type which depend on friction for their anchorage are not acceptable for use in aircraft structures.
(4) Self-locking nuts may be used on aircraft engines and accessories when their use is specified by the engine manufacturer in his bulletins or manuals.
b. Aircraft Castle Nut (AN-310). The castle nut is used with drilled-shank AN hex-head bolts, clevis bolts, eye bolts, drilled-head bolts or studs, and is designed to accommodate a cotter pin or lockwire as a means of safetying.
c. Miscellaneous Aircraft Nuts.
(1) The plain nut (AN-315 and AN-385) has limited use on aircraft structures and re- Par 230 AC 43.13 quires an auxiliary locking device such as checknut or lockwasher.
(2) Light hex-nuts (AN-840 and AN-345 are used in miscellaneous applications an must be locked by an auxiliary device.
(3) The checknut (AN-316) is used as locking device for plain nuts, screws, threade rod ends, and other devices.
(4) The castellated shear nut (AN-320) i designed for use with clevis bolts and threade taper pins, which are normally subjected t shearing stress only.
(5) Wing nuts (AN-350) are intended fo we were the desiren i battes is onditiont obtained by the use of the fingers or han tools.
(6) Sheet spring nuts, such as speed nuts are used with standard and sheet metal self tapping screws in nonstructural locations They find various uses in supporting lin clamps, conduit clamps, electrical equipment access doors, and the like, and are available i several types.
(7) Two commercial types of high-strengt internal or external wrenching nuts are availa ble, the internal and external wrenching elastic stop nut and the Unbrako internal and externa wrenching nut. Both are of the self-lockin type, are heat-treated, and are capable of carry ing the high-strength bolt-tension load.
231. WASHERS. The types of washers used i aircraft structure are: plain washers, lock washers, and special washers.
a. Plain washers (AN-960 and AN-970) ar widely used under hex nuts to provide smoothbearing surface, to act as a shim and t adjust holes in bolts. Use plain washers unde lockwashers to prevent damage to surfaces Cadmiumplated steel washers are recom mended for use under boltheads or nuts on alu minum alloy or magnesium structures wher corrosion, if it occurs, will then be between the washer and the steel. The AN-970 stee washer provides a greater bearing area than th plain type, and is used in wooden structure:
under both boltheads and nuts to prevent loca crushing of the surface.
Chap !
|43.13-1A
b. Lock washers (AN-935 and AN-936) may be ed with machine screws or bolts whenever e self-locking or castellated type of nut is t applicable. They are not to be used as fasnings to primary or secondary structures, or here subject to frequent removal or corrosive nditions.
c. Ball-socket and seat-washers (AN-950 and V-955) are used in special applications where e bolt is installed at an angle to the surface, ' when perfect alinement with the surface is quired at all times. These washers are used gether.
d. Taper-pin washers (AN-975) are used with le threaded taper pin.
e. NAS-143 washers are used with NAS inernal wrenching bolts and internal wrenching uts. Type "C" is countersunk to seat the boltead shank radius and a plain-type washer is sed under the nut. Both of these washers are eat treated from 125,000 to 145,000 p.s.i.
32. TYPES OF RIVETS.
a. Standard solid-shank rivets and the univeral head rivets (AN-470) are used in aircraft onstruction in both interior and exterior locaions.
b. Roundhead rivets (AN-430) are used in the nterior of aircraft except where clearance is equired for adjacent members.
c. Flathead rivets (AN-442) are used in the inerior of the aircraft where interference of adacent members does not permit the use of 'oundhead rivets.
d. Brazierhead rivets (AN-455 and AN-456) tre used on the exterior surfaces of aircraft where flush riveting is not essential.
e. All protruding head rivets may be replaced y MS-20470 (supersedes AN-470) rivets.
This has been adopted as the standard for proruding head rivets in this country.
f. Countersunk head rivets MS-20426 (supersedes AN-426 100° ) are used on the exterior surfaces of aircraft to provide a smooth aerodynamic surface, and in other applications where a smooth finish is desired. The 100° Chap S Page 121 countersunk head has been adopted as the standard in this country.
233, MATERIAL APPLICATIONS.
a, 2117-13 is the most commonly used rivet material utilized in aluminum alloy structures.
Its main advantage lies in the fact that it may be used in the condition received without further treatment.
b. The 2017-T3, 2017-731, and 2024-74 rivets are used in aluminum alloy structures where strength higher than that of the 2117-T8 rivet is needed. See Handbook MIL-HDBK-5 for differences between the two types of 17ST rivets specified here.
c. The 1100 rivets of pure aluminum are used for riveting nonstructural parts fabricated from the softer aluminum alloys, such as 1100, 3003, and 5052.
d. When riveting magnesium alloy structures, 5056 rivets are used exclusively due to their corrosion-resistant qualities in combination with the magnesium alloys.
•. Mild steel rivets are used primarily in riveting steel parts. Do not use galvanized rivets on steel parts subjected to high heat.
f. Corrosion-resistant steel rivets are used primarily in riveting corrosion-resistant steel parts such as firewalls, exhaust stack bracket attachments, and similar structures.
g. Monel rivets are used in special cases for riveting high-nickel steel alloys and nickel alloys. They may be used interchangeably with stainless steel rivets as they are more easily driven. However, it is preferable to use stainless steel rivets in stainless steel parts.
h. Copper rivets are used for riveting copper alloys, leather, and other nonmetallic materials. This rivet has only limited usage in aircraft.
I. Hi-shear rivets are sometimes used in connections where the shearing loads are the primary design consideration. Its use is restricted to such connections. It should be noted that hishear rivet patterns are not to be used for the installation of control surface hinges and hinge Par 231
brackets. Do not paint the rivets prior to assembly, even where dissimilar metals are being joined. However, it is advisable to touch up each end of the driven rivet with zinc chromate primer to allow the later application of the general airplane finish.
i. Blind rivets in the MS-20600 through MS- 20603 series rivets and the mechanically-locked stem NAS 1898, 1399, 1738, and 1739 rivets may be substituted for solid rivets in accordance with the blind rivet manufacturer's recommendations. They should not be used where the looseness or failure of a few rivets will impair the airworthiness of the aircraft. Design allowables for blind rivets are specified in MIL- HDBK-5, Metallic Materials and Elements for Flight Vehicle Structures. Specific structural applications are outlined in MS-33522. Non- Par 233 AC 43.13- structural applications for such blind rivets MS-20604 and MS-20605 are contained in MS 33557.
234. FASTENERS (COWL AND FAIRING). A nun ber of patented fasteners are in use on aircraf A variety of these fasteners are commel cially available and the manufacturer's recon mendations concerning the proper use of thes types of fasteners should always be considere in other than replacement application.
235. UNCONVENTIONAL ATTACHMENTS. Do no use unconventional or new attachment device in the primary structure unless approved by representative of the Federal Aviation Admin istration.
236.-246. RESERVED.
Chap s
43.13-1A Page 133 Chapter 6. CORROSION PROTECTION
7. TYPES OF CORROSION. Almost all metals ed in aircraft are subject to corrosion. The tack may take place over an entire metal surce, or it may be penetrating in nature, formg deep pits. It may follow grain boundaries its attack on metallic surfaces or it may penrate a surface at random. It may be accenated by stresses from external loads or existg in the metallic structure from lack of mogeneity or improper heat treatment. It is romoted by contact of the metals with marials that absorb water, such as wood, sponge abber, felt, dirt, surface film, etc. Corrosion is ferred to as the following types:
a. Direct Surface Atfack, The most common pe of general surface corrosion results from rect reaction of metal surface with oxygen in e air. Unless properly protected, steel will ist and aluminum and magnesium will form rrosion products. The attack may be accelerted by salt spray or salt-bearing air, by inustrial gases, or by the aircraft engine exaust gases.
b. Dissimilar Metals Corrosion. When two dismilar metals are in contact and are connected y an electrolyte (continuous liquid or gas ath-salt spray, exhaust gas, condensate) acelerated corrosion of one of the metals may ccur. The most easily oxidized surface beomes the anode and corrodes. The less active ember of the couple becomes the cathode of he galvanic cell. The degree of attack depends n the relative activity of the two surfaces; the reater the difference in activity, the more seere the attack. The materials listed in Group I re quite active and corrode easily. They reuire maximum protection. Group IV materials re the least active and therefore require minium protection. Except as noted below, whenver metals from two different groups are in ontact with each other, special protection is equired to assure that dissimilar metal corrosion does not occur. Although aluminum alloys and tin are in different groups than magnesium, tin and the 5000 and 6000 series aluminum alloys may each be used in contact with magnesium without such protection. Tin may also be used with all aluminum alloys without special protection.
(1) Group I. Magnesium and its alloys.
(2) Group II. All aluminum alloys, cadmium, zine.
(a) Subgroup A. 1100, 3003, 5052, 6061, 220, 855, 856. All clad alloys.
(b) Subgroup B. 2014, 2017, 2023, 7075,
195. Under severe corrosive conditions, the subgroups should be considered as dissimilar metals insofar as corrosion protection is concerned.
This is particularly true when a large area of an alloy of Subgroup B is in contact with a small area of Subgroup A. Severe corrosion of the alloy from Subgroup A may be expected.
(3) Group III. Iron, lead, and tin and their alloys (except stainless steels).
(4) Group IV. Stainless steels, titanium, chromium, nickel, and copper and their alloys, graphite (including dry film lubricants containing graphite).
c. Pitting. While pitting may occur in any metal, it is particularly characteristic of passive materials such as the alloys of aluminum, nickel, and chromium. It is usually a localized breakdown of protection and may be due to a lack of homogeneity in the alloy surface, either from mechanical working or faulty heat treatment. It may also be due to an inclusion or rough spot in the metal surface or from localized contamination that breaks down the surface protection. Pitting takes place at random with no selective attack along grain boundaries. Isolated areas become anodic to the rest of the surface. Corrosion products formed accentuate the anodic characteristics in the pit hap 6
area, and deep penetrating attack develops rather than a general surface attack.
d. Intergranular Corrosion. Selective attack along the grain boundaries of metal alloys is referred to as intergranular corrosion. It results from lack of uniformity in the alloy structure. It ia particularly characteristic of precipitation hardened alloys of aluminum and some stainless steels. Aluminum alloys 2024 and 7075 which contain appreciable amounts of copper and zinc respectively are highly vulnerable to this type of attack if not quenched rapidly during heat treatment or given other special treatment such as the T78 temper condition for the 7075 alloys. Aluminum extrusions and forgings in general may contain nonuniform areas, which in turn may result in galvanic attack along the grain boundaries.
This type of corrosion is difficult to detect in its original stage although ultrasonic and eddy current inspection methods are being used.
When attack is well advanced, the metal may blister or delaminate. This is referred to as "exfoliation."
e. Stress Corrosion. This results from the combined effect of static tensile stresses applied to a surface over a period of time under corrosive conditions. In general, cracking susceptibility increases with stress, particularly at stresses approaching the yield point, and with increasing temperature, exposure time, and concentration oi corrosive ingredients in the surrounding environment. Aluminum alloy bellcranks employing pressed-in taper pins, landing gear shock struts with pipe thread-type grease fittings, clevis joints, and shrink fits are examples of parts which are susceptible to stress corrosion cracking.
f. Corrosion Fatigue. Corrosion fatigue is a type of stress corrosion resulting from cyclic stresses on a metal in corrosive surroundings.
Corrosion may start at the bottom of a shallow pit in the stressed area. Once attack begins, the continuous flexing prevents the repair of protective surface coating or oxide films and additional corrosion takes place in the area of stress. It is difficult to detect this type of attack in advance except as cracking develops.
Par 247 AC 43.1
g. Fretting, Fretting corrosion is a lim type of attack that develops when relative tion of small amplitude takes place betw close fitting components. The rubbing con destroys any protective film that may be p ent on the metallic surface and addition removes small particles of virgin metal f the surface. These particles act as an abra:
and prevent the formation of any protec oxide film and exposes fresh active metal to atmosphere. If the contact areas are small.
sharp, deep grooves resembling brinnell me ings or pressure indentations may be worr the rubbing surface. As a result, this type corrosion has also been called false brinnell when developed on bearing surfaces.
248. CORROSION PROTECTION MEASURES I BASIC MATERIALS. In the repair or alteratior aircraft, apply corrosion proofing of the st type or equivalent to that originally appl unless the repair or alteration would resul increased susceptibility to corrosion, in wh case use additional corrosion protection me ures. Aluminum and magnesium alloys n be protected by a variety of surface tre ments. Most aluminum alloy structural surfa have been electrically anodized in chromicfuric acid tanks before fabrication. Magnesi sheet has received cold nitric-chromic a treatment; magnesium castings have usua received hot tank processing in fluoride dich mate mixtures. Steel surfaces may have b oxidized or plated during manufacture.
a. Anodizing and Related Processes. In a dizing, aluminum alloys are placed in an el trolytic bath causing a thin film of alumin oxide to form on the surface of the alumin:
This is resistant to corrosion and affords a g‹ paint base. Other processes which do not p vide as good a corrosive protection as anodiz are, however, good paint bases. These p cesses are:
(1) Alkaline cleaning followed by chror acid dip.
(2) Alcoholic phosphoric acid cleaner.
(3) Alkaline dichromate treatment.
b. Plating. Steels are commonly plated w other metale to prevent corrosion. Plating Chal
3.13-1A mplished by placing the article in an elecytic bath and metal from the plating solu- I is deposited on it. Various metals used in ting vary in the corrosion protection they ord steel. For instance, cadmium and zinc rode before the steel; hence, slight breaks cracks through the plating of these metals I not result in rusting of the exposed steel, ce the surface metal is corroded and prots the steel. Chromium does not protect steel this method, as steel will corrode before the omium and thus depends on the tightness of plating for its protection. The process of tplate bake treatment to relieve hydrogen brittlement is a necessary part of replating ›cedures for high-strength steel parts.
gh-strength nuts and bolts are highly sus- ›tible to failure from hydrogen embrittlent, at the many stress risers and notches in ir design, through normal usage of susned and dynamic stresses. Because of the poitial failures of embrittled parts, careful trol over the heat treatment, grinding, preite cleaning, plating, and postplate baking of rh-strength parts is necessary.
c. Sherardizing. Steel parts may be sherardd by heating them in an atmosphere of zine wder; however, this is not considered to be effective against corrosion as zinc or cadum plating.
d. Phosphate Rust-Proofing, This process is mmercially known as Parkerizing, Bonderiz- 3, Granodizing, etc. The coating placed on e part is used to protect steel parts after chining and before painting.
e. Chrome-Pickle Treatment. Magnesium parts lich have been immersed or brushed with a lution of nitric acid and sodium dichromate Il be protected for temporary storage. The ating also will serve as a bond for subseent organic finishes. Sealed chrome-pickle eatment is used on magnesium parts for long rm protection. Diluted chromic acid is a uch-up treatment. It is less critical to apply d can be applied over previously applied thin romate films.
f. Dichromate Treatment. The dichromate treatent consists of boiling magnesium parts in a ap 6 Page 125 solution of sodium dichromate. This treatment provides good paint base and protective qualities on all standard wrought magnesium alloys except the magnesium-thorium alloys HK 31A, HM 21A, and HM 31A. No coating forms on these alloys. Acid pickling of the magnesium surface prior to application of the dichromate treatment is required if maximum corrosion resistance of the finish is expected.
g. Stannate Immersion Treatment. This treatment deposits a layer of tin. It is a protective paint base for magnesium alloy parts which contain inserts and fasteners of a dissimilar metal such as brass, copper, or steel. This treatment cannot be used with parts containing aluminum inserts or fasteners because the high alkalinity of the bath attacks the aluminum.
h. Galvanic Anodizing Treatment. This is an electrolytic process used to provide a paint base and corrosion preventive film on magnesium alloys containing manganese.
I. Cladding, Aluminum alloys which are susceptible to corrosion are frequently clad with pure aluminum. Slight pits, scratches, or other detects through the cladding material will not result in corrosion of the core, since the pure aluminum on the edges of the defect will be preferentially corroded, protecting the core.
I. Metal Spraying. Metal is melted and sprayed on the surface to be protected. The surface must be properly prepared and thoroughly cleaned to prevent peeling of the sprayed coat.
k. Shot-Peening. Shot-peening and other treatments by which the surface can be placed in compression are effective in preventing stress corrosion.
1. Organic Coatings. Zinc chromate primer, enamels, chlorinated rubber compounds, etc., are organic coatings commonly used to protect metals.
m. Dopeproofing. When doped fabrics are applied over an organic finished metal structure, the dope will have a tendency to loosen the finish on the metal. For this reason, organic coatings on the metal are usually covered Par 248
with a dopeproof paint, with metal foil, or with cellulose tape to prevent the dope from striking through.
n. Tube Interiors. Protect the interiors of structural steel and aluminum tubing against corrosion. A small amount of water entrapped in a tube can corrode entirely through the tube thickness in a short period of time. Coat the tube interior by flushing with hot linseed oil, paralketone, or other corrosion inhibitor.
The flushing liquid is usually introduced through small holes drilled in the tubing.
Allow the flushing liquid to drain and plug the holes with a screw or by other means to prevent entry of moisture. Air and watertight sealing of the tubing will also give adequate protection against corrosion if the tubing is internally dry before being sealed.
249. CONSTRUCTION OF CORROSION RESISTANT STRUCTURE. During fabrication, the use of such practices as listed below will reduce the sources of corrosion initiation.
o. Use combinations of metals which are as close together as possible in the galvanic series -do not use small aluminum clips on large stainless steel webs; use stainless steel fasteners in stainless steel assemblies.
b. Insulate dissimilar metals but do not use materials which absorb moisture or conduct it in "wick" fashion.
c. Paint cut edges.
d. Seal edges of faying surfaces on butt joints.
e. Provide adequate drainholes.
250. CORROSION REMOVAL. When corrosion is detected, remove it as quickly as possible and protect the surface from further corrosion. In those cases where the corrosion has progressed extensively, the strength of the part may be in jeopardy and the part may need to be replaced.
a. For steel parts, except for highly stressed steel or stainless steel surfaces, the use of abrasive papers, buffers, hand wire brushing, and steel wool are acceptable cleanup procedures. However, it should be recognized that it Par 248 AC 43 18 practically impossible to remove a.. c sion products from the bottom of small and crevices. As a result, a part once rusty ally corrodes again, more easily than it di first time. Removing corrosion products highly stressed steel parta requires ca handling.
b. For aluminum parts, treatment include mechanical removal of as much of the c sion products as practicable, the inhibitic residual material by chemical means, folk by the restoration of permanent surface ings. Do not use steel wool, emery cloth, (except stainless steel) wire brushes, or st abrasive materials because particles of steel wool or emery cloth will become en ded in the soft material and cause corro Hand polishing corroded areas with house abrasives or with metal polish available u Specification MIL-P-6888 is acceptable fo:
on clad aluminum but must not be used or odized aluminum since it is severe enoug actually remove the protective anodized If the surface is particularly difficult clean. Type II material under Specifica MIL-C-5410 mixed 50-50 percent with sol or mineral spirits may be used. Treat any perficial corrosion with a 10 percent solutic sodium dichromate to which one percen chromium trioxide has been added or material available under Specification N C-5541. Allow these solutions to remair the corroded area for 5 to 20 minutes then wipe the surface dry. A more se cleaning procedure consists of using a 10 cent solution of chromic acid to which has added approximately 20 drops of battery trolyte per gallon. Thorough brushing wi stiff fiber brush should loosen or remove !
existing corrosion and assure complete I tration of the inhibitor into crevices and Allow the chromic acid to remain in place at least 5 minutes, then remove the exces.
flushing with water or wiping with a cloth. Apply a protective coating the same that the corrosion treatment is accomplis
c. When an anodized surface coating is d aged, it can only be partially restored by chi cal surface treatment. Therefore, exercise CH
aning process to avoid unnecessary f the protective film, particularly at of the aluminum sheet. Chromic acid inhibitive treatments tend to restore ilm.
severe cleaning is necessary with inr corrosion (attack along grain
s). The mechanical removal of all products and visible delaminated rs must be accomplished in order to the extent of the destruction and to he remaining structural strength of onent. Inspection with a 5- to 10- gnifying glass or the use of dye peneassist in determining if all unsound I corrosion products have been reinding to blend or fair out the edges ed areas can best be accomplished by minum oxide-impregnated rubberels. Chemically inhibit the exposed und restore chemical surface films or he same manner as for other alumiices.
esium is the most chemically active of s used in aircraft construction and is the most difficult to protect. The ad complete correction of the coating imperative if serious structural dambe avoided. Treat the corroded area ercent chromic acid solution to which added approximately 20 drops of batrolyte per gallon, in the same manaluminum alloys.
ROSION PROOFING OF LANDPLANES LANES. In the repair or alteration of use corrosion proofing materials the or equivalent to, that originally apss the repair or alteration would recreased susceptibility to corrosion, in e, employ additional corrosion protecures.
ROSION PROOFING OF LANDPLANES D TO SEAPLANES. A special problem tered in the conversion of landplanes es. In general, landplanes do not reosion proofing to the same extent as nes manufactured as such. Corro- Page 127 sion-proofing standards for landplanes converted to seaplanes are divided into two classes: (1) Necessary minimum precautions;
and (2) Recommended precautions. Regardless of such precautions, it is imperative that the exterior surfaces of seaplanes be washed with clear fresh water immediately following extended water operation, or at least once a day when operated in salty or brackish water. Wash interior surfaces of seaplanes exposed to spray, taking care to prevent damage to electrical circuits or other items subject to injury.
a. Necessary Minimum Precautions. The following procedures are considered the minimum to safeguard the airworthiness of the converted aircraft and are not in themselves intended to maintain airworthiness for an indefinite period.
(1) Unless already protected, treat exposed fittings or fittings which can be reached through inspection openings with two coats of zinc chromate primer, paralketone, nonwatersoluble heavy grease, or comparable materials.
This applies to items such as wing-root fitwing-strut fittings, control-surface hinges, horns, mating edges of fittings, and attach bolts, etc.
(2) Coat nonstainless control cables with grease or paralketone or other comparable protective coating, if not replaced with corrosion-resistant cables.
(3) Inspect all accessible sections of aircraft structure. Clean structural parts showing corrosion and refinish if corrosion attack is superficial. If a part is severely corroded, replace with an adequately corrosion-proofed part.
b. Recommended Precautions. The recommended precautions are those which are suggested as a means of maintaining such aircraft in condition for safe operation over extended periods of time.
(1) Provide additional inspection openings to assist in detecting corrosion. Experience has shown openings to allow inspection of lower and rearward portion of the fuselage to be particularly desirable.
(2) Incorporate additional provisions for free drainage and ventilation of all interiors to Par 250
Page 128 AC 43.1:
prevent collection of moisture (scoop type drain grommets).
(3) Protect the interior of structural steel tubing. This may be done by air and watertight sealing or by flushing with hot linseed oil and plugging the openings. Inspect tubing for missing sealing screws, presence of entrapped water.
local corrosion around sealing screws, welded clusters, and bolted fittings which may be indicative of entrapped moisture.
(4) Slit the fabric of fabric covered aircraft longitudinally on the bottom of the fuselage and tail structure for access to these sections. Cont teracts any advantages in their speec fectiveness. Ise materials which are neutral and easy to remove.
c. Removal of Spilled Battery Acid.
to neutralize spilled battery acid, us bicarbonate (baking soda). or sodiu (borax) 20 percent by weight dissolved After neutralization, remove alkali :
pletely with copious quantities of wate vent corrosion. An application of paint to the structure surrounding th may be an effective control for this tyl rosion.
the lower structural members with zine chromate primer (two coats) ; follow by a coat of dope proof paint or wrap with cellophane tape and rejoin the fabric. This precaution is advisable within a few nonths after start of operation as a seaplane.
(5) Spray the interior of metal-covered wings and fuselages with an adherent corrosion inhibitor.
(6) Place bags of potassium or sodium dichromate in the bottom of floats and boat hulls to inhibit corrosion.
* 254. HANDLING AND CARE OF AIRCRAF ERED FROM WATER IMMERSION. Aircr were recovered from partial or total i in water, including flash floods, have lowed to air dry, in certain instances.
safety precantions other than a cursor tion of the aircraft exterior. The la adequate cleanup of water-immersed a subsequently adversely affect the safet aircraft. That is, water immersion inc probability of corrosive attack, the re lubrication, the deterioration of airc
(7) Prevent the entry of water by sealing.
as completely as possible, all openings in wings, fuselage, control-surface members, openings for control cables, tail-wherl wells, ete.
253. CLEANERS, POLISHES, BRIGHTENERS, 11 iS important that aircraft be kept thoroughly clean terials, and/or degradation of electi avionic equipment.
Sea water, because of salt content, corrosive than surface fresh water.
fresh water may contain varying amou and, as drying occurs, the salt concen increased and corrosive attack accelerat of deposits containing contaminating substances such as oil, grease, dirt, and other foreign materials.
a. Materials. Avoid damage to aircraft by not using harmful cleaning, polishing, brightening, or paint-removing naterials. Use only those compounds whieh conform to existing government or established industry specifications or The most important factor following of an aircraft from sea or fresh water i is prompt action. Components of the which have been water immersed, suc poverplant, accessories, airframe section ing mechanisms, screws, bearings, worl faces, fuel and oil systens, wiring, ra radar should be disassembled. to the ex product- that have been specifically recommended by be a reraft manufacturer as being satisfactory for the intended application. Observe the product manufacturer's recommendations concerning de of his agent.
b. Cherical Cleaners. Chemical cleaners must be used with preat care in cleaning assembled sidered necessary, so that the contamir be completely removed.
a. Initial Fresh Water/Detergent Wc soon as possible after the aircraft is 1 from water immersion, thoroughly w taminated internal and external areas of craft using a water/detergent solution as aireraft. The danger of entrapping corrosive 01) Mix liquid detergent (MI- materials in faving surfaces and crevices cou- Type I) and isopropyl alcohol (TT-I Por 252
CHG T ight parts detergent to 20 parts of dd the detergent/alcohol mixture to tap water and mix thoroughly. For ne part of the foregoing concentrate ts of tap water (warm water if availnix thoroughly.
the above specified detergent/alcohol re not available, use water emulsion ›mpound (MIL-C-43613). Add one und to nine parts water. If the MIL ompound is not available, use any ild household detergent solution with 'ater.
Precautions. The following safety i should be observed:
ctrically ground the aircraft. Attach lead to the aircraft at a point which the area that could contain explosive the landing gear of land planes is
• supporting mechanism, install a ir, jury strut, landing gear downlocks itable devices to insure that the gear ollapse. If the landing gear is not insure that the aircraft is solidly to prevent hazardous movement.
connect and remove wet- and/or dryes and isolate aircraft from all sources ty or other spark-producing devices.
lucing static electricity is generated at air hose outlets, so this method should ed for ventilating or purging fuel nove all fuel, oil, and hydraulic fluid.
sh all fuel and oil cells with clean late tires, especially on magnesium epressurize landing gear struts, pneums, and hydraulic accumulators.
scating Engines and Propellers. The would be removed from the engine and from the aircraft. The exterior of the propeller should be washed with ot or cold fresh water.
›r accessories, engine parts, etc., should I and all surfaces flushed with fresh erably hot. If facilities are available, ed parts, size permitting, should be Page 128-1 immersed in hot water or hot oil, 180° F., for a short period of time. Soft water is preferred and should be changed frequently. All parts must be completely dried by air blast or other means. If no heat drying facility is available, wipe the cleaned parts with suitable drying cloths.
Constant speed propeller mechanism should be disassembled, as required, to permit complete decontamination. Clean parts with steam or hot or cold fresh water. Dry the cleaned parts in an oven, but if a heat drying facility is not available, wipe the cleaned parts with suitable drying
d. Gas Turbine, Turboprop and Turboshaft En- The engine exhaust shield, insulation blankets, separate exhaust collectors, compressor housing, pinion cowl and/or upper pinion housing should be removed. The engine accessories, outer housing exhaust shields, and other exposed parts should be steam cleaned. The steamcleaned parts should be dried in an oven at approxímately 200° F., or with hot air from a portable engine heater, or with clean wiping cloths.
Immerse remainder of engine in 10-20 percent water solution of sodium dichromate, or hot, fresh water and apply sufficient agitation to provide complete flushing.
If immersion cannot be accomplished, flood the lower section of the compressor housing and thoroughly flush rotor blades with sodium dichromate solution or warm fresh water. Seal off combustion chamber openings and alternately fill and drain the combustion chamber with fresh water. Dry clean parts in an oven, or use dry air from a portable engine heater or wipe with suitable drying cloths.
e. Airframe. The salvageable components of the fuselage, wings, empennage, seaplane and amphibian hulls and floats, and movable surfaces should be processed as follows:
(1) The fabric from fabric-covered surfaces should be removed and replaced.
(2) The sircraft interior and exterior should be cleaned using steam under pressure with steam-cleaning compound. The steam should be directed into all seams and crevices where corrosive water may have penetrated. Avoid steam * Par 254
*cleaning electrical equipment, such as terminal boards and relays.
(3) Areas that have been steam cleaned should be rinsed immediately with either hot or cold fresh water.
(4) Touch up all scratches and scars on painted surfaces using zinc chromate primer or preservative.
(5) Undrained hollow spaces or fluid entrapment areas should be provided temporary draining facilities by drilling out rivets at lowest point. Install new rivets after drainage.
(6) All leather, fabric upholstery, and insulation should be removed and replaced. Plastic or rubber foam which cannot be cleaned of all to cleanes corrosive water should be replaced.
lar structures should be removed and the structure blown out with compressed air. If corrosive water has reached the tubular interiors, carefully flush with hot, fresh water and blow out water with compressed air. Roll the structure as necessary to remove water from pockets. Fill the tubes with hot linseed oil at approximately 180° F. Drain oil and replace drain plugs or drive screws.
(8) Clean sealed wood, metalite, and other nonmetallic areas, excluding acrylic plastics, with warm water. Wood, metalite, and other porous materials exposed to water immersion should be replaced, unless surfaces are adequately sealed to prevent penetration by corrosive water. Virtually all solvents and phenolic type cleaning agents are detrimental to acrylics and will either
f. Helicopter Rofor Dynamic Components.
(1) All evidence of corrosive water should be removed from the exterior of transmissions and gear boxes by flushing with clean hot or cold fresh water.
(2) Where it is possible that corrosive water has reached the interior of the transmission or gear boxes, remove plugs and/or covers and drain completely. Flush interior of part with hot or cold fresh water. Drain residual water, replace plugs and/or covers, and reapply proper lubricant.
g. Helicopter Blades. Except for blades with wooden or other nonmetallic constructions, treat Par 254 AC 43.1:
helicopter blades the same as propelle ciprocating engines. Clean nonmetal by hand, using warm water. Dry wi cloths or a warm air blast. When clea copter rotor blades, insure that nonsen members, such as the spars and blad are cleaned and dried.
h. Fuel and Oil Systems. Contamir and oil systems should be processed as :
(1) Flush oil system, including li water-displacing preservative.
(2) Open fuel systems. Purge cell lines. Check effectiveness of the pur combustible gas indicator. Remove bli self-sealing type fuel cells and all cal or pads.
(3) Use clean, fresh water to wash After drying, spray interior walls witł
(4) Chemically treat bare metal si cleaned aluminum tanks with 10-21 water solution of sodium dichromate.
(5) Flush fuel lines with hot water maximum). Dry, using clean, dry, a air.
1. Landing Gear. Process salvageab nents of the landing gear, wheels, and follows:
(1) Remove tires and wheels.
(2) Steam clean wheels, rinse in fr and dry.
(3) Remove wheel bearings and cl dry cleaning solvent.
(4) Immerse bearings in methyl al dry the cleaned bearings in air blast.
permit bearings to rotate during air bla Reapply proper lubricant.
(5) Remove brakes, steam clean, :
with fresh water and dry.
I. Electrical Equipment.
(1) Wet cell batteries. The risk in using wet cell batteries that have been in sea water may outweigh any ecor vantage and should be replaced.
(2) Because of possible flight haz later defects caused by progressive cor tack, all electrical wiring immersed sive water should be replaced. If