Materials & Hardware

Steel is iron plus carbon; alloying with chromium, nickel and molybdenum gives strength and corrosion resistance. Heat treatments: annealing (soften), normalising (refine grain), hardening (quench) and tempering (restore toughness). Case hardening gives a hard surface with a tough core — used for gears and bearing races. SAE/AISI four-digit codes identify steels (e.g. 4130 chrome-moly).

Aluminium alloys dominate airframes: 2024 (Cu, damage-tolerant) and 7075 (Zn, high strength). Temper designations: -O annealed, -T3 solution treated and cold worked, -T6 solution treated and artificially aged. Alclad is a pure-aluminium cladding for corrosion protection. Titanium offers strength at high temperature; magnesium is very light but highly corrodible and a fire risk when machined.

Composites combine reinforcement (glass, carbon, aramid/Kevlar) in a matrix (epoxy resin), often as honeycomb sandwich for stiffness. Inspect by tap test, ultrasonic or thermography for delamination and water ingress. Store prepreg frozen and observe out-life. Carbon fibre in contact with aluminium causes galvanic corrosion — a barrier ply or sealant is required.

Types: surface/uniform, pitting, intergranular, exfoliation, galvanic (dissimilar metals), stress corrosion cracking, fretting and filiform. Prevention: anodising, alodine/chromate conversion, priming and topcoat, sealants, drainage, and correct dissimilar-metal isolation. Treatment involves removal of all products, blend-out within limits from the SRM, and re-protection.

AN/MS/NAS bolt part numbers encode diameter and grip length. Bolts should be fitted with the head up or forward where possible, with one to three threads showing past the nut. Screws, self-locking nuts, castellated nuts with split pins, Hi-Lok and Hi-Lite fasteners, and rivets each have defined applications. Never substitute a fastener without an approved data reference.

Rigid pipes are identified by colour-coded bands; flare fittings are AN 37° (aviation) versus JIC/SAE 45°. Flexible hoses have a lay line that must not twist and a life limit. Springs: helical compression, tension, torsion and leaf. Bearings: plain, ball, roller and needle — inspect for brinelling, spalling and corrosion. Control cables are 7×7 or 7×19 stainless/carbon steel, inspected for broken wires, wear and correct tension using a tensiometer with temperature correction.