Aircraft Materials, Hardware, and Hand Tools
This domain tests whether you can identify the alloy, select the correct fastener, and use the tool without damaging the structure. Most marks come from standard hardware and riveting arithmetic.
Common airframe materials
- 2024-T3: copper-bearing, good fatigue resistance, common in fuselage skin; not readily weldable.
- 7075-T6: zinc-bearing, highest strength of the common alloys, lower corrosion resistance; not readily weldable.
- 6061-T6: magnesium and silicon bearing, weldable, good corrosion resistance, used for structures and fittings.
- 5052: good formability and corrosion resistance, lower strength. Alclad sheet has a pure aluminium coating for corrosion protection.
Hardware
AN, MS and NAS numbers identify bolts, nuts, washers, pins and fittings. Grip length must match the total thickness so no more than about three threads show outside the nut. Cotter pins and safety wire prevent rotation; double-twist safety wire is normally 0.032 in for small bolts and 0.041 in for larger ones, with 6 to 8 twists per inch.
Worked example
You are riveting two sheets of 0.040 in and 0.050 in with 1/8 in universal-head rivets. Combined thickness = 0.090 in. Required rivet length = thickness + 1.5 x diameter = 0.090 + 0.1875 = 0.2775 in. Select the next standard length, 9/32 in (0.281 in). Drill with a #30 bit for a 1/8 in rivet, and use AN470 for universal head or AN426 for 100-degree countersunk.
Traps that cost marks
- Substituting a hardware-store bolt for an AN or NAS bolt.
- Using a longer bolt with extra washers to make grip length fit.
- Applying dry-torque values to lubricated threads.
- Confusing AN470 and AN426 head types.
- Using an uncalibrated torque wrench or a cheater bar on a torque wrench.