Core crush
Impact or clamp pressure collapses cells. Faces may look fine while stiffness is gone. Soft spots and “oil can” feel are red flags — inspect before you pull fasteners or apply load.
Alloys, tempers & product forms
Know what you are forming before you load the press. Wrong temper ruins parts; sanding through Alclad ruins corrosion protection. Sandwich and honeycomb show up on panels and fairings — learn the vocabulary even when primary structure is still riveted aluminum.
On this page
Jump to alloys, tempers, or the expanded sandwich / honeycomb section with process demos.
Product forms
| Form | Typical use on 707-family work |
|---|---|
| Sheet | Skins, webs, light brackets, formed channels |
| Plate | Thick fittings, machined from solid, spar caps / fittings where plate stock is called |
| Extrusion | Stringers, longerons, some frame sections |
| Forging | High-load fittings, landing-gear related parts, complex fittings |
| Bar / rod | Machined pins, bushings blanks, small fittings |
| Honeycomb / sandwich | Core + face sheets for panels, fairings, floors, control surfaces, interiors — see Sandwich / honeycomb |
Alloys you will see
| Alloy | Role | Notes |
|---|---|---|
| 2024 | Skins, lower wing structure, many formed sheet parts; common face-sheet alloy on metallic sandwich | Workhorse aero sheet/plate. Often Alclad. Strong in T3/T4 family. |
| 7075 | Stringers, fittings, high-strength machined parts | Higher strength than 2024; stress-corrosion watch — T73 family often preferred for fittings. |
| 7178 | Legacy upper wing / high-strength applications (watch-out) | Historical high-strength alloy. Know it on drawings; treat carefully for SCC and availability. |
| 7079 | Legacy thick forgings / fittings (watch-out) | Older alloy with known issues in some thick sections. Flag on prints; follow engineering disposition. |
Watch-outs: 7178 & 7079
These show up on older 707-family drawings. Do not casually substitute. Engineering owns alloy swaps — shop owns forming the called temper correctly.
Tempers
| Temper | Meaning (shop view) |
|---|---|
| O | Annealed — softest; form freely, then heat treat to final temper |
| W | Solution heat-treated, unstable — form soon after quench; then age |
| T3 / T4 | Solution treated + cold work / naturally aged — common for 2024 sheet in service |
| T6 / T651 | Solution treated + artificially aged (651 = stress relieved) — high strength |
| T73 / T76 | Overaged for SCC resistance (esp. 7075 family fittings) |
Shop rule
Form in O or W. Fly in T3 / T6 / T73 (as called). Trying to stretch or brake hard T6 sheet is how you crack parts and scrap material.
Alclad
Many 2024 sheets carry a pure aluminum cladding for corrosion protection. Do not sand through it. Blend carefully; if cladding is gone, the part may need rework or scrap per engineering.
Sandwich panels & honeycomb
General aerospace knowledge for bonded shop work — not a claim of ship-specific E-3/E-6 sandwich design or SRM repair numbers.
707 honesty check
707-family primary structure is mostly riveted aluminum (skins, stringers, frames, spars). Honeycomb and sandwich still appear widely on transport-category and military airframes as secondary structure, fairings, floors, control surfaces, and interior panels. Treat them as part of metallic/composite bonded shop work in sustainment — not as “the wing is all honeycomb.” Follow the drawing and the approved SRM/AMM for that part number.
What a sandwich panel is
Two thin, stiff face sheets bonded to a thick, light core. The core keeps the faces apart (high bending stiffness for little weight) and carries shear. Crush the core or disbond a face and the panel loses that stiffness fast — that is why handling, potting, and repair mindset matter.
| Element | Shop vocabulary | Notes |
|---|---|---|
| Aluminum honeycomb core | Cell size, density, ribbon direction, foil alloy | Common metallic core. Orientation (ribbon) is an engineering call — do not casually rotate cores when splicing. |
| Nomex / aramid honeycomb | Phenolic-impregnated aramid paper cells | Very common in aerospace interiors and many composite sandwich parts. Light, fire-resistant grades exist; handle differently than aluminum core (crush, moisture, sanding dust). |
| Other cores (general) | Foam, balsa, corrugated | Show up industry-wide; honeycomb is the focus here because it dominates aero sandwich language on the floor. |
| Face sheets | Aluminum (often 2024 / skin alloys), fiberglass, carbon, or hybrids | Metallic faces feel like sheet-metal work with bonded rules. Composite faces bring layup/scarfing skills. Match materials to the drawing — do not invent substitutions. |
| Adhesive | Film adhesive, paste, foaming splice adhesives | Bonds faces to core and splices core pieces. Process controls (prep, out-time, cure) belong to engineering/process specs. |
| Potting | Potting compound / syntactic fill | Fills selected cells for densification, edge closeouts, or hard points under inserts. Heavier than open core — weight and stiffness change locally. |
| Inserts | Threaded / floating inserts, potted hard points | Give fasteners something solid to bear on. Never treat open honeycomb like solid plate when drilling and torquing. |
| Edge closeouts | Channels, densified edges, sealed edges | Protect open cells from moisture and damage; provide attach edges. Damaged closeouts invite water intrusion. |
Damage modes you will hear
Disbond / delamination
Face sheet separates from core or plies separate. Tap test, thermography, ultrasonic, or shearography may be called — method belongs to engineering/NDI, not habit.
Water intrusion
Open edges, puncture, or failed seals let moisture in. Water adds weight, can freeze, and drives corrosion on aluminum core/faces. Seal and closeout discipline matter.
Insert / potting failure
Over-torque, wrong insert, or poor potting lets fasteners spin or pull out. Repair may mean re-potting or panel replace — follow the approved data.
Repair vs replace (sustainment mindset)
FAA AMT and OEM SRMs teach a spectrum: small core damage may get potting/filler repairs that restore some capability; larger damage needs core plug/replacement and face repair (scarf, stepped patch, etc.); beyond published limits you replace the panel or get engineering disposition. This site does not invent Boeing E-3/E-6 SRM limits or part numbers. On the floor: stop at the drawing and approved repair data, calculate weight/balance when required (control surfaces), and do not assume a cosmetic fill is a permanent structural fix.
Shop handling rules (general)
- Support panels — do not set heavy tools on unsupported sandwich.
- Protect open edges; bag or seal when the process calls for it.
- Drill and countersink with backing and depth control — honeycomb does not forgive plunge mistakes the way solid plate sometimes does.
- Use specified inserts/potting; never “make it work” with a longer bolt and hope.
- Tooling notes for core cut / bond / potting live on Fixtures → Honeycomb / sandwich.
Watch: honeycomb & sandwich how-it-works
Public demos — manufacture, potting, inserts, and repair overview. Not E-3/E-6 or Boeing-approved training.
How’s it Made — The Gill Corporation
Why watch: See industrial honeycomb and sandwich panel making language — core, faces, and bonded construction from a known aero supplier context.
Inside an aerospace honeycomb core plant
Why watch: Walk a honeycomb core plant — how ultralight structural core is produced before it ever meets a face sheet.
Honeycomb potting — automated filling for aircraft interiors
Why watch: Cells filled for stability and hard points — the same potting idea behind inserts and edge densification on sandwich panels.
Potted insert in honeycomb panel
Why watch: Insert potting on a sandwich panel — how fasteners get a solid path without crushing the core.
Composite repair overview (T2 P2)
Why watch: Composite/sandwich repair orientation — damage assessment and repair-vs-replace thinking before you open an SRM.