Nomex honeycomb: density classes (HexWeb HRH-10, 1/8 in cell)
| Designation | Density, lb/ft³ | Density, kg/m³ (converted) | Bare compressive, psi typ | Plate shear L, psi typ | Plate shear W, psi typ |
|---|---|---|---|---|---|
| HRH-10 – 1/8 – 1.8 | 1.8 | 29 | 105 | 90 | 50 |
| HRH-10 – 1/8 – 3.0 | 3.0 | 48 | 300 | 175 | 100 |
| HRH-10 – 1/8 – 4.0 (2.5 mil) | 4.0 | 64 | 520 | 255 | 140 |
| HRH-10 – 1/8 – 5.0 | 5.0 | 80 | 700 | 325 | 175 |
| HRH-10 – 1/8 – 6.0 | 6.0 | 96 | 1,050 | 385 | 200 |
| HRH-10 – 1/8 – 8.0 | 8.0 | 128 | 1,675 | 480 | 260 |
| HRH-10 – 1/8 – 9.0 | 9.0 | 144 | 2,000 | 515 | 300 |
Hexcel HexWeb HRH-10 product data sheet (inch version), mechanical properties table, tested per AMS-STD-401 at 0.500 in core thickness. Designation is material, cell size in inches, nominal density in lb/ft³. Density tolerance is ±10 % measured on at least 100 in³ of core. Other cell sizes (for example 3/16) and densities are in the same table. kg/m³ converted at 16.02 per lb/ft³.
How to read a core callout
The most common core for aircraft honeycomb is aramid paper (Nomex or Korex); fiberglass honeycomb is used for higher strength (AMT Handbook, p. 7-11). Small cell sizes support the face sheets better, and higher density core is stronger and stiffer (p. 7-12).
The ribbon direction (L) is parallel to the sheets. Plate shear is higher in L than in W, as the table shows. Overexpanded core bends easily across the ribbon and suits simple curves; bell-shaped flexicore curves in all directions (p. 7-12).
Replacement core in a repair is the type, cell size and density the SRM names. Density alone does not identify core.
Vacuum bagging consumables: typical values
| Item | Typical value | Source |
|---|---|---|
| Breather, polyester, FAA guidance | 4 oz below 50 psi; 10 oz for 50–100 psi | FAA-H-8083-31, p. 7-21 |
| Airweave N-4 breather/bleeder (polyester) | 4 oz/yd² (135 g/m²); max recommended 400 °F (204 °C) | Airtech Airweave data sheet, p. 3 |
| Airweave N-7 | 7 oz/yd² (237 g/m²); 400 °F (204 °C) | Airtech Airweave data sheet, p. 3 |
| Airweave N-10 | 10 oz/yd² (339 g/m²); 400 °F (204 °C) | Airtech Airweave data sheet, p. 3 |
| Airweave Super 18 | 18 oz/yd² (610 g/m²); 400 °F (204 °C) | Airtech Airweave data sheet, p. 3 |
| Airweave A (rayon, waffle bleeder for wet layup) | 1.6 oz/yd² (54.3 g/m²); 400 °F (204 °C) | Airtech Airweave data sheet, p. 3 |
| Peel ply / release fabric: Release Ease 234 TFP (PTFE-coated glass) | 0.060 mm (0.0024 in) thick; max 288 °C (550 °F); weight not stated on the sheet | Airtech Release Ease 234 TFP data sheet |
| Bagging film: Wrightlon 7400 (nylon) | 50 µm (0.002 in) or 75 µm (0.003 in); 400 % elongation, 55 MPa tensile; max 204 °C; avoid phenolic resins | Airtech Wrightlon 7400 data sheet |
| Sealant tape: AT-200Y (synthetic rubber, yellow) | 1/8 × 1/2 in (3 × 12 mm); max 400 °F (204 °C) | Airtech AT-200Y data sheet |
The FAA handbook gives breather weights and pressures only; it gives no weights for bleeder, peel ply, film or tape. Airweave and tape numbers are Airtech's nominal values for that product; other makes differ.
What each item does
From the AMT Handbook (pp. 7-21 to 7-22): processing materials do not become part of the repair and are discarded after it.
Release agent lets the part come off the tool or caul plate. Bleeder ply gives air and volatiles a path out and collects excess resin; it can be fiberglass, nonwoven polyester or perforated Teflon-coated material, and the SRM gives the type and the number of plies. As a general rule, the thicker the laminate, the more bleeder plies.
Peel ply leaves a clean bonding surface when it is removed just before bonding. The preferred material is polyester that has been heat-set to eliminate shrinkage; it can be hard to remove if overheated, and some coated plies leave contamination.
Perforated release film lets air and volatiles out and keeps the bleeder from sticking; solid release film keeps plies off the working surface and keeps resin from reaching the heat blanket or caul plate. Breather gives the air a way out of the bag and must contact the bleeder.
Sealant tape seals the bag to the part or tool; check its temperature rating. The bag comes in different temperature ratings, so confirm it can take the cure temperature (p. 7-21 to 7-22). Plan the pressure with the vacuum bag at altitude calculator.
Questions people actually ask
Is 3 pcf the same as 48 kg/m³?
Yes, to rounding: 3.0 lb/ft³ × 16.02 = 48.06 kg/m³.
Which breather for a hot-bonder repair?
The AMT Handbook ties the choice to pressure: 4 oz polyester below 50 psi, 10 oz for 50 to 100 psi. A vacuum bag cannot exceed atmospheric pressure, about 14.7 psi at sea level, so the 4 oz weight sits inside its range.
Limits — when NOT to use this
- Not a bagging schedule. The stack, plies and cure come from the SRM or the repair data. These tables only identify typical products.
- Not a core substitution table. Core type, cell size, density and thickness are engineering data; a different density is a different part.
- Temperature ratings are maximums, not working points. They depend on time at temperature; test before use.
- Compatibility. Check each film, tape and breather against the resin system and cure temperature on the repair data sheet.
Sources
- Hexcel HexWeb HRH-10 Product Data Sheet (inch) — designation, density tolerance, mechanical properties table.
- Airtech Airweave Non-Woven Polyester Breathers/Bleeders data sheet, p. 3 — nominal weights and maximum recommended use temperatures.
- Airtech Wrightlon 7400 Nylon Vacuum Bagging Film data sheet — thickness, elongation, tensile strength, maximum use temperature.
- Airtech AT-200Y data sheet — base material, size, maximum use temperature.
- Airtech Release Ease 234 TFP data sheet — PTFE-coated fiberglass release fabric, thickness and temperature rating.
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1, Chapter 7, pp. 7-11, 7-12, 7-21, 7-22 — core materials and vacuum bagging process description.