Aircraft Honeycomb Core and Sandwich Panels

Why aircraft use honeycomb sandwich structures

A sandwich panel works like an I-beam. The two skins carry bending loads in tension and compression, and the core holds them apart and carries shear. Doubling the core thickness of a panel roughly increases its bending stiffness about seven-fold while adding only a few per cent to its weight, which is why honeycomb is everywhere in aircraft that must save every kilogram.

Honeycomb is the most efficient core geometry because its thin cell walls run perpendicular to the skins. They resist crushing and shear far better than foam of the same density, and the open cells keep weight very low: typical aerospace cores weigh 30 – 130 kg/m³, compared with 2,700 kg/m³ for solid aluminium. Aluminium honeycomb also absorbs energy predictably as it crushes, which is used in crash-energy absorbers and landing-gear components.

Sandwich panels have been used on aircraft since the 1940s. Today they are found in cabin floors, sidewalls and ceilings, galleys and lavatories, overhead bins, cargo liners, trailing-edge flaps and spoilers, rudders and elevators, wing-to-body fairings, radomes, helicopter rotor blades and engine nacelle acoustic liners.

Honeycomb core materials compared

Aluminium core gives the highest shear strength and stiffness per unit weight and conducts heat well, so it dominates structural panels. Aramid core is preferred inside the cabin because it does not corrode, is less prone to permanent denting, and is used in panels that must pass the strict fire, smoke and toxicity requirements. Many interior panels pair aramid core with glass or carbon facings, while floor panels in aircraft and helicopters often pair aluminium core with aluminium or composite skins.

Reading an aluminium honeycomb core callout

Aerospace core is described by a short designation that gives cell size, alloy, foil thickness and density. For example, 1/8-5052-.001 4.5 means 1/8 inch (3.2 mm) cells, 5052 alloy foil 0.001 inch (25 µm) thick, giving a nominal density of 4.5 lb/ft³ (about 72 kg/m³).

As an indication of scale, one manufacturer publishes typical values for 1/8-inch, 3.1 lb/ft³ 5056 core of about 2.4 MPa stabilised compressive strength, 1.8 MPa shear in the L direction and 1.1 MPa in the W direction at room temperature. These are typical figures, not design minimums. Design values come from AMS-C-7438 or the qualified supplier specification for the exact core you buy, and core properties drop at elevated temperature.

Facing (skin) materials for aircraft panels

Metal facings are bonded to aluminium core with structural film adhesives, typically modified epoxies cured at 120 °C or 175 °C, after the skins are prepared by phosphoric acid anodising or a similar treatment that gives a durable bond. Mixing aluminium core with carbon skins needs a glass-fibre or adhesive isolation layer to prevent galvanic corrosion.

Where honeycomb is used on an aircraft

A typical bonded floor panel has two thin aluminium or carbon skins, a 10 mm core, and local high-density inserts or potted areas where seat tracks, fasteners and fittings pass through. Because inserts concentrate load, panel designers specify potting compound, insert type and edge closeouts as carefully as the core itself.

Standards, test methods and certification

Aircraft programmes add their own material and process specifications on top of these, and panels for flight use are made only from qualified materials by approved processes. When ordering core for a qualified part, quote the airframe or customer specification as well as AMS-C-7438, and ask for the certificate of conformance with lot test results.

Design and processing points for honeycomb panels

• Orient the ribbon: align the stronger L direction with the main shear load path
• Check skin dimpling and wrinkling: thin skins over large cells buckle into the cells; choose a smaller cell for skins under about 0.5 mm
• Seal the edges: moisture entering aluminium core through damaged edges or fasteners causes corrosion and freeze-thaw damage; use edge fillers and sealant
• Use perforated core with care: it vents cure volatiles but also lets water travel through the panel if the skin is breached
• Machine core correctly: use high-speed routers, freeze or wax-fill thin slices, and avoid crushing cell walls at chamfers
• Plan inspections: tap testing, ultrasonic and thermographic inspection detect disbonds; design access accordingly
• Isolate dissimilar metals: keep carbon fibre and steel fasteners away from bare aluminium core and skins

How to order aerospace honeycomb materials from Metline

1. Define the coreCell size, alloy, foil gauge, density, perforation, and block or slice dimensions (L × W × T), or a drawing for machined parts.
2. Name the specificationAMS-C-7438 or the customer core specification, plus any surface treatment requirement.
3. Add facingsFacing alloy and temper (for example 2024-T3 Alclad or 6061-T6), gauge and size, if you need sheet as well as core.
4. QuoteWe confirm availability, certification, packing and delivery terms (EXW, FOB, CIF or DAP).
5. ShipCore is packed in rigid cartons or crates to prevent crushing, with the certificate of conformance and test results.

Related honeycomb, aerospace and sheet pages

Aircraft honeycomb core: frequently asked questions