Aircraft Structural Design2 min read
Successful aircraft design incorporates a finely balanced blend of high-tech materials, structural advances, and traditional design know-how. Aircraft shape is now optimized for all airframe components using computational fluid dynamics. Computational fluid dynamics can cut drag by several percent.
The Airbus A380, for example, with its sheer scale, its double-decker configuration and a wealth of new materials, such as GLARE and reinforced thermoplastics. The aircraft also features carbon-fibre-reinforced plastic frames in the tail cone section and, never used in aircraft design before, welded stringers in the lower fuselage.
A design service goal is often set in advance. Advanced aluminium alloys form the semi-monocoque structure of the fuselage, while the skins are chemically milled or machined to reduce weight. GLARE, “GLAss-REinforced” Fibre Metal Laminate FML, is used for the upper and lateral fuselage skins of the forward and aft section above the main-deck level. Welded stringer panels are used in the lower fuselage sections below the main deck floor.
Aircraft stress analysis.
Stresses have to be calculated for aircraft structural design. They are prevalent at cutout surrounds around doors and hatches, the wing root area, nose and centre fuselage, in other words, pressurised areas.
In the A380, the fuselage containing the flight deck, crew rest area, electronics bays, and passenger door number 1 are stiffened with welded longitudinal stringers. Much is made of the increasing use of composites in aircraft structural design. Primarily, structures made of aerospace composites are weight saving. In the A380, an enormous belly fairing is formed from a series of panels made up of a Nomex honeycomb and hybrid epoxy skin sandwich. An aluminium substructure that supports these panels helps transfer some of the fuselage loads to the fairing by deformation between the primary structure of the fuselage and the belly fairing support structure. A dome-shaped carbon-fibre-reinforced plastic rear-pressure bulkhead separates the tail section from the rest of the aircraft.
Physically smaller bits of the structure can be the most complex aircraft assemblies. Loaded frames, which support the attachment for the massive vertical tailplane, are machined from high strength aluminium alloys, while weight-saving resin transfer mouldings are used for less loaded frames. A titanium rear fairing covers the aft-facing APU exhaust, while the compartment itself is lined with firewalls made from titanium sheets. So, it is the combining of accumulated knowledge about available materials and their properties that is the skill of the designers and the complex combinations that now make up the most advanced passenger aircraft. Massive wings, each supporting two engine pylons have now come a long way from the concept of a rolled tube of aluminium with stringers inside.