rigid
An airship whose shape is maintained solely by an internal and/or external rigid structural framework, without using internal gas pressure to stiffen the vehicle (the lifting gas is at atmospheric pressure); typically also equipped with multiple redundant gasbags, unlike other types of airship.
rigid: airship held up by skeleton, not pressure
A rigid airship maintains its shape through an internal framework of girders and ring frames, not through pressurization of the lifting gas. The gas cells themselves sit inside this structure at or near atmospheric pressure, which means the hull can be damaged without immediate catastrophic collapse. This fundamental design difference separates rigids from blimps (pressure airships) and semi-rigids (which use both methods). The framework, traditionally built from aluminum alloy or duralumin, carries all bending and shear loads; the gas envelope is primarily a gas-tight container.
Rigids typically incorporate multiple independent gasbags subdivided within the frame. A Zeppelin-type rigid might have 16 or more separate cells, so puncture or leakage of one cell does not render the entire aircraft uncontrollable. This redundancy is crucial for safety and range. The rigid's skeleton allows much greater size and payload capacity than pressure airships of similar volume; the LZ 129 Hindenburg reached 245 meters in length, a scale impossible for a non-rigid design.
Structure and materials
The internal frame consists of longitudinal girders running nose to tail, connected by transverse ring frames spaced several meters apart. Wire bracing between frame members provides torsional stiffness. The outer covering, traditionally fabric doped with cotton and cellulose compounds, or in modern designs laminated plastic films, needs only to hold internal pressure modest enough to maintain aerodynamic shape and contain the lifting gas. The framework weight is significant: accounting for perhaps 15 to 25 percent of the gross weight of a rigid, compared to 5 to 10 percent for a pressure airship.
Inspection of the framework requires access into the interior, where corrosion of aluminum joints, fatigue cracking at rivets, and failure of wire bracing must be monitored. Gas cell deterioration, particularly at seams and patch repairs, is a chronic maintenance item. Rigids are less forgiving than blimps of external damage; a gash in the envelope can allow structural loads to shift unpredictably onto the frame.
The term rigid dates to early German airship design and has remained standard in engineering literature, even as operational rigids have become rare. Most rigids operated commercially between 1920 and 1940, and military patrol and observation models through the 1960s. Modern interest in rigids centers on their efficiency at very large payloads and long endurance, though the engineering complexity and cost limit new construction.