Design of a motor glider landing gear strut – The role of failure analysis in structural integrity

• Identification of factors affecting structural reliability in home-built aircraft.
• We used failure analysis in redesign of key components.
• Fatigue analysis linked with measured flight cycle stresses.
• This leads to a revised design strategy for safety-critical components.

The structural integrity performance of light aircraft homebuilt from kits supplied by the designer is unlikely to be as statistically reliable as is the case for commercially produced aircraft. The homebuilt nature of the aircraft means that the culpability of the designer of the kits for the consequences of any structural accident is limited, provided that the design is structurally sound. However, in the case of phenomena such as fatigue where materials, manufacturing and performance are intricately linked the design may be far from sound, and problems can arise early in the operation of the aircraft. This paper presents a case study involving failure of a landing gear strut on a homebuilt motor glider design. The failure analysis established the importance of fatigue crack initiation and growth in the failure and identified contributory manufacturing procedures that were subsequently improved.