FATIGUE OF HELICOPTERS—TESTS AND CALCULATIONS

Helicopter development, although relatively more recent than conventional aircraft development, very rapidly underlined the primary importance of fatigue problems, as the rotors are an important source of vibration which is transmitted not only to the components of the rotors but also to the aircraft structure itself. It follows that the static dimensional requirements usually taken into consideration for any type of construction are insufficient in the rotary wing aircraft field and that it was necessary to develop test and stress analysis methods capable of ensuring the safety of this type of aircraft. The problem of fuselage fatigue—little different from that of conventional aircraft structures, for which abundant technical data exist—will not be treated here, in order to concentrate on the study of mechanical parts subjected to fatigue occurring at very high numbers of cycles. This paper deals with the methods used to overcome fatigue problems: Laboratory tests, measurement of flight stresses, determination of fatigue life of critical parts and quality control in production. It also covers certain stress analysis methods used and compares them with practical experience gained.