Abstract: During g-factor spectrum compiling of aircraft cg based on flight data, part cycles maybe disappear. This is a serious problem because most of these disappeared cycles have high amplitude and originally belong to serious loads, which are significant for structure fatigue damage of aircrafts. In order to get these cycles back, two causes of the problem, i.e. load grading and period compressing, are researched. Based on the research, a method called Long & Short Period Test Spectrum is put forward: using average single flight time as short period to make basic spectrum block; determining long period by referring to serious loads occurring law; delaying basic block into a delayed spectrum according to long period; compressing by delayed spectrum period in order to find most disappeared cycles; inserting found cycles into delayed spectrum in proper manner to construct the accelerated test spectrum block. The method is proved to be valid by an example and the damage is closer to original damage than usual test spectrum block.

Key words: Aircraft structure fatigue, Fatigue test, Flight g-factor loads, Load spectrum, Periodic spectrum block