The transmission system is one of the “three major moving parts” of the helicopter. As the core part of the transmission system, the reducer should be subject to the fatigue test of the gear on the transmission chain to determine the fatigue limit and life of the gear.
The research on gear chain fatigue test of single rotor helicopter reducer has been carried out for many years in China, and several types of helicopter reducers have been tested. However, the research on coaxial twin rotor helicopters has been blank. By summarizing the fatigue test methods of gear chain of domestic helicopter reducer, the key points of the gear chain fatigue test methods are summarized, the power distribution of coaxial twin rotor helicopter is analyzed and calculated, the transmission power of each gear is determined, the test time and applied load of each gear during the gear chain fatigue test are defined, and the test program is formulated in combination with the transmission characteristics, and the general method of fatigue test of gear chain of coaxial twin rotor helicopter reducer is systematically described.
Through the design of gear chain fatigue test of coaxial twin rotor helicopter reducer taking VR-252 reducer as an example, the summarized test method is applied concretely. This method is also applicable to other types of helicopter reducers, and can guide the specific implementation of gear chain fatigue test of reducer. The main conclusions are as follows:
A. Clarification of test purpose and objective is the premise. To determine the life design principle, the fatigue life can be preliminarily evaluated by adjusting the load repeatedly and iteratively, and the infinite life design or safe life design can be determined by comparing the design indicators. Evaluate the gear safety factor according to the corresponding standards, and determine the gear to be tested for fatigue.
B. Gear load calculation is a necessary analysis process. Pay attention to the power distribution of the reducer, and accurately evaluate the load required for each gear test according to the transmission characteristics. Considering the working characteristics, the test load shall be corrected according to the number of test pieces.
C. The number of test cycles is the basis for preparing the test spectrum. The fatigue life under a certain number of cycles shall be preliminarily evaluated, the design index shall be compared, and the test assessment time shall be determined. It is necessary to ensure that the gear with the lowest speed meets a certain number of cycles.
D. In order to reduce the test risk and cost, the test procedure must be reasonably optimized. On the premise of ensuring the test load requirements, shorten the total test time as much as possible.