Criterion assessment of the possibility to prolong the service life limit of the helicopter tail drive shaft

Low life time of home-produced helicopter transmission elements in comparison with foreign analogues is one of the problems of Russian helicopter industry. For example, the service life limit of Mi-2 drive shaft is 4,500 hours, the time between overhauls is 1,500 hours. The time between overhauls for the drive shaft of a similar helicopter Bell 429 is 3200 hours, for the Eurocopter AS350 it is 3000 hours. The service life limit of the drive shafts of Bell 429 and Eurocopter AS350 is not specified. As the financing of operations to prolong the service life limit of high-load elements of aircraft structure is very limited it is necessary to suggest other, less labor-intensive ways of assessing the technical condition of these elements in order to prolong the service life limit. New criteria need to be introduced to solve this problem. New criteria for the assessment of the possibility of prolonging the assigned life of helicopter tail rotor drive shafts are proposed and scientifically justified in this article. The criteria indicate changes in chemical, physical and mechanical properties, as well as strength properties of products after some time of service. Comparing the properties with their maximum values we can make a conclusion about the possibility to prolong the life cycle of helicopter transmission components. An example of the criteria calculation for the Mi-2 helicopter tail drive shaft with an expired Service Life Limit of 4500 hours is given.