United States Army T55-L-712 Gas Turbine Engine Torquemeter System Test Improvements

This paper presents the issues and improvements to the T55-L-712 engine torquemeter kit system adjustment and test regime at the Corpus Christi Army Depot. The problems, analysis, and improvements will be presented. CH47 helicopter operation experiences 8-10 percent torque splits from the T55-L-712 gas turbine engine magnetostrictive torque system produced by the Corpus Christi Army Depot. A four-year effort to understand the design of the T55-L-712 torquemeter system and its limitations was accomplished. Understanding the theory of the magnetostrictive torque system was undertaken. This included testing the output of the T55-L-712 magnetostrictive torque system signal from the torquemeter static bench test through engine testing. Configuration of the torquemeter test cell and static test stand was ultimately modified to give consistent and repeatable signals. Both static bench test and engine test cell procedural changes are being implemented at the Corpus Christi Army Depot. Improvements are centering on upgrading static bench test equipment with an improved test procedure and standardizing engine test cell circuitry along with the power supply configuration. The 8-10 percent difference in torque splits experienced on the Army’s helicopter should be reduced with this new equipment and test methodology. In addition, it was found that the test cell comparison plays an important step in identifying test cell related T55-L-712 torquemeter torque curve adjustment errors. This new test equipment with an improved test procedure is expected to reduce overhaul test time and improve readiness for the Army CH47 aircraft field units flying with T55-L-712 engines.