Helicopter Powertrain Testing Beyond 90 Degrees

Long a staple in the automotive world, multi-platform powertrain testing has been a persistent challenge for helicopter dynamic components. Because of the complex and varied geometries of helicopter transmissions and gearboxes along with the diverse dynamic operation and load requirements, universal test stands had been few and far between. In addition, helicopter testing software and machine controls have been developed around individual OEM requirements, particular types of testing, and test system manufacturer preferences. The result has been unique test interfaces for each test article, each helicopter, each OEM, and even each testing facility.

We recently took on this challenge for the US Department of Defense (DoD). With more than 20 aging, dedicated test stands, each designed to accommodate a specific type of Army helicopter transmission or gearbox, testing was complex and inconsistent. Worker environments were less than optimal, the testing process took days, spare parts were sparse and expensive, and most of the energy used during testing was converted to wasted heat. The DoD looked to the engineering community to devise modern, cost-reducing solutions.

There were three new parts to the project -- an overhauled testing process, flexible powertrain test stands, and universal testing software. First, a new process was designed to significantly reduce test time, increasing machine availability and throughput. Second, flexible test stands were engineered with modular gearboxes and flexible connections to handle the complex geometries and varying dynamics of all the required test articles. Third, a modular set of software options was developed so that test operators could execute and monitor an entire test from a uniform interface, reducing training costs and improving testing accuracy.

In the existing environment, the test article was assembled, dressed, tested, and torn down, all while inside the test stand. This meant that the stand was unavailable for actual component testing during a majority of the process time, leading to days of system inactivity. The redesigned process moved all test prep and breakdown outside the test cell. Custom transportable test fixtures were designed with quick connect features so that a fully prepped test component could be quickly mechanically aligned, loaded, and electrically connected to the stand. Machine mounted RFID readers use fixture mounted tags to identify the component type prior to test and automatically configure the machine and load the appropriate automated test profile. Instead of taking hours to build up and break down the test article inside the stand, the quick connect process requires about 15 minutes for each. Depending on the test duration, throughput could increase by up to 400 percent.

The new test stands are designed with modular gearboxes, so each can accommodate multiple powertrain components. The size of a two-story building, a single main transmission test system can handle seven or more different helicopter transmissions as well as countless future variants. Separate flexible stands were engineered to handle tail and intermediate gearboxes, as well as other critical dynamic components. Test stand commercial gearboxes are designed to be modular and mobile, swapping out or changing position to allow capability of testing different components. Electrical re-gen was implemented to provide load control and load absorption to allow up to 80 percent of the power required during testing to be recaptured, either to power the test stand itself or to be returned to the grid.

It's estimated that the main transmission flexible test system, while running at full capacity, will cost about $400 less per hour to operate than the former DoD systems. This could easily translate into savings of $500,000/year on one test stand. Taxpayer savings is one of the primary drivers of this project.

The final challenge was to come up with a machine software and control package that would perform all the required dynamic tests and allow an operator trained on one test system to be competent on any of the others. The old system-specific programs with unique icons, processes, and interactions for each stand meant multiplying operator training and documentation.

Industrial software can't contain less usability and flexibility than any other software it interacts with. A modular software system and HMI platform was designed for all five test stands, with a common user interface and plug-in architecture, common function blocks, I/O coding, and CAT 4 safety functions. The test profiles, formerly hard coded into each stand, are now generated and stored independently from the hardware. Test profiles are identified to test each article via RFID and the resulting data is captured and stored to create a traceable test history for each transmission and gearbox.

Chris Lake is the vice-president and chief engineer of testing systems at RedViking Engineering.

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