SKY’S THE LIMIT FOR BRANCH HYDRAULIC SYSTEMS, SUPPLYING LEADING EDGE TEST RIG FOR HELICOPTER GEARBOXES

Phil Black - PII Editor 22/11/2011

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Bespoke engineering solutions provider, Branch Hydraulic Systems (Branch) has built and supplied a testing unit for Compact Orbital Gears (COG), a specialist gearbox and test rig manufacturer based in Mid Wales. As part of a supply-chain-partnership, the Branch test unit is being integrated with a high-speed slave gearbox, designed and manufactured by COG, for the testing of main rotor gearboxes for a world leading helicopter manufacturer.

The new test unit allows the helicopter gearboxes to be tested in hours compared to days, as is the current schedule. This significant reduction in the test cycle helps to reduce the risk of component damage, cuts unnecessary man-hours, minimises critical maintenance and downtime, and ultimately saves on expenditure.

Following an intensive evaluation phase, which included implemented parts supply, building the rig, installation, testing and commissioning on-site, Branch Hydraulic Systems was pleased the new system and process had exceeded the stringent and challenging demands of the specification.

Fully Automated Test Unit
A division of leading hydraulic and fluid power specialist, Group HES, Branch Hydraulic Systems developed the test system based on the concepts of hydraulic technology yet powered and monitored by high precision instrumentation. By consistently using a closed control PID loop in the hydraulic cylinders and monitoring system parameters, Branch developed an algorithm to balance the output torque conditions within the gearbox; controlled by a programmable logic controller (PLC) incorporated in the unit.

The team was able to provide a semi-automatic test environment facility to test the gearboxes under all states; equal and unequal torque condition. By driving the PQ valve natively from the PLC Branch was able to eradicate the need for manual intervention in torque balancing which not only minimises the risk of damage to the production gearboxes during testing but also helps to reduce costly maintenance and minimise man-hours. Ordinarily, with vendor specific hardware, customers are reliant on the expertise of specialist engineers to tackle any issues or make changes.

Advanced Technology Delivers Reduced Test Cycle
A standard gearbox functions with a single input and equal 50:50 outputs, on the port and starboard sides, when operating normally. However a situation may arise, for example, where if a shaft were to become jammed this would cause an uneven load on the outputs and so one of the requirements of the unit was to test the gearbox under an uneven torque. Together the COG and Branch engineers developed the control programme to achieve this and designed a facility so that an operator can select either a 50:50 torque balancing or biased torque balancing; for example between 40:60 and 60:40 at the port and starboard output ends.

At 19,000 RPM, the helicopter gearbox is at very high speed and this requires precision control when testing. Utilising its expertise in hi-performance, fast control equipments, Branch positioned a hi-precision servo valve, from global manufacturer, designer and integrator, Moog, onto each of the hydraulic cylinders. Changing the pressure applied to each cylinder and continuously monitoring the piston positions, using LVDT sensors, can distribute the torque from port to starboard side, depending on the selected ratio. To maintain precision control under test conditions (i.e. torque differential of less than 5 lb-ft) Branch implemented a PQ control. This uses a variable mode, of pressure and flow, to give high-speed precision, integral to success of the testing process.

Managing director at Compact Orbital Gears, Gareth La-Pajne said: “By developing an effective control philosophy, the team at Branch has not only employed a technique that many people think of as impossible but they have also allowed us to provide our customer with a semi-automatic, multi-faceted, value-added solution. The working concept was also proven within five days, a rapid and unexpected response time, culminating in a very impressive system.”

For further information visit www.compactorbitalgears.com or contact 0044-1597-811676