Energy Absorber Test System Facilitates Test of F-35 Actuators

Methods of adjusting flight control surfaces have evolved since the early years of flight when simple mechanical linkages controlled the first adjustable surfaces, with the pilot providing the power. One stop along the way of this evolution was the incorporation of centralized hydraulic systems to deliver hydraulic power to operate actuators at each control surface. But these systems had significant drawbacks. They required extensive lengths of piping to carry the hydraulic fluid throughout the aircraft as well as a large number of joints. The systems added to the aircraft’s weight and were subject to leaks of the corrosive hydraulic fluid and other failures. An alternative to these centralized hydraulic systems is to replace the hydraulic lines with wires that carry electrical power to the actuators. This approach—called Power-by-Wire (PBW)—improves reliability and reduces maintenance costs.1 PBW systems in turn come in multiple types. Electromechanicalactuation systems use electric motors and gears to control the surfaces, but the gears can add a backlash, and the mechanisms are subject to solid contaminants that can cause them to jam. Electrohydrostatic Actuator Other PBW systems leverage both electronic and hydraulic subsystems. One such system currently in use is the electrohydrostatic actuator (EHA), which incorporates its own self-contained hydraulic subsystem, including a bidirectional pump typically driven by a brushless DC motor. The EHA also includes an accumulator and control elements as well as the hydraulic actuator itself.2 The EHA requires only electrical power and electronic control inputs rather than external hydraulic power. With individual self-contained EHAs at the various control surfaces, the failure of one EHA will not affect the others, and the need for centralized hydraulic power and the attendant long pipe lengths is eliminated. The F-35 joint strike fighter uses EHAs to control flight surfaces including flaperons, the horizontal tail, and the rudder. EHAs are electronically controlled and electrically powered, with the electrical power converted to hydraulic power within the EHA to move control surfaces. The actuator regenerates energy back to the aircraft’s electrical system when the flight surfaces are driven back to their original position after very fast pulsed loads. EHA Test Challenges EHAs present significant test challenges. First, test fixturing must be created to mimic the functional end-use environment. Power must be provided to the actuator’s electronic control unit (EC), and control signals that would normally be provided by the aircraft’s vehiclemanagement computer (VMC) must be simulated. The test fixture must also incorporate an opposing hydraulic test actuator that drives the EHA backwards, and control signals must also be sent to this opposing actuator. Finally, the test system must absorb the regenerated energy from the EHA in response to the operation of the opposing actuator. Since this energy appears as fast pulses at high levels of power, the test system must be similarly fast to protect the EC and other components and subsystems from damage. To address the power needs of an EHA test system, AMETEK Programmable Power offers the Energy Absorber Test System, nicknamed “The Sponge.” The system was developed from the company’s Engineered Solutions business, which builds systems for customers whose requirements cannot be met with a standard catalog product. To remain cost-effective, the Engineered Solutions business adapts standard products to customers’ needs to the extent possible. For an EHA test application, several aerospace companies employ a version of the Energy Absorber Test System in both research and development and in manufacturing/production test scenarios. The Energy Absorber Test System provides a programmable DC voltage to the EC, which in turn feeds the EHA. The system also contains a very fast-acting sense and load-shedding subsystem. These aerospace companies chose AMETEK Programmable Power because of its expertise in power- and solutions-level applications and its reputation for reliability and support.
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