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58 Engine control Frigerio explains that engine control is done via an ECU operating the fuel pump and the propeller. “If the rotor shaft starts slowing you need more power, so when that happens the ECU commands the pump to go faster to put more fuel into the engine,” he says. “When that happens the turbine inlet temperature is higher, so you are expanding the air from a higher temperature, so the power output of the engine goes up and the shaft speed goes back up. “The opposite is also true. If you start over-speeding, the ECU slows the pump and the turbine inlet temperature goes down, and the engine slows until the required operating speed is regained.” In operation, the ECU controls the fuel pump’s speed and the two solenoids governing the variable-pitch mechanism. During the start it also controls the starter generator and the ignitor, ensuring a safe reliable start. The starter/generator switches from a motor to a generator during normal operation, and its output is controlled by the power control unit, according to the electrical requirements of the vehicle. The ECU knows what the generator is doing so it can take that into account, but it doesn’t control it. The key inputs to the ECU are the electrical power requirement and the conditions of the engine – shaft speed, intake air temperature and density, and exhaust gas temperature. It also monitors basic health conditions such as oil pressure, temperature and vibration. Performance The engine air intake is on top to avoid pick-up from underneath on take-off or landing. “There is an air filter in it so we can operate in dusty environments. There isn’t much danger of compressor erosion because of the material it’s made from, but the air filter stops dust clogging the recuperator passages,” explains Frigerio. The only items that require cooling are the oil system and the electronics, December/January 2017 | Unmanned Systems Technology The gearbox of the UTP 50 hp recuperated gas turbine The UTP 50 hp recuperated gas turbine seen from right-hand side