Unmanned Systems Technology 002 | Scion SA-400 | Commercial UAV Show report | Vision sensors | Danielson Trident I Security and safety systems | MIRA MACE | Additive manufacturing | Marine UUVs

23 Scion UAS SA-400 optionally piloted helicopter | Dossier “You just vary how much fuel you flow in, but you are always flowing some fuel into the engine,” remarks Sampson. “When we put pitch into the rotor blades the turbine is in danger of losing rpm; the governor sees that and gives it more fuel to maintain 61,000 rpm. If I fly manually and aggressively, it still only changes speed momentarily by about 100 rpm out of 61,000 rpm. That is remarkable!” Moreover, the vibration level is so low that the turbine can be hard-mounted to the airframe. In fact, more vibration comes from the rotors than the engine. “We do have anti-vibration mounts on the electronics though, specifically for the autopilot, and normally for the payload,” says Sampson. The transmission The T-62 is centrally mounted in the SA-400 with its output shaft horizontal, underneath and in parallel with a shaft taking the drive back to the tail rotor. Both the tail and main rotors are driven from a shaft coaxial with the tail rotor shaft. The driveshaft runs above the forward- projecting T-62 output shaft, and both shafts are connected via drive belts. As well as sending power back to the tail rotor, the belt-powered driveshaft sends the drive forward and up to the main rotor via a 90 º bevel drive. In the T-62 the drive to the output shaft is reduced from 61,000 compressor/ turbine wheel speed to 3000 rpm via gearing. The belts then drive the main transmission and the tail rotor at 3000 rpm. The bevel drive has a fixed ratio of 4.8:1 so that the main rotor (since it is much bigger in diameter than the tail rotor) runs at 620 rpm. Sampson adds, “The bevel drive runs in an oil bath; it is positively lubricated, not splash, and we have an oil cooler to maintain oil temperature in that pressurised system.” Some gears are transferred from the original bevel drive gearbox, others are new in the Eagle R&D production. The various gearshafts run in a combination of ball and taper-roller bearings. Despite the fact that for start-up a single-spool turbine needs all load Unmanned Systems Technology | Spring 2015 The SA-400 has simple landing gear but those skids house load sensors that are crucial to its autonomous operation When we put pitch into the rotor blades the turbine risks losing rpm, but the governor sees that and gives it more fuel