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31 such as Alpha to program it, but explains that the simpler the logic the faster users can learn to operate it and gain confidence in it. The software for the PCM was written in C++ by Alpha engineers. That has overcome the cultural challenge presented by the fact that the people who write the code are typically computer or electronics engineers, while those who define what it should do are often mechanical or aerospace engineers, which can generate some misunderstandings, Escarpenter says. Exactly which combination of navigation sensors is integrated into the Alpha 800 depends largely on the mission. However the company has put a lot of effort, particularly during testing, into minimising the number required in addition to those that come with the autopilot as standard. Extra sensors might be needed for flights near the poles, near infrastructure or to land on vessels, where the vehicle would need GPS heading, Escarpenter says, which might require an extra GPS antenna. “For mapping operations RTK is recommended, and while deploying magnetometers that make it necessary to fly as close as possible to the ground we integrate a radio altimeter or a laser altimeter,” he says. The aspect of the autopilot that took the most development effort was the Alpha 800’s emergency auto-rotation capability. Like any conventional helicopter, it inherently has the option of auto-rotating to the ground in the event of an engine failure. That involves quickly reducing the collective pitch to maintain a safe rotor speed and descent rate, then adding more collective pitch at just the right moment to cushion the landing. That means the Alpha 800 has no need for a recovery parachute, saving weight, complication and cost. “Even when it works at the level of autopilot logic it requires very fine tuning to reach the optimal glide speed,” Escarpenter says. “It has to be tested under many different scenarios, combinations of wind speed and payload configuration, and so on. “We discovered that, with very fine tuning, the descent rate in auto-rotation was not that different from that achieved with a parachute, which would be a permanent load of 1.3 to 1.5 kg on the helicopter.” Parachutes on helicopters are also tricky, he adds. “You have to stop the rotor before deploying the parachute; that may be a 2-3 s manoeuvre, which reduces the success rate of the recovery significantly.” Comms and ground control The heart of the Alpha 800’s comms system is a digital data link that uses coded orthogonal frequency division multiplexing (COFDM) and MIMO techniques for reliability at high data rates. Combined with encryption and multi-channel capability, this provides a lot of flexibility in terms of payloads. Key components include the data link module, which is an off-the-shelf item integrated into the PCM, aerospace industry blade antennas and high-quality RF cabling. The antennas are attached to the landing gear to give a clear line of sight to the GCS antenna. Alpha provides its own double-screen, high-brightness GCS. It’s a portable system that can work in standalone mode or as the interface for a larger ground data terminal or tracking antenna. The case also has a payload bay that can take an internal data link, for example, using antennas mounted on the case for operations within visual range or relay commands to an external device such as a tracking antenna for extended ranges. The GCS is modular, and the payload bay in the case is accessible by undoing four bolts. Two manual piloting options are available. One is an assisted mode in which the user controls the aircraft with limited authority via a gamepad; the other is a full-authority handset transceiver supplied by Alpha, the main role of which is to serve as the source for pre-flight checks of control surfaces, although it can also be used as an emergency back-up. Integrated payloads Alpha has integrated and tested electro- optical payloads from a variety of manufacturers including Controp, DST, Octopus ISR and cameras from Variocam and FLIR Systems, with the system offered depending on the mission to be performed, according to Escarpenter. While Alpha has no particular tie-in with any of those companies, most of the latest aircraft that have been delivered were for ISTAR missions. “Right now, Octopus cameras have a high level of integration, and thanks to the sightline video processing module, the workload of and training required for the payload operator is drastically reduced,” Escarpenter says. Most payloads run on 12 or 24 V and communicate via RS-232 or Ethernet, sometimes both. Unmanned Systems Technology | June/July 2018 Alpha Unmanned Systems Alpha 800 | Dossier The pitot tube is part of the Alpha 800’s air data system and is paired with a static port behind the rotor mast to measure air speed (Courtesy of Alpha)