Unmanned Systems Technology 021 | Robot Aviation FX450 l Imaging Sensors focus l UAVs Insight l Liquid-Piston X-Mini l Riptide l Eurosatory 2018 show report l Zipline l Electric Motors focus l ASTS show report

28 Dossier | Robot Aviation FX450 Structure and materials The fuselage, canards, wings and winglets are all moulded in a combination of carbon fibre reinforced plastic (CFRP) for its high strength and stiffness-to-weight ratio, and glass fibre- reinforced plastic for its RF transparency and toughness. They are all hollow stressed-skin monocoque structures with moulded-in ribs and stringers. Small amounts of aluminium alloy, steel and titanium are also incorporated. Guy emphasises the importance of using the right materials in the right places. Despite the pressure to assume carbon fibre is always best, he says, the FX450 airframe has carbon where it makes sense to use it and glass fibre where that makes more sense. Most of the fuselage is glass fibre but the primary structures are carbon fibre, with more of the black stuff where necessary to beef up openings or other highly loaded areas. Nyroth comments that overuse of carbon fibre can cause problems because of its stiffness, commenting that if there’s no escape for vibration because the material has few or no natural damping characteristics, it can make integrating payloads – particularly cameras – more challenging. “I was very happy to see that this company is not one of those ‘carbon crazy’ outfits, and it actually uses glass fibre,” he says. “You only want that stiffness and strength where you really need it.” To hold the aircraft together, the company is using a mixture of bonding using high-grade adhesives and aerospace-grade fasteners. “We are doing a lot of bonding, probably more than I would feel comfortable with in a manned platform.” Guy says. He adds that they are doing as much bonding as they can to avoid potential maintenance headaches associated with stripped fasteners. Where necessary, there are metal inserts in composite parts to take the bolting loads, but there are no rivets in the primary structure and just a few in sub-assemblies. Undercarriage and brakes The undercarriage is fixed, a decision based on a trade-off between the extra drag of legs and wheels dangling in the wind and the extra weight, complexity and potential failure modes of retraction and deployment mechanisms. The main wheels are mounted on a bow-shaped composite member that passes through the belly fairing to bolt into metallic inserts in the CFRP August/September 2018 | Unmanned Systems Technology Wing span: 7.2 m Length: 4.0 m Empty weight: 80 kg Max take-off weight: 180 kg Payload and fuel: 100 kg Primary structure: carbon fibre reinforced plastic Secondary structure: glass fibre reinforced plastic Engine: single- or twin-cylinder two-stroke capable of running on gasoline or JP5/JP8 Electrical power: up to 2.8 kW Sensors: multi-sensor/multi-axis stabilised gimbal, 100 MP high- resolution camera in the fuselage bay, Lidar as a future option Comms: tactical phased array broadband data links with range options up to 200 km, satcom hardware with compression software, ‘flying cell tower’ radio relay Some key suppliers Autopilot: Micropilot Engine: Hirth or Zanzottera Propeller: Helix Wiring: Berget Wheels and brakes: Beringer Electro-optics: FLIR Systems, DST Electro-optics: DST Gimbal: Trillium Engineering Data link: Radionor Satcom: Cobham Comms software: Ansur Technologies Cellular relay: Telenor Assembly, integration and flight test facilities: Eggemoen Aviation and Technology Park, Andoya Space Center Data sheet Technicians in the composites shop work on a CFRP wing structure. Carbon fibre is used only where essential (Courtesy of Robot Aviation)