Unmanned Systems Technology 004 | Delair-Tech DT18 | Autopilots | Rotron RT600 | Unmanned surface vehicles | AMRC | Motion control | Batteries

60 Dossier | AMRC structure heads after each printed layer. However, a self-supporting design is constrained to a maximum angle in the machine’s vertical orientation, which places complex geometrical limits on the design, since every angle on a component is restricted to a minimum radius as the material can only be layered by a very small offset in the x direction for every layer in the y direction. Several CAD models of the aircraft were created for evaluation using a range of design configurations, including sweep angles, chord lengths, taper ratios and aerofoil sections. The design solution found to be suitable for manufacture using AM included a wall thickness of 0.2254 mm and a double-wall construction with an internal support structure that allowed each part to be self-supporting throughout the manufacturing process. As development engineer and AM lead, Mark Cocking, explains, “By understanding the capability of the FDM process and associated software, we were able to manipulate the design to contain a number of unique features and prevent build deformation. All parts required for the airframe can be combined onto a single build in the FDM machine, taking less than 24 hours with the ABS-M30 material.” Project engineer at the DPG, Sam Bull, adds, “Doubling the number of walls was a way of getting around how the tool paths were programmed for the printer. If you try to print the geometry we wanted with a single bead it creates extremely weak spots at the joints where the internal structure meets the skin. The way we have designed the UAV is such that the internal structure is printed in one piece, and so is the outer skin, bonding itself to the internal layer in the process. Assembling the UAV is quick and simple. Short spars at the front and rear of the airframe clip into sockets formed within each wing half, allowing fast set-up time and avoiding the need for separate fixings. Trailing edge elevons are the UAV’s only control surfaces and are designed to snap-fit onto two hinges protruding from the outer wing section. They are controlled by a direct-acting servo in each wing which are fixed onto mounting spigots housed in the body of the aircraft. The wing tips are capped by flat end fences that clip into the ends of the aerofoil sections. They provide yaw stability and serve as a retaining structure for the elevons. Fully assembled, the UAV weighs just under 2 kg, and to prove the design the UAV was flight tested as a radio controlled slope-soaring glider. This part of the project shows that design for manufacture can be optimised for the FDM process such that only build material is required without any support structures, giving considerable savings in manufacturing time and cost. Before the advent of design for AM optimisation, this airframe would have taken more than 120 hours to produce. Powered version Following the success of that part of the project, the airframe was optimised further to incorporate blended curved winglets and twin electric ducted fan (EDF) propulsion in order to achieve a target flight speed of 20 m/s. The flying wing concept was retained for the powered version to ensure that design parameters such as longitudinal balance point and control surface throws could be transferred easily. Wherever possible, the use of AM techniques was once again Autumn 2015 | Unmanned Systems Technology First flights of the glider version were successful and proved the concept of a rapid additive manufactured UAV All parts for the airframe can be combined into a single build in the FDM machine, taking less than 24 hours with the ABS material