Unmanned Systems Technology 026 I Tecdron TC800-FF I Propellers I USVs I AUVSI 2019 part 1 I Robby Moto UAVE I Singular Aircraft FlyOx I Teledyne SeaRaptor I Simulation & Testing I Ocean Business 2019 report

36 Focus | Propellers These variables and others, such as estimates of lift and drag forces, can be more accurately gauged as propeller designers amass more and more test data (such as from wind tunnels) to refine their models. Combining these with data from engine and motor manufacturers – or, for companies that manufacture motors as well as propellers, their own data – means accurate calculations of critical values such as thrust, power and torque coefficients are possible. These are important for modelling properties such as a propeller’s real- world efficiency by seeing how much thrust it generates compared with how much power it ‘consumes’, as well as its losses at the tips and hub, and its static thrust while hovering. Alongside aerodynamic analysis, it is increasingly common among manufacturers to perform structural and fatigue analyses on their propellers, as these will also influence the prop’s aerodynamic performance as well as its lifespan. It is also worth noting that judicious FEA simulations by the manufacturer can help predict which segments or areas along the blades can be expected to show signs of wear over time. That can help with the safety case for their vehicles (and therefore the case for regulators to accept increasing urban integration of UASs) if they are informed in advance of where any damage is most likely. Through FEA software such as Nastrel or Femap, propeller designers can identify the effects of aerodynamic, centrifugal and gravitational loads on the blades and hub, for example by seeing if the highest stress levels are experienced at the blade tips, blade roots, trailing edges or elsewhere. They can also model where cracks might appear and how they might grow over time, depending on the expected frequency of use and service life of the prop. That can be used to further improve the structure or to inform the vehicle’s operators for future safety inspections. Modelling technology also allows users to simulate the effects of the prop’s material in FEA, be it carbon composite, thermoplastic or aluminium alloy, as the balance between a material’s cost and its properties (such as durability or flexibility) will still typically influence design choices. Software can also account for the roughness or smoothness of a blade surface, which can vary according to how much the end-user is willing to invest in quality of manufacturing. After simulation, it is increasingly common for propeller manufacturers to conduct tests on prototypes of the modelled design. These vary between companies, and include combinations of test stands, acoustic chambers and wind tunnels, either in-house or those from third parties. And although additive printing is June/July 2019 | Unmanned Systems Technology The great majority of UAVs now use propellers made from carbon composite, although wood and fibre glass still find some use (Courtesy of Sensenich) Software is available for running aerodynamic analysis, as well as structural and fatigue analyses of propeller designs (Courtesy of DARcorporation)