Co-authors​ :

 Ziqi DAI (NEW ZEALAND), Digby SYMONS (NEW ZEALAND), John PEARSE , Riul JUNG , Michael KINGAN  

Design and manufacturing methodologies for skewed (swept back) composite rotor blades in contra-rotating systems are addressed in this research. Skewed rotor blades are a promising method for reducing the noise generated by coaxial contra-rotating rotor systems. Contra-rotating systems are attractive due to their high efficiency and thrust generation. This research is driven by a desire to enhance the performance of unmanned aerial vehicles (UAVs or drones) through the development of improved rotor blades. Optimal design and manufacturing methodologies for such skewed composite rotor blades remain insufficiently investigated. The development of skewed composite rotor blades poses challenges in terms of structural behaviour and associated cost-effective manufacturing methodologies. The structural analysis becomes complicated with skewed geometry, which not only introduces coupled bend and twist deflections but also adds complexity to the lay-up process during manufacturing. Additionally, the use of a thin blade profile with, ideally, varying thickness but a constant number of plies adds to the challenge of both the structural analysis and manufacturing method. These challenges are being addressed within both the design and manufacturing realms through the integration of computational and experimental methods. As a common composite material in the aerospace industry, prepreg unidirectional carbon fibre (CFRP) was chosen for its superior strength-to-weight ratio and flexibility for modifying lay-up to meet specific design requirements. Utilising 3D-printed moulds facilitated the creation of the unique skewed planform and blade cross-section with the required precision. Finite element analysis (FEA) with shell elements was utilised to model the structural behaviour of three sets of blades with different skew angles. Two distinct composite lay-up methods (and thus ply orientation) for the skewed blades were investigated. Aerodynamic loads were calculated using blade element momentum theory (BEMT). These loads depend on blade deformation, so the BEMT algorithm is coupled to the FEA model, benefiting from rapid convergence achieved within a few iterations, thus addressing the aeroelastic problem. The coupled FEA and BEMT results were validated with experimental measurements to quantify the impact of different blade geometries and composite lay-ups on the overall aerodynamic performance. The results suggest that the lay-up choice for skewed blade geometries has a significant impact on rotor aerodynamic performance. The computational results agree well with the experimental measurements, which provides confidence in the FEM technique employed. Improved accuracy in thrust prediction can be achieved with the coupled FEA and BEMT algorithm. The outcome of this research provides valuable insights into the development of skewed composite UAV rotor blades and offers a methodology for future design optimisation.