Small Unmanned Fixed-wing Aircraft Design A Practical Approach

[Prince Aboubakar]

Theutility and benefits of small unmanned aircraft systems (sUAS) are being increasingly recognized across the aviation industry. While this technology is not new, its ability to support domestic public and private operators is becoming better understood, opening up new uses to government organizations and commercial enterprise. Small UAS are expected to become the most prevalent and affordable form of unmanned aircraft available, with applications for both business and recreation ranging from hobby model aircraft communities to defense contracting.

Beginning with the history and evolution of UAS, this book covers typical sUAS designs (including types of multirotor, fixed-wing, and hybrid), major elements and equipment, related technology, common uses, and safety practices, while also providing guidance and resources to help you make well-informed decisions regarding purchase and use and determine a path forward through the complex legal, business, operational, and support considerations.

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The book covers both the practical aspects of designing, manufacturing and flight testing and outlines and the essential calculations needed to underpin successful designs. It describes the entire process of UAV design from requirements definition to configuration layout and sizing, through preliminary design and analysis using simple panel codes and spreadsheets to full CFD and FEA models and on to detailed design with parametric CAD tools. Its focus is on modest cost approaches that draw heavily on the latest digital design and manufacturing methods, including a strong emphasis on utilizing off-the-shelf components, low cost analysis, automated geometry modelling and 3D printing.

It deliberately avoids a deep theoretical coverage of aerodynamics or structural mechanics; rather it provides a design team with sufficient insights and guidance to get the essentials undertaken more pragmatically. The book contains many all-colour illustrations of the dozens of aircraft built by the authors and their students over the last ten years giving much detailed information on what works best. It is predominantly aimed at under-graduate and MSc level student design and build projects, but will be of interest to anyone engaged in the practical problems of getting quite complex unmanned aircraft flying. It should also appeal to the more sophisticated aero-modeller and those engaged on research based around fixed wing UAVs.

Figure 4.8 Typical engine and motor mounts for SLS nylon fuselages and nacelles. Note the steel engine bearer in first view, engine hours meter in second image, and vibration isolation in third setup.

Figure 4.14 Three-axis gimbal system and Sony video camera mounted in front of the nose wheel. Note the video receiver system on the bench that links to the camera via a dedicated radio channel.

Figure 4.16 Aircraft with SLS nylon fuselage formed in three parts: front camera section attached by bayonet to rear two sections joined by tension rods. Note the steel tension rod inside the hull just behind bayonet in the right-hand image.

Figure 5.13 SPOTTER fuel tank level sensors. One sensor lies behind the central flap in the upper wider part of the tank (just visible in the right-hand image), while the second one lies at the bottom just above the payload interface.

Figure 6.17 Baseboard with mil spec connections on left- and right-hand edges. Note SkyCircuits SC2 autopilot fitted top right with GPS antenna on top and switch-over unit in the center with very many wiring connections.

Figure 6.23 A selection of professional-grade 5.8 GHz video radiolink equipment: (front) transmitter with omnidirectional antenna in ruggedized case, and (rear left to right) receiver, directional antenna, and combined receiver/high intensity screen unit.

Figure 10.2 Four semi-randomly chosen points in an immense space of unmanned aircraft topologies: (starting at the top) the Scaled Composites Proteus, the NASA Prandtl-D research aircraft, the AeroVironment RQ-11 Raven, and the NASA Helios (images courtesy of NASA and the USAF).

Figure 10.6 Typical constraint diagram. Each constraint bites a chunk out of the c010-math-058 versus c010-math-059 space; whatever is left is the feasible region, wherein the design will have to be positioned.

Figure 13.21 Experimental and computational lift and drag data for the Sivells and Spooner [21] wing with enhanced c013-math-111 SST Harpoon mesh of 76 million cells and c013-math-112 for the enhanced mesh.

Figure 13.23 XFLR5 model of Decode-1 airframe as generated by AirCONICS with main wing setting angle of c013-math-116 and elevator setting angle of c013-math-117 , at an angle of attack of c013-math-118 and 30 m/s. Note the use of cambered sections for the main wing and symmetrical profiles for the elevator and fins. The green bars indicate the section lift, with the tail producing downforce to ensure pitch stability.

Figure 13.32 Polar plot for Decode-1 airframe at 30 m/s showing both Fluent and XLFR5 results for lift and drag. Those for Fluent include results for just the lifting surfaces and with the complete airframe fuselage, control surfaces, and undercarriage gear; those for XFLR5 show also the impact of adding a fixed parasitic drag coefficient of 0.0375.

Figure 14.4 Deflection and slope variations for the Decode-1 main spar when flying at 30 m/s and an angle of attack of c014-math-083 using loading taken from XFLR5, a load factor of c014-math-084 , and simple beam theory analysis. The spar is assumed to be made from a circular CFRP section of outer diameter 20 mm, wall thickness 2 mm, Young's modulus of 70 GPa, and extending the full span of the aircraft, being clamped on the center plane.

Figure 14.5 Preliminary spar layout for Decode-1. Here the linking parts are taken directly from AirCONICS without being reduced to either thick-walled or thin-walled rib-reinforced structures.

Figure 14.8 Abaqus loading for full Decode-1 spar model under wing flight loads taken from XFLR5 together with a load factor of c014-math-092 plus elevator and fin loading based on Cl values of unity.

Figure 14.9 Deformed shape and von Mises stress plot for full Decode-1 spar model under wing flight loads taken from XFLR5 together with a load factor of c014-math-093 plus elevator and fin loading based on Cl values of unity. The main spar tip deflections are 143.9 mm, the elevator spar tip deflections are 10.8 mm, and the fin spar tip deflections are 11.1 mm.

Figure 14.10 Further details of the deformed shape and von Mises stress plot for full Decode-1 spar model under wing flight loads taken from XFLR5 together with a load factor of c014-math-094 plus elevator and fin loading based on Cl values of unity.

Figure 14.11 Deformed shape and von Mises stress plot for nylon support part in full Decode-1 spar model under wing flight loads taken from XFLR5 together with a load factor of c014-math-095 plus elevator and fin loading based on Cl values of unity.

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