Employing a small, closely integrated team of engineers at the University of Bath has facilitated the rapid iteration of designs. Each team member took ownership of a subsystem, first developing analytical and empirical models for initial sizing. Initial concept generation was conducted using TRIZ before the team navigated the design loop three times with the fidelity of the design increasing with each iteration. The team took advantage of computational methods like CFD and FEA for rapid optimisation of the design. Meanwhile, these results were validated using wind tunnel testing, a low-speed flight prototype, jet engine testing, and a hardware-in-the-loop setup.
The current design, the Kingfisher, is a 1.3m long blended delta wing powered by a Jetcat P300 Pro micro-turbojet engine. The Kingfisher will launch from a catapult before performing a series of accelerated turns to reach 570 mph (Mach 0.75 at sea level) in the timing track. After two passes through the timing track in alternate directions, the Kingfisher will perform a belly landing on grass, with the underside fuselage doubling as a skid. The Kingfisher carries a parachute flight termination system, along with redundant avionics and telemetry systems to ensure it never leaves the test range.
The fibreglass semi-monocoque structure, chosen for its radio transparency, was optimised using Finite Element Analysis, with internal aluminium ribs, bulkheads and spars also providing mounting points for off-the-shelf components and access hatches for maintainability. Four elevons control the aircraft in pitch and roll, with the inboard elevons used alone at high speeds for improved sensitivity. These are controlled using a Pixhawk Cube autopilot, while an FPV camera enables the pilot to see the aircraft's orientation as it moves through the sky at 250 metres per second. The avionics and control systems were tested using an iron bird. Meanwhile, a 60% scale 3D-printed electric flight prototype provided further analysis of the Kingfisher's handling, with this sized to match the Kingfisher's wing cube loading of 37.
The delta-wing uses leading-edge vortices to maximise its lift on landing, like Concorde. Meanwhile, its low thickness helps to minimise drag. The aircraft has a thrust-to-weight ratio of nearly 3:1 on take-off, with the s-duct air intake shaped to deliver uniform, slow-moving airflow at the compressor face, to prevent stall. The inlet was sized to minimise spillage drag at Mach 0.75, at the expense of a slight thrust penalty at low speeds, where the aircraft is heavily overpowered. Experimental testing of the P300 Pro jet engine with the inlet showed good resilience to stall at high angles of attack, using two electric-ducted fans to simulate cross-flow. Meanwhile, thermocouples, placed around the engine, informed a thermal analysis model to ensure no damage to the surrounding structure. The aerodynamic design was accelerated using Simcenter Star-CCM+, providing a fast and inexpensive method of characterising the 3-dimensional flow over the airframe. This enabled the team to understand the vortex generation over the wing at low speeds, quantify the drag at Mach 0.75, and ensure the s-duct inlet can decelerate the flow entering the engine with minimal pressure losses and recirculation. These CFD results were validated during wind tunnel tests which enabled the team to characterise the lift, drag, pitching moment and elevon torque at different angles of attack and elevon deflections. Moreover, these results were passed through a MATLAB control model to simulate the Kingfisher's flight.
Before converging on the Kingfisher’s high subsonic design. The team initially looked at what it would take to break the sound barrier, developing the Mach 1.2 capable supersonic concept shown above.
The shape was focused on managing the formation of shocks. As an aircraft approaches the sound barrier, shock waves form, consuming large amounts of energy and causing a sharp increase in drag. The drag increase from Mach 0.8 to Mach 1 can be as great as 3-fold, and breaking the sound barrier requires sufficient thrust to exceed this drag, with small-scale turbojet engines ideal thanks to their wide range of operating speeds, high dynamic thrust, and relatively small form factor. After months of iteration, the resulting concept was a 2m long carbon fibre monocoque design, weighing 22kg when fuelled and gaining thrust from an afterburning Jetcat P400 Pro micro-turbojet engine. Its shape was optimised using the area rule to smooth out changes in cross-sectional area and minimise wave drag, while also providing sufficient volume for avionics, servo actuators, the fuel system and retractable landing gear.
The P400 Pro alone provides insufficient thrust to reach Mach 1, so the team added an afterburner: a lightweight modification that adds 50% more dynamic thrust without increasing the diameter of the fuselage (minimising drag). Even with these additions, the design would not be able to break the sound barrier at sea level, instead having to ascend to 11km altitude where the atmosphere is thinner and the speed of sound is lower, consuming half of its 6L fuel tank in the process. The aircraft would then enter a 30-degree dive where the effect of gravity provides additional “thrust”. In this configuration, a predicted top speed of Mach 1.2 could be momentarily reached.
Additionally, a normal shock inlet decelerates the flow entering the engine to subsonic speeds, ensuring the compressor doesn’t stall. Meanwhile, the highly swept delta-wing, with its 4% thickness, minimises drag at supersonic speeds, while providing sufficient lift at landing. Even so, the aircraft would have to land at 80 mph since if the wings were made any larger, the drag would be too high.
It is clear at this point that building and flying this aircraft would be beyond the scope of a student team, which is why the team instead opted for a subsonic Mach 0.8-capable design called “Kingfisher”. The Kingfisher has a larger wing area and a lower landing speed, making it more pilot-friendly. Moreover, it can reach its top speed at sea level without an afterburner, bypassing other logistical challenges.
