3DP Mark-I and 3DP Mark-II were created to test the autonomous avionics systems, and flight dynamics of Phase-One. The size and aerodynamic profile are nearly identical to Phase-I, providing a low-cost means of technical de-risking. This will ensure that the Phase-I design can operate safely and reliably before it enters manufacture.
The iconic blue 3DP Mark-I completed construction in April 2021, before being superseded by 3DP Mark-II (pictured at the USRI Aerospace Conference) in July 2021.
For simplicity, the aircraft replaces the gas turbine used on Phase-I with a 120mm EDF (Electric Ducted Fan). An emphasis was placed on minimising the mass of the 3D-printed parts, so a unique lattice structure was designed, using a series of internal ribs placed at 45-degree angles to provide the necessary structural support while allowing the vehicle to be printed without a support structure. This technique allowed us to achieve a thickness of 1.2mm on all walls, reducing the total aircraft mass to 7.6 kg.
The Phase-I aircraft, set to fly in 2022, aims to use its Jetcat P300-Pro jet engine to accelerate to Mach 0.73 (575 mph) and break the world record for the fastest model aircraft, currently held by the RC Speeder “Inferno” which achieved a top speed of Mach 0.6 (465 mph) after rolling out in 2013. The aircraft is currently in manufacture and will be used as a test-bed for our more ambitious Phase-Two aircraft that aims to break the sound barrier.
Drag the cursor around to see the Phase-I aircraft for yourself…
The design was a collaborative effort between the aerodynamics, propulsion, structures, recovery, avionics and CFD teams. The separately designed parts integrate together to form an autonomous aircraft that can reach Mach 0.7 and break the current speed record.
Selecting a recovery system meant balancing several conflicting requirements. The test range lacks a runway so retractable landing gear was not an option, meanwhile, a net was discarded over; size requirements, concerns surrounding the accuracy required to land on it and the risk of missing. Belly landings are not possible due to the bottom-mounted inlet, which improves engine performance, so a parachute was chosen. This uses a piston-fed ejection charge system to release a 2.4m parachute and lower the vehicle to the ground slowly. This also acts as an insurance policy, should there be a loss of control, with redundant systems providing the required reliability.
The avionics systems are the brains of the aircraft, using data from a wide range of sensors to actuate the control surfaces, manage the throttle and initialise key events such as parachute ejection. They also transmit flight data and live video back to the ground station. The team required a safe, reliable and autonomous system, eventually converging on the Pixhawk Cube and CUAV X7 flight controllers. Having benefited from years of development, they provide the required redundancy and customisability. Within the avionics team, a rigorous research and testing schedule ensures that the chosen components will be able to reliably operate in the transonic regime.
The shape of the airframe was the craftsmanship of the aerodynamics team, which analysed several airfoils and bodies to meet our lift and stall speed requirements while minimising drag at Mach 0.7. Constant collaboration with the CFD (Computational Fluid Dynamics) team allowed us to analyse flow conditions and optimise the aero-body in an iterative process, utilising the full capabilities of the CFD package, Star-CCM+, provided by our sponsor, Siemens. As we move to higher speeds in Phase-II the importance of minimising wave-making drag will ever-increase, so the design will be optimised using the area rule.
(Infographic Coming Soon)
The propulsion team managed the selection of a gas turbine engine, the design of an inlet and nozzle, and performance analysis. For Phase-I a Jetcat P300-Pro was chosen, this offers unrivalled reliability when compared to competitors while meeting our thrust and fuel consumption requirements. The bottom-mounted inlet decelerates air to Mach 0.3 to minimise performance losses at higher speeds, while the 3D-printed (SLM) nozzle converts excess pressure into velocity while providing necessary temperature resistance.
(Infographic Coming Soon)
The Phase-I fuselage uses a monocoque design comprised of two main halves separated at the horizontal midplane, along with a fibreglass nose cone and 3D-printed control surfaces. The fuselage halves are made from carbon fibre and heat shaped Divinycell core, with a joggle type connection between them, and a split mould technique is used to create the geometry into the shells. The nose cone is made of fibreglass due to its RF transparency, while the 3D-printed components use carbon fibre infused polycarbonate. The operating temperature of the aircraft can reach up to 85°C, hence the shell is cured in a DIY oven and materials with suitable glass transition temperatures were chosen for 3D printing. The critical load on the aircraft is from the parachute deployment estimated to be around 15g during an abort procedure. This will be transmitted to the aircraft through two bulkheads, chemically bonded to the fuselage shells with the core to provide bending resistance. The Integration and Recovery Team have designed a test plan for ensuring this criterion is met. The avionics mount to an I-beam which is ideal for transferring pitching moments from the canards, while offering accessible space for mounting the avionics. The fuel tank is comprised of fibreglass and kevlar for impact resistance, meanwhile, the inlet is a two-part sub-assembly, allowing the external portion to be 3D printed for easy replacement after a rough landing. Finally, the engine cradle is 3D printed to provide a minimal restriction on the bypass airflow for better cooling while maintaining a robust connection. Prototypes made of PC-CF will be tested to evaluate performance at peak engine temperatures, along with further insulation at the interface.
(Infographic Coming Soon)