Innovation, contribution to the outside world.
A flying wing, utilising the unconventional bell shape lift distribution, for applications such as autonomous surveillance of farmers’ fields or delivery of goods: Project Aurora is a prototype for the aerodynamic design, and a test bed for the development of solar powered electronics.
The team is currently divided in the following subteams:
- Production Design and Management
- Flight Performance
- Ground Segment
- Control Systems
The aerodynamic design was conducted using software such as XFLR5 to evaluate lift curves, stability margins, eigenmodes of the wing design. The iterations were made by choosing the airfoils (varying linearly across the span), modelling the wing sweep in order for the lift distribution to be as close as possible to the theoretical ‘bell shaped’ lift distribution.
The required twist angle spanwise in each section of the wing was computed by running an optimisation program written in MATLAB. Given the theoretical ‘bell shaped’ curve equation, it could evaluate the performance using the 3D panel method.
The surface area of the wing was iterated accounting for the required solar panel area to power the engine and the drag generated by the wing profile. The required dimensions for the ailerons were derived by iterating the design with XFLR5.
It was decided to design for a sawtooth pattern flight profile, optimal for our applications because power efficient compared to a continuous thrust design.
The engine will operate at its optimum efficiency, allowing for a smaller solar cell area and mass. Furthermore, the engine will only be used for short periods, which will allow for the engine to cool down.
The main drawback to this approach is that a higher peak power has to be drawn from the batteries. This means that Aurora will have to carry a bigger battery compared to a wing with a continuous thrust design.
Structural and Production Design
The structural design of the wing was worked out together with the design of the production methods and materials. The prototype will be produced with vacuum infusion on glass fibre, from negative moulds made by CNC machining.
The skin of the wing will be produced by vacuum infusion in the following months, with four layers of glass fibre laid in the directions 90,-90,45,-45. After the skin has been cured, the top and bottom will be joined by inserting a foam core, that will increase the stiffness of the prototype. The core will be produced out of two phase expandable foam. The fuselage of the wing will encapsulate the electronics for the data acquisition and transmission, as well as the batteries and all the electronics required for the solar panels.
The aileron surfaces will be cut out from the full wing, the wires and servos required for their operations will be encapsulated in the expandable foam core.
The production design of the wing, of which the results have been reported in the previous paragraph, was carefully engineered in order to reduce both the safety risks for the people involved in manufacturing (especially of the composite parts) and the risk of production mistakes. Production temperatures and pressures, composition of the material and possible reactions of chemicals have all been taken into account.
Ground Segment Design
During the conceptual phase of the development of the UAV, ideas rose to not only develop an aerial unit, but also a ground station, making it a true Unmanned Aerial System (UAS). Eventually, it was our goal to make the UAV have a certain degree of autonomy. Also, in early stages of the aerodynamics design the team came to a realisation that conducting flight tests and acquiring data from those tests would be of high value. With these needs in mind, sub team ground-control started development of what would become a modular telemetry and data acquisition system.
This teensy (ARM micro-controller development platform) based data system collects data points from various sensors on the UAV, such as airspeed from the pitot-tube, pressure-altitude, orientation and axial motion with respect to the earth axis with the Inertial Measurement Unit. A GPS unit will collect datapoints on altitude, groundspeed, heading, longitude and latitude.
Through serial communication to other subsystems, such as power management and propulsion, data on solar panel efficiency, battery voltages and power usage will be obtained. Having collected all the data, the system will store the data on an onboard storage device, and then transferred to the ground station with a radio downlink.
The first iteration of the aerodynamic and structural design of Aurora is now complete.
The team is currently busy with production of the prototype, as well as the completion of the electronics design and the design of a flight data management system.
The flight performance team is evaluating the thrust produced by the engine selected for our platform, in order to evaluate the impact of heat dissipation on the performance of Aurora, and to design an engine mount able to sustain the loads while keeping the engine cooled.