Hardware-in-the-loop simulators (HiL) have been used in manned aviation for a long time to reduce the risk of system failures and pilot errors. A HiL enables testing of the entire system with actuators and displays and training of pilots on aircraft with new (flight control) systems and/or displays. A variety of solutions for HiL exists for UAS, but a high level of safety is required in aviation. The goal was to establish a toolchain for the most widely used flight control computer, the Pixhawk, to test the system safely with commercial software and hardware that is already used in manned aviation. For this purpose, the Pixhawk ought to be connected to CANoe via the CAN interface.
Building a digital twin and linking the digital world with the real world via the CAN interface
Two main components are needed to build a high-quality HiL: i) a digital twin of the UAS with all its components (flight dynamics, sensor models, actuator models) and ii) a bridge between the digital world and the real existing flight control computer/system (FCS) with all its components, such as data link and remote control. The digital twin was replicated in a Simulink model. In system identifications, the real behavior of flight dynamics, sensors and actuators were determined and formulated into mathematical models in Simulink. The Simulink model was linked to CANoe. The Pixhawk has a CAN interface that can be configured for different operating modes. However, a direct connection to CANoe was not possible. Therefore, the FlightStack was modified. In addition, software modules that normally read out the sensors were adapted so that the measurement data (IMU, GPS) were replaced by the corresponding CAN messages from CANoe. Commands from the FCS to the actuators are transmitted via CAN messages back to CANoe and thus also to the Simulink model. This allows to simulate a flight with all components. In addition, specific error cases can be implemented. To visualize the flight movement, the Virtual Flight Test Environment is used, which provides a three-dimensional view of the UAS flight in a real environment presented in the web browser.
Reduction of system and human failures in unmanned aviation with a reliable toolchain
Increase safety for UAS and payload by reducing risks of system failures and human error in real world operation
Testing with valid state-of-the-art test software and hardware to ensure a high-quality standard of safety
Applicability of the entire concept to any UAS that has a Pixhawk flight control computer
Testing of UAS with conventional drone hardware (Pixhawk, Datalink to ground station) and software (QGroundControl)
Training of UAS pilots on aircraft with new (flight control) systems and/or displays to reduce costs for real flight tests