Ongoing test method development and characterization of RPAS vehicle response for complex airflow applications

The National Research Council Canada (NRC) is engaged in an ongoing effort to support government partners Transport Canada (TC) and Defence Research and Development Canada (DRDC) in the safe operation and regulation of Advanced Air Mobility (AAM) vehicles in the complex flows associated with urban and shipboard environments. The goals of the project were achieved: by evaluating the stability of a group of Small Remotely Piloted Aircraft Systems (sRPAS) in airflow conditions similar to the flow direction and turbulence in real Canadian cities using Complex Flow Testing (CFT); and by demonstrating the process of developing an engineered Flying Qualities (FQ) test designed to challenge the performance limits of selected sRPAS as if they were in complex flows use of a wind tunnel facility. The project demonstrated new testing capabilities, including new equipment for characterizing complex flows, new equipment for measuring vehicle performance, and new flow control devices designed to create representative flow fields for testing purposes. The key findings from the sRPAS CFT include: • Local normalized turbulence intensities of 0.15 and flow direction pitch-angles of -25◦ caused most of the vehicles to become unstable, or have degraded controllability, below the manufacturer’s sustained wind speed tolerance; and • Downdraft of between -25◦ and -45◦ reduced the wind speed limit for the tested sRPAS by as much as a local turbulence intensity of between 0.15 and 0.40, respectively. Key findings from the FQ testing demonstration include: • The Maximum Vertical Speed (MVS) test, designed to provide the maximum available vehicle RPM, was successful only for one of the vehicles tested, highlighting the importance of understanding the control system on vehicle characterization; and • The Mission Task Element (MTE) was able to challenge the vehicle performance including maximum RPM, roll angles, vertical acceleration, position maintenance, and Handling Qualities Rating (HQR), all of which were comparable between the Mission Task Element (MTE) and the Complex Flow Testing (CFT). The MTE and the CFT revealed multiple influences and relationships between vehicle performance and stability; however, no single performance parameter explained the wind speed limit results. This highlights that a more complex understanding of the vehicle systems and aerodynamics are required to be able to predict and test for safe conditions for all types of vehicles. As a result, the demonstration MTE did not allow the identification of vehicle performance limit. However, this test has allowed the identification of clear avenues for future study and additional considerations to modify the MTE design in the future.

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