| Abstract | During the third year of the remotely piloted aircraft systems (RPAS) operator guidance and safety assurance tools for the urban environment project, between Transport Canada (TC) and the National Research Council Canada (NRC), a wind tunnel test was conducted to evaluate small RPAS performance in representative urban airflow types identified during year one as having potential to challenge RPAS stability including speed, direction, shear, turbulence and vorticity (S1 D S2 T V). During year two the urban airflow of sub-scale models of Canadian cities was measured to determine the magnitudes and locations of the identified flow types. For year three, the subject of this report, a group of 12 RPAS, including nine within the weight range for the TC Canadian Aviation Regulations Part IX small RPAS (sRPAS) category, along with two below and one above the weight range, were tested in representative urban airflow for each S1D S2T V flow type. This report covers the details and results of testing for the RPAS in all five target flow types (S1D S2T V).
Key findings from the RPAS tests included:
• Speed (S1): when compared to the manufacturers specifications for sustained wind speed tolerance, the wind tunnel test results showed inconsistency between manufacturers, where some results were lower and some results were higher than the specification. This discrepancy indicates that a standard method for evaluating small RPAS for wind conditions is not consistent within the industry.
• Direction (D): pitch flow, including downdraft and updraft, of approximately ±10◦ had a significant effect on sRPAS stability reducing the sustained wind speed limit by an average of approximately 2 m/s for the sRPAS tested.
• Shear (S2): the change in force across the width of the RPAS caused by a lateral wind speed gradient (shear layer) decreased the sustained wind speed limit by an average of 2 m/s for a group of smaller RPAS and 5 m/s for a larger RPAS, where all models were within the small RPAS weight range.
• Turbulence (T): RPAS response to turbulence intensity was found to be most strongly correlated with the w-component of the flow for a frequency range up to the wavelength size relative to the RPAS overall width. A strong correlation between changes in turbulence intensity and sustained wind speed limit was evident for RPAS with test environment positional accuracy.
• Vorticity (V): for the level of vorticity tested, the results showed no significant reduction in sustained wind speed limit as a result of hovering within a horizontal vortex imposing an aerodynamic moment across the width of the RPAS.
The results suggest that the tested RPAS manufacturer-specified sustained wind speed tolerance does not take into account conditions within Canadian urban environments. Specifically, the intensity of turbulence, the direction of airflow, particularly pitch-flow and the shear layers developed in the wakes of tall high rise buildings should be considered when defining criteria for safe RPAS operation in urban environments. viii |
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