| Abstract | This report details phase 4 of the work on remotely piloted aircraft systems (RPAS) icing encounters and concentrates on methods by which tolerance to flight in icing conditions can be demonstrated. Tests have been performed in the NRC’s RPAS icing facility using a 0.56 m (22 inch) diameter rotor under Appendix C, freezing drizzle and freezing rain conditions that examine the ability of the rotor to maintain predefined thrust, torque and power performance throughout an icing encounter of fixed duration. For the purposes of this study, the rotor performance is determined by considering a hypothetical quadcopter RPAS concept with vehicle weights of 15 kg and 17 kg and a minimum operation time necessary to affect a safe landing from an altitude of 122 m (400 ft) at a descent rate of 1 m/s.
It is shown that, under Appendix C icing conditions, the time taken for the rotor to reach its operational limit reduces as the liquid water content increases and that, at high LWCs, the rotor is not able to maintain adequate thrust within the specified time limit. For freezing drizzle conditions, the rotor also showed performance degradation and was able to maintain adequate operation for only the lighter precipitation rates tested. Similarly, for freezing rain conditions, the rotor reached its operational limit before the specified time for all but the lighter precipitation conditions and was shown to be more susceptible to icing at warmer test temperatures. This was likely due to the increasing three-dimensionality of the ice shapes formed at this condition.
A means by which performance degradation due to icing can be simulated in dry test environments through the use of roughness attached to the rotor blades has also been investigated. The ability to simulate icing conditions in this way has the potential to offer RPAS developers a method by which tolerance to flight in icing can be assessed without needing access to dedicated icing facilities. It has been shown that, using silicon carbide grit spaced over the leading-edge region of the rotor blades (between 16% and 32% chord length), it may be possible to simulate performance degradation due to icing of individual rotor loading characteristics, e.g., thrust, torque or power, but does not offer a means by which the overall performance of the blade and, therefore, the impact of the RPAS operation under icing, can be established. |
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