PrISM (Propeller Ice Shed Measurement) is a three-year project, concluding in December 2024, with the aim of generating 3D propeller ice accumulation and shedding data via simulation, and validating using ice tunnel test results.
Conducted by a consortium consisting of AeroTex GmbH, Dowty, a GE Aerospace company, Rail Tec Arsenal (RTA) and the Austrian Institute for Icing Sciences (AIIS), the project also aims to assess the impact of standard and supercooled large droplet (SLD) icing conditions on propellers and their de-icing systems, and further understand ice shedding mechanisms with regards to system design and ice impact.
Recently, Engineering and Development Test teams from Dowty prepared and conducted final tests for the PrISM project using a purpose-built test propeller. Following the success of the first campaign in April 2024, where feasibility of novel measurement equipment developed within the project was proven on an existing test propeller, this second test took learnings acquired from the previous test as well as new analysis tools developed from those results, and used a test propeller designed specifically to mimic one appropriate to a large transport aircraft. It created a broad range of icing conditions (including supercooled large droplets) and corresponding shedding events representative of a larger propeller, providing new insight into the impact of icing on regional transport aircraft.
Supercooled Large Droplet (SLD) consist of water droplets with diameters in excess of 100 microns and up to diameters of around 2mm that remain a liquid in the air at temperatures below 0°C, and are typical of freezing drizzle and rain conditions. They can be particularly hazardous to aircraft due to the larger volume of water striking the surface and therefore the ice that can rapidly accumulate on the airframe and propulsion components, including propellers. The complex dynamics of the larger droplets as they strike the surface of the aircraft can also lead to different ice formation characteristics compared to the smaller droplets that were historically considered in aircraft and ice protection system design.
As a result of increased knowledge of these atmospheric conditions, and a number of fatal accidents where SLD conditions were identified as a contributory factor, the certification regulations related to icing conditions have been expanded to include SLD conditions as Appendix O to 14CFR/CS-25.
Dowty provided the test propeller, ice protection system and design input for 3D icing and heating simulations carried out by PrISM’s lead partner, AeroTex GmbH, who also coordinated the testing in RTA’s large climatic wind tunnel. The propeller rig itself, upgraded for the project to achieve higher power, was also provided by RTA and is capable of measuring key propeller performance parameters such as thrust, torque, power and vibration during ice accumulation and shedding. Data from thermocouples and strain gauges embedded in the propeller were also acquired for monitoring purposes. The novel measurement equipment provided by AIIS allowed for the tracking of ice as it is shed from the test propeller as well as assessment of the kinetic energy of the ice.
The project received funding from the Federal Ministry of Austria for Climate Action, Environment, Energy, Mobility, Innovation and Technology (BMK) as part of the Austrian Aeronautics Programme TAKE OFF via the Austrian Research Promotion Agency (FFG).