Aviation Icing Tests IV - Cloud Generation for Realistic Icing Tests on Aircraft Components, With and Without De-Icing or Anti-Icing Facilities

this research project will examine consequent research topics with a focus on increasing the LWC (Liquid Water Content) for Appendix C as well as the distribution and reduction of the LWC for Supercooled Large Drops (SLD). It is building on research projects Aviation Icing Tests, Aviation Icing Tests II and Aviation Icing Tests III that have already been carried out.

Short Description


The icing system, which has been in operation since 2013, has already been used successfully in numerous customer and research projects. The limitation of insufficient LWC according to EASA CS-25/CS-29 Appendix C led to a lack of understanding among customers. In SLD research, technical challenges associated with the "freezing rain" simulation were already identified in 2016. 

RTA has since then intensively dealt with the subject. The recent publication and presentation of a scientific paper during the International Conference on Icing of Aircraft, Engines, and Structures in June 2019 has led to a specific cooperation proposition of the FAA and NASA, and it underlines the increasing international significance of the RTA Icing Wind Tunnel Vienna.


  • Increasing the liquid water content (LWC) for CS-29 Appendix C.
  • Supercooled large drops (SLD) cloud simulation according to CS-29 Appendix O.


The next step in increasing the LWC in the Icing Wind Tunnel is to carry out detailed investigations with additional nozzles/bars, taking into account the aerodynamic influences and possibly resulting "icing" of the existing bars. The research results and analysis should lead to a concept for extending the LWC area and the complete fulfillment of the EASA CS-25 and CS-29 Appendix C specifications.
With regard to the SLD, a technical study will be carried out in the course of a concept study in order to reduce the LWC and achieve supercooling of the large droplets. This will further expand the "freezing rain" unique selling point.


The extension of the LWC range should be possible by doubling the number of nozzles (second row of bars). It is necessary to validate the operational reliability (operation with two rows of bars) and to determine the threshold value. For this, "dummies" and a fully operational intermediate bar will be constructed and put to use. Additional accompanying aerodynamic measurements to determine the actual state of the velocity distribution at the nozzle plane will be carried out with a specially developed traversing device.

Based on the findings from the previous research project, the achieved affected area for "freezing rain" is to be expanded in order to be able to fully ice over a NACA0012 aerofoil. Furthermore, the supercooling of large droplets is to be ensured by extending the water pre-cooling system and validated by means of measurements. Initial investigations and tests to reduce the LWC for "freezing drizzle/rain > 40 μm" should also be carried out.

Expected results

Based on Aviation Icing Tests I to III, the following results are expected in the follow-up project IV:

  • Solution concepts to increase the LWC without negatively influencing the existing aerodynamic situation in the Icing Wind Tunnel (distribution of the clouds, velocity profile, temperature range).
  • Complete icing possibility of an aerofoil up to approximately 3.0m under "freezing rain" conditions, whereby the supercooling has been further validated and the reliability of the prototype has been further improved.


The results of the Aviation Icing Tests I to IV were extremely satisfactory, and they opened up completely new possibilities, which in each case also led to follow-up projects.

Project Partners