„Optimisation multi-user measurements RTA/All-Weather-Drone“

Experimental tests under critical weather conditions are an essential part of the development and certification of aircraft. This also includes unmanned aerial vehicles such as multirotor systems, fixed-wing drones or VTOL UAVs. However, this type of testing is often associated with significant costs and time expenditure. It is therefore important to design experimental tests in a particularly efficient way in order to minimise costs for developers and/or operators. The overall objective of this project is to demonstrate the innovative possibilities for the parallel testing of ‘small’ UAS rotors under extreme weather conditions.

The tests were carried out as an independent innovation project in addition to the TAKE-OFF research project ‘All-weather Drone’. The ‘All-weather Drone’ project focuses on investigating the effects of specific weather conditions such as rain, snow and icing on the operation of multi-rotor drones with a maximum take-off weight of 25 kg. The tests focussed in particular on performance parameters and flight safety. Due to the limited knowledge of rotors under such extreme weather conditions, experimental research is invaluable for users, developers and authorities alike. However, as this type of research incurs considerable costs, efficient realisation is crucial. The innovation project therefore investigated whether and with what consequences several rotor test rigs can be operated in parallel in the Climatic Wind Tunnel. In contrast to the already proven multi-user concept (AIRlabs, RTA, FHJ and AIIS), several rotor test rigs were operated in parallel (on different height levels) in this project, which represents a new challenge. There was a possibility that the flow fields of the rotors could influence each other and that slipping ice could be problematic for the neighbouring test rigs.

Furthermore, it can be assumed that the test rigs influence the test conditions, particularly the local water content in the air flow. It was therefore planned to carry out the tests in the following scenario: Positioning of three identical rotor test stands parallel to each other, whereby these had a vertical separation (different height of the rotor plane). This separation is introduced to protect the test rigs from slipping ice from other test rigs.

These investigations have a high practical relevance and therefore contribute significantly to the expansion of knowledge about the performance of rotors under extreme weather conditions and are of great importance for the development of innovative technologies in the drone industry. The climatic test conditions are based on relevant existing aviation standards such as Appendix C for icing from EASA certification regulations CS-25, taking into account typical flight missions for a multi-rotor drone, the flight envelope and the expected lower cruising speed and altitude (compared to manned aviation).

Key parameters such as power, speed, torque etc. are recorded during the tests. In order to evaluate the multi-user possibilities, the same test setup (rotor, orientation and speed) is selected for each of the front three test rigs. As a result, AIRlabs was provided with data from the All-weather Drone project partners (in particular RTA, AeroTex, AIIS and FH JOANNEUM) in order to be able to estimate the mutual influence of several UAS rotors for future tests. This makes it possible for AIRlabs to support customers in the planning and execution of multi-user tests in RTA’s Climatic Wind Tunnel.

This can reduce the effort (costs and time) for customers. In this context, the methodological knowledge of multi-object tests in RTA’s climatic wind tunnel was further expanded. AIRlabs has already gained initial experience in carrying out multi-object measurements in two measurement campaigns together with partners. The results of the methodological learning are to be validated on the one hand and new aspects/technologies/test arrangements are to be explored on the other.

1. Demonstration of the parallel testing of several rotors in RTA’s Climatic Wind Tunnel.
2. The installation of mobile cameras to improve the observability of icing processes is to be tested.
3. An improvement in project management processes for multi-user projects and different test objects.

The tests were carried out in the Climatic Wind Tunnel in February 2023. The smaller Climatic Wind Tunnel (SWT, Small Icing Wind Tunnel) with a cross-section of approx. 5x6m and a length of 33.8m was selected. The SWT can generate flow velocities of up to 45m/s and is equipped with fixed ceiling cameras, which are used to monitor the experiments.

The test setup consisted of three 26‘’ propellers arranged in parallel (1-3 in the picture). These were set up next to each other on measuring stands at different heights.

The experimental tests carried out showed no significant influence of the three test benches operated in parallel in the Climatic Wind Tunnel. Any minor differences in the performance data can possibly be attributed to structural differences in the test stands, the accuracy of the measurement hardware and the local icing parameters in the Climatic Wind Tunnel.

In conclusion, it can be stated that it is basically possible to operate three rotor test rigs with a 26‘ propeller in parallel in the RTA icing wind tunnel without major interference if they are set up next to each other at a sufficient distance and at different heights (’vertical separation’).

In the course of the investigations carried out, it was shown that the operation of three rotor test stands in one plane is possible in principle. There does not appear to be any significant influence on the test rigs. Positioning the propellers at different heights has proven to be particularly effective with regard to slipping ice particles. No damage was detected

In addition to the standard cameras installed in the Climatic Wind Tunnel, a mobile camera and a high-speed camera were also installed. Using these camera systems, it was possible to observe the three test stands sufficiently well during the tests. The ice accumulation during the test could be qualitatively assessed using the high-speed camera.

The collaboration within the consortium proved to be very effective and positive. Due to the high complexity of carrying out tests with many separately operated test benches, special attention had to be paid to coordination. This requires in-depth expertise in the planning, execution and documentation of icing tests. Early communication with all partners and detailed planning of the test setup is essential. Power supply and data recording must be defined as early as possible to ensure a smooth process.