Parcel-delivery drones, air taxis and uncrewed inspection aircraft will to fly over cities and interact with one another in the future. They must be able to recognise and avoid one another, ideally before even taking off. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and its partners in the City Air Traffic Management (City-ATM) project conducted successful flight tests around the Köhlbrand Bridge in late April 2019 to demonstrate how drones are already able to cooperate with one another, as demonstrated by flying around a bridge, amid active shipping and road traffic.
"Under highly realistic conditions, we demonstrated how two automatically operated camera drones can work in parallel – from flight planning to detection and identification, through to flight monitoring and conflict detection and avoidance," explains Project Leader Stefan Kern of the DLR Institute of Flight Guidance. "The use case of a bridge flight provided an ideal test scenario, as it required the drones to work together particularly closely and in a very dynamic way."
Multiple communications safeguards against failure
On 24 April 2019, the flights were cleared for take-off and two drones ascended in quick succession. During their flight missions and taking account of the ships sailing below, both drones flew along their pre-set routes to the side of and underneath the Köhlbrand Bridge. Two of the three drones available were in the air simultaneously. The uncrewed aircraft, provided by the DLR institutes of Flight Guidance, Flight Systems and Communications and Navigation, were equipped with special technology that enabled determination of their location and status, as well as multiple failsafe communications links ('HydraCom') between the drones and the control station. Deutsche Flugsicherung (DFS), the company responsible for air traffic control in Germany, tracked their locations and was thus able to provide an integrated air situation display. Continuous transmission of the drone locations gave the pilots at the control station a picture of the situation in the air, including any conflicts. In addition to testing the overall system during several flights, the researchers also successfully demonstrated the detection of hairline cracks.
Detailed flight planning
The flight tests, which were carried out in cooperation with the Hamburg Port Authority (HPA) and the project partners NXP, KopterKraft OÜCity Air Traffic Management, FlyNex GmbH, DFS Deutsche Flugsicherung GmbH, the Center of Applied Aeronautical Research (Zentrum für Angewandte Luftfahrtforschung GmbH; ZAL) and Auterion AG, form part of the City-ATM project, in which researchers and application partners are working on concepts and new technologies for safely integrating drones – as new participants in the air transport system – into urban airspace. The system developed for City-ATM involves several steps. First, the pilots and drones are electronically registered for take-off clearance and authenticated using NXP and FlyNex technology. At the same time, the flight missions are planned, taking spatial flight restrictions (referred to as geofences) into consideration. Once the basic waypoint planning has been completed, this information is used to generate flightpaths (trajectories). The system also takes account of the flight performance of the equipment, as well as local conditions and time constraints. This allows potential conflicts to be identified even before take-off. It is particularly important that drone flights covering large distances – as in the case of drones that fly out of the line of sight of those controlling them – should be able to detect and avoid other airspace users at an early stage. The U-Fly ground control station for drones, belonging to the Institute of Flight Guidance, was used for the test flights in Hamburg.
The City-ATM system will be supplemented with additional services and tested for other use cases in the follow-up project phases, which will run until late 2020. The researchers will investigate areas such as the optimal use of drones for rescue workers. The City-ATM research project is funded via DLR's Aeronautics research programme, among other sources.