Out of space: connection under this number

In order not to harm the environment, the drone should be able to travel for as long as possible and also have an environmentally friendly propulsion system – a fuel cell system fulfills precisely these requirements. This should enable the platform to fly emission-free for nine days at a stretch. An ideal solution – if it weren’t for the extreme environmental conditions at altitude: For fuel cells to work optimally, they need overpressure and a cooling water temperature of around 70 egrees Celsius. In the stratosphere, however, the air pressure is extremely low and the temperature is -60 degrees Celsius or less. And, of course, the drone’s climb and descent into the stratosphere must also go smoothly.

To get the idea off the ground and first develop the concept for the fuel cell system and then get proof of function, SPL turned to IAV. “That was quite a challenge for us, also in light of the extreme operating environment,” says Katharina Schütte, Team Manager Fuel Cell Systems Development, who was in charge of the project. It took a year and a half to design the system – with the support of IAV’s fuel cell system simulation – and then set up the demonstrator.

For the functional verification on the ground, components from the automotive industry were mainly used, as they had already proven their worth.

Katharina Schütte’s team worked closely with IAV’s networked software experts on the project. In addition, an external partner, Pankl Turbosystems GmbH, was on board to develop a multistage compressor for the project. This complex system was commissioned together with the partner at the IAV fuel cell test station. The multistage compressor made it possible to generate overpressure when air enters the fuel cell stack. “The compressor makes the fuel cell work as if it was on the ground. The low atmospheric pressure in the stratosphere is compensated by the system,” says Schütte. What was challenging in the development of the system layout and control was the requirement that the fuel cell system must also provide the required power during climb and descent. The system thus has to function just as well at 1 bar ambient pressure as at 70 mbar in the stratosphere.

IAV’s interconnected software experts also developed the control system for the system and implemented it on the basis of the Dragoon control unit, one of IAV’s own developments. On the test station, the colleagues were then challenged once again – because in order to simulate the conditions in the stratosphere at the air inlet of the fuel cell system, some modifications had to be made to the test station. “Everything turned out very well. And in the end, we showed that the demonstrator is functional on the ground under simulated stratospheric conditions,” Schütte says. According to SPL, the first unmanned platforms are expected to make their way into the stratosphere in 2024. The end of blackspots is not far off.

The article was published in automotion 01/2021, the automotive engineering magazine of IAV. Here you can order the automotion free of charge.