After 1.5 years of conversion work in the frame of the federally funded project “SiFlA” (LuFo VI-1), our flying testbed e-Genius has recently reached a major milestone of the project. It became one of only three battery electrical powered aircraft able of towing sailplanes, of which only two are operational at the time.
To reach this outstanding achievement, modifications had to be made to the e-Genius. The propulsion system was upgraded by installing a proven and powerful EMRAX 268 electric engine, along with a capable inverter which drives a 3-bladed MT-Propeller MTV-7, reaching a diameter of 2.03 m. The newly designed modular high-power battery system with a stored energy of 40 kWh, supplied by our project partner AirEnergy, enables the aircraft to perform several aerotows to 800 m before needing approximately 1.5 h of recharging. The second objective of the project is the use of an automated flight control system (which is basically an autopilot) for pilot workload relief. The intelligent flight path planning incorporates automatic traffic avoidance, the use of updrafts for maximizing climb efficiency and noise abatement procedures to reduce the impact of flight operations on the public. The human machine interface displays and software for the path planning and following functions are supplied by our second project partner AirAvionics, while the control algorithms were developed by our partner Institute of Aircraft Mechanics and Controls.
The first flights with the new system upgrades took place at our homebase, the AREA BW test field at the Regio Airport Mengen-Hohentengen (EDTM) in June and July and quickly showed unprecedented takeoff and climb performance, a key element for it being the use of a much larger radiator for cooling the electric components.
In the beginning of August, we then traveled to Stendal in the north of Saxony-Anhalt to join the Idaflieg ”Sommertreffen” as a cooperating partner for three intense weeks of flight testing.
After accumulating some flight hours and gaining trust in our new systems we installed the already existing towing hook and made use of the unique infrastructure and environment of the Idaflieg “Sommertreffen”, which supplied us with many different types of sailplanes and capable pilots for the upcoming towing tests.
The first towing flight took place in the evening of August 19, launching a Discus CS to an altitude of 1300 m over a flight time of 20 minutes. The takeoff power of over 105 kW allowed for a short takeoff run and an initial climb rate of almost 4 m/s. The continuous power is currently limited to around 50 kW, which still corresponds to a climb rate of 1 m/s with a light single seat glider, by the thermal limit of the cables connecting the inverter to the motor.
The large amount of excess power during takeoff enabled us to quickly increase the mass of the towed sailplanes. The first double seater, a Duo Discus T was towed the following day and by August 24 we had reached 750 kg of towing capacity, demonstrated by launching a fully loaded Arcus to an altitude of 600 m with an initial climb rate of still well over 2 m/s. With this flight the e-Genius set the new record for the heaviest sailplane towed by an electric aircraft.
This, once more shows the versatility of the e-Genius as a research platform, and its capability to perform many different flight missions, from long range world records to unmatched climb performance and endurance.
We would like to thank both the Idaflieg and the DLR as the host and supporter of the “Sommertreffen” for the great opportunity to take a part in it. We are proud of having been able to write another piece of history of electric airplanes during that event. Also, a big thanks to our project partners and all other supporters for the great teamwork!
The next milestone, then again in Mengen, will be the test of the automation functions in flight and more detailed noise measurements to show the possible impact that electric propulsion and intelligent assistance systems can have on the aerotow of sailplanes. This application seems to suit electric aircraft like no others and we are excited to share our results in more detail in the upcoming weeks and months.