Hybrid-electric propulsion for drones and eVTOLs – reasons why

Zurich/Visp, March 23, 2023: Another milestone in the development of Aero2. In early March, Dufour Aerospace put the hybrid unit, consisting of a two-cylinder engine from Suter Industries, a generator from Plettenberg and our own digital control hardware, into operation for the first time on its own test bench. Some further optimisation and testing work still remains to be done before the drive can then be installed on the Aero2 X2.3 prototype.

From the start, Dufour Aerospace has been working towards a hybrid-electric drive system and has decided against a purely battery-powered drive. Again and again we are asked: why not a purely electric propulsion system?

Aero2 is built to transport a payload of up to 40 kg / 88 lbs payload over a distance of 400 km / 250 miles (or much more with reduced payload) and to be able to take off and land vertically. A purely electric propulsion system does not yet allow this due to the still relatively high mass and low specific energy of the batteries. Until lighter batteries or fuel cells are available, the small and light combustion engine in combination with batteries and electric motors is the right choice. Dufour Aerospace's hybrid propulsion system is designed to allow for fully recharging the batteries within a few minutes during the flight, so that the full battery charge is available both for landing and for any abnormal situations. This increases operational safety, but also means that the batteries of the Aero2 do not have to be recharged after landing before taking off again. Ground time can thus be kept very short – and no complex and expensive charging or battery swapping infrastructure is required at the landing site, which is particularly important for remote or improvised landing sites.

Another advantage of a hybrid system over a purely electric system is that the batteries are used more sparingly. In regular operation, only around 20% of the battery capacity is used, which means that they last longer than if they are discharged to a deeper level. This results in a reduced total environmental footprint compared to a purely electric configuration.

Purely electric propulsion certainly has its place in aviation. However, for the applications that Dufour Aerospace covers with the uncrewed Aero2 and also for those of the crewed Aero3, a hybrid-electric approach makes the most sense.