Meet hybrid eVTOL — a solid first step for The Urban Air Mobility
Compared to traditional VTOL aircraft, passenger vertical take-off and landing vehicles with electric powertrains (eVTOL) have several significant advantages; these lend weight to the forecasts of the emergence of an eVTOL- based industry worth over $1tn in the next two decades. One of the principal benefits is improved safety and this is achieved by redundancy of propulsion drivers, the powertrain’s simplicity. Other key benefits, namely enhanced efficiency and reduced noise, result from the application of new aerodynamic designs.
The combination of these and other factors contribute to more sustainable vehicles that are better suited to use in cities. This will help Urban Air Mobility take market share from terrestrial means of transportation and increase the size of the overall passenger mobility pie. In addition, eVTOLs may substitute some regional aircraft and operate in other niche applications.
Currently one key industry bottleneck is the relatively low specific energy density of batteries available for airborne applications. Commercially available batteries with acceptable charge cycles have power densities of around 150–200 Wh/kg, steadily growing at 5–6% CAGR. This parameter affects flight range and payload, the pillars of flying vehicle economics.
The specific energy density of fossil fuel is 60–150 times greater than that of a battery; it is, therefore, worth studying hybrid-electric VTOL, or hVTOL: such aircraft combine the high levels of safety as electric vehicles with the substantial flight range of VTOLs with traditional engines.
A hybrid power unit here implies a system containing a microturbine with integrated electric generator, power electronics, batteries and fuel. Using a gas turbine as the foundation of a hybrid-electric system is considered by many as the most rational technology choice, due in large part to its high power-to-weight ratio, but also thanks to its reliability and the extensive knowledge of its maintenance in the industry.
We consider jet fuel (kerosene) as a primary fuel. Despite hydrogen’s higher heat capacity, storage issues complicate its use. Nevertheless, as light-weight cryogenic means of storage evolve, gas turbines can be adapted to run on hydrogen fuel without significant changes in design.
Batteries in such a system function to provide peak power to the propellers during take-off, hover and landing, as well as holding emergency energy utilized in case of turbogenerator malfunction.
In the series of following articles, we review hybrid eVTOL of various types, evaluate other hybridization technologies, and look at the economics and opportunities that this technology brings to the Urban Air Mobility industry.
Check the first study report — hybrid Airbus Vahana
Hybrid power systems can become the enabler that drives VTOLs towards a mass market in the shortest time-frame. Hybrid concept can make vehicles versatile and viable for decades to come and once all-electric technology matures, offers the potential for hVTOL to operate in special environments long-term.
Stay tuned!
