Evaluation of on-demand air mobility concepts with utilization of electric powered small aircraft

  • Bewertung von On-Demand Luftverkehrskonzepten unter Einsatz elektrisch angetriebener Kleinflugzeuge

Kreimeier, Michael; Stumpf, Eike (Thesis advisor); Reichmuth, Johannes (Thesis advisor)

Aachen (2018)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2018


Within so called thin-haul On-Demand Air Mobility (ODAM) concepts, small, pilotless aircraft, comparable to CS-23 class aircraft, are envisioned to be used as a viable transportation option for regional travel distances for which nowadays mostly ground based transportation options are utilized. In contrast to intra-urban mobility, for which aircraft with a vertical take-off and landing (VTOL) ability are required, thin-haul suitable ODAM aircraft utilize local airfields. Omitting this VTOL ability increases flight performance because a VTOL ability leads to additional weight and requires a trade-off of cruise and hover performance. Additionally, an electric or at least hybrid-electric powertrain is applied for such ODAM aircraft due to sustainability goals, e.g. Flightpath 2050 (-90 % nitrogen oxides and -75 % carbon dioxide emissions).The successful introduction and the continuing development of ODAM systems highly depend on the economic feasibility. Therefore, two main objectives are pursued within this thesis. The first objective is to estimate potential ODAM market volume for Germany and to derive reasonable Top Level Aircraft Requirements (TLAR). Census 2011 data discretizing Germany into 1 x 1 km² grid cells are utilized in this context. The second objective is to determine a suitable preliminary ODAM aircraft design in order to reliably estimate ODAM service provision costs. For this purpose, a multidisciplinary preliminary aircraft design tool is developed. Because electric engines enable a wider design space, distributed electric propulsion is included in the design tool as well. Market analysis shows huge potential for Germany leading to a bottleneck of airfield infrastructure capacity rather than missing demand. A total of 394 airfields (excluding the busiest 20 airports) are generally feasible for thin-haul ODAM application, of which 157 airfields possess an equivalent sea level runway length above 800 m. These 157 airfields cover 17 % of the German population within 10 km linear distance and about 45 % within 20 km. Results indicate that 96 % of the ODAM trips occur within 500 km range, 85 % within 400 km and 63 % within 300 km linear distance. A small aircraft with four passenger seats is evaluated to be suitable. Application of distributed electric propulsion is beneficial at 300 km/h cruise speed at an altitude of 12,000 ft and a stall speed of 61 kts. ODAM service provision costs vary in between 0.35-0.4 €/revenue seat kilometer depending on specific TLAR. Service provision costs are based on a passenger utilization of 60 %, a deadhead ratio of 10 % to account for repositioning of aircraft and a battery specific energy of 400 Wh/kg. Integration of aircraft design results with the market model yields that 250-300 km/h cruise speed is most beneficial as lower travel time does not compensate increased costs due to higher cruise speed. At realistic car costs of 0.30 €/km, roughly 13,400 airfield to airfield connections are estimated with a demand of more than five passengers per day and 6,600 of them with more than 20 daily passengers. This results in 269 million passenger trips per year for the mentioned 13,400 connections. Considering that only 157 airfields are involved, airfield capacity becomes the restricting constraint.