The use of fuel cells for the primary drive propulsion system for aircraft of general aviation offers significant benefits, which could not be gained with conventional piston engines. This applies especially to operational and maintenance costs, security and comfort for pilot and passengers. And in some specific disciplines like range it is also predominant to battery powered aircraft.
Increase in Security
Every year, more than 70 % of technical defects, accidents and serious interferences in the operation of aircraft in general aviation fall upon the drive-train and are next to human error the largest single item in the accident statistics in Germany for aircraft with a maximum take-off weight under two tons.
fig 1: accident statistics in general aviation (source: Bundesstelle für Flugunfalluntersuchung: Jahresbericht 2004, 2005, 2006)Electric drives allow new security and redundancy concepts to reduce the failure probability of the powertrain. Full electric hybrids tolerate the total loss of one energy source since the modular structure prevents a total performance failure. Back-up power sources can be integrated in electric propulsion systems to provide short term energy for a safe landing.
Decrease in Costs
In general aviation, the operating and maintenance costs are much more important than the purchase price. Due to the high approval requirements of the air authorities the development of aircraft engine lags decades behind modern vehicle engines. So a fuel consumption of about 50 litres per hour of avgas for a 4-seater aircraft is more rule than exception.
Due to the higher energy content of hydrogen, the higher efficiency of electrical propulsion systems and the separation of power and propulsion generation fuel costs can today be reduced by 50 to 100 percent. The current price for one kilogram hydrogen is about 8 €. Related to the diesel equivalent the price is about 2,4 € per liter. With respect to the higher system efficiency we gain a price of about 1,2 € per liter. In comparison the current price for avgas is 2,25 € per liter. By an usual fuel consumption of 50 liters per hour and an annual utilization of 400 flying hours this leads to a saving of 21000 € per year only due to the fuel costs.fig 2: fuel consumption and fuel costs for 2-seated aircraft (source: Peter Bachmann: Ein- und zweimotorige Flugzeuge: Bilder, Daten, Kosten)
For conventional aircraft maintenance costs are the main cost driver. Typically, there are small checks every 50 flying hours, with the change of motor-oil, sparking plug and other consumables. Additionally, every 100, 200, 400 flying hours as well as annually the aircraft is completely grounded for several days because of detailed inspections of motor and other highly loaded parts. Fuel cell and battery systems require fewer consumables and can be monitored electronically. This results in lower maintenance effort and longer inspection cycles and therefore in further economies especially for flight schools or charter carriers with a high utilization.
Environmental Compatibility
The CO2 emissions per passenger kilometre of small aircraft are the largest compared to all other vehicles. When using hydrogen in combination with a fuel cell no direct CO2 and NOX are emitted. Only water vapour will be ejected but not in hights where it could harm the climate. The extremly low noise of the powertrain additionally leads to fewer limitations in airfields and lower landing fees and more relaxed airfield residents.
Aviation: Pioneer in Hydrogen Infrastructure
Providing international and larger regional airports with hydrogen stations allows an area-wide aircraft operation at relatively little investment compared to the required infrastructure for fuel cell powered automotives. Furthermore, apron vehicles in isolated operation guarantee their continuous utilisation.
So the general aviation represents an early market for fuel cell and hydrogen infrastructure and contributes to their growing importance.