When it comes to energy efficiency and aircraft, there is still a lot of room for improvement. The most modern long-haul aircraft such as the Airbus A380 and the Boeing 787 are inefficient modes of transport if you look at them objectively. One reason for this is the full fuel tank at take-off. The stored jet fuel makes up around one-third of the entire weight of the aircraft. As part of a European research project, the Centre for Aviation (ZAV) at the ZHAW School of Engineering decided to investigate a scenario that up until now has only been used for military aircraft: fuelling while in flight.

Under the acronym RECREATE (Research for a CRuiser Enabled Air Transport Environment), the ZAV worked with an international research team for three years on a ‘cruiser feeder’ design for the aviation industry. The aim of the concept is for long-haul aircraft to be able to take off with an almost empty fuel tank – and thus far less weight – and have their tanks filled only after reaching cruising altitude. This would require the use of tanker aircraft. ““In order for the fuel tanker aircraft not to cancel out the saved CO2 emissions, it would carry jet fuel for three to five commercial jets and circle a specific area,” Leonardo Manfriani, heading up the project on behalf of the ZAV, explains. “These flying fuel stations should be located far enough away from residential areas, of course, but also directly on main flight routes. For example, the Atlantic Ocean east of Canada and south of Greenland would be an ideal area for trans-Atlantic flights.” According to the researchers’ calculations, this concept would enable savings of around 20% of fuel expenditures.

The concept for air-to-air fuelling would not only save on jet fuel but also ensure additional comfort for passengers. Flights around the world would be possible without stopovers even for smaller aircraft, which would in turn relieve the intercontinental aviation hubs. A further positive side effect of air-to-air fuelling would be lower noise emissions at airports, according to Leonardo Manfriani: “The larger and heavier the aircraft, the louder it is when taking off. Those residing close to the airport would also benefit from air-to-air fuelling.”

In a second project phase, the researchers went one step further and made their concept even more visionary: giant passenger jets would be able to fly around the world several times without stopovers, and the fuel they need could be supplied by smaller aircraft while in flight. Luggage, rubbish and even passengers could be exchanged between the aircraft while in flight – but of course that is all still very futuristic.

The RECREATE project is a collaboration between nine European universities and research institutions from five countries, led by the Netherlands Aerospace Centre (NLR). The ZHAW School of Engineering with its Centre for Aviation is the only partner institution from Switzerland.