Refuelling long-haul passenger jets in mid-air could revolutionise air transportation, reducing overall fuel consumption by up to 20 per cent, a study has found.
The cruiser feeder concept, developed as part of the EU-funded RECREATE (Research for a CRuiser Enabled Air Transport Environment) project, would allow aircraft to take off with a small amount of fuel on board, reducing overall weight for the energy-demanding take off and ascent and only filling the tanks fully after reaching a cruising altitude of 10,000m.
The concept, inspired by existing military technology, was tested by researchers at the Zurich University of Applied Sciences (ZHAW) with the help of professional pilots. Instead of flying real aircraft, the pilots were flying aviation simulators.
“In the simulation we studied how to refuel an aircraft in air in the safest possible way,” said project leader Leonardo Manfriani from ZHAW. “Unlike the air force, pilots of civilian aircraft should be able to perform a refuelling manoeuvre in the air without requiring additional training.”
Taking off with a full fuel tank is by itself increasing fuel consumption. In fact, kerosene makes up a third of the take-off mass of a long-haul jetliner. As a result, operations of even the lightest and most energy-efficient of today’s aircraft are rather uneconomical.
To reduce not only the energy consumption but also the carbon footprint of aviation, aircraft should take off carrying only the necessary amount of fuel to reach a flying refuelling station.
“The refuelling aircraft would carry kerosene for three to five jetliners to help reduce carbon emissions,” Manfriani said. “The flying refuelling station would circle locally. It would have to be far enough from inhabited areas but on the other hand located directly on important flight routes.”
For example, the researcher said, areas east of the coast of Canada above the Atlantic Ocean or south of Greenland would be suitable to serve aircraft on transatlantic routes.
The flying refuelling stations would not only allow aircraft to climb to the cruising altitude considerably lighter, they would also allow planes to cover large distances without having to land to refuel along the way. This would in turn relieve some of the busiest air transportation hubs – not only in terms of service work demands but also in the amount of noise produced be aircraft take-offs.
“The larger and heavier the airplane, the noisier it is during take-off,” Manfriani remarked. “Residents near airports would definitely benefit from airborne refuelling.”
The aerial refuelling process could be completely automated, the researchers believe, taking advantage of air currents.
In future, the researchers envision, aircraft could not only exchange fuel in air but also luggage, waste and even passengers, creating a sort of a ‘Tube in the air’ system.
RECREATE is a joint project between nine European universities and research institution led by the Dutch aerospace agency (NLR)