Experimental seaplane

Researchers have developed a design concept for a transatlantic flying boat featuring a blended wing body.

Classic flying boats lost popularity in the 1950s because they were inefficient compared with more aerodynamic airliners able to fly large numbers of passengers directly to land-based airports.

However, as rules on pollution and noise get ever tougher, limiting expansion at many major airports, the flying boat could be on its way back.

Researchers at Imperial College London have developed a design concept for a transatlantic flying boat that would move the low-level flight paths of large aircraft offshore, away from heavily populated areas.

“What we really wanted to do with this project is take a look whether the application of new technology, and the new ideas coming into industry such as blended wing bodies, would actually result in an aircraft that is designed both conceptually, so in the overall configuration, and in the preliminary design process, that can actually alleviate the historical downsides of a flying boat, ” said Dr Errikos Levis, a teaching fellow at Imperial’s Department of Aeronautics.

“Seaplanes of the past had a weight penalty and an aerodynamic penalty, and fuel consumption is inversely proportional to both, basically. So the bigger the weight penalty, the more fuel inefficient you are, and the bigger the aerodynamic penalty, the more fuel inefficient you are.”

The team designed a range of aircraft from a 200-passenger model capable of flying 5, 600km to a 2, 000-passenger behemoth able to fly 15, 000km.

The 2, 000-passenger model is about 80m long and 20m high from bottom to tip, and has a 160m span. The Airbus A380 is 72.72m long and 24.09m high and has a wingspan of 79.75m. The A380 has a range of 15, 200km and typically seats 544 passengers, although it can carry a maximum of 853.

As far as operating on choppy water and aircraft efficiency was concerned, the researchers found that biggest was best. “The fact you are operating from seas means that you will have to either make a choice to put in wave barriers, maybe somewhere offshore to cut down the intensity of waves coming in, or you are going to have to accept that you are not going to be able to take off some of the time, ” Levis said.

“Overall, size actually solves the problem, in addition to making the aircraft more efficient overall. The bigger you go, the more likely you are going to be able to use it 24/7, 365 days a year.”

Size also helped to solve the problem of emergency egress from a blended wing aircraft caused by the large number of passengers and the placing of emergency exits dictated by the shape of the craft.

“With traditional blended wing bodies, it is actually a pretty big deal, but in our design, because we have to raise the wings high enough above the waterline so that they don’t get hit by spray, there is a very nice, almost vertical or slightly sloped side just underneath the wing that extends the entire cabin length, ” Levis said.

“Now obviously similar issues to a standard blended wing body will appear here because you have a very high passenger density in the middle and a smaller perimeter area from which they can egress, but this design tries to maximise the surface area available for emergency exits to be placed. It doesn’t completely solve the problem but it does go some way towards a solution.”

Classic flying boats suffered increased drag and structural weight because their fuselage had to be shaped and reinforced to allow them to operate on water. While the blended wing body design allows the aircraft to float, it offers reduced drag when it is in the air.

“What we found is that by using this particular configuration, we could get rid of a lot of the structural penalties that were associated with things such as tip floats, ” Levis said.

Tip floats ensure flying boats are laterally stable on the water surface. They provide drag and weight, not only by their use but because their weight has to be counteracted by strengthening the wing to take on the extra weight at the tip.

“What we did instead was say is there any way we could use part of the fuselage or part of the wing to provide lateral stability, ” Levis said. “What you see is there is a hull that rides up. Outboard of that there is a proportion of the fuselage that stays almost parallel or even has a little anhedral [goes downwards]. That means that the aircraft can actually right itself and maintain itself on the water using a very thick piece of structure that doesn’t need to be strengthened substantially because it is already supposed to take substantial loads when flying.”

The design needs to have excellent fuel efficiency if it is to compete with traditional aircraft. Current state-of-the-art aircraft require around one to 1.1 megajoules per available seat kilometre, Levis said. “For a 550-passenger aircraft, we are getting 1.149 megajoules per available seat kilometre, and going up to 2, 000 we can get that down to 0.94, so it is substantial improvements, although that assumes that we can fill the aircraft.”

The engines are on top of the fuselage, which limits the effects of spray. The design was found to provide a massive amount of empty volume in the lower part of the fuselage, as passengers cannot be underneath the waterline for safety reasons. This led to the idea of using alternative fuels such as hydrogen, which is more environmentally friendly but takes up about four times the volume per energy given compared with Jet A-1, according to Levis