The AKOYA, an ultra-lightweight two-seat amphibious aircraft built by French aeronautical innovator LISA Airplanes, is made entirely from composites and aeronautical metallic alloys.
Carbon prepreg and carbon sandwich structures (carbon fiber reinforced polymer with a foam core) are used in all the weight-bearing primary structures, including the fuselage, wings and horizontal stabilizer, as well as other parts. To ensure all the composite parts perform well in water environments, LISA uses a special pre-impregnated resin made by Umeco’s Advance Composites Group (ACG), a layer of Kevlar to protect the area under the fuselage during water impact and external fiberglass layers to set the seal for optimal waterproofing. A glass composite material, produced with high glass transition temperature (Tg) and epoxy resin, is used to finish parts inside the cockpit.
“We chose these materials because they are lightweight – a constraint we have in light aviation – but mainly because we needed to design and produce extremely high-performance aeronautical shapes,” says Erick Herzberger, founder and CEO of LISA Airplanes. What’s more, thanks to LISA’s patented multiaccess technology, the uniquely designed AKOYA can just as easily take off and land on water or snow as on a strip of land less than 220 yards long with no prior modification required. “The AKOYA is the first seaplane equipped with Seafoils that maintain good aeronautics in flight,” he says. The plane also has skis on the retractable landing gear.
Engineering the AKOYA Skiplane
The biggest problem the high-tech company based in LeBourget du Lac, France, had to overcome in designing the first airplane with hydrofoils was not to make the aircraft lighter, stronger or more stable, as one might expect. Herzberger says, “Our main challenge in designing the AKOYA was to place the engine at the back of the airplane on top of the vertical stabilizer.” The solution, once again, arose from using composite materials. “We had to place the engine where it would not interfere with water operations,” Herzberger says. “After several rounds of calculations, simulations, characterization of the materials and tests on samples and representative parts, the conclusion was that carbon composite (CFRP) was the best material to solve this structural design issue because it ensures the engine mount is strong enough to hold the weight. CFRP offers the best compromise between resistance and weight. This was the material to use to support the weight and stresses of the engine, the wings and the hydrofoils.”