Fixing the engines to the top of the wing also helps reduce drag, particularly at high speeds. As planes approach the speed of sound, air moving over some parts of the wing reaches supersonic speeds, causing a big increase in drag (a phenomenon known as wave drag). The placement of the engines helps slow down the flow of air in this area of the wing, which keeps the wave drag from kicking in and let allows the plane to fly faster. Avoiding wave drag is also essential for letting the plane fly faster than other airplanes while using less fuel. The plane flies at 420 knots, or about 780 kilometers per hour—about 80 kilometers per hour faster than other planes its size.
Together with GE, Honda developed a new engine for the plane that further increases its efficiency. The ratio of air compressed in the front of the engine to air compressed in the interior turbines is unusually high (this is similar to increasing the compression ratio in car engines to improve efficiency). Fujino estimates that about half the fuel savings come from extending natural laminar flow, and most of the rest from the new engine and the placement of the engines over the wing.
The plane is about 20 decibels quieter than other jets its size, in part because the wings block the engine noise from reaching the ground. Because the plane is quieter, it could be allowed to operate at more airports in congested areas such as Los Angeles.
Fujima says that the basic design principles for this plane can be used for larger planes, although there is a limit to how large planes can be and still achieve laminar flow. Airflow is turbulent over the whole surface of large commercial jets, Drela says. Honda isn’t disclosing its plans for future, larger jets.