January 05, 2011

Honda Jet has unique fuel efficient shape made possible by composites

Composite image: The new jet from Honda, pictured here, is built largely of composite materials and features a unique over-the-wing engine mount.
Credit: Honda


Honda has moved closer to bringing its first jet to market—one that uses 20 percent less fuel than similar-sized planes while also flying faster.

A prototype of Honda's light jet, which will seat five to six passengers and is scheduled to go on sale next year, made its first flight last month. The plane flies at 420 knots, or about 780 kilometers per hour—about 80 kilometers per hour faster than other planes its size. Fujino estimates that about half the fuel savings come from extending natural laminar flow, and most of the rest from the new GE 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.

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.



The airplane makes extensive use of composite materials—a combination of carbon fiber and resins that reduces a plane's weight. So far the materials are rare in business jets, though they've become common in small, home-built kit planes. They are also beginning to see more use by big jet makers such as Airbus and Boeing, which are seeking ways to reduce fuel consumption.

The composites allow Honda not only to decrease the weight of its plane but also to give it a unique shape that reduces drag. The novel design of the plane also involves mounting the engines on the top of the wing, rather than underneath it or on the fuselage. This helps decrease drag at high speeds.

The shape of the fuselage and wings allows air to move more smoothly over the skin of the plane. This smooth flow of air is called natural laminar flow, and it's usually limited to small parts of the surface of a business jet. The air over the rest of the surface is turbulent, creating drag. Honda sought to extend how far the laminar flow extends along the fuselage and the wing. The shape of its plane features subtle bulges on the nose of the plane and on the wings that create "a very complex pressure distribution," Fujino says. As air moves over these bulges, it first accelerates, then decelerates, then accelerates again, he says, creating areas of high and low pressure. The changes in pressure essentially "suck the laminar flow toward the end of the wing," he says.

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