Honda reveals new details about the cabin of its jet

 - December 18, 2006, 12:11 PM

During a briefing held on November 20, Honda Aircraft president Michimasa Fujino showed off the extensive research and testing that the Honda team has accomplished thus far on the HondaJet and parceled out a few more details about the program.

“We may not have big news today,” Fujino said, but the fact that Honda Aircraft had already logged 268 hours of flight testing and conducted many ground tests in advance of certification is significant. The HondaJet is no conceptual airplane but is already in its final configuration and preparing for the rigors of the FAA certification process.

During its flight testing thus far, the HondaJet has reached its planned maximum altitude of 43,000 feet and a max speed of 412 knots. All flight testing is monitored by a team of engineers viewing real-time data downlinked from 300 sensors on the airplane.

Fujino also revealed additional details about the cabin of the HondaJet. When he began work on the airplane, he confronted a central problem: he wanted to build an efficient business jet that could hold many passengers. However, “to reduce cost, we have to reduce the size of the airplane. But if you want to make the airplane smaller, you have to sacrifice comfort. I wanted to make the airplane smaller but I did not want to sacrifice inside the cabin.”

Fujino realized that if he could build an airplane with the engines mounted beside but not on the fuselage, “We can maximize inside space without increasing the size of the airplane.” He accomplished that with the airplane’s over-the-wing engine placement.

“Generally, airframe design students have been taught never to put anything above the wing; it’s the first class in the university. It was tried before [the German VFW 614] but the design was a flop, so everybody wants to stay away from that concept.”
The breakthrough came as Fujino pressed on with the over-the-wing concept, because it completely removed all engine structure and systems from the rear fuselage, greatly expanding available interior space. “One day,” he said, “I thought that if we could place the engine to get a favorable pressure gradient at [certain] locations–that means favorable interference between the nacelle and the wing–I thought we might be able to manage the high-speed drag.”

What Fujino found was that an over-the-wing engine placed in exactly the right spot could help delay the onset of the drag-producing shock wave that builds as jets gain speed. Or as Fujino put it, “There is a strong interference between the high accelerated flow and the engines, so generally, it causes a strong shock wave and you cannot fly at high speed. But in the HondaJet case, I could find the kind of sweet spot, the best location to minimize the shock wave, and we could find five percent better fuel [efficiency] by having the sweet spot locations.”

For the HondaJet, the sweet spot is 75 percent of the wing chord, with careful design of the engine pylon so that it doesn’t generate too much side lift or drag. Asked about the placement of the VFW 614’s [Rolls-Royce/Snecma M45H] engines, Fujino said they were at 50 percent of chord, the worst possible place, although other design considerations may have taken precedence on that airplane. Fujino and engineer Yuichi Kawamura received a U.S. patent for this “method of reducing wave resistance in airplane” on Oct. 30, 2001.

The HondaJet fuselage is made of a co-cured laminate composite with four plies of carbon fiber and copper mesh embedded for lightning protection. Fujino isn’t a fan of honeycomb laminate for composite fuselages. Honeycomb structure is too stiff and ends up causing excessive airflow noise, he said. The wings and empennage are all-metal. The added wing structure needed to accommodate the engine pylons helps alleviate the bending moment applied to the wing root by normal lifting forces, which contributes to an overall reduction in structural weight. A fuselage fuel tank feeds constantly to the wing tanks to keep them as full as possible, also helping to keep the wing bending moment low, Fujino said.

Fujino positions the $3.65 million HondaJet between the Cessna Mustang and CJ1, from a pricing standpoint. He claimed that the HondaJet will perform better than the CJ1 in terms of speed and range. He added that the HondaJet also has a larger cockpit/cabin volume and baggage volume.

The HondaJet’s cabin volume is 324 cu ft and the single aft baggage area measures 66 cu ft, 47 percent more than the CJ1’s, according to Fujino. With one baggage hold instead of two separate areas, the HondaJet can carry plenty of large items such as golf bags.

“The concept of the HondaJet interior,” Fujino said, “is we want to maximize space and we do not want to sacrifice a private lavatory and comfortable cabin and good cockpit as well.”

The larger cabin volume lets facing passengers sit comfortably without overlapping feet. Fujino is keen on the comfortable enclosed lavatory in the HondaJet. “Sometimes I use business jets,” he said, “but I hesitate to use the lavatory. In the HondaJet you might not hesitate to use it.”

At the beginning of the program, Fujino planned to offer seating for two pilots and four passengers (or one pilot as the airplane will be single-pilot certified under Part 23 regulations), but that has expanded to two pilots, five passengers or one pilot and six passengers because of strong interest from air-taxi companies.

Since the October 2006 NBAA Convention, when Honda began taking orders for the HondaJet, the company hasn’t strayed from saying that it has orders for more than 100 aircraft. “There has been a lot of interest from fleet customers,” said Doug Danuser, general manager sales and marketing and former head of Honda’s Acura division sales and marketing. “Large corporate and fractional ownership [operators] account for a lot of current opportunity. The startup of air-taxi companies shows future potential.” International markets look healthy, too, he added. “Strong interest in the HondaJet has come from Europe, South America and the Middle East.”

Certification and first delivery of the HondaJet are expected in 2010. A manufacturing location has not been announced, but the HondaJet will be built in the U.S. The next HondaJet built will be a conforming prototype, Fujino said.