Honda’s ‘compact jet’ takes its first test drive

 - January 26, 2007, 10:31 AM

Honda’s “research project” light jet now has its first logbook entry. The six-passenger HondaJet (its now-official provisional name) broke ground for the first time on December 3 from Honda’s purpose-built research facility at Piedmont Triad Regional Airport (GSO), Greensboro, N.C., on the leasehold of FBO and mod specialist Atlantic Aero.

As important as the first flight, Honda has broken its official silence on the project. Though Jeffrey Smith, a Honda spokesman, reaffirmed that the company “has no business plan” to certify or manufacture the HondaJet, the company’s corporate headquarters officially acknowledged its existence for the first time last month with a December 16 press release. The release announced the first flight and provided some preliminary specifications. Smith said, “This is an experimental jet. The [first] test flight and all subsequent test flights are designed to validate the technology. Honda continues to challenge itself in a wide range of technologies from jet aircraft to fuel cells to humanoid robotics. It’s in our nature.” The HondaJet’s test regime is expected to include 200 hours of flight testing.

Honda released no details on the first flight regarding crew, length of time aloft, altitude achieved or systems checks performed. Smith did say that the company expects to release further technical details as early as this month, though he declined to elaborate.

The HondaJet’s fuselage is described as “co-cured composite and honeycomb sandwich.” The wings and empennage are aluminum. In July, Honda R&D Americas chief engineer Michimasa Fujino presented the 17-page paper on the development of the HondaJet at a meeting of the American Institute of Aeronautics and Astronautics (AIAA). Following up last month’s press releases, the Honda spokesman told AIN that all the data outlined in the AIAA document still applies. The illustrated paper (42 photos, graphs and line drawings) revealed comprehensive details on the airplane and correctly predicted the first flight by year-end. Among the most interesting elements of the design is its over-the-wing mount configuration for the airplane’s twin HF118 turbofans, designed by Honda and rated at 1,670 pounds of thrust each.

In the market survey that preceded development of the airplane, Honda identified passenger comfort at the top of the list of desired attributes. With no carry-through structure needed in the aft fuselage for engine pylons, the HondaJet’s over-the-wing configuration allows a full-width cabin all the way aft, providing a claimed 30-percent increase in cabin space compared with “conventional aircraft.”

Tradeoffs of the over-the-wing configuration included the challenge of countering wave-drag interference from the pylons atop the laminar-flow wings at high speeds and aeroelasticity issues–designing the wing/pylon combination with just the right stiffness to eliminate the possibility of wing flutter. Using computational fluid dynamics software combined with wind-tunnel tests, Honda was able to adjust the engine pylons’ sweep and the nacelles’ angles to deliver what the company says is equal lift and efficiency as would be derived with a clean wing. Sufficient airflow to the engine inlets–especially at high angles of attack–was another concern. Further computer and wind-tunnel testing confirmed to Honda engineers that they had all the angles properly covered.

Honda calls its airplane a “compact jet,” a familiar automotive term that could come to characterize an entire class of entries into the category. The HondaJet is 41.14 feet long, 13.21 feet high (at its T tail), and has a wingspan of 39.87 feet. Max takeoff weight is quoted as 9,200 pounds and estimated max speed is 420 knots at 30,000 feet. Honda computes specific range as 0.8 nm/pound at 389 knots at 41,000 feet for an IFR range of 1,100 nm. Inside, the 4.89-foot-high, flat-floor cabin is 15.09 feet long, allowing a more utilitarian eight-seat layout (including both cockpit seats) in place of the roomier six-seat floor plan envisioned as the normal configuration. Pressure differential is projected as 8.7 psi, for an 8,000-foot cabin at 44,000 feet. The anti-icing system consists of bleed-air heating for the wing leading edges and an electrically heated windshield.

Development milestones to date include:
• Honda’s in-house-designed and -built, twin-spool, 1,670-pound-thrust HF118 turbofan has been in flight test for more than a year on the left pylon of a CitationJet.
• Honda R&D’s new-design, SHM-1 natural laminar-flow wing section has been test flown (as a gloved section) on a T-33 testbed aircraft.
• Detailed structural and wind tunnel tests have been performed on the aluminum wing (with its radical over-the-wing engine nacelles).
• The composite fuselage (with laminar-flow nose section) and aluminum empennage have also been tested in low-speed and transonic wind tunnels and structural analysis performed.

In last month’s press release, Honda wrote that the six-seat configuration would be arranged as “two pilots and four passengers, or one pilot and five passengers.” The announcement indicates that Honda expects the airplane to be certifiable for single-pilot operation. The test aircraft is equipped with a Garmin 1000 avionics suite.

Honda’s goal in designing its SMH-1 laminar-flow airfoil was to achieve a high drag divergence Mach number and slight nose-down pitching moment while retaining the NLF’s characteristic low drag for efficiency at cruise speed. Docile stall habits and tolerance for leading-edge contamination were priorities, along with the need to maintain a 15-percent-chord thickness to ensure the wing could hold enough fuel for the airplane’s designed 1,100-nm range.

The resulting airfoil was tested in both low-speed and transonic wind tunnels, as well as in flight tests using a modified Lockheed T-33. The T-33’s entire wing was covered with polyurethane foam contoured in the desired shape, then covered with fiberglass skin. Incorporated into the “glove” were 119 static pressure holes on the upper and lower surfaces to measure pressure differential. Besides the data-collection computers plugged into the sensors, Honda mounted an infrared camera in the T-33 cockpit to record the laminar-to-turbulent boundary-layer transition throughout the flight testing. The effects of surface roughness and wing steps were also part of the flight-test regimen.

Results of wind-tunnel and flight tests were consistent with the predictions Honda engineers had made based on computer projections for the airfoil. Part of the 200 hours of upcoming flight tests for the HondaJet will be to confirm that the HSM-1 airfoil, with winglets to increase aspect ratio, will provide the right combination of lift, room for fuel, docile stall characteristics, low susceptibility to contamination and favorable high-speed pitch-down tendency to be compatible with a compact business jet.

For last month’s issue, AIN polled readers on whether they would consider operating a light jet built by Honda. In volume of responses received, it was one of the strongest reactions to any poll so far. The reaction was overwhelmingly positive. One reader responded, in part: “I have driven Hondas for nearly 20 years. If there is a way to automate and mass-produce airplanes, Honda will find a way to do it. Aviation needs the competition and a shot in the arm. Given Honda’s track record with reliability and engineering, a competitive price would put it ahead of the rest.”