Honda provides more details about its HondaJet program

October 4, 2007, 9:23 AM

If the HondaJet were being developed by a traditional business jet manufacturer, we would undoubtedly know a lot more about its future. Those who follow new-aircraft projects are used to receiving regular updates on milestones and test results along the way as the manufacturer seeks to reassure stockholders, lure new investors–or both. Though less grandiose than in years past, ceremonies marking rollouts and first flights represent a significant part of the protocol of developing a new aircraft design. We’ve gotten used to it.

But with Honda, all that protocol goes out the window. The HondaJet program appears to be a series of contradictions when viewed as a traditional new-airplane project. Honda spokesman Jeffrey Smith dispenses information in small doses, while steadfastly repeating that the company has “no business plan” in place for production and marketing of its jet. But engineering reports authored by Honda R&D Americas project leader Michimasa Fujino have twice referred to an eight-city U.S. market analysis.

Honda didn’t even acknowledge the existence of the HondaJet until its first flight last December, and there has been precious little information released about the program through the usual media outlets. But one of Honda’s Web sites features a 10-minute video of the airplane in flight and shows a pair of two-page magazine ad spreads (though it doesn’t say where they have appeared) featuring the HondaJet and the words “Up, Up and Away.”

Some have speculated that Honda has developed its unconventional airframe primarily as a dedicated testbed for the carmaker’s HF118 turbofan–for which the company does admit to having a business plan. Last February Honda joined forces with GE to develop, certify and market the engine, though the companies have not revealed a launch customer. Honda also announced in July that it will form Honda Aero Inc., a small U.S. business unit to shepherd commercialization, contract negotiations, procurement and preparation for production of the 1,670-pound-thrust engine. Some have made the point that Honda may be loath to announce plans to produce its small-jet airframe for fear of alienating potential customers for the HF118.

As far as the HondaJet is concerned, we may know little about its commercial future, but we know more about its technical development than we do about most other gestating airplanes at this stage. Fujino has presented a series of papers at various engineering conferences in the U.S. and, most recently, at the 24th Congress of the International Council of the Aeronautical Sciences last month in Yokohama, Japan. AIN first published a detailed analysis of two of Fujino’s papers (AIN September 2003, page 1) some three months before the December 3 first flight of the HondaJet and Honda’s public recognition that the airplane existed. In those papers, Fujino revealed engineering details of the development of the design and, specifically, the development of its natural laminar flow (NLF) airfoil.

At the Yokohama conference, Fujino updated his previous paper on the development of the project and presented a new paper titled “Initial Flight Testing of the HondaJet.”

Honda R&D Americas has its hangar and research facility on the leasehold of Atlantic Aero in Greensboro, N.C., where flight testing of the HondaJet is under way. In his latest 10-page document on the HondaJet’s initial flight tests (said to have included at least some 40 hours to date), Fujino opens with a discussion of the project’s data-gathering instrumentation.

The sophisticated telemetry instrumentation consists of onboard sensors, a data recorder and an ST-810 transmitter feeding data to the ground station. That complement includes an automatic tracking antenna and control unit; a receiver; a backup data recorder; and a PC-based L-3 VTS-100 visual test system. Flight-test sensor data is analyzed using the company’s proprietary Honda Handling Quality Analysis Program, comparing actual flight sensor input to the numbers predicted by wind-tunnel tests. Cameras are also installed to record flap and landing-gear actuation, tuft testing of airflow and other real-time flight-test parameters.

The first round of flight tests, scheduled for completion by year-end, is aimed at providing detailed performance evaluations and comparing them to computer and wind-tunnel projections. The flight-test program is designed to validate and confirm that computer numbers projected for the systems, handling qualities and performance are true in the real world. Stall and flutter tests (for which the telemetry system’s data-acquisition sampling rate will be increased from 30 Hz to 200 Hz) will begin next year, according to Fujino.

System Function Tests
After establishing the credibility of flight-test results by outlining the data-recording technique, Fujino’s paper provided an account of the landing-gear operation tests. The electrically controlled, hydraulically actuated gear performed as expected during tests involving various airspeeds and sideslip conditions. The emergency gear-extension system–with a dump valve and manual-unlocking element– was tested and found to operate effectively. Further, landing-gear-door loads and vibration were measured by strain gauges and found to be within limits; pitch changes during the gear cycle were found to be minimal; and flight characteristics during gear extension and retraction were deemed acceptable.

The HondaJet’s 30-percent-chord double-slotted flaps (also an electric/hydraulic system) were tested at various airspeeds below the (unspecified) flap-operation speed. The flaps have two extended positions available–15.7 degrees for takeoff and 50 degrees for landing. The left and right flaps are mechanically interconnected to prevent asymmetric movement. The company’s vibration tests showed the system to perform as predicted. Pitch change and flight characteristics during flap operation were acceptable throughout the speed range tested.

Honda has also tested the HondaJet’s pressurization system as part of the flight-test regime. The system consists of pre-cooled engine bleed air pumped into the cabin and controlled by two outflow valves on the front pressure bulkhead. Honda conducted tests at various altitudes, monitoring the temperatures of the structures surrounding the bleed-air tubes and validating the automatic cabin-pressure regulation system.

Handling Qualities Tests
Test pilots experimented with the HondaJet’s static longitudinal stability, finding “generally good” agreement between what they expected from computer analysis and what they actually experienced in the airplane. Tests were performed for “stick-fixed” and “stick-free” conditions. According to Fujino’s report, the airplane has positive static stability at the 24-percent and 27-percent cg locations and the neutral point is estimated to be “about 45 percent of mean aerodynamic chord at 150 knots.” Test pilots also tested the so-called “short-period mode” by using an elevator doublet input. They found the aircraft to exhibit heavy damping in this mode with only one or two overshoots before the pitch attitude stabilized.

Similarly, the test pilots excited Dutch roll with a rudder doublet input, finding “adequate damping at mid to high speeds and less damping at low speeds,” but Fujino is satisfied that the tests came in “within the range of MIL-8785C level-1 requirements.”

Sometimes, however, even the most minute computer predictions give way to trial and error. During the initial flight tests, the HondaJet exhibited a small-amplitude rudder oscillation in the mid-speed range, according to Fujino. He wrote, “T strips of various sizes were added to the trailing edge of the rudder” to eliminate the discrepancy. Apparently, Honda engineers were able to arrive at the proper size and configuration for a T strip to eliminate the oscillation.

Performance Tests
Fujino posted results of cruise and climb performance testing to date. He used the speed-power method to evaluate cruise performance, testing to determine the drag, fuel flow and range for various airspeeds and weights. Tests were conducted at 10,000 feet and 25,000 feet, indicating that measured cruise performance “is in good agreement with that from analysis.” The HondaJet is projected to have a normal cruise speed of 420 knots at 30,000 feet and a maximum range of 1,100 nm.

Honda evaluated climb performance using what Fujino described as “a sawtooth test, in which a series of timed climbs is made over an altitude band bracketing the selected pressure altitude.” Honda also used the level-acceleration method to evaluate climb performance. Excess power was measured by maintaining a constant altitude and recording the change in true airspeed with time. Based on both testing methods, Honda determined that its climb-performance predictions for the HondaJet are accurate.

Yokohama Update
Besides his paper on flight testing the HondaJet, Fujino also presented at the Yokohama conference a 17-page update of his previous paper, “Development of the HondaJet,” upon which AIN based its September 2003 article. The updated paper included some noteworthy additional information. First, Fujino revisits his decision to mount the engines on over-the-wing pylons, rather than at the traditional location attached to the aft fuselage. Besides the benefit of allowing a longer cabin for a given fuselage length, the over-the-wing configuration provides a cleaner laminar-flow capability, as shown by computer analysis. Fujino wrote, “The shock wave is minimized and drag divergence occurs at a Mach number higher than that for the clean-wing configuration when the nacelle is located at the optimum position relative to the wing. The over-the-wing engine-mount configuration exhibits lower drag than does the conventional rear-fuselage engine-mount configuration.”

Aerodynamicist John Roncz, who designed Burt Rutan’s Voyager airfoil among many others, told AIN recently that detailed computational fluid dynamics programming could, indeed, produce an optimum over-the-wing design. Previous attempts to use the configuration were based on trial and error–and none has been successful.
At the slow end of the speed scale, Fujino developed his own “critical-section method” of testing, which he combined with other, more traditional computer-generated predictions to design elements of the wing for optimum stall behavior. The result is a wing with 5.1 degrees of washout and a taper ratio of 0.38, which Fujino said produces good stall characteristics with minimum induced drag penalty.

In last year’s paper Fujino described the research that went into configuring the engine-pylon interface such that inlet air pressure was consistent at adequate sideslip angles and angles of attack. In the new paper, he not only provides detailed numbers on total-pressure distortion and mass-flow ratios, but also provides a graphic presentation supporting his research and results from test flying.

Computer-generated Simulation
Based on computer projections of performance and handling qualities, Honda developed a nonlinear aerodynamics flight simulator to evaluate normal flight conditions and critical modes such as deep-stall, spin and one-engine-out conditions. During the deep-stall simulation testing, Honda determined that the HondaJet could be recovered from the condition with a spin chute under emergency conditions. Fujino wrote, “The simulation results were also used to design the support structure for the spin chute.”

Those simple words, embedded on the eighth page of the 17-page report, are a tantalizing example of the mystery cloaking the HondaJet. Will the final product (if there ever is one) have an integral spin chute, or is Fujino referring only to the spin chute installed on this prototype test aircraft? Ballistic Recovery Systems (BRS), the Minnesota company that designed and manufactures the emergency parachute on the Cirrus piston single, has said it is researching a high-speed, whole-airplane parachute for light jets. Much more demanding than the Cirrus equipment, the new system would involve two canopies deploying in sequence–the first a smaller one designed to slow the aircraft to a speed at which the second, main chute could deploy safely. A BRS spokesman told AIN his company would consider marketing the initial canopy separately as a spin-recovery chute if the market demanded. Could this be the system Fujino is referring to?

Because of the ground rules Honda has established for journalists, Fujino is unavailable to answer that, or any other, specific follow-up question. Both GE/Honda and GE’s aircraft engine division are exhibiting at this month’s NBAA Convention in Las Vegas, but it’s unlikely Fujino will be available there to answer questions.
Once again, Honda’s non-strategy for non-promotion of the HondaJet is difficult
to fathom when viewed from conventional angles. Most other aircraft manufacturers would be burning the midnight oil to bring the prototype–stuffed as it might be with flight-test telemetry equipment–to business aviation’s big party.

But it’s difficult to believe that Honda’s commitment to aviation is not sincere when you listen to the words of president and CEO Takeo Fukui, who said at the North American International Auto Show last January, “Mobility is a basic desire, right and joy for all people. Honda continues to pursue mobility from all dimensions. Mobility in the third dimension–the sky–was a dream we have had since shortly after our company was founded. The words of our founder, ‘Do not imitate others,’ are burned in the minds of everyone at Honda. We have no interest in following. The value of creation is not only in technology. The value is in the Honda engineers who create that technology, and who will create new products for our customers in the future.”

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