BA609 tiltrotor expands its flight envelope
The first Bell/Agusta BA609 tiltrotor performed its first full conversion to airplane mode in Texas this past August. The maneuver has become routine, and the ground-breaking aircraft has gone on to pass the 250-knot airspeed milestone. Agusta test pilot Pietro Venanzi, preparing at press time to take on the responsibility of flight testing the second prototype in Italy, briefed Aviation International News on what the test team learned from this fundamental expansion of the flight envelope.
“During the first conversion flight we stayed at 100 percent rpm, to assess all the aeroelastic modes and torsional stability in that regime. In fact, [by our standards] we enter full airplane mode only when the rpm has been reduced to 84 percent, and we achieved that soon afterwards,” he explained. “We were able to appreciate the exceptional smoothness of this machine. It’s quiet and vibration free up to Vcon [200 kcas at zero degrees nacelle and 100 percent rpm].”
Bell/Agusta continues to analyze the cause of an increasing three-per-rev vibration that occurs at 84-percent rpm, but whatever the reason, the anomaly hasn’t dampened Venanzi’s enthusiasm for the aircraft’s performance attributes.
“The CitationJet we have been using as a chase aircraft can’t keep up with our eye-watering rates of climb–exceeding 2,500 feet per minute at 140 kcas,” said Venanzi. “Bear in mind that we take off very close to our maximum gross weight of 16,800 pounds.
“Besides some marginal directional stability issues at 60-degree nacelle while descending at high sink rates–but only there and then–the aircraft shows very well-harmonized flight controls, excellent stability on all axes, well tuned sensitivity and control power. It flies just like the simulator,” he concluded.
Getting to this stage has posed a continuous set of challenges for Venanzi who, like all Italian test pilots, draws from experience in both fixed- and rotary-wing aircraft. “The BA609 is an unconventional aircraft and so demands a very flexible approach to testing,” he explained. “Everything is highly interfaced and it can send out complex messages that may be difficult to interpret. During a recent flight we experienced a number of seemingly unrelated crew alert captions that turned out to be related to a false VSI [vertical speed indicator] reading. We didn’t see the relationship until the engineers explained it back on the ground.”
After achieving 250 kcas, BA609 project test pilot Roy Hopkins reported that the airplane won’t fly again until mechanics replace the fuel control units.
When the second aircraft enters the flight test program from Cameri air force base, northeast of Milan, the partners will start live data linkage between Italy and Texas. “Data collected in Italy will go to a common server, allowing the U.S. to pick up in the morning where Italy left off in the afternoon,” explained Bell/Agusta Aerospace managing director Lou Bartolotta. Testing will be a continuous process, no longer conducted–and often duplicated–in parallel.”
Every change made to the first aircraft gets repeated, often in real-time, on the second aircraft in Italy. In fact, Venanzi described the second ship as a “clone” of the first. Engineers have already started functional testing and instrumentation checks, in preparation for imminent ground runs and shake-down trials, followed by first flight just before year-end. Milan will retain program lead status with the introduction of a third aircraft, nearing completion in Italy, and a fourth “green” ship, currently in the Bell hangar at Fort Worth, Texas.
By the time the BA609 wins certification in 2008, it will be pressurized and certified for instrument flight into known-icing conditions. Its composite material construction, advanced glass cockpit and digital flight controls will provide, according to Bartolotta, “new levels of performance, reliability and affordability to the aviation world.”
Armed with the fact that the nine-passenger aircraft flies twice the speed of typical helicopters of comparable capacity, Bell/Agusta marketers will no doubt tag the BA609 with the title of best multimission business aircraft in the world. Bartolotta calculates that an executive could take off from the helipad of a country house outside London, fly in comfort to a meeting in Frankfurt in 60 minutes; then repeat the exercise to Zurich and Milan, before flying home for an early dinner.