Bell/Agusta 609 tiltrotor returns to flight status
Pietro Venanzi took the left seat in the BA609 during the tiltrotor’s return to flight status, at Bell’s XworX center near Fort Worth, Texas, on June 3. The 80-minute hop in aircraft one (A/C1), witnessed by AIN, was not the Italian test pilot’s first time at the controls of the tiltrotor. He had taken them on several occasions alongside project test pilot Roy Hopkins, during the first flight-test phase between February and June 2003.
However, the June flight might have been his last in the copilot’s seat. Venanzi needs to build some pilot-in-command time now, in preparation for a return to Italy in September and the opportunity to fly A/C2, as it gets closer to its own first flight later this year.
This new A/C1 flight-test phase will not only last longer than the previous one, stretching as it does a full year toward preparations for FAA certification testing. It also heralds a more immediate challenge: expanding the flight envelope to embrace its raison d’être.
By mid-June, the BA609 had flown with landing gear up and prop-rotor nacelles rotated to 60 degrees from the vertical. “We believe conversion to full airplane mode is only a few flights away,” executive program director Don Barbour told reporters at the Paris Air Show. The aircraft reached a speed of 125 knots, just under half its predicted VNE in full airplane mode.
Once the first flight program was completed in 2003, working toward this new one involved more than uploading new software to the flight-control computers. Using feedback from the aircrew and onboard telemetry, engineers made adjustments to the whole aircraft setup–including fine-tuning the flight controls and their relationship to the flight surfaces and prop-rotors.
Engineers then qualified these and other improvements in the vehicle management system integration laboratory adjacent to the XworX hangar at Bell’s Plant 6 flight research center and implemented them on A/C1 during six weeks of ground runs. This phase included several conversions to airplane mode carried out in the tiedown stand, where engineers measured every load and stability factor under near-forward flight conditions. (Although the helicopter stand can handle full vertical power, its lateral tolerances are limited.)
With the return-to-flight-status flight under its belt, the A/C1 team will qualify all the changes made since the first phase and then move on to flight envelope expansion. At every stage of the mode conversion (from 75 down to zero degrees), engine controls and responses have to be checked, restart drill procedures formulated and airflow distortion inside the engine intakes measured under a range of angle-of-attack, center-of-gravity and weight permutations.
Engineers in Italy duplicate every change made to A/C1, often in real-time, on the A/C2 setup there. Functional testing and instrumentation checks are already under way, in preparation for ground runs and shakedown trials in September and October. First flight is expected to take place before Christmas.
Venanzi has been involved in the tiltrotor project since 2001. He moved to Texas that summer, expecting to become fully involved in the build-up toward first flight. At the time, all four test aircraft were expected to fly from Fort Worth.
However 9/11 (and the fallout from two fatal crashes of the V-22 Osprey, the BA609’s larger sibling) forced a reappraisal of the whole tiltrotor project and Venanzi was sent back to Italy the next month.
During the slowdown, financing and risk-share elements of both Bell/Agusta programs were reorganized and, as a result, the Italian company’s contribution to the BA609 program increased significantly. Agusta assumed responsibility for flight-testing three of the four aircraft: A/C 2 and 3, which are already in Italy, and a “green” A/C4, which sits in the XworX hangar.
Venanzi was reintroduced to the program, and his task now is to learn as much as he can from flying A/C1, so he can take up the reins of A/C2. At first he will be supported in Italy by Bell test pilot Herb Moran but, in time and as A/C3 and 4 come online, the pilots will fly solo with a flight-test engineer in the left seat. Dual FAA and EASA certification is expected in 2008.
The BA609’s primary controls–cyclic stick, (collective) power lever and yaw pedals–are the same as those in any helicopter, although engineers and pilots don’t use the word “collective.” Flap and landing gear handles are mounted on the front cockpit panel between the crew stations and the engine controls are on the overhead panel.
The nacelle controller at the front of the power lever is a four-position thumb switch, spring-loaded to a neutral position. When converting to helicopter mode the pilot can bring the nacelles back, at three degrees per second, to the upper detent range of 75 degrees to 95 degrees (five degrees aft of vertical). Within that range he can manually adjust the nacelles rearward until entering the hover at 90 degrees. For airplane mode, detents at 75, 60 and 0 degrees (fully forward) allow the pilot to command the nacelles forward at three degrees per second with a series of pushes.
The pilot can stop anywhere between any of the detents by touching the switch in the opposite direction. A fast-rate reconversion mode, activated by overriding a rear force detent, brings the nacelles back from any position to 95 degrees, at eight degrees per second. This accommodates emergencies such as a double engine failure and allows quick deceleration. During conversion to airplane mode, downstop loading prevents the nacelles’ applying excessive forces to the structure.
Venanzi explained, “It is always important to have continuity in a flight test program,” he said. “But that is especially true for this aircraft.
“The BA609 is an unconventional aircraft and therefore demands a flexible approach to testing. Everything is highly interfaced and it can send out complex messages that may be difficult to interpret. During the June 3 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.”