Hot-and-high testing validates Bell 429 performance specs

 - November 29, 2007, 6:42 AM

The Bell 429 can hover out of ground effect (OGE) at 11,000 feet at its maximum takeoff weight of 7,000 pounds. The altitude exceeds Bell’s previous customer commitment of a maximum OGE hover of 9,300 feet. It was the most significant finding during high-altitude and hot-temperature testing of the two flying Bell 429 prototypes conducted this fall in Arizona and Colorado, according to Bill Stromberg, the company’s executive director of commercial program management.

Stromberg said that the testing also validated the 429’s service ceiling of 20,000 feet. Both helicopters flew to their U.S. test sites from Bell’s Mirabel, Quebec plant and together had accumulated 430 hours of flight time before the hot-and-high testing. The validation tests were flown by Transport Canada certification pilots and allowed Bell to “bank a lot of certification data,” according to Stromberg.

Bell expects the $4.865 million (2007) light twin turbine to receive certification in September next year. The order book for the 429 currently stands at more
than 240, creating a sizeable backlog.

A helicopter ordered today would not be delivered until 2014, although Stromberg said that Bell is looking at ways to increase production rate short of licensing.

Minor Modifications to Production Model
Based on the results of the hot-and-high testing, Bell announced that the 429’s design was “frozen” at the end of October. However, production helicopters will incorporate small changes that stem from the recent tests. For example, as a result of the Colorado testing, the vertical fin will be sculpted to increase tail-rotor authority. A strake will also be added to the left side of the tailboom to improve handling qualities. Aside from those items, the exterior lines of the 429 “had pretty much been defined” before this latest round of tests, Stromberg said.

He credited the fact that there are few changes necessary to flight testing of the 429’s main rotor system and engine cowling conducted more than a year-and-
a-half ago on a Bell 427 testbed. Those tests allowed the company to develop the lines for the engine inlets and exhausts, as well as the oil breathers. Development of the 429’s external lines was largely finished by June, Stromberg said. That, combined with safety of flight and flight envelope expansion tests, completed phase one of the development program.

The results of the Arizona tests might yield a few more minor changes with regard to rotor dynamics, but the tests did confirm that the engine compartment and avionics bay have adequate cooling. Maximum temperatures at the Lake Havasu test site were estimated to be in the mid-90 degrees range.

Phase-two development includes addressing all the issues raised in phase one as well as doing the autopilot, flight control computer, control laws, software and other IFR work. Stromberg said that part of the program is on track for completion by January. “That is really the big pacing item now,” he said. Bell brought these items in-house on the 429. Bell Engineering will design both the autopilot and the flight computer using the same team that worked on the company’s Eagle Eye tiltrotor vertical unmanned aerial vehicle program for the U.S. Coast Guard.

Moving the work in-house is “faster, more seamless, and less expensive,” said Stromberg. “It is one of our core competencies. We are also doing the aircraft data interface” in-house, he said.

The interface will take data from around the aircraft and display it on a six-inch by eight-inch Rogerson Kratos multi-function display (MFD) in the cockpit. Stromberg said the displays provide excellent off-angle viewing from either pilot or copilot seat and run cool to the touch. A memory chip in the system will store the last 75 hours of flight information on the MFD and allow it to be downloaded to a personal computer.

The interface is not crashworthy and does not replace the need for a digital flight data recorder for helicopters in commercial operations. However, Stromberg said it will give “maintenance people a lot of information and is a simple way to assist with maintenance planning.” Stromberg said Bell’s 429 Pilot Advisory Group had a significant influence on both the cockpit design and the format of the data displays.

The company is also gearing up its 429 pilot training program, with instructors scheduled to begin training in March and customers in August. Frasca will be providing a Level 7 flight-training device (FTD) for 429 training at Bell’s customer training academy at Fort Worth’s Alliance Airport. The initial transition course will consist of 32 classroom hours, 6.5 hours in the FTD and 5.5 hours flying the helicopter. The recurrent course will feature 16 hours of classroom instruction, four in the FTD and five in the helicopter.

Concurrent with flight testing, Bell is continuing fatigue and life-cycle testing of 429 components, including the main rotor blades, actuators and dampeners. That testing will continue several years after aircraft certification, according to Stromberg.

The third phase of the 429 test program will begin early next year when three production test aircraft join the two prototypes. The first production aircraft was turned over to the flight test department in mid-November but will not fly until early next year. That helicopter will initially be dispatched to Bell’s Fort Worth facility for ground vibration testing. The current test program calls for this combined fleet to fly 1,400 to 1,500 hours before certification. The current timetable calls for all test flying and certification reports to be completed by next summer. “We have a ways to go, but I’m optimistic,” Stromberg concluded.