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Bell 525 Prepping To Resume Flight Testing

by Matt Thurber

 - March 6, 2017, 9:45 AM

Bell Helicopter hopes to soon resume flight testing of its super medium Bell 525. Flight testing has been halted since the crash of FTV1 last July in Italy, Texas.

Bell Helicopter is preparing the next Relentless flight test helicopter (aircraft 003) for its first flight and resumption of the 525 flight test program. Flight testing was halted after the crash of FTV1 last July in Italy, Texas, in which both test pilots were killed, but it should resume in the “next several months,” according to a Bell spokesman. The National Transportation Safety Board final accident report “is not our driver for return to flight timing,” he added. “Bell Helicopter continues to work closely with the NTSB and FAA to complete the NTSB investigation of the Bell 525 accident.”

Added Larry Thimmesch, vice-president of 525 sales and business development, “The NTSB and Bell Helicopter have focused the investigation on a sequence of events for which corrective actions are being implemented. Obviously we need to wait until the NTSB comes out with the summary of the findings to talk about what those are.”

Asked whether the NTSB had requested that Bell try to simulate the accident scenario, Thimmesch said, “We have been integrally involved with them through every step of the process to understand the whole aspect. And Bell Helicopter has gone beyond that to look at everything that we do. It’s a perfect opportunity for us to always look at process improvement to validate everything that we’re doing so that when we go back to the air, we’re completely certain we will provide a safe and reliable aircraft as a result of that. So obviously a tragic event–the accident–we’re doing everything we can to leverage all of our learning and move forward with a very safe and reliable aircraft.”

Aircraft 004 and 005 are in the build process and will be the first two production-conforming 525s, and these will join the flight test program later this summer or early this fall, according to Thimmesch. These 525s will also be the platforms for certification of kits and will also fly customer demonstration flights. 

Last December, Bell applied for an extension to the 525 type certificate program because the initial application expired at the end of 2016. “That extension just took us through the end of 2018,” he said, “so somewhere in that timeframe is our objective to certify the aircraft, and we’ll come out with more information on that when we have that full flight test plan.”

Bell is putting the finishing touches on its 525 full flight simulator, manufactured by sister company Tru Simulation + Training, at the Bell Training Academy in Fort Worth, Texas. The simulator will be operational in the third quarter of this year.

Aircraft 003 is Bell’s third development 525, and in early February this helicopter was on its way to undergo pylon pull and control system stiffness or proof testing. The latter tests are done to calibrate aircraft systems to flight test instrumentation, he explained, “so when we see instrumentation through our telemetry lab we know exactly what’s happening on the aircraft.” The pull testing involves connecting devices to the blade attach fittings on the main rotor hub, and these also validate actuation against test instruments. Similar tests are underway on the tailrotor system.

Alongside physical testing of the 525s in preparation for return to flight, Bell engineers have been running ongoing tests in the Relentless Advanced Systems Integration Lab (RASIL) at the Bell XworX facility in Arlington, Texas. “I call it aircraft zero, and it’s been in a flight-type testing mode for over two years,” said Thimmesch. “Everything we’ve done in the aircraft we’ve already done in the RASIL.” Meanwhile, development activities continue, including work with certification authorities. “They’re very involved in everything on the program,” he said. “Component testing has continued. Every system has to be tested, and those are best done on the ground, in the test labs. Maturing the product, learning through the component and systems tests, all that’s been moving forward, and there’s a tremendous amount of activity in a clean-sheet program to test and validate everything to its requirements for certification.”

“This is an R&D facility, an engineer’s dream,” said RASIL supervisor Larry Hudson. The RASIL hosts three separate 525 systems integration labs, one for the helicopter’s Garmin G5000H avionics, one for its fly-by-wire flight controls and a third for the electrical system. Bell designed and built the flight control system, which runs on three BAE Systems flight control computers and Moog electrohydraulic actuators. 

The collective and cyclic, made by Sagem, are mechanically interconnected (as are the anti-torque pedals) so they move in concert. Bell elected not to adopt electronically connected flight controls, due to the need for additional electronics to manage that connection and ensure reliability and redundancy. “That’s a lot of work,” Hudson said. “I think we have a very good design. When you have your hands on the controls and you feel the other [pilot] move them, that’s like getting a punch in the arm. You don’t have to look at anything, if somebody moves that control, you know it.”

When pilots climb into the cockpit of the 525, they will notice a big difference compared to other helicopters. The cyclic isn’t mounted between the pilot’s legs on a pivoting mechanism, but protrudes from the end of a housing in front of an adjustable armrest. Because the controls are fly-by-wire, it was easier to mount the cyclic this way, and the design means no more hunching over the controls and resting an arm on a leg. The armrest positions the pilot’s wrist comfortably and conveniently for the full range of cyclic movement. The collective is conventionally located on the pilot’s left side, but also has its own armrest for maximum comfort.

The RASIL includes a full cockpit rig with a visual display much like a non-motion simulator, but hooked into all the lab equipment that replicates the 525’s systems. “We’re able to connect either [test] bench to the cockpit rig, and can also tie in the avionics bench and the electrical bench,” Hudson said. This is far more efficient than previous lab systems, which each had to be tested individually then only came together in the actual helicopter. “We can tie and integrate these systems with everything operating together,” he said, and this means “flying” the simulation using real hardware and software and loads on actuators, allowing engineers to “evaluate the whole system in real-time,” he added.

The 525 will be certified for full flight into known icing condition, but not at initial certification due to the need to chase natural icing conditions. Full icing approval is expected in 2019 or early 2020, according to Thimmesch. Bell will also obtain limited icing capability for North Sea operations at the same time as the full icing approval. 

Bell decided not to build another test aircraft after the accident, so four will be used to finish the flight test program. “The aircraft has proven to be very reliable,” he said. “Our efficiency allows us, once we get back in the air–plus the aircraft is more mature–we believe we can be very efficient in our remaining flight test program to hit that certification date.”

The 525s that have flown have logged just under 200 hours. Some ground testing is under way as Bell prepares to resume flight testing, although not engine runs, and this helps advance the program even without flying. “The next insertion point for flying the aircraft is going to be a more mature production representative configuration,” Thimmesch explained.

Bell holds “around 80” letters of intent for the 525, he said. “We have many customers around the world that are following this program very closely. We understand the aircraft, we have validated our vibrational elimination, which will be best in class. We have validated our speed, which has exceeded our expectations, and our hover performance, which has exceeded our expectations. This aircraft has proven itself to be an incredibly capable aircraft.”