Bell Textron is aiming for the 18-seat Bell 525 Relentless to claim the title of the first certified civil helicopter to have a fly-by-wire (FBW) control system.
The Relentless, which has been in constant development for 10 years, is due for FAR Part 29 certification by the end of this year, with the FBW system being touted as a game-changer for the civil helicopter industry.
Bell's Business Development Director Australasia Daniel McQuestin told a gathering at the Australian International Airshow late last month that the 525's FBW system would be a step-change in helicopter safety.
"Bell wanted to be the first to bring FBW technology into the commercial market," he said. "It's not very often that a clean-sheet design comes along and to try to design a 21st century aircraft with a focus on safety, which was driven not only by a safety culture, but also by the working groups that had input into this helicopter.
"In the rotorcraft industry offshore oil and gas has been a big driver of safety."
FBW is already in use in military rotary-wing operations, and has been on commercial fixed-wing aircraft for over 30 years, which has given Bell the confidence to go ahead with certifying the 525 with FBW.
According to Bell, FBW systems mean mechanical linkages are removed, triple redundancy takes over from dual redundancy, pilot workload is reduced, situational awareness is increased and the system delivers precise handling and envelope protection.
"With fly-by-wire, what you're doing is removing the mechanical linkage between the pilot's control in the cockpit and the actuators and flight servos that are actually controlling the aircraft's flight path and operations," McQuestin explained.
"Because it has been in the airline industry for over 30 years, we have statistical data for the increase in safety; millions of hours and the reduction in incidents and accidents over those 30 years. Bringing that into the helicopter domain, it's pretty simple that by removing mechanical linkages we're getting the benefits as well.
"When you need control rods and bell cranks, cables and pulleys through the entirety of an aircraft close to the airframe and other components, and in helicopters we try to keep things as light as possible and as compact as possible, you instantly remove 70% of the airframe's single-point failure."
In a FBW system, pilot controls inputs are converted to electrical signals that are sent to a flight control computer that decides what the pilot wanted to do and affects the actuators appropriately.
"FBW gives precise digital control over flight systems to fly precise flight paths like rates of turn, angles of bank and g forces that make the flight comfortable," McQuestin said. "In terms of safety, pilots are going to be less fatigued because they are flying in a more comfortable environment.
"A good side-effect of that is that passengers also get a good ride."
History has shown that FBW has its own error modes, such as the ability for the pilots to input contrary commands. To eliminate this, Bell has retained mechanical linkages between the pilot and the co-pilot controls, making contrary commands impossible.
Further, Bell designed the 525 FBW as a triplex system, which means it has three flight computers, triplex main and tail rotor actuators, triplex power and hydraulic systems and three altitude and heading reference systems (AHRS). Each system alone is capable of controlling the aircraft.
"We weren't going to get a certified FBW helicopter with a dual system," McQuestin explained. "A triplex system is a massive step forward, which eliminates not just single system failures, but dual system failures.
"That means you're essentially a third safer straight away than a conventional rotorcraft that has dual actuators.
"In this digital system, which is controlled by computers in a smart way, it is quite simple to find out which system isn't working to the optimum level. When you've got two systems and one says 'I'm high' and the other one says 'I'm low', which one is correct?
"Once you add a third system, if two say 'I'm high' and the other one says 'I'm low' there is a probability that the two that say 'I'm high' are right."
Bell has designed the FBW as a modular system, which means maintainers can swap-out components without having to significantly disassemble the helicopter in the process. McQuestin pointed out that this reduces downtime, but also limits opportunity for errors in maintenance that could have an impact later in the airframe's life.
But McQuestin says the biggest benefits of FBW come from an increase in helicopter handling.
For example, the FBW system will allow pilots to increase collective only to move into a hover, with the flight system making the adjustments to the other controls. The pilot, however, retains full command over the cyclic, pedals and collective if needed.
"Situational awareness to a helicopter pilot is integral to safe flight," McQuestin said. "The more time we can be thinking outside and further ahead of the helicopter, the safer the flight is going to be.
"In a traditional helicopter, as soon as you make one movement with one control, you have to make a movement with other controls, which goes back to the first control and you do it again. That takes up a lot of brain space, a lot of energy and a lot of concentration.
"That high work-load environment is greatly reduced by having FBW system. You can reduce the work load because the pilot is not having to consider the effects of controls every time. You can get your eyes outside, which is a much safer way to fly."
Bell Textron is also expecting the 525 to handle difficult conditions and confined spaces–such as an oil rig platform–much better than a conventional helicopter thanks to the FBW and flight computer.
McQuestin also predicted that future developments from Bell would likely see FBW and new technology proliferate.
"The 525 is going to come out with entry-level autopilot, with all the modes you would see in a four-axis autopilot, but the future growth here is high rate-of-descent protection, maybe vortex-ring state protection and single-engine failure category A and PC1, PC2 departure profiles automatic," he said.
"At Bell, you'll see a lot of our aircraft differently design: 525, V-280 and our autonomous aircraft moving forward optionally-manned.
"So we're not trying to get rid of the pilot, but you might get a digital co-pilot."