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The walls of the Airbus Helicopters customer center at Donauwörth are adorned with images celebrating the achievements of Messerschmitt, Bölkow and Blohm (MBB); legendary aircraft designers whose eponymous company produced the Bo.105 light twin helicopter in the late 1960s.
That iconic design pioneered a hingeless titanium monoblock rotor head that was truly ahead of its time, providing direct control and excellent maneuverability. It was so successful that when MBB collaborated with Kawasaki Heavy Industries in 1977 to design the BK-117 to replace it, they used the 105’s head as a basis for the new rotor system.
Four decades later MBB has, through various acquisitions, become Airbus Helicopters. So too has their helicopter of the late ’70s subtly but perceptibly changed. More powerful engines progressively increased its 6,283-pound (2,850-kilogram) gross weight, and the integration of technology from the (then Eurocopter) EC135 further expanded its utility. In the new millennium, it got a facelift that gave marketers an opportunity to change the name on the sales literature, if not the type certificate, as it became the EC145.
By 2014, the wholesale replacement of the tail with a Fenestron and the integration of Airbus Helicopters’ proprietary Helionix avionics brought the aircraft right up to date, retitled as the H145, now tipping the scales at a maximum takeoff weight of 8,157 lb. (3,700 kg). Despite the name changes, you don’t have to look far to find its heritage. BK-117 still features in its type certificate and, throughout its life and in all its guises, the heart of the H145 has always been the MBB rotor head. Until now.
In early 2019, Airbus Helicopters announced the development of an entirely new rotor system for the H145, based on work that had been done on their Bluecopter prototype. The venerated MBB rotor is entirely gone on the new aircraft, with the new head featuring a bearingless design similar to that of the company’s smaller H135.
Axel Humpert, Airbus’s head of program for the H145, explained its inception: “The five-bladed H145 came up after research activity where we flew this type of rotor on a prototype based on the [H]135,” he said.
“We were receiving requests from the market all over the world asking for even more payload,” explained Humpert. “We took the chance of installing the new rotor on the H145 and the results were so promising . . . that we decided to go into serialization.”
I had the opportunity to fly one of the five-bladed H145 prototypes in late October. Demonstrating the aircraft was Volker Bau, chief test pilot at Donauwörth since 2010. He joined Airbus Helicopters in 2006 after a 20-year career flying in the German military.
In the cabin was Antoine Van Gent, Airbus Helicopters head of flight test since 2009. Having started as an F-16 maintenance officer, he flew almost every aircraft in the Royal Netherlands Air Force inventory during a 17-year career that included test pilot training, before joining Airbus Helicopters Germany in 2005.
Van Gent walked me around the machine prior to start and, understandably, the focus was on the rotor head.
Tricks up the sleeve
Unlike the previous four-blade system, the roots of the five new blades are attached directly onto the rotor mast. A composite flex beam buried inside the blade absorbs all the feathering and dragging loads, while the construction of the blade itself allows it to flap. Although the original design catered for flapping loads in the same way, the elimination of blade forks that attached the blades to the titanium star has moved the effective flapping hinge offset inboard, from 12 percent to seven percent of the blade span. In theory, this should grant more direct control and reduce any cross-coupling.
The whole arrangement certainly reduces maintenance, as the sleeve and spindle feathering hinge of the original is completely absent, and with it goes the necessity for lubrication and maintenance inspections. But that much technology literally baked into the blade comes at a cost. As any H135 owner who has dinged one on a hangar door will tell you, the place you’ll feel it the most is in your wallet. This system gets around that by separating the blade cuff, which contains the really expensive flex-beam, from the outboard blade with an attachment joint. This adds the facility to easily fold all the blades by removing one of the two bolts at each attachment joint. The new blades are already shorter than those that they replace, but this system dramatically reduces the aircraft footprint still further. Folded, it will fit inside a medium-sized transport aircraft, small hangar or large yacht, and can be prepared to fly again within about half an hour.
The sleek rotor hub has also significantly reduced rotor drag, providing more effective power that not only delivered an increase in gross weight to 8,377 lb. (3,800 kg), but also allowed Alex Neuhaus (Airbus Helicopters’ experimental test pilot) and Van Gent to land the unmodified prototype (including flight test equipment) on the summit of Aconcagua in Argentina; the highest mountain in the Southern Hemisphere at over 22,000 feet (6,705 meters).
Van Gent explained that from that 220-lb. (100-kg) increase in gross weight, the new aircraft was able to get an extra 330 lb. (150 kg) useful load. This was a result of the rotor head design and removal of the active vibration control systems, saving 116 lb. (53 kg). Impressive when you consider that they’ve added 25 percent more blades.
The new rotor system will also be available as a retrofit to its immediate forebear, the H145. While it will take around 250 hours of work to complete, it will be possible for any EASA (European Aviation Safety Agency) part 145 approved maintenance organization to carry out the procedure, so larger operators should be able to do this in-house.
I wanted to focus the flight test on the handling and performance of the aircraft, as the complex arrangement of opposing forces that keep a helicopter airborne mean that even minor tinkering with the rotor system is likely to have repercussions throughout the flight envelope, as Van Gent explained. “Normally you can have some surprises because of changes in rotor downwash, especially in the hover or at low speed, but here we didn’t need any aerodynamic fixes, it was very stable from the beginning.”
This trend continued throughout the flight test regime, Bau told me: “Normally you find a corner [of the flight envelope that means] the aircraft needs some modification, and you have to adjust the airframe, which is expensive. Here there was almost nothing.”
Being a prototype, our machine had some idiosyncrasies that included an elongated pitot probe/airflow vane attached to the nose and 130 kg (285 lb.) of flight test equipment in the cabin, from which flowed the associated orange cabling (this will, of course, be absent in production aircraft and their exposed conduits covered by aircraft interior trim).
With Bau in the right-hand pilot seat and me in the left, Van Gent was joined by Vertical photographer Lloyd Horgan in the cabin, bringing our takeoff weight to around 7,937 lb. (3,600 kg) with around 75 percent fuel. Outside it was a chilly, but not unpleasant, 6 C (43 F) at Donauwörth’s airfield, at an elevation of 1,315 feet above mean sea level. We had about 10 knots of wind.
With power on in the aircraft, the Airbus proprietary Helionix avionics system was brought to life and we were ready to fly in just over five minutes using the normal start procedure, even with a delay to carry out built-in-tests of the flight test equipment. In an operational scenario, Airbus said the aircraft can go from cold and dark to ready to fly within two minutes.
Lifting into the hover, the reason for the removal of the active vibration control was immediately apparent — there wouldn’t be anything for it to do. The hover and hover-taxi were startlingly smooth and, although not entirely eliminated, the vibration was very subtle. Whether as a result of a reduction in magnitude, or an increase in frequency, felt vibration levels in the front-left seat were so low that I had to consciously focus on it to discern it. Horgan – who has certainly flown in more helicopter cabins than I have – was equally impressed in the cabin. With the H145’s popularity as a helicopter emergency medical services (HEMS) platform, medical professionals may benefit from the smooth ride — and their patients even more so.
“I was project pilot and did all three first flights,” Bau told me, referring to the three developmental stages of the rotor. “We expected there would be a reduction in vibration with this rotor, but we were still surprised by how much.” He later clarified that the rotor on the production aircraft is “99 percent” the same as the original test blade.
Positioning over the “H” at Donauwörth, Bau demonstrated the GTCH (Ground Trajectory Command Hover) mode, in which the aircraft is held in a GPS-derived position or can maintain a vector as demanded by the pilot. “I call it the ‘follow the boat’ mode,” he told me. With a bit of time flying search-and-rescue in my past, my winchmen doubtless would have appreciated that function.
The new H145 will be certified up to its maximum gross weight in Performance Class 1 (PC1), and the profile has already been approved by EASA. “Alex Neuhaus developed it,” Bau explained. “He’s very creative and it’s a bit different.”
With the aircraft held in a GTCH hover, a slight increase in power was all that was necessary to start the aircraft climbing vertically, with a blue line on the first limit indicator providing a cue to assess engine power in case of a failure. At around 200 feet, pressing the “train” button simulated an engine failure, complete with transient main rotor speed (Nr) droop and a slight kick of yaw. A subtle check down on the collective was all that was necessary to reject the takeoff and begin a descent. With the “H” now invisible directly beneath me, my references had all but disappeared. But that didn’t matter to the autopilot, as it guided us vertically straight back down to a low hover precisely where we started, from which a single-engine landing would have been easily performed.
As luck would have it, the weather was beautiful for our flight, with clear blue skies as we left Donauwörth behind us. However, Bau demonstrated that should a pilot inadvertently enter cloud, with one push of a button on the cyclic the aircraft would right itself and recover to straight and level flight. From there, the HTAWS (helicopter terrain avoidance and warning system) and the synthetic vision system would help a disoriented pilot regain situational awareness, using a representation of the terrain in front and providing audio warnings.
Even up to 140 knots, the aircraft itself was still unnervingly smooth and as expected, the four-axis autopilot integrated into the Helionix system provided a very stable cruise. But I wasn’t here to let the computer have all the fun, so Bau sequentially disengaged the automation, initially retaining the attitude hold mode. Flying the aircraft on the trim switch is recommended in this mode, with the aircraft responding promptly and without the lag present in some similar systems. As expected, disengaging the stability augmentation entirely resulted in the nose moving around a little more, but the aircraft remained remarkably stable and this improved further once I’d figured out where exactly the speed stable attitude was. The direct control feel was evident in this regime and subtle movements of the cyclic were required, but the control forces were enough that it never felt at all twitchy.
With the attitude hold mode back on, we repositioned for an approach into an unfamiliar (for me, at least) off-field landing site; a local gliding field surrounded by woods. The vast areas of transparency in the cockpit made it easy to keep the landing site in view throughout the circuit and approach, even though I made the approach slightly steeper than I had intended. As we decelerated to the hover, the vibration increased but only just enough to be noticeable. The aircraft was as stable as expected in the hover and the position was easily maintained without any skittishness in the ground cushion. The site that we were in wasn’t particularly confined, especially in comparison to the places that HEMS operators will expect to take this aircraft, but they will doubtless appreciate the extra flexibility and margin that the reduced rotor diameter offers.
Reentering GTCH mode, I carried out a vertical climb and departed back in the direction of Donauwörth, with the aircraft flying through translational lift with less of a rumble than it had on the way in.
With our time in the air coming to an end, I handed the controls back to Bau so that he could demonstrate some more advanced maneuvering back at Donauwörth. There followed a series of wingovers, tight turns and rapid entries to the hover in various relative wind directions, which were smoothly flown and smoothly absorbed by the aircraft. Naturally, these kinds of profiles increased the vibration to a level that might have raised the eyebrows of VIP passengers, but operators required to perform such vigorous maneuvers are typically transporting passengers of a slightly more robust — and possibly less discerning — nature.
On the topic of para-public and military roles, the increased gross weight is likely to be a higher priority than the improved ride quality; however, given that the crew on such operations might well be required to spend lengthy periods in the aircraft, the cumulative effect of vibration on crew fatigue shouldn’t be trivialized.
Left alone on the ramp with the aircraft as Bau completed the post-flight paperwork, I had a chance to reflect on the experience.
The basic design of the aircraft’s principal components is not new. The rotor system is a direct descendent from that of an H135 — albeit with an additional blade — and the fuselage is effectively the same as the H145 it will replace. While it is undoubtedly an improvement, some might suggest that the new rotor system is simply an opportunity for Airbus Helicopters to recoup some of the R&D euros that were spent bolstering its eco-credentials. I think this is an overly cynical view. Market desire for an aircraft with more usable weight undoubtedly existed, and Airbus Helicopters’ previous offering to meet this demand was a stripped-down version of the legacy airframe, compromising its instrument flight rules (IFR) capability and at odds with the company’s own drive towards consolidation of the type.
With weight-saving from a well-understood and highly integrated platform seemingly not an option, Airbus Helicopters was left needing more power. Bigger engines wouldn’t be an easy fix, and would also likely mean upgrading the transmission, which is a Kawasaki responsibility. With such a seemingly intractable problem, the trial results from the over-scale Bluecopter rotor must have seemed like serendipity, but in the moment, it’s not always easy to match the solution with the problem. Over lunch, Van Gent explained to me that alongside the technical challenge was the necessity to convince colleagues that the new blades would even work. Axel Humpert had joked, “All we needed from the engineers was more lift and less drag — easy!”
So no, the new five-bladed H145 doesn’t represent a leap in capability and it hasn’t turned the aircraft into a new helicopter, but it wasn’t designed to. It provides a tried and trusted workhorse with a truly innovative rotor system worthy of taking the place of its ground-breaking MBB forerunner. The new aircraft is expected to receive EASA certification in 2020, with the last of the original H145s likely to roll off the production line in 2021. The increased performance and reduced maintenance overheads offered by the new version might coax EC- and even BK- legacy operators to upgrade, particularly as the new aircraft will be available in the same price bracket as its precursor. Likewise, with an expected availability date shortly after aircraft certification, the retrofit is likely to be popular with existing H145 users that need the additional usable load. Larger operations with their own part 145 facility stand to benefit the most. Finally, of course, there will always be the few for whom comfort in the cruise has no price; they will certainly feel the benefit.