The battery-electric motor STC retrofit of the popular Robinson R44 offers a low-cost, low-risk path to sustainable vertical flight.
The helicopter has dominated the vertical flight industry since the 1940s, but with the recent advent of electric propulsion, many aviation startups have seemingly tossed the helicopter aside in favor of radically new electric vertical takeoff and landing (eVTOL) aircraft designs.
In fact, in the past decade, more than $10B has been invested in the design and development of futuristic eVTOL designs that employ distributed electric propulsion in a wide range of vectored thrust, lift-plus-cruise and multicopter aircraft configurations.
If you believe the tremendous hype generated by these companies and their backers, the radical transformation of vertical flight is just around the corner, but there are a handful of startup companies that believe that the electric helicopter will also have a very important place in tomorrow’s skies.
Walk into the single-story red brick workshops of Tier 1 Engineering on South Main Street in Santa Ana, California, and you will find a small engineering team working on the company’s third-generation battery-electric conversion of the hugely popular four-seat Robinson R44 piston-engine helicopter.
For the past six years, Tier 1 Engineering founder and principal Glen Dromgoole and his team have been developing a kit that will allow the operators of more than 7,400 R44s delivered worldwide since 1993 to easily convert their helicopters to electric propulsion. Tier 1 believes this zero-emissions helicopter will cost about 20% less to operate than the piston-powered R44, thanks to lower energy and maintenance costs, and will also be about 20% quieter and easier to operate.
Supplementary Type Certificates (STCs) have long been used by aerospace innovators as a means to insert new technology engines, avionics and other systems into proven aircraft to reduce pilot workload while improving performance, operating economics and safety.
Tier 1 Engineering’s low-profile e-R44 battery-electric retrofit STC program was launched in 2016 as a result of Dr. Martine Rothblatt’s quest to develop a fleet of zero-emissions aircraft that could deliver transplant organs to hospitals quickly and without polluting.
In the aviation world, Rothblatt has become one of the world’s leading champions of electric vertical flight and is the 2022 recipient of the Vertical Flight Society’sPaul E. Haueter Award, which is given for an outstanding technical contribution to the field of vertical takeoff and landing (VTOL) aircraft development other than a helicopter or an operational vertical flight aircraft type.
Elsewhere, Rothblatt is recognized as the founder of what became SiriusXM satellite and streaming audio service in 1990, a champion for transgender rights, and CEO/Chair of United Therapeutics (UT), a $1.7B revenue biotechnology company that’s developing manufactured organs for lifesaving surgeries, among other medical therapies.
If you heard about the heart of a pig being transplanted into a patient with life-threatening heart disease in January (see sidebar, "Martine Rothblatt: Serial Entrepreneur"), or a transplant lung being flown between hospitals by drone in Canada, you are already aware of Rothblatt’s visionary work. The milestone surgery relied on genetically modified pigs a United Therapeutics subsidiary designed to provide a supply of organs for people who are unable to receive human organ donations.
A century ago, the pioneers of emergency medicine and the treatment of shock trauma lay the groundwork for the civil air ambulance helicopter network. Now, the need for a low-cost and reliable means of delivering an increasing supply of manufactured transplant organs to hospitals promises to bring the first electric aircraft to market in the next two-to-three year’s time.
Tier 1 Engineering
Dromgoole grew up in New Zealand and graduated from the University of Auckland with a master’s degree in mechanical engineering and a specialization in composite structures. The university’s Centre for Advanced Composite Materials (CACM) is world-renowned for its high-performance yacht research, and the design and testing of composite boats competing in the America’s Cup and other leading regattas.
An avid aviation enthusiast and pilot, Dromgoole decided to pursue a career in the emerging composite aircraft industry and moved to the United States in 1996 where NASA’s Advanced General Aviation Transport Experiments (AGATE) consortium was stimulating a lot of startup activity.
His first job was with Kestrel Aircraft Corp. in Oklahoma, helping to develop the Kestrel K250 (originally designated KL-1) composite light aircraft. Then he joined AAR Corp. in Florida, which was subcontracted to design and build the composite airframe of the Visionaire Vantage very light jet.
Then, after spending a decade consulting to Gulfstream, Northrop Grumman and Boeing on the design and development of commercial and military aircraft, he founded Tier 1 Engineering in California in 2008 to pursue innovative and inspiring consulting aerospace projects.
The company’s initial expertise was in the areas of mechanical design and drafting using a variety of 2D and 3D computer-aided design (CAD) systems to support the design of lightweight aircraft structures. This attracted a client list that included ATK Aerospace, Boeing, Composite Horizons, EAM Worldwide, Encore Composites, Janicki Industries, Mecaer Aviation Group, Panasonic Avionics, United Technologies and Zodiac Aerospace.
In 2015, Glen Dromgoole learned through a colleague at Kaman that the CEO of a large US pharmaceutical company was seeking advice on a new aerospace project.
“I heard about Martine Rothblatt and her effort to try and find someone that would support her idea of developing an electric helicopter for the delivery of human organs. She had approached several of the large aerospace companies to gather support for this project she wanted to pursue, but there was very little belief in her idea. She was told it was impossible. That battery technology wasn’t there, or at least 50 years away.”
During their first meeting at the XPrize Foundation headquarters in nearby Culver City, California, Rothblatt presented Dromgoole with some hand calculations that compared the power output of her Tesla S Roadster automobile to her twin-engine Bell 429 helicopter. She postulated that electric vertical flight was viable, but after six months of contemplation Rothblatt needed an expert to validate if the assumptions made sense.
“I took the notes and reviewed them,” recalled Dromgoole. “And after a week I called back and said, ‘Hey, you know what? Let’s give it a go!’ And she signed us up to do a feasibility study!”
Tier 1 Engineering’s first project for Rothblatt was a three-month feasibility study completed in 2015 for electric rotorcraft configured to transport human organs, which became known as the Electrically-Powered Semi-Autonomous Rotorcraft for Organ Delivery (EPSAROD).
The mission requirements included two pilots, three manufactured organs with a total payload of 600 lb (272 kg), an endurance of not less than 150 minutes (including a 30-minute reserve) and a one-hour charge time.
The relationship with Tier 1 Engineering led to two new projects to explore what was possible. The first was the conceptual design of an electric tiltwing aircraft that could deliver transplant organs to hospitals over longer distances. The second was an empirical project to validate the performance of an electric rotorcraft in practice, with the goal of flying an aircraft as quickly as possible using commercial off-the-shelf technology. Dromgoole said, “The best way to step into this was to take a conventionally certified aircraft, remove the engine and use the mass for batteries and a lightweight electric engine.
“The Robinson R44 is a very impressive aircraft in terms of the empty-weight fraction and the efficient low disk loading rotor system. It really provided us with the best chance of flying an electric helicopter out of any of the different light helicopter models we reviewed.”
Robinson Helicopter Corp. started developing the four-seat R44 in the late 1980s and first flew the prototype at Torrance Airport on March 31, 1990, less than 15 years after the prototype two-seat R22 flew in August 1975 (see sidebar, “Robinson R44 Family”).
Robinson definitely had its finger on the vertical flight market, with the R44 becoming the world’s best-selling general aviation aircraft of the 21st century (airplane or helicopter), closely rivaled by the composite Cirrus SR20/SR22 family of fixed-wing aircraft.
The project began when Lung Biotechnology purchased a 2006 model R44 Raven II (registration N3115T) for about $300,000 in early 2016. Dromgoole’s team removed the aircraft’s bulky 260-hp Lycoming IO-540-AE1A5, which weighed about 500 lb (225 kg), including accessories, as well as the complete fuel system.
“At the time, there was very little information available, and the electric vehicle industry had a tremendous hesitation to do anything with aviation because they perceived the risk to be quite high,” recalled Dromgoole. However, with the help of Rothblatt’s company, they were able to line up a few key suppliers active in the electric vehicle business in the US and UK to support the project.
Electric motorcycle maker Brammo of Oregon provided the lithium polymer batteries. Formula 1 hybrid-electric supplier Rinehart Motion Systems of Oregon provided the inverter/motor controllers. Autoflight of New Zealand provided the reduction gearbox, and YASA Motors of Oxford, UK, provided the two axialflux electric motors packaged together with a common driveshaft.
Tier 1 Engineering received two of the early P400HC electric motors sold by YASA that were stacked in parallel and powered by separate inverters for redundancy. The unit was light enough to install by hand and could achieve the rated power required for the R44, producing peak shaft power of 183 kW (245 hp) for five minutes and continuous shaft power of 153 kW (205 hp), Rothblatt said in a presentation to the Tesla Motor Club Connect conference in 2016.
In the ever-changing world of electric vehicles, Brammo’s motorcycle business was acquired by Polaris in 2015 and its battery business by Cummings in 2017. Rinehart Motion Systems was acquired by BorgWarner in 2019 became part of Cascadia Motion, LLC. YASA Motor’s ultra-high-performance, low-weight motor line optimized for aerospace applications was spun off as Evolito, just before the rest of YASA’s motor business was acquired by Mercedes-Benz in July 2021. One of Evolito’s engines powers the all-electric Rolls-Royce “Spirit of Innovation” aircraft that set three world records in November 2021.
Tier 1’s engine installation was completed in July 2016 by a team of three people from Tier 1; some team members were pilots who had previously built their own aircraft. A new truss structure was bolted to the engine mounts on the airframe to install the new motor.
The proof-of-concept e-R44 maintained the Raven II gross weight of 2,500 lb (1,135 kg) and a basic empty weight of 1,250 lb (566 kg). The 11 Brammo battery modules weighed a total of 1,100 lb (500 kg), with the motor controllers, inverters and motor weighing an additional 100 lb (45 kg). No changes were made to the flight controls, but a digital cockpit display was added utilizing a laptop computer to provide torque and power readings, and also log test flight data.
The first ground test took place at John Wayne Airport in Orange County, California. Then, the e-R44 was trailered to Los Alamitos Army Airfield (KSLI), which is located inland from Seal Beach National Wildlife Refuge and six miles (9.6 km) east of Long Beach Airport. That’s where the e-R44 made its first successful hover on Sept. 13, 2016, its first hover-taxi the following day, and a record five-minute cruise flight on Sept. 21, which drained approximately 20% of the battery energy.
At the time, Dromgoole called the flight a “historic breakthrough in aviation. Never before has a conventional, manned helicopter performed a vertical takeoff, cruise and landing solely on battery power, and we are thrilled to have achieved 400-ft [122-m] altitude and 80 kt [148 km/h] during our first full test flight.” The YouTube video of the record flight includes the instrument readings for current, torque and airspeed superimposed over the view out the helicopter cockpit.
Ric Webb of OC Helicopters was the test pilot for all the flights under a special airworthiness certificate in the experimental category issued by the FAA’s Los Angeles Manufacturing Inspection District Office (MIDO). Robinson Helicopters had no advanced knowledge of the project when the e-R44 first flew, and has played no direct role in the project, to date. At the time, the range of the eR44 was estimated to be 20 minutes or approximately 30 nm (55 km), but the team expected this would improve by using higher-energy-density batteries, a more efficient electrical drivetrain, and a more aerodynamic airframe.
The first all-electric flight of the world’s top-selling helicopter didn’t generate a lot of publicity or enthusiasm when it first occurred. But a month later, popular interest in electric aircraft started to change after ride-sharing company Uber released its audacious, tech-savvy Elevate white paper, “Fast-Forwarding to a Future of On-Demand Urban Air Transportation,” promoted by a well-orchestrated social media campaign.
On Feb. 16, 2017, Tier 1 Engineering raised the bar when it set out to establish a series of world records for “duration, altitude, payload, weight and speed of battery-powered rotorcraft or helicopter flight.”
The flight lasted 30 minutes, reached 800 ft (244 m) and at peak speed of 80 kt (148 km/hr) with an 8% battery state-of-charge remaining after a safe hover landing. Tier 1 stated the average power drawn in cruise was 105 kW, but 140 kW during hover in ground effect (HIGE) and 160 kW in hover out of ground effect (HOGE). The temperatures were normal throughout the propulsion system, which incorporated an experimental cooling system. “There has never been a full-sized… person-carrying helicopter powered solely by batteries that has flown this long, or this fast or this high. [And] there has never been a battery-powered helicopter weighing nearly 2,500 pounds,” wrote Rothblatt in the commentary posted with the Vimeo video, which highlighted that the e-R44 had been conceived, built and successfully demonstrated in under one year for under $1M by a team of 10 people.
To claim the world’s first two-pilot electric helicopter flight, the battery capacity was reduced by 18% to allow Rothblatt to fly with Webb.
However, official international recognition had to wait until Dec. 7, 2018, when Webb made another flight to set a Guinness World Record for the farthest distance traveled by an electric helicopter. The flight covered 30.7 nm (56.87 km) at an average speed of 80 kt (148 km/h) over a circular course entirely within the confides of the Los Alamitos military base, which was witnessed by an official adjudicator.
In parallel, the Tier 1 Engineering team worked on a conceptional design of an electric tiltwing aircraft design optimized to provide the best payload, speed and range for time-sensitive organ delivery missions. After 18 months of work on the tiltwing concept, Dromgoole realized that the challenges developing a clean-sheet eVTOL aircraft “would scale up in complexity and difficulty” with an electric propulsion system because of the lack of a clear certification path.
“The design effort was paused so we could address the challenges of certifying an electric propulsion system,” Dromgoole added.
“We were quite surprised what we could even accomplish with off-the-shelf technology, since none of the hardware was optimized. That gave us the confidence to move forward with a supplemental type certification (STC) effort for the Robinson R44,” said Dromgoole. Rothblatt agreed to help support the program, with Lung Biotechnology signing up to buy an unspecified number of e-R44s once the FAA granted Tier 1 Engineering an STC for the retrofit kit.
At the July 2021 VFS-sponsored virtual Electric Aircraft Symposium, Dromgroole outlined why the STC program makes a lot of sense from a business, certification and safety perspective. “The R44 has great utility and it’s the most produced [modern] general aviation aircraft in the world (since 1999). There’s over 7,000 of them built that are readily available… and there is infrastructure for servicing the aircraft in place… worldwide.”
Thus, Robinson has already proven that there is a huge worldwide market for a helicopter in this size and seat class.
“Minimal pilot training will be required to change from regular piston R44 to electric propulsion. And at 2,200 hours, the airframe and Lycoming engine requires an overhaul, which provides a good opportunity for operators to do the engine conversion,” he said.
“Another benefit of doing a conversion — as opposed to a brand-new clean-sheet design — is that you don’t need to type certify the airframe. With a supplemental type certificate, you’re just dealing with a modification of the aircraft alone. So, we don’t need to certify the airframe to today’s rules, which are always tougher than yesterday’s rules,” Dromgoole explained.
“That allows us to focus on the novel technology, which is electrical propulsion. The airframe for the R44 has a very low weight fraction. So, it’s very efficient, structurally. That’s very important for electric flight because as we know the batteries are not anywhere close to the energy density of fuel, so any efficiencies we can get structurally or in the propulsive propulsion systems help us in terms of range of the aircraft.
“And, the R44 has very low disk loading. So, that gives us good propulsive efficiency and relatively low noise,” he emphasized.
Second Generation e-R44
In 2017, work began on a second-generation e-R44 prototype (see “Tier 1 Engineering Reveals its Second Battery-Electric Robinson R44 Helicopter,” Vertiflite, Sept/Oct 2021). This time, Tier 1 Engineering’s goal was to move away from individual suppliers and developed plans to produce three critical components — the motor, motor controller and battery system — in-house to meet the required airworthiness requirements. “We feel that the market is so small and it’s so specialized that the only way to really develop a highly optimized system is to do it through vertical integration,” said Dromgoole during an interview with VFS at HAI Heli-Expo in January 2020 where the second-generation e-R44 was officially unveiled (see the VFS Video Library at www.vtol.org/videos).
The first priority was optimizing the design of the battery pack, which reduced the weight from 1,100 lb (500 kg) to 800 lb (365 kg) by early 2020. The weight reduction was achieved by using higher energy density cells, improving pack design and designing a new lightweight and streamlined structure to support the cells. Development of the lighter battery pack now meant the e-R44 could fly with a pilot, co-pilot and organ transfer system.
However, the COVID-19 pandemic slowed down work on the aircraft when Tier 1 employees had to work remotely, and the delivery of parts was hit when the supply chain slowed down.
In addition, the new electric motor and inverter being developed for the e-R44 did not perform as expected during ground tests. Consequently, Tier 1 installed the YASA motor and Rinehart Motion Systems inverters in “bird two” so flight testing could continue while a new aviation-certifiable motor was sourced. The inverter converts DC battery power to AC power for the three-phase electric motor.
Since the YASA motor rotated at 5,600 RPM (twice the speed of the original Lycoming engine), a 2:1 reduction gearbox was used to reduce the speed to the 2,700 RPM required by the helicopter drivetrain, which retained the four double-vee drive-belts used to transfer engine power to the rotor system. The second iteration of the e-R44 included four independent onboard liquid cooling systems in the engine bay for the motors (packaged as a single unit), the inverters, reduction gearbox and battery pack.
“It’s difficult to combine the cooling systems because each component has a different operating temperature requiring different flow rates. In the case of the motor, it has to be cooled with non-electrically conductive [dielectric] fluid, whereas for the motor controllers, we use ethylene glycol, which has high conductivity. There are too many trade-offs if you’re trying to optimize with one cooling system,” said Dromgoole.
In the cockpit, the twist grip throttle on the collective was removed and rotor RPM is now fully controlled by the electric motor controller. “There is no need for pilot input into the throttle,” he said.
The toggle switch on the end of the right seat collective used to switch the RPM governor on and off is now used to select 100% RPM for normal operations, or 90% RPM to allow autorotation training. That allows the pilot during a practice autorotation to adjust the rotor speed using the cyclic and collective, and “if the rotor RPM was to drop to 90% or less, the motor will automatically pick up and apply torque, which is an added safety feature,” noted Dromgoole.
Webb flew the second-generation e-R44 (N484AK) for the first time at Los Alamitos on July 26, 2021, with the new, 800-lb (363-kg) battery pack providing the same power and endurance as the 1,100-lb (500-kg) battery pack on the original e-R44.
Since the first flight, the cockpit instrumentation has also been refined and a new United Therapeutics interior installed in the rear cabin with tie downs for an organ handling system in place of the rear seats.
After the 9th Annual Electric VTOL Symposium in San Jose, California, attendees had an opportunity to see the e-R44 on display at San Carlos Airport, California, on Jan. 28 when VFS held one of the world’s first static displays of eVTOL aircraft at the Hiller Aviation Museum.
The e-R44 program gained fresh momentum in December 2021 when Tier 1 Engineering selected the magniX magni350 electric motor for its e-R44 design targeted for STC certification (see “Tier 1 Teams with magniX for New e-R44,” Vertiflite, Jan/Feb 2022).
This is the first time the Redmond, Washington-based electric motor company was selected to provide an electric motor for a VTOL aircraft, with all of its previous applications for conventional takeoff and landing (CTOL) aircraft, including a Harbour Air DHC-2 Beaver eSeaplane that flew in 2019, an AeroTEC Cessna 208B Grand Caravan that flew in 2020 and the twin engine Eviation Alice (developed by magniX’s sister company) that’s expected to fly this summer. magniX has now expanded its partnerships and gained funding from NASA (see “Electric CTOL/STOL News,” Vertiflite, Jul/Aug 2022).
“magniX was chosen as they are leading the industry in the development of aviation-specific electric propulsion, and we recognized that significant progress had been made towards obtaining FAA certification. With magniX’s technology, we are now much closer to obtaining STC approval of the e-R44 and transforming the delivery of life-saving human organs,” said Dromgoole when the deal was announced.
In November 2020, the FAA issued its proposed special conditions for the Part 33 certification of the magniX magni250 and magni500 engine models. After a year of public consultations, the special conditions went into effect on Oct. 27, 2021, now updated for the current designations, the magni350 and magni650 models.
Third Generation e-R44
Tier 1 Engineering took delivery of a prototype magni250 on Dec. 6 to integrate into its third-generation e-R44, which will be the basis for its FAA STC application. The airframe of the proof-of-concept e-R44 aircraft, N3115T, is being reused as a platform for the new electric motor.
The initial ground runs of the third-generation e-R44 began behind the Tier 1 offices in Santa Ana on March 31 with Webb and Rothblatt performing system checks to validate the cooling system and engine controls of the magni250 electric engine.
The FAA granted an experimental airworthiness certificate for “bird three” in March. The first flight at Los Alamitos on June 4 lasted three minutes, with Webb and Rothblatt once again at the controls.
Dromgoole said Tier 1 conducted more than 50 ground tests before the e-R44 was ready to make its first hover. The tests included low and high-power runs with the aircraft anchored firmly to the ground. Some of the tests simulated various engine fault scenarios and the pilot response.
The magniX motor is designed with an electric integrated liquid cooling system allowing full performance, regardless of the environmental conditions. The magni250 engine has two independent three-phase motor segments for redundancy, increased reliability and “graceful” degradation should a fault occur.
Last year, Tier 1 conducted extensive flight tests using its piston-powered R44 Raven II to determine how much emergency power one electric motor segment would have to produce for the e-R44 to keep flying if one motor segment or inverter failed, which is one of the company’s design goals.
The tests were conducted with the R44 at a maximum gross weight of 2,500 lb (1,135 kg) at a 4,000-ft (1,200-m) density altitude. Each segment of the magni350 motor will be able to produce 65% of takeoff power to allow the aircraft to continue flight after one segment fails.
The FAA said that because applicable airworthiness regulations for motors don’t contain adequate or appropriate safety standards for “an electric motor, controller, and high-voltage systems as the primary source of propulsion for an aircraft,” the special conditions were required that contain the additional safety standards that the FAA considers necessary to establish a level of safety equivalent to existing airworthiness standards.
The prototype magni250 and production magni350 are about twice the diameter of the original YASA motor but produce more torque and are designed to match the output RPM of the R44’s original Lycoming engine.
This has allowed Tier 1 to simplify the rotor drive system on the third-generation e-R44 by replacing the engine reduction gearbox (required for the 5,600 RPM YASA motor) as well as the R44’s original vee-belt drive and automatic tensioner with a synchronous belt drive. The changes will simplify pilot workload and result in additional weight savings.
The internal configuration of the magni250 and magni350 are very similar, but the external interfaces differ. Tier 1 expects to take delivery of a production magni350 engine at the end of the year for what will be Tier 1’s fourth generation e-R44.
No changes are being made, however, to the freewheeling unit on the R44 called a sprag clutch, which allows the main rotor to continue turning, even if the engine is not running, to facilitate an autorotation.
One of the benefits of time is that battery technology has improved over the six years of developing the e-R44. Dromgoole observed that energy density of cells has improved while the internal resistance (which creates heat in a battery pack) has been reduced. “In the second-generation e-R44, we have a cooling system for the battery that is used in flight. For the new aircraft, we expect to move away from liquid cooling in flight, and only require a cooling system for the battery when we are charging on the ground.”
The new battery installation is also designed to facilitate quick battery swaps between flights. The battery pack is attached at four points to the underside of the helicopter and the production pack will be designed so it can be replaced in just a few minutes, helping to ensure the aircraft can work all day.
A liquid cooling system will be retained for the motors and the motor controllers in flight.
The flight controls and instrumentation will be similar to those found on the second-generation e-R44, with the instrument panel featuring three basic instruments required by the helicopter — air speed, vertical speed and altimeter — and new digital screens for engine management. This includes a tachometer for the electric motor and rotor, the battery state-of-charge (“which is your fuel indicator”) and voltage, which serves as a backup to the state-of-charge indicator. There will also be digital temperature indicators for the battery pack, motor, motor controller, but the indicator for the reduction gearbox for the YASA motor will no longer be required.
Dromgoole said that one of the challenges of designing an aircraft with electric propulsion is that you need to fully understand the safety considerations contained within the certification requirements, even if you are only pursuing an STC.
“In our application we have two guiding standards. One is [FAR] Part 33, which covers the engine itself. And the other is Part 27 that covers the rotorcraft itself, or the installation of the engine. The applicability of those two regulations really depends on the architecture of the aircraft,” he said. “The current understanding with the FAA is that for electric engines installed in federated systems architectures — that is an architecture where the engine is clearly separated from the rest of the aircraft systems — may require two type certificates. One would be for the engine and the other would be for the STC to install it [in the airframe].”
According to the FAA, “a supplemental type certificate (STC) is a type certificate (TC) issued when an applicant has received FAA approval to modify an aeronautical product from its original design. The STC, which incorporates by reference the related TC, approves not only the modification but also how that modification affects the original design.”
In addition, each applicant for a supplemental type certificate must show that the altered product meets applicable requirements specified in 14 CFR 21.101 for the original aircraft.
Dromgoole said another of the challenges, even for an STC retrofit, is that the Part 23 certification requirements for light aircraft and Part 27 rules for rotorcraft only partially address electric propulsion.
That’s where three industry committees have been very active interpreting airworthiness standards and develop consensus standards specifically for electric propulsion systems. This includes the General Aviation Manufacturers Association (GAMA) committees, the ASTM International standards groups and the SAE International committees (e.g., E-40 Electrified Propulsion Committee).
He said that the two consensus standards that are very useful for designers of electric propulsion aircraft are ASTM F3338-20, which covers the electric propulsion unit (EPU) for general aviation aircraft, and ASTM F3235-17, which covers battery systems.
Tier 1 Engineering has been an active participant in the consensus committees, but Dromgoole observes that some leading eVTOL developers have played a more passive role.
In parallel with developing the best possible STC kit design, Dromgoole said a lot of Tier 1 Engineering’s time has been spent understanding what is known as the “means of compliance” with the new rules to validate the systems.
Three such issues were outlined by Dromgoole at the VFS Electric Aircraft Symposium in 2021, including how to ensure continued safe flight and landing after a single electrical fault (such as from motor failures, power electronics failures, contactor failures and motor controller failures), how to contain thermal runaway within energy storage systems, and safety initiatives to decrease the likelihood of a post-crash fire (since current rules only address fuel systems).
All electric aircraft developers are going to have to address these same issues in their certification plans and documentation.
e-R44 Operating Costs
Today, Robinson estimates that the total operating cost of a R44 Raven I is $244.36 per hour based on 500 hours a year, including $22.20 in fixed costs (e.g., insurance), $97.78 in overhaul reserves, and $124.36 in direct costs.
Robinson estimates a reserve for the piston engine overhaul is $19.55 per hour (based on $43,000 with an engine exchange) or 20% of the total overhaul reserve. And the cost of fuel and oil is $92.46 per hour (at $6.09 per gallon of avgas) — 74% of the direct operating cost per flight hour.
Dromgoole estimates that the e-R44 will have 20% lower operating costs than the piston-powered R44 as a result of maintenance savings and lower energy costs, which will be quite revolutionary in an industry that has seen continually rising operating costs. However, the exact cost saving will only be known once the cost and replacement life of the battery cells is known.
Of course, these costs assume that aviation gasoline (avgas) will be available at a nearby airport to fuel the helicopter. The FAA says that “avgas remains the only transportation fuel in the United States to contain lead.” However, community initiatives that came to the forefront this year aim to eliminate the local use of 100-octane low-lead fuel (100LL), which contains tetraethyl-lead (TEL), an additive to prevent engine damage at higher power settings.
These efforts to reduce or restrict the availability of 100LL at airports, could change the historic operating cost assumptions for the piston R44, to the e-R44’s benefit. One way to obviate the need for lead-polluting engines would be to replace them with drop-in replacement electric motors.
In addition to eliminating the production of carbon dioxide and lead into the atmosphere, the e-R44 generates less noise without the combustion engine, another community irritant. There is also a very noticeable reduction in engine vibration when the aircraft is idling on the ground and flying, which Dromgoole believes will reduce component fatigue, which could result in an extension of time between overhauls (TBO) and further cost savings at a later date.
All R44 helicopters require a factory overhaul every 2,200 flight hours or 12 years. Robinson designed the aircraft so that the dynamic components and the engine come due at the same time. The base price for this overhaul (effective January 2020) for a R44 Raven I was $230,000 and $247,000 for a R44 Raven II, plus upgrades.
During the process, the engine is inspected by Robinson or Lycoming, and six major components on the drivetrain are exchanged — the main and tailrotor gearbox, swashplate, clutch, actuator and fanwheel. In addition, more than 20 different new parts are installed (e.g., the main rotor hub, spindle and blades; tailrotor assembly, driveshaft and pitch controls; windshields, skid shoes, bellcrank, upper frame, etc.) and required upgrades (e.g., hydraulic flight controls, pop-out float overhaul, fuel bladder tanks, etc.) and optional equipment (e.g., air conditioning or avionics) installed.
At the Robinson Helicopter Corp. factory in Torrance, California, there is a separate line for customer aircraft that have been sent back to the factory. Owners can also have their aircraft overhauled at an authorized service center.
e-R44 Conversion Line
Dromgoole believes that the best economic time for Tier 1 Engineering to retrofit an R44 is when an R44 aircraft is due for its 2,200-hour maintenance and inspection.
The company plans to start doing the e-R44 conversions inhouse at its workshop in Santa Ana for United Therapeutics and other customers, such as Webb’s OC Helicopters-subsidiary Eco Helicopters, which has bought a limited number of early aircraft as well (see “Electric VTOL News: Eco Helicopters Coming to LA,” Vertiflite, Nov/Dec 2020).
Besides organ delivery, Dromgoole sees lots of market opportunities for the e-R44 in flight training, sight-seeing and charter flights of about one-hour duration or less.
He also believes that the e-R44 will be an attractive helicopter option in “off grid” locations where the cost of delivering fuel is prohibitive or restricted by legislation. For example, no aviation fuel is allowed at the airport on Catalina Island off the coast of California because of local environmental legislation. Dromgoole believes this would be an ideal location to recharge an e-R44 using solar or wind power.
Dromgoole said the company may eventually offer a conversion kit that customers could install at an authorized service center rather that in Santa Ana, but that’s some years away. Tier 1 Engineering hasn’t released a price for the conversion kit or the expected operating costs of the e-R44, since both are highly dependent on the cost and life of the batteries that will be used once the STC is approved by the FAA and other regulatory agencies.
Down the road, Tier 1 Engineering hopes that Robinson will consider offering the STC electric propulsion kit as an option for installation on new R44s coming off the production line. Robinson is now following the e-R44 program closely, but the company is reserving judgement until a FAA STC is granted and the first e-R44s have entered the field.
About the Author
Ken Swartz is a senior aerospace marketing communications strategist, running Aeromedia Communications in Toronto, Canada. He specializes in aerospace market analysis and corporate communications. He’s worked in the regional airline, commercial helicopter and commercial aircraft manufacturing industries for 30+ years and has reported on vertical flight since 1978. In 2010, he received the Helicopter Association International’s “Communicator of the Year” award.
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