Printed headline:Electric Propulsion Primer
While it may be as much as a decade or more away, some type of commercial aircraft powered by electric propulsion may become as common as electric automobiles are today.
Should that happen, as industry experts predict, it would profoundly change the engine MRO industry’s traditional business model, after generations of maintaining fossil-fuel-powered reciprocating and turbine designs. To appreciate that, it is helpful to understand where electric propulsion development is today and where it is likely to go.
According to a survey published by Roland Berger, a global aviation consultancy, as of October 2018, there were 134 aviation-related electric propulsion projects in progress, primarily in North America and Europe. Of those projects, 70% were focused on pure electric engines, using motors that draw power from batteries recharged at ground-based charging stations.
In fact, all-electric propulsion is already in use, with one example being the Pipistrel Alpha Electro, a two-seat, single-engine trainer built by Pipistrel Vertical Solutions in Slovenia. The model is certified as a light sport aircraft (LSA) in France, Norway, Switzerland and Australia. In the U.S., it holds an FAA special airworthiness certificate, but Pipistrel is working with the FAA to certify it as an LSA so that it can be used as a for-hire trainer. To do so would mean changing current regulations, however, which require reciprocating power for certification.
The other 30% of the projects in the Roland Berger survey focus on hybrid-electric technology, which uses a combination of battery, generator and turbine engine powered by jet fuel.
Within the hybrid-electric group, there are two basic types. One, referred to as a “parallel” hybrid, incorporates a mechanical connection between engine and propeller, allowing the operator to run the engine drawing power either from the battery exclusively or via the turbine engine, says Nikhil Sachdeva, a senior consultant in Roland Berger’s London office. The operator may switch between them as needed. The other, known as the “series” hybrid, has no mechanical connection between engine and propeller, with the turbine charging the battery, which provides the energy for propulsion. Research is being done to identify the most efficient hybrid architectures, potentially incorporating the features of both parallel and series types, he says.
“Conventional engine architecture is extremely complex and expensive,” Sachdeva points out. “If the purpose of the turbine in the future will be limited to generating electricity, the engine will be less complex, smaller and less expensive, and less likely to have to deal with off-design factors such as exposure to temperature extremes, lightning or bird strikes,” he says. “This means that the MRO aftermarket will logically decline.”
Sachdeva reports that, based on Roland Berger’s surveys of aerospace industry executives, the first hybrid-electric airliner will likely enter service by about 2032, specifically as a 50-seat, revenue-generating aircraft that would typically fly stage lengths in the 340-km (211-mi.) range. “That is roughly the distance between London and Paris,” he notes.
Unlike hybrid-electric propulsion technology, which favors larger aircraft, all-electric engines will most likely be applied to smaller aircraft in the 2-4-seat category such as urban air taxis and trainers, Sachdeva notes. “However, we could see some application to the sub-regional segment—aircraft with 19 seats or less,” he says.
Given that electric propulsion technology is still largely in its infancy, the extent to which it will upend or disrupt the engine aftermarket service sector is largely unknown. “It is almost impossible to provide a clear answer to this question today, especially if we look at the complete aircraft and not only the propulsion system,” says Rolf Henke, a professor and member of the Board for Aeronautics and Technology of the German Aerospace Center, commonly known as the DLR, in Cologne.
An electric motor, he explains, will probably require “less service effort” than a gas turbine or piston engine in terms of numbers of parts and materials. “The propulsion itself will not change too much since thrust will come from a fan, which does not care whether it is driven by an electric motor or a gas turbine,” Henke explains, adding that while batteries and cables may need slightly fewer repairs than the tanks and pipes on conventional fuel-burning engines, they may need to be exchanged more often.
Henke also stresses that the final design of an electric or hybrid-electric propulsion system certified for transporting passengers over a long distance does not exist today; nor is it known what skillsets or qualifications will be needed to service the engines.
“Taking an MRO company‘s view, a hybrid system will be more complicated and, therefore, need more qualification plus increased maintenance effort,” he says. “However, our current MRO companies are somewhat prepared, since one of the most complex parts of a hybrid-electric propulsion system will still be a gas turbine, which they already know. Batteries will simply be exchanged, and not repaired,” says Henke.
Upon entry into service, and at least for the short term thereafter, he says, electric propulsion systems—both pure electric and hybrid-electric—will generate considerable repair activity due to the new technologies involved. “That applies to, and will be driven by, the complete system, including its integration into the aircraft,” he stresses. “Any such new technology most probably will result in more repairs at the beginning, before benefits may pay off in terms of service effort. This may include the number of service intervals given by authorities, who will have to take a very close look at the new technologies. Later on, this may be relaxed after experience has been gained,” Henke explains.
Not surprisingly, how engine aftermarket service will change once electric aircraft enter the fleet is a matter of debate. For MROs that will be supporting electric propulsion, the changes will mostly involve digital solutions, according to Amanda King, senior director of breakthrough technologies for Honeywell Aerospace. The OEM, reports King, is engaged in research and development to support a suite of electric propulsion solutions for aircraft ranging in size from a small urban air taxi to a larger fixed-wing regional airliner.
“More software will be imbedded in these engines, which means that for MROs there will be more software-enabled repairs, such as updates,” King says.
In that regard, King explains, with better-connected systems, the MRO models will be more service-based, rather than event-spaced.
“I predict that maintenance in the electric- and hybrid- propulsion aircraft will be based on connected software with health monitoring, which will likely be a ‘service’ for an operator. When the state of health is indicated as at or below a certain threshold, the health-monitoring service will tell the operator to get maintenance. That is different than how most parts work today, where maintenance is based on a time-schedule of either flight hours, months, etc., and the maintenance is performed whether it is required or not,” says King.
She points out that this should save operators time and money “by preventing failures that may otherwise occur between regular maintenance checks in the traditional model. For the evolving [vertical-takeoff-and-landing] market, up time will be increasingly critical to the success of these operators.”
For MROs, a whole new approach to training will be required to service electric propulsion systems, King stresses. “As they evolve, a training system will have to be developed in parallel,” she says. “To do that, the OEMs will have to have an extensive amount of input from the MROs at the design phase to minimize repair complexity. Unfortunately, we haven’t seen much involvement of the MROs at the electric engine development stage. That is something that will have to change.”
King also raises another interesting point that could be a disruptive influence on engine MROs. “Today’s aircraft are powered by engines that will be in service 20-30 years. But with the emerging electrically powered air taxi model, there will be more expendability and greater rates of replacement—without compromising safety—as new versions of the engines come about—much as people replace smartphones or other electronics today,” she says. “I think this is something the MROs will need to take into account.”
An Epic Shift Is Coming
Fergal Whelan-Porter, CEO of Aeolus Engine Services, a Dublin-based specialist in turbine engine light maintenance, condition monitoring and trouble-shooting, predicts that electric propulsion will “drive an epic shift” in the way engine MRO providers do business. “It will be a destructive force with respect to the traditional aircraft engine service model, since it will involve new technologies, new materials and new facilities,” he says.
On the positive side, Whelan-Porter points out that the capital investment required to establish facilities that service electric-propulsion engines should be considerably less than for conventional engines. To illustrate, he says, servicing electric-propulsion engines will be less labor-intensive and will not require heavy equipment, such as the space-consuming, immoveable grinding machines needed to repair today’s turbine engines. In addition, electric engines will employ fewer components so fewer spare parts will be needed, and repair procedures will differ.
“It will be a lot more cost-effective to set up the facilities to service electric engines, based on these factors,” Whelan-Porter says.
He also agrees that servicing electric propulsion systems will be more dependent on software solutions, which means more maintenance will be done by the operator and less by MRO facilities. “There will be a transition from today’s heavy maintenance to more line service, since data can be downloaded anywhere,” Whelan-Porter predicts. “There will also be fewer manual labor procedures that need to be carried out, and consequently, new skills will be needed for the new technologies. Effectively, one MRO market will be replaced by another.”
“Additional support hardware and software tooling will be needed for the new propulsion system, and this will be developed in support of the safety case as the project progresses,” says Paul Hutton, CEO of Cranfield Aerospace Solutions, with reference to a project to apply electric-propulsion retrofits to the piston and turbine versions of the Britten-Norman Islander at the demonstration level by 2021. The high voltages involved in the new propulsion system will require skills development for the MRO organization to ensure worker safety. “As well as airlines, we are in discussion with an airports operator to ensure that the support infrastructure for both operation and maintenance is identified and planned for upon entry into commercial service in 2023,” says Hutton.
Also anticipating major changes in the MRO market generated by electric propulsion is Roei Ganzarski, CEO of MagniX, the Redmond, Washington-based company that is actively pursuing pure electric power for the commercial and military markets. Ganzarski reports that by 2020, MagniX expects to certify its Magni250 and Magni500 engines, rated at 375 and 750 hp, respectively.
“We are working with OEMs that are designing new electric aircraft, but there is also a potential market for conversion kits to enable owners of existing aircraft to convert their aircraft to all-electric from traditional powerplants,” he explains.
The initial target for the conversion kit, says Ganzarski, is the Cessna Caravan, a single-turboprop-powered utility aircraft, which is a mainstay of the short-haul commercial cargo market. It will use the Magni500 to replace its Pratt & Whitney Canada PT6. A first flight is slated in 2019, with certification by 2022. “The Caravan’s typical day-to-day operation is 100 mi. or less, making it an ideal testbed for the electric motor we are developing, which we anticipate would have a range of 100-200 mi.,” he notes.
In Ganzarski’s view, electric propulsion will create a hugely disruptive impact on the aftermarket engine services industry. One example he cites goes to the heart of today’s engine OEM customer support.
“Turbine- or piston-engine OEMs will normally sell their engines for very low prices, with the intention of making up their costs through their maintenance plans. But, for an electric engine, that model will disappear, because with significantly fewer moving parts—which account for the majority of maintenance—the whole notion of A, B or C checks goes away.”