Printed headline: Electric Propulsion
As the automotive industry is finding out, the move to electric propulsion is reshaping not only the supply chain, but also the aftermarket. Electric vehicles require less, and different, maintenance, and the long-term impact on the repair sector is expected to be existential.
It is still too early to predict the extent to which electric propulsion will change aviation and the MRO industry. It looks most likely to reshape the light-aircraft sector, and the promise of lower energy costs, emissions and noise could create new markets in urban air mobility and short-haul regional transport.
But whether electric drivetrains will come to large commercial aircraft, and to what extent, is harder to foresee. Electrification of aircraft systems is already underway, led by the more electric Boeing 787, and all the major engine OEMs see some long-term place for electric technology in propulsion.
Some impact on the aviation MRO market from propulsion electrification can be expected, although it is unlikely to be as dramatic as that projected for the automotive ecosystem. A 2016 report by McKinsey & Co. projected 20-30% lower maintenance spending on automotive electric drivetrains by 2030.
A 2017 research note by JP Morgan Cazenove estimated running costs for electric vehicles could be just 10% of those using internal combustion and predicted meaningful risks for car dealers relying on after-sales service for profitability.
Although not as dramatic, savings are expected from the electrification of aviation, for fundamental reasons. With their electric machines, energy storage, power electronics and distribution systems, electric drivetrains are more complex than turbines, but they have far fewer moving parts to wear out.
Wear and tear is the lifeblood of aviation MRO, requiring a steady cycle of inspection, repair and replacement. Electric generators and motors are mechanically simple, with less complex cooling and lubrication systems, and their lower vibration levels put less stress on other aircraft components.
But although they generally require less servicing than combustion or turbine engines, electric machines are not maintenance-free, says a study of maintenance considerations for electric aircraft conducted by Georgia Tech and presented at the American Institute of Aeronautics and Astronautics’ Propulsion & Energy Forum in Cincinnati in July.
High-speed bearings inside the motor cores need monitoring and regular replacement. Windings can short out from contamination, abrasion, vibration or voltage surges. Thermal damage of insulation components is possible and permanent-magnet motors need to be inspected for magnet security. “Motor cores may not be entirely field-serviceable” and may have to be removed and shipped to a dedicated shop for overhaul, the report cautions.
As electrification is beginning with small aircraft because of the energy-density limitations of today’s batteries, the Georgia Tech study focused on general aviation and the emerging urban air-taxi market. But it may hold lessons longer term for commercial-aircraft MRO.
High-power batteries will have inspection and repair requirements that necessitate special training, the report says. Likely issues include connector damage on removable batteries and the potential for impact damage and subsequent risk of fire if a battery is dropped during removal or installation.
Batteries are heavy, and large packs that are integrated into the wing or fuselage to maximize energy capability will require special handling equipment if they have to be swapped out for recharging or replaced at the end of their lives. High-power battery packs are expected to need replacement several times over an aircraft’s life, particularly at the high utilization rates foreseen for urban air mobility.
Ground equipment for rapid, high-power recharging will come with its own maintenance needs, particularly as charging stations are also expected to provide liquid cooling to the batteries to prevent them from overheating during charging between flights.
One of the major attractions of electrification is its ability to enable new aircraft configurations in which propulsion is tightly integrated with the airframe. Instead of one or two engines, multiple fans or props can be distributed around the aircraft and positioned to improve aerodynamics and increase efficiency.
But unconventional configurations will bring unusual maintenance issues such as the accessibility of distributed propulsion components and the safety issues of working with high-voltage propulsion buses. Such systems are likely to be highly modular, reusing the same motors and controllers, but the study also notes the inventory challenges in keeping sufficient numbers of replacements in stock at all times.
The Georgia Tech researchers recommend that the emerging electric-aircraft industry involve mechanics and technicians early in the design process to obtain practical feedback about maintainability. They also encourage stakeholders in electric propulsion to establish consensus standards for the training and certification of mechanics.