Flying electric
June 2019
Aerospace innovators should look to history as they seek to carve a place in the market for electric aircraft amid enormous societal stakes. Today’s aircraft have significant carbon footprints; more passengers than ever want to travel by air; and the supply of fossil fuels in the world is finite. Amir S. Gohardani explains.
A New York Times reporter was about to witness something spectacular. Stooped over a table in a laboratory in Menlo Park, New Jersey, Thomas Alva Edison observed the makeshift filament of a lamp. Moments earlier, he had tested its vacuum and asked his assistant to seal it. As the dynamo bled power to the lamp, the reflection of light started shining in Edison’s blue eyes, according to the reporter’s account from 1879.
Many recognize Edison as the first inventor of incandescent light. Yet, Edison was not the first person to create it. In fact, he studied the work of many other prominent inventors and researchers to accomplish his unique breakthrough. Unlike previous electric lamp designs, Edison’s solution required less power and lasted longer. The current state of affairs with electric aircraft bears some resemblance to the development of incandescent light. If all-electric aviation for large numbers of passenger transport ever happens, it will not occur overnight. Small feats of invention will be needed along the way to achieve an optimal solution.
Rethinking transportation
As exciting as aerial electrification is, air travel is not the only contender for future transportation. Emerging trends of electrification are sweeping through the transportation sector with identified targets such as surface vehicles, trains and ships. But what could be the key underlying reason for such trends? A possible answer is the urgency for rethinking transportation due to its environmental impact and the chance that fossil fuels will run out.
According to the U.S. Bureau of Transportation Statistics, transportation became the largest source of carbon dioxide emissions in the United States in 2016 and continued to be the largest emitter of this greenhouse gas in 2017. The transportation sector relies on petroleum for 92.2% of its energy requirements and accounted for 70.6% of U.S. petroleum consumption in 2017, the highest level since 2009.
Overcoming these energy-supply and environmental hurdles is about to become even more challenging, given expectations of increasing demand for air travel. The FAA forecasts that the number of domestic passengers in the U.S. will grow by 1.8% each year through 2039. The solution won’t be as simple as introducing additional aircraft to meet the demand. Since the first powered, heavier-than-air machine achieved controlled, sustained flight, this sector has gradually reduced noise and emissions, while achieving new fuel efficiency levels. There is an opportunity for even more progress by developing electrified aerial platforms, a catch-all phrase covering everything from hybrid aircraft to today’s power-hungry Airbus 380s and Boeing 787s to all-electric aircraft.
Despite their potential advantages, however, electric aircraft also face hindrances. Critics of electric aviation commonly highlight its shortcomings and confinement to platforms solely suitable for a small number of airborne passengers or short aircraft range. Moreover, visions for all-electric aircraft capable of transporting a large number of air travelers are occasionally brushed off as dreamlike concepts unlikely to materialize. These criticisms are not simply rooted in blind pessimism. They often stem from genuine insights into the deficiencies of supporting technologies that will need to be addressed before electric aviation can expand. These are the smaller inventions akin to those that ultimately empowered Edison to impress the New York Times reporter with his incandescent lamp.
Usually, one of the distinct characteristics of electric aircraft is the employment of electric motors instead of internal combustion engines. All-electric concepts, which unlike hybrids aren’t aided by combustion engines, have in recent years demonstrated their benefits in terms of noise and hazardous-emission reductions mostly for unmanned applications and aircraft with small numbers of passengers. Currently, they also show limited promises for someday carrying a larger number of passengers. Now, designers are increasingly exploring a host of innovations under the all-electric banner, including solar cells, fuel cells, ultra-capacitors, better batteries and motors. A power-by-wire concept, for instance, provides many benefits, including moving aircraft flight surfaces electrically, minimizing or eliminating hydraulic systems with their flammable liquids and specific temperature and pressure requirements.
Nonetheless, due to the typical impractical weight per power unit of some all-electric architectures, a distinct conflict arises when the all-electric aircraft vision is applied to a larger airframe with increased gross weight. Still to be solved is the complexity of combining the hydraulic and pneumatic power systems with the electrical system, while maintaining safe flight. The air transportation industry has taken steps in that direction with what are known as MEAs, or More Electric Aircraft, the architectures of the Airbus 380 and Boeing 787 being prime examples. On the Airbus A380, the horizontal stabilizer backup and thrust reverser actuation function electrically. On the 787, electrical system features include environmental control systems and electro-hydraulic pumps for actuation.
Going forward, engineers will need to identify remedies to raise technical readiness levels and assess the optimized capabilities of safe electric aviation. A leaf out of the history books reveals that such efforts typically consist of various phases of technology life cycles. The trials ahead for electric aircraft do not translate only to inadequacies of battery technology or limited payload, range and endurance. In essence, they are not even exclusively technology driven. Environmental policies, legislative aspects and business incentives favoring more environmentally friendly transportation solutions are all important elements affecting future electric aviation.
Through a macroscopic lens, the transportation sector can either choose to ignore its impact on the environment entirely or to reinvent itself with more environmental friendly footprints. Based on current environmental challenges and global access to finite sources of fossil fuels, the second alternative is likely to gain momentum only if its value proposition is aligned with regulating governmental bodies or if it is embraced by the business sector due to distinct incentives.
It can be argued that current electrification endeavors are part of an S-curve of technological progress, a graph that shows the rate of progress over time. The progress starts slowly (the bottom edge of the standing S) in an embryonic, new invention period; the middle part marks rapid growth in the technology improvement period, and the upper part marks a mature technology period. This final phase exemplifies a period when the technology performance parameter reaches its physical limit. Based on the technical achievements of one technology, the S-curve of the same or an adjacent technical field can be juxtaposed next to it, and work on the electric aircraft can therefore begin at a higher embryonic or technical readiness level.
Electric aviation
During World War II, or more exactly, on Feb. 2, 1943, power engineer Lee Kilgore and his colleagues filed a patent application on behalf of Westinghouse Electric Corp. titled “Electrical Airplane Propulsion.” Kilgore and a number of fellow inventors highlighted weight obstacles associated with electric power transmission that left electric airplanes in the realm of impracticability. They unveiled their notable achievement of weight-reduction per horsepower. Decades after this patent application, the aerospace industry still struggles with weight aspects of electric aircraft. Now more than ever, energy storage onboard electrified platforms is of paramount importance.
In pace with the adoption of additional electrical components, such as electric motors, in support of electric aircraft architectures, an uptick in energy demand is also noted. This demand stems from operating additional electrical systems to minimize mechanical and pneumatic means to the extent possible.
Over time, increasing the size of electric generators has consequentially required increasing the size of engine nacelles and electric motors. Higher energy density storage advancements are unceasingly being investigated to enable better usage of electric power distribution. Distinctly, batteries still signify one of the technical challenges of electric aviation. Electric aircraft featuring battery technologies are specifically impacted as batteries remain as payloads and are not burnt away as jet fuel. Moreover, the energy density of existing batteries is not yet comparable to that of jet fuel. Despite the higher efficiency of electric motors — compared to fuel engines — all-electric concepts and demonstration aircraft continue to battle with their shortcomings in terms of aircraft range and transportation of large numbers of passengers. Yet, there is hope. The glimmer of hope rests with prominent researchers, educators, engineers and those who seek to address the shortcomings of electric aviation. Whether the issues are low energy-density storage, limitations with respect to electronic parts or excessive weight per power unit, and other topics, an abundant number of organizations seek solutions, including the U.S. Defense Department, FAA, NASA, and other educational, research and government institutions.
NASA has spearheaded a significant share of research into electric aircraft. The agency is investigating hybrid electric aircraft to gain further insight into the capabilities of such concepts. Following the success of NASA’s Environmentally Responsible Aviation project, the agency has revived its exploratory opportunities for aircraft fuel savings, noise reductions, and reductions in emissions of carbon and nitrogen pollutants, with specific considerations for on-demand mobility and safety. Even so, NASA is not the only entity seeking electrically enhanced propulsion systems or hybrid-electric solutions. As a matter of fact, for a portion of the industrial sector, the path to all-electric aircraft that can transport larger numbers of passengers starts with hybrid-electric architectures. This is particularly an intermediate solution as currently the technical readiness levels of supporting technologies limit all-electric aviation to short-range flight and a small number of passengers. Hybrid-electric aircraft architecture could bring some advantages. For example, hybrid gas-electric propulsion enables heavier payload, new mission capabilities including duration and durability, as well as noise, emission and operational cost reductions.
Future electric aviation and transportation
As different organizations investigate energy storage, component characteristics, propulsion-airframe integration aspects, energy conversion technologies and a myriad of supporting measures to enable electric aviation, the industry is carefully tracking the two key alternatives electrification technologies are likely to affect aerial transportation. Whether an evolutionary transformation aligned with further development of electric aircraft or a revolutionary transformation that advocates electric propulsion, the electrification process is not solely a function of technology. On the contrary, environmental, political, sustainable, legal and business incentives also bear weight in the evolutionary or revolutionary shifts of electrified aerial platforms, whether hybrid or all-electric. Societal solutions are best viewed from a holistic perspective. Therefore, more electric aircraft or all-electric aircraft should be viewed based on their overall impact on society. Moreover, enabling technologies should also be considered based on the environmental impact they have throughout their entire lifecycle. For example, if an enabling technology consistently results in excessive carbon dioxide emissions in its manufacturing process, the severity of its environmental footprint might overshadow a potential positive environmental impact it might have on an electric aircraft.
As the transportation sector explores new modes of transport, all options should remain on the table. Electric aviation might be a viable solution for future societies. Whether all-electric aircraft platforms for a larger number of passengers ever will be possible or hybrid-electric aircraft would be more suitable for a large number of passengers needs to be investigated. But the transportation sector should not treat one specific mode of transport as a threat to the others. Rather, different modes of transport should be considered as complementing each other for meeting U.S. passenger transport demands. For instance, if trains can assist passengers on shorter routes or assist the aviation sector to access airports, such synergistic effects should be considered. Finally, in a throwback to Edison’s incandescent light, the global aviation industry is likely to benefit from the equivalent likes of inventors Joseph Swan and Humphrey Davy, who made significant contributions to incandescent light. The Edisons of electric aviation could emerge from the incremental research contributions of independent entities repeatedly targeting the shortcomings of electric aircraft in anticipation of sustainable breakthroughs.
AMIR S. GOHARDANI
is an AIAA associate fellow and the chair of the institute’s Society and Aerospace Technology Integration and Outreach Committee. He is president of the nonprofit educational organization Springs of Dreams Corp.
