It’s called “power density,” and it defines the boundary between the present and our long-awaited electric aircraft future.

The burden is on the aviation industry to innovate rapidly. In July 2023, the UN organization ICAO Environment issued its “Electric Innovations for Sustainable Aviation.”[1] The document proposes significant progress in long-term (post-2040) reduction of air pollution, noise, maintenance costs and factors affecting climate change. However, among the challenges, it notes that “applicability [is] very limited by power density.” This limitation especially prevents larger aircraft from taking advantage of electrical power.

In other words, how do you get the maximum energy from the least weight? This problem has perennially vexed aircraft designers, regardless of the platform’s mission. As David McCullogh notes in his biography of the Wright Brothers, “It was shortly before the New Year (1903) when the Wright brothers sent out letters to manufacturers of automobile engines in seven states asking if they could supply an off-the-shelf engine light enough in weight but with sufficient power for their purposes.”[2] They got no takers, an indication of the propulsion vs. weight challenges that would trail manufacturers and operators.

Robert C. Haywood, the global product director focused on aerospace electrification with W. L. Gore & Associates, corroborates this fact: “Whether it's civil or DOD, it's really the same physics, and it's the same technical challenges. It really comes back to power density at the end of the day. How do you get more electrified power on board without adding significant weight, size or space? Obviously, all optimized with cost as well. Power density is a key challenge.”

Gore is a materials science company with technology that enables greater operating temperature and/or voltage in capacitors, wire & cable and motor windings, which can be key design knobs to improve overall power density. What ratio of wattage to kilograms can safely transport an economically viable number of passengers a desired distance? The practical experimentation thus far has been only a small step for the aviation community to achieve the projected zero emissions.

For example, the Elysian E9X, proposed to fly in 2033, features a battery pack with an energy density of 360 Wh (watt-hour) per kilogram. Thus powered, it could transport 90 passengers over distances up to 800 kilometers or about 500 miles, e.g., New York City to Detroit. Some airframe manufacturers naturally have their sights set on an eventual carbon neutrality for their entire longer-range fleets. This task will demand technological innovations in such areas as hybridization, fuel cells and electric motors.

Thus, current advancements are being separated by the degree of electrification into categories that do necessarily electrify propulsive systems. For instance, the so-called More Electric Aircraft or MEA focuses on the aircraft’s hydraulic and pneumatic systems, which also contribute negatively to the environment.

Per Haywood: “The More Electric Aircraft is getting at the flight systems themselves, including braking systems, flight controls, ailerons, rudders, where you're getting rid of these heavy mechanical, pneumatic or hydraulic systems, which also have their own maintenance challenges. Weight is a primary driver. If you can get more electric power on board by generating it from the jet propulsion system, then distributing that electric power to drive these systems, you get that weight out of the overall aircraft.”

MEA calls for replacing the current hydraulic and pneumatic systems with more electrical components. These innovations will help reduce fuel consumption and emissions on the environment and decrease maintenance for higher operating profitability.

The emerging MEA generation of aircraft will have even more advantages over current conventional airliners. The greater efficiency will free up operators to make decisions about routes and balance sheets. The reduced weight can translate into more passengers (or in defense aircraft a heavier payload). The fewer mechanical components will mean fewer that can fail. Overall, operators and their stakeholders can benefit from improved aircraft performance.

Perhaps most importantly, MEA will provide that critical intermediary stage between fossil fuels and the all-electric aircraft, geared to moving an increasing number of air travelers with optimal respect for the environment.