Preparing Your Airport for Electric Aircraft and Hydrogen Technologies (2022)

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10 What Are Electric Aircraft? 2.1 Electric Aircraft Concepts Around 100 electric aircraft designs are under development worldwide, each somewhat unique in their configurations and capabilities and reflecting the assumptions made by their designers and the different markets they target. These designs can be best understood by grouping them based on their configuration, capabilities, and missions (Figure 3). The ACRP Project 03-51 research effort focused on fixed-wing manned aircraft used for private and recreational flights, training purposes, air taxi services, small commuter flights, and regional aviation. It does not cover small UAS and eVTOL vehicles even though they are considered electric aircraft, per se. Although the current state of the technology does not yet meet their mission requirements, larger commercial service electric aircraft are also discussed. Long-endurance, unmanned, aerial electric vehicles primarily used by the Department of Defense, law enforcement, and federal and state agencies are not specifically addressed in this report. Their needs are mostly similar to those of manned aircraft with regard to the airport operational challenges and the electricity demand. The lower gravimetric energy density of batteries compared to jet fuel limits the capabilities of pure electric vehicles, and in particular, their range and passenger capacity. Larger aircraft may have to be equipped with hybrid-electric powertrains (either parallel or turboelectric) to increase range and passenger capacity. As a result, many of the electric aircraft that are under develop- ment are smaller and have lower capacity. These vehicles will fly shorter missions, whether urban, suburban, or regional air mobility. These emerging aviation markets operated with new generations of electric aircraft are also known as advanced air mobility (AAM). Urban air mobility (UAM) missions typically require a vertical takeoff and landing (VTOL) capability owing to the limited ground footprint available to design and build vertiports over valuable land close to city centers. These vehicles provide connectivity within a dense metropolitan area, and with other modes of transportation including existing airports. São Paulo, Brazil, is one of the few cities in the world with an effective UAM system, operated with conventional helicopters. Its downtown accommodates more than 400,000 operations per year. Use of eVTOLs might facilitate the implementation of UAM at many more large cities over the coming decades since they are significantly quieter, greener, and potentially cheaper to operate than conventional VTOLs (helicopters). Some short-haul inter-urban connections—suburban or community air mobility—might use constrained facilities with runways shorter than 5,000 feet (1500 meters) that cannot be expanded because of encroachment or other physical limitations. On-demand and scheduled flights could be performed by short takeoff and landing (STOL) capable aircraft. Most of these aircraft should have a slightly higher capacity and range than VTOLs. Billy Bishop Toronto City Airport in Canada and London City Airport in the United Kingdom are the C H A P T E R   2

What Are Electric Aircraft? 11   busiest urban STOLports in the world. As for UAM, electric aircraft can provide more socially acceptable operations than conventional aircraft and revive the interest for STOL facilities. Regional air mobility missions—at least, initially—are flown by horizontal (or “conventional”) takeoff and landing vehicles (CTOL), owing to the longer-range requirements and the resulting need for greater energy efficiency. On-demand and scheduled flights should be offered from smaller airports to other community airports or larger aviation facilities. The current operations of air carriers such as Cape Air in the northeast region and Harbour Air in the Puget Sound (Seattle-Vancouver area) have regional air mobility features. Cape Air operates from small facilities (e.g., Nantucket Memorial Airport) and large hub airports as in Boston Logan International Airport (BOS) and St. Louis Lambert International Airport (STL). This will depend on local geographical constraints, local regulatory constraints, and market demand. Consequently, a diverse subset of configurations has been explored by the industry, in addition to traditional fixed-wing aircraft designs. Figure 4 highlights a subset of designs that are capable of VTOLs. Each configuration has a different level of energy efficiency, which affects both the type of mission that it is optimized for and the nature of the infrastructure required to support operations. Figure 5 details the relative efficiency of various configurations of VTOL vehicles. For these configurations and for comparison, the maximum takeoff weight (MTOW) is set at 5,000 pounds, the cruise speed is set at 150 miles per hour (mph), and the mission length is set at 24 miles. An exhaustive review of each of the 170 aircraft designs is beyond the scope of this report. Instead, the various electric-vehicle designs are characterized according to their overall con- figuration and overall size, classified into eight primary categories. These include the fixed-wing aircraft category, which is further divided according to passenger capacity into the 1- to 4-seat, the 6- to 9-seat, and the 40- to 80-seat categories, as well as the helicopters, the tilt rotors, the tilt wing, and the lift plus cruise. Figure 3. Electric aircraft market segments.

12 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies Note: United Technologies Corporation (UTC) Project 804 Concept in terms of regional aviation. Figure 4. Examples of electric aircraft per mission. Figure 5. Energy efciency in vertical ight of various aircraft congurations.

What Are Electric Aircraft? 13   Figure 6 and Figure 7 show the evolution of the engine power and battery capacity for electric aircraft per their year of effective or expected first flight. Meanwhile, high-level characteristics are shown in Table 1, and the baseline aircraft retained for the study of six use-case scenarios that will be defined in the subsequent section are found in Table 2. 2.2 Electric Aircraft Energy Efficiency With the higher energy efficiency of electric powertrains (Figure 8) and the relatively stable energy cost of electricity against jet fuel (Figure 9), several aerospace industry groups have implemented sizable development programs to further advance electrified aircraft platforms for larger scale, commercial applications. Several key challenges still exist, however, when moving toward these commercial aircraft platforms. The following top priorities to enable future electrified aircraft platforms remain: • Required improvements in areas related to specific energy (weight reduction) of electrical energy storage systems; • Increased specific and rated power; • Aviation-compatible packaging of electric machines; • Strategic approaches to thermal management; and • Integration impact assessments. Assuming success is achieved in these key areas, many aircraft developers are targeting entry into service date ranges of approximately 2030 to 2035 for electrified variants of regional aircraft (fewer than 30 to 80 passengers) and dates closer to 2050 for electrified variants of single-aisle aircraft (130 to 180 passengers). Figure 6. Evolution of the electric aircraft engine power.

14 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies Figure 7. Evolution of electric aircraft battery capacity. Table 1. Configuration and classes of electric vehicles.

What Are Electric Aircraft? 15   Table 2. Baseline aircraft concepts for use cases. Figure 8. Efficiency of traditional and electrified powertrains.