Save for later Print Download Share LinkedIn Twitter Electric propulsion for aircraft is no longer a pipe dream. A flurry of projects holds the promise of transforming urban, regional and eventually commercial transport in the 2025-40 timeframe, with Nasa leading the charge toward what researchers view as an aviation renaissance. "I feel we are at a tipping point in commercial aviation," says Jim Heidmann, manager of Nasa's Advanced Air Transport Technology Project. Nasa is facilitating the transition to electric propulsion with a wide range of projects to develop new concepts such as different fuselage shapes, longer and more blended wing configurations, innovative materials and components, as well as highly integrated engine systems. "We are exploring and developing game-changing technologies and concepts for aircraft and propulsion systems that can dramatically improve efficiency and reduce environmental impact and accelerate the introduction of new aircraft," Heidmann says (JFI Oct.31'16). Stepping Stones The transition toward electric propulsion involves several stepping stones, from hybrid and turboelectric concepts to a fully electric plane. The early adapters, or first candidates into commercial operations, are likely to be lightweight, small commuter and business aircraft flying shorter distances. These planes would have batteries with gas-powered engines that extend their range and reduce fuel consumption and emissions (JFI Dec.19'16). This concept would be especially attractive for the general aviation business, which uses avgas containing lead that is known to cause environmental damage and health problems (JFI Jul.3'17). Over the longer term, once new technologies are developed and battery energy density and lifecycle make advances, a hybrid plane is envisioned for large-scale commercial operations. Since maximum power is used for takeoff, current aircraft use larger engines than are needed during the cruise phase of a flight. Existing aircraft could be retrofitted with smaller engines that burn less fuel if batteries could supplement propulsion during takeoff. Nasa is working with commercial partners to build and certify battery packages suitable for aircraft. Hybrid and turboelectric concepts would extend the function of electrical components even further, optimizing the power systems over the entire flight envelope. Maxwell's Legacy Nasa is demonstrating proof-of-concept for an all-electric plane with a small experimental aircraft known as the X-57 Maxwell, after the Scottish physicist who helped lay the foundation for quantum mechanics. Fitted with two fully electric onboard motors, it is powered solely by batteries and is expected to take flight in March of next year over California. Its goal is to demonstrate a 500% increase in high-speed cruise efficiency, zero carbon emissions and a much quieter flight for communities on the ground. Nasa engineers reached an important milestone earlier this month with the successful testing of the X-57's battery system, which proved that it had the necessary capacity to safely power Nasa's first manned X-plane in 20 years. The test also confirmed that the design of the lithium-ion batteries could isolate potential overheating issues to single battery cells, preventing "thermal runaway" problems that plagued Boeing's 787 during a few of its early commercial flights. In its final configuration, the X-57 will feature 12 smaller electric high-lift motors that will be used during takeoff and landing, in addition to the two wing-tip cruise motors. Nasa is collaborating with California-based Empirical Systems Aerospace and Joby Aviation on the project at its Armstrong Flight Research Center. Collaboration with private industry is a crucial component of Nasa's aeronautical research and development programs. Researcher Amy Jankovsky of Nasa's Glenn Research center heads up the agency's project to design a turboelectric commercial aircraft that could eventually replace the Boeing 737. Nasa recently awarded contracts to two teams comprised of Boeing/Georgia Tech and Liberty Works/ES Aero to come up with a preliminary design for a single-aisle, 150-seat aircraft that uses turboelectric propulsion. These concepts, along with Nasa's own concept known as STARC-ABl, look similar to a Boeing 737 with smaller engines, and feature a horizontal stabilizer with a ducted fan on its tail. That T-tail configuration is driven by electric power derived from generators mounted to the underwing engines. About three megawatts are used for turboelectric propulsion, in addition to the electricity needed to power subsystems that include flight controls, avionics and de-icing. The engines mounted on the wings would supply 80% of the thrust needed during takeoff and 55% at cruise, with the all-electric fan mounted on the tail providing the remaining thrust. From these design projects, Jankovsky says, "we'll identify key performance parameters for components such as motors, generators and power electronics, and any wind tunnel, altitude and other ground tests and flight demonstrations that are appropriate." She tells Jet Fuel Intelligence that engaging with private industry, venture capital firms and original equipment manufacturers is an effective model to compete in what she describes as "the race" to transform the aeronautical industry. Swiss Prototype A pioneering aircraft is already in the skies over Switzerland, thanks to the H55 venture cofounded by Andre Borschberg, who is using lessons learned from his Solar Impulse project. Along with Swiss explorer Bertrand Piccard, he flew a solar-powered experimental plane around the world in 2015-16 that sets the stage for widespread adoption of new technologies that are helping to provoke a paradigm shift in mobility -- from urban to regional and eventually to global transport. Borschberg tells JFI that involves taking an entirely different approach as to how airplanes are designed and operated, in the same way that Elon Musk disrupted the automobile industry by introducing an electric vehicle. He explains that electric motors offer an immediate increase in torque when provided with electric current that can be used to stabilize and control an aircraft -- and not only for propulsion. Unlike jet engines that are typically limited to two per aircraft for cost and maintenance reasons, the motors of an electric plane can be split into more components to provide distributed propulsion at much lower operating costs. That redundancy offers huge safety benefits, alongside environmental advantages in terms of zero pollution and limited noise. "If you get rid of the jet engine you have a completely clean form of transport," Borschberg tells JFI. The H55 venture in Switzerland is one of many projects aimed at transforming urban mobility, including air taxis and vertical takeoff and landing (VTOL) flying cars. Certification will be the main challenge to getting these new ventures off the ground. H55 has a demonstrator aircraft that has flown more than 50 hours and exceeded one hour for battery use. Its next step will be a two-seater aircraft intended for flight training that should be up and running next year with the potential to fly two hours on batteries. To facilitate the rigorous certification process, Borschberg can leverage his experience in getting the Solar Impulse plane certified by national authorities around the world to fly over urban areas. That included Shanghai in China with a population of more than 24 million. Chinese authorities gave the green light to overfly the city in 2015 even though most of China's airspace is for military use only -- with commercial airlines restricted to specific corridors. Dynamism in the electric aircraft space has helped H55 secure funding, which has come from the Swiss federal and local canton governments, research institutions as well as venture capital firms in Europe and Silicon Valley.
