Aviation trailblazers have dreamed about the possibility of electric flight for decades. Long before the Wright Brothers, innovators were experimenting with batteries and electric motors to power airships and balloons. With the global emphasis on aviation emission controls, the concept of electric powered aircraft has come to the forefront. During this blog, we'll explore current trends in electric aviation, as well as their potential for the future.
Electrically powered model aircraft have been flown since the late 1960's. By the early 2000's they developed into unmanned aerial vehicles, or drones, which have a number of commercial applications. While limited manned flights of a tethered electric helicopter date back to 1917, the first manned flight of an electrically powered aircraft, the MB-E1 did not occur until 1973. Though most manned electric aircraft are in the experimental stage today, in 2015-16, the unmanned Solar Impulse 2 completed a circumnavigation of the Earth using solar power. NASA's Pathfinder, Pathfinder Plus, Centurion and Helios were a series of unmanned aerial vehicles developed by AeroVironment, Inc. from 1983 to 2003 under NASA's Environmental Research Aircraft and Sensor Technology program. In September 1995, the Pathfinder set an unofficial altitude record for a solar-powered aircraft of 50,000 ft. during a twelve hour flight. Two years later a modified Pathfinder, flown from the Hawaiian island of Kauai, set another altitude record of 71,530 ft., which qualified for both a solar-powered and propeller-driven aircraft. The following year, both records were increased to an altitude of 80,201ft. In August 2001, Helios set an altitude record for a solar-powered aircraft (wing) of 96,863 ft. The QinetiQ Zephyr, a lightweight solar-powered UAV set an endurance record in July 2010 of 336 hrs.
The first commercially available production electric-powered manned aircraft, the Alisport Silent Club glider, first flew in 1997. The Silent Club was a single-seat, self-launching glider powered by a 17 hp. DC electric motor running on 88 lbs. of batteries with a 1.4 kWh life. Though the battery was optional, it proved the potential of electric-powered flight. The first certificate of standards for an electric-powered aircraft was granted to the Lange Antares 20E in 2003. The Antares, also a manned single-seat glider, had a 66 ft. wingspan and was powered by a 42 kWh (56 hp) DC/DC brushless motor and lithium-ion batteries. The Antares could attain an altitude of 9,800 ft. when fully charged, winning the Berblinger competition in 2011. A more recently developed electric-powered manned aircraft, the Long-ESA set five speed records in 2013, beating out two single-engine Cessna models, the 172 and 182, as well as the Cirrus SR22-G2. The ESA had a higher rate of climb than both Cessna planes and the Cirrus. The Long aircraft also achieved a higher altitude than its competitors, in addition to a cost of one-third to one-half of the Cessna and Cirrus planes. Though the ESA's lightweight frame and 258 horsepower electric motor contributed to its performance, another factor influenced the outcome. As with battery-powered automobiles, electric planes offer a major benefit over gasoline-powered aircraft. A gasoline engine needs to pull in oxygen to work. The higher a plane flies, the less available oxygen there is, so the rate of climb drops as altitude increases. Conversely, a battery-powered aircraft will continue to climb until its power is depleted.
Electric planes offer a number of advantages over gasoline-powered units. Decreased fuel costs offered by electric planes are a prime advantage. Fuel costs are a major variable expense for both airlines and general aviation pilots. For the airlines, high fuel prices translate into high ticket prices. For the general aviation pilot, fuel costs are a significant expense and could be an obstacle to more frequent flights. For example, the De Havilland Beaver seaplane, when modified to run on a 750-horsepower electric propulsion system with a four-blade Hartzell composite propeller costs about $12 per hour to operate while operating costs of a piston engine range from $300 to $450 per hour. Another advantage of electric planes is electric motors have fewer moving parts, as opposed to piston or jet engines, which may have several hundred parts. Also, both piston and jet engines lose much of their energy from fuel in the form of waste heat. With fewer moving parts, electric motors require less maintenance, thus reducing their costs of operation. Electric planes are also quieter than their piston-engine and jet-engine counterparts. Due to noise reduction programs by the aviation industry, significant aviation noise exposure in the U.S. has declined from approximately 7 million to just over 400,000 today, according to the FAA. Electric and hybrid planes are drastically quieter than jets and turboprop aircraft. Electric planes are also more flexible in the areas they fly in, such as cities, port facilities and wildlife areas without annoying nearby residents. Perhaps most importantly, electric planes have zero carbon-dioxide atmospheric emissions, unlike piston and jet aircraft, which are currently responsible for 2.5 per cent of all global emissions.
However, electric aircraft also have their share of disadvantages. In comparison with piston and jet aircraft, electric-powered planes have a reduced energy density. Energy density is defined in terms of the number of watt-hours (Wh) you get per kilogram (kg). For example, a lithium-ion battery's energy could reach 250 Wh per kg, while the energy density of jet fuel, or kerosene, is approximately 12,000 Wh per kg. Though electrical propulsion systems can be designed to operate more efficiently, fossil fuel systems currently have 14 times more energy density than battery-powered units. For a long-haul global jetliner to maintain its current range, it would need batteries weighing 30 times more than its fuel stores. Another aspect of this problem is the weight of a battery stays the same, even if it is dead. As a fossil fuel aircraft is in flight, its fuel is burned up, thus making the plane lighter and requiring less fuel to stay airborne. Two possible approaches to overcome this problem are to increase battery capacity and efficiency to extend the range of the battery-powered aircraft. Current battery types powering electric motors are primarily lithium-based with a limited range between charges. In addition to improvements in battery efficiency, a practical means of charging the battery in mid air, as with the automobile, could complement the larger capacity battery without the necessity of charging it at designated stations. Another concept, which is feasible in the near term, is to produce a hybrid electric plane, which combines a gas turbine with an energy storage system that drives an electric motor during certain phases of the flight. Interestingly enough, electric cars evolved in the same manner.
In spite of the current battery limitations, the trend toward electric-powered aircraft is gaining momentum. According to the consulting firm Roland Berger, there are currently 170 electric aircraft projects in progress globally, with half of them started within the last three years. Though many of the projects are aimed at developing electrically-powered private planes and short-haul airliners, major firms such as Boeing and Airbus have announced plans to electrify their own aircraft. In 2017 the British budget carrier EasyJet announced it was developing an electric 180 seat with Wright Electric. Founded in 2016, US based Wright Electric built a two-seat proof-of-concept plane with 600 lbs. of batteries and believes they can be scaled up with substantially lighter new battery chemistries. A 291 mile range would suffice for about 20 per cent of EasyJet passengers. Wright Electric then plans to develop a ten seat aircraft, followed by a 120 passenger short haul airliner with a fifty per cent noise reduction and ten per cent lower costs. In March 2018, Israel Aerospace Industries announced plans to develop a short-haul electric airliner, building on its small UAS electric power systems experience. Los Angeles based Ampire is developing six, nine and nineteen passenger electric aircraft prototypes. Ampire's philosophy is to apply electric flight technology to existing airframes, saving both time and money. The Los Angeles firm successfully tested a five-passenger aircraft with an electric motor powering a propeller in the back of the plane with a normal combustion engine driving the propeller at the front of the plane. The retrofit, originally a Cessna Skymaster, can travel up to 200 miles on a single charge and uses 55 per cent less fuel than an unmodified plane and costs fifty per cent less to maintain. Though electric flight for large global airliners may be at least twenty years away, the potential for electric passenger plane flights in the short-haul (500 miles) routes is a strong possibility, based upon the application of current technology. Due to the reduced operating costs of electric aircraft, they have the potential to create their own market segment, serving routes which are unprofitable for combustion aircraft. Imagine living near an airport and seeing planes take off and land in silence.