Electric aircraft

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The Velis Electro became the first type certificated crewed electric aircraft on 10 June 2020.
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An electric aircraft is an aircraft powered by electricity, almost always via one or more electric motors which drive propellers. Electricity may be supplied by a variety of methods, the most common being batteries or solar cells.

Electrically powered model aircraft have been flown at least since the 1970s and were the forerunners of the small unmanned aerial vehicles (UAV) or drones, which in the twenty-first century have become widely used for many purposes.

Although crewed flights in an electrically-powered tethered helicopter go back to 1917 and in airships to the previous century, the first crewed free flight by an electrically powered aeroplane, the MB-E1, was not made until October 1973 and most crewed electric aircraft today are still only experimental prototypes. Between 2015 and 2016, Solar Impulse 2 completed a circumnavigation of the Earth using solar power. More recently, interest in electric passenger aircraft has grown, for both commercial airliners and personal air vehicles.[1]

Power storage and supply[]

Almost all electric aircraft to date have been powered by electric motors driving thrust-generating propellers or lift-generating rotors.[2] Some of the propeller-driven types have been airships.

CO
2 emissions, through their effect on climate change, have recently become a major driving force for the development of electric aircraft, with a zero-emissions electric powertrain being the goal for some development teams. Aviation accounts for 2.4% of all fossil fuel derived CO2 emissions, and its share of the total increased by 32% between 2013 and 2018.[3] Another benefit is the potential for noise reduction, in an industry with a severe noise pollution and abatement problem.[4] Electric motors also do not lose power with altitude, unlike internal-combustion engines,[5] avoiding the need for complex and costly measures used to prevent this, such as the use of turbochargers.

Mechanisms for storing and supplying the necessary electricity vary considerably, and each has distinct advantages and disadvantages. Mechanisms used include:

  • Solar cells convert sunlight directly into electricity using photovoltaic materials.
  • Batteries which use a chemical reaction to generate electricity which is reversed when recharged.
  • Fuel cells consume fuel and an oxidizer in a chemical reaction to generate electricity, they need to be refueled, typically with hydrogen.
  • Ultracapacitors are a battery/capacitor hybrid[citation needed] that releases stored energy in an electro-chemical reaction, and can be recharged quickly.
  • Microwave energy that is beamed from a remote transmitter.
  • Power cables connected to a ground-based electrical supply.

Solar cells[]

A solar cell converts sunlight directly into electricity, either for direct power or temporary storage. The power output of solar cells is low and requires that many be connected together, which limits their use. Typical solar panels running at 15-20% conversion efficiency (sunlight energy to electrical power) produce about 150–200 W/m2 (0.019–0.025 hp/sq ft) in direct sunlight.[6] Usable areas are further limited as output from a poorly performing panel impacts the output of all the panels on its circuit, meaning they all require similar conditions, including being at a similar angle to the sun, and not being masked by shadow.[7]

Between 2010 and 2020, solar power modules have declined in cost by 90% and continue to drop by 13-15% per year.[8] Solar cell efficiency has also risen substantially, from 2% in 1955 to 20% in 1985, and some experimental systems now exceed 44%.[9]

The free availability of sunlight makes solar power attractive for high-altitude, long-endurance applications, where the cold and reduced atmospheric interference make them significantly more efficient than on the ground.[10][11] The drop in the dry-air temperature as altitude increases, called the environmental lapse rate (ELR), averages 6.49 °C/km[12] (memorized in pilot training as 1.98 °C/1,000 ft or 3.56 °F/1,000 feet) so that temperature for a typical airliner's cruising altitude of around 35,000 ft (11,000 m) will be substantially lower than at ground level.

Night flying, such for endurance flights and with aircraft providing 24 hour coverage over an area typically require a backup storage system, which is charged during the day from surplus power, and supplies power during the hours of darkness.

Batteries[]

Batteries are the most common onboard energy storage component of electric aircraft, due to their relatively high storage capacity. Batteries first powered airships in the nineteenth century but the lead-acid batteries were very heavy and it was not until the arrival of other chemistries, such as nickel-cadmium (NiCd) later in the twentieth century, that batteries became practical for heavier-than-air aircraft. Modern batteries are mostly rechargeable types based on lithium technologies.

In 2017 the power available from batteries was estimated at around 170 Wh/kg, 145 Wh/kg at the shaft including the system efficiency, while a gas turbine extracted 6,545 Wh/kg of shaft power from a 11,900 Wh/kg fuel.[13] In 2018 Lithium-ion batteries including packaging and accessories were estimated to give 160 Wh/kg while aviation fuel gave 12,500 Wh/kg.[14]

The potential of all-electric propulsion remains limited for general aviation, as in 2018 the specific energy of electricity storage was still only 2% of aviation fuel.[15] This 1:50 ratio makes electric propulsion impractical for long-range aircraft, as a 500 nmi (930 km) mission for an all-electric, 12-passenger aircraft would require a six-fold increase in battery power density.[16]

As of 2019, the best Li-ion batteries achieved 250-300 Wh/kg, sufficient for a small aircraft, while a regional airliner would have needed a 500 Wh/kg battery pack and an Airbus A320-sized single-aisle would need 2 kWh/kg.[16] Such batteries can reduce the overall operating costs for some short-range flights. For example the 300 kWh battery pack used in the Harbour Air Beavers costs them around $30 Canadian to charge compared to $160 to run the Pratt & Whitney R-985 Wasp Junior petrol engine for one hour, when it burns 91 l; 24 US gal (20 imp gal).[4]

Charging[]

The SAE International AE-7D[17] committee was formed by in 2018 to standardise electric aircraft charging and energy storage. One of the first documents developed was the AS6968 standard for sub-megawatt electric aircraft charging of electric aircraft. The AE-7D committee is also developing Aerospace Information Report AIR7357 for megawatt power level charging.

Ultracapacitors[]

An ultracapacitor is an hybrid electrochemical energy storage system bridging batteries and capacitors, and has some advantages over batteries in being able to charge and discharge much faster with higher peak currents, while not being as limited in the number of charge-discharge cycles, as the reaction is not just chemical but also electrical.[18]

Their energy density, typically around 5 Wh/kg, is however well below that of batteries, and they are considerably more expensive, even when their longer lifespan is factored in.[19]

Fuel cells[]

A fuel cell uses the reaction between two chemicals such as hydrogen and oxygen to create electricity, much like a liquid-propellant rocket motor, but generating electricity in a controlled chemical reaction, instead of thrust. While the aircraft must carry the hydrogen (or a similar fuel), with its own complications and risks, the oxygen can be obtained from the atmosphere.

A Diamond HK36 Super Dimona motor-glider modified by Boeing as a fuel cell demonstrator airplane made piloted test flights in 2008 with a proton exchange membrane (PEM) fuel cell/lithium-ion battery hybrid system,[20] and they have been used in several NASA vehicles including satellites and space capsules, although these must also carry an oxidizer.

Further research and development work is required before they are competitive in aircraft, as they are more than ten times as expensive as batteries.[21]

Microwaves[]

Power beaming of electromagnetic energy such as microwaves relies on a ground-based power source. However, compared to using a power cable, power beaming allows the aircraft to move laterally and carries a much lower weight penalty, particularly as altitude increases. The technology has only been demonstrated on small models and awaits practical development at larger scales.[22]

External power cables[]

For powered vehicles replacing tethered aerostats, an electrical power cable can be connected to a ground-based supply, such as an electric generator or the local power grid. At low altitudes this avoids having to lift batteries, and was used by the experimental Petróczy-Kármán-Žurovec PKZ-1 observation vehicle of 1917. However the higher it flies, the heavier the length of cable it lifts becomes.

Propulsion[]

Electric motors[]

While the batteries weigh more than the equivalent in fuel, electric motors weigh less than their piston-engine counterparts and in smaller aircraft used for shorter flights, can improve the disparity between electric and gasoline energy densities. The MagniX Magni500 electric motor used in the Harbour Air electric de Havilland Canada Beaver weighs 135 kg (297 lb) dry and develops 560 kW (750 shp) compared to the Pratt & Whitney R-985 Wasp Junior with a dry weight of 290 kg (640 lb), producing 300 kW (400 bhp) it is replacing.[4] Other motors being developed, such as at Siemens provide an even better power to weight ratio.[23]

On the Cessna 208 Caravan, the Pratt & Whitney Canada PT6A-114A outputs 503 kW (675 shp) and weighs 160 kg (360 lb) dry.[24]

Siemens has a 260 kW (350 hp) electric motor that weighs only 50 kg (110 lb), specifically designed for aircraft use.[25] The comparable Continental IO-550-A reciprocating engine outputs 220 kW (300 hp) and has a dry weight of 195.37 kg (430.72 lb).[26] Besides the motor itself, an electric propulsion system also includes a power inverter and must account for the fuel reserve equivalent, while the gasoline engines have generators, oil coolers, fuel lines, pumps and other equipment that need to be fully factored into any comparison that are not all included in the dry weight.

Additionally, the increase in power, combined with Supplemental Type Certificate (STC) modifications can offset the weight of the batteries by increasing the airplane's gross operating weights, including crucially, the landing weight.[5] Aircraft that use fossil fuels are lighter when they land, which allows the structure that needs to absorb the impact to be lighter. With a battery powered aircraft, the weight remains the same, and so may require reinforcement.[5]

Hybrid power[]

Main article: Hybrid electric aircraft

A hybrid electric aircraft is an aircraft with a hybrid electric powertrain. It typically takes off and lands under clean and quiet electric power, and cruises under conventional piston or jet engine power. This makes long flights practical, while reducing their carbon footprint.[14] By May 2018, there were over 30 projects, and short-haul hybrid-electric airliners were envisioned from 2032.[27] The most advanced are the Zunum Aero 10-seater,[28] the Airbus E-Fan X demonstrator,[29] the VoltAero Cassio,[30] UTC is modifying a Bombardier Dash 8,[31] while an prototype first flew on 6 June 2019.[32]

Magnetohydrodynamics[]

In November 2018, MIT engineers achieved the first free flight with a model aircraft having no moving parts, the EAD Airframe Version 2. It is propelled by creating an ion wind using magnetohydrodynamics (MHD).[33][34] MHD has been used to achieve vertical lift in the past, but only by cabling up the MHD ion generator system to an external power supply.

History[]

Pioneers[]

The use of electricity for aircraft propulsion was first experimented with during the development of the airship in the latter part of the nineteenth century. On 8 October 1883, Gaston Tissandier flew the first electrically-powered airship.[35]:292 The following year, Charles Renard and Arthur Krebs flew La France with a more powerful motor.[35]:306 Even with the lifting capacity of an airship, the heavy accumulators needed to store the electricity severely limited the speed and range of such early airships.

For a tethered device such as an air observation platform, it is possible to run the power up the tether. In an attempt to create a more practical solution than the clumsy balloons then in use, the Austro-Hungarian Petróczy-Kármán-Žurovec PKZ-1 electric-powered helicopter was flown in 1917. It had a specially-designed 190 hp (140 kW) continuous-rated electric motor made by Austro-Daimler and received its power up a cable from a ground-based DC generator. However electric motors were not yet powerful enough for such applications and the motor burned out after only a few flights.[36]

In 1909, an electric free flight model was claimed to have been flown eight minutes, but this claim has been disputed by the builder of the first recorded electric Radio-Controlled model aircraft flight in 1957.[37] Power density for electric flight was problematic even for small models.

In 1964, William C. Brown at Raytheon flew a model helicopter that received all of the power needed for flight by microwave power transmission.[38]

First prototypes[]

Success in a full-sized aeroplane would not be achieved until Nickel-cadmium (NiCad) batteries were developed, having a much higher energy storage-to-weight ratio than lead-acid batteries. In 1973, and converted a Brditschka HB-3 motor glider to an electric aircraft, the Militky MB-E1. On 21 October, it flew for 14 minutes to become the first electric aircraft to fly under its own power with a person on board.[39][40]

Developed almost in parallel with NiCad technology, solar cells were also slowly becoming a practicable power source. Following a successful model test in 1974, the world's first official flight in a solar-powered, person-carrying aircraft took place on April 29, 1979. The Mauro Solar Riser used photovoltaic cells to deliver 350 W (0.47 hp) at 30 volts. These charged a small battery, which in turn powered the motor. The battery alone was capable of powering the motor for 3 to 5 minutes, following a 1.5-hour charge, enabling it to reach a gliding altitude.[41]

Under the direction of Freddie To, an architect and member of the Kremer prize committee, the Solar One was designed by David Williams and produced by Solar-Powered Aircraft Developments. A motor-glider type aircraft originally built as a pedal-powered airplane to attempt the Channel crossing, the airplane proved too heavy to be successfully powered by human power and was then converted to solar power,[42] using an electric motor driven by batteries that were charged before flight by a solar cell array on the wing.[43] The maiden flight of Solar One took place at Lasham Airfield, Hampshire, on June 13, 1979.[44]

Following successful human-powered flight, a relaunched Kremer prize allowed the crew to store energy before takeoff.[45] In the 1980s several such designs stored electricity generated by pedalling, including the Massachusetts Institute of Technology Monarch and the Aerovironment Bionic Bat.[46]

The human piloted Solair 1, developed by Günther Rochelt, flew in 1983 with notably improved performance.[47][48] It employed 2499 wing-mounted solar cells.[47]

The German solar-powered aircraft "Icaré II" was designed and built by the institute of aircraft design (Institut für Flugzeugbau) of the University of Stuttgart in 1996. The leader of the project and often pilot of the aircraft is Rudolf Voit-Nitschmann, the head of the institute. The design won the Berblinger prize in 1996, the EAA Special Achievement Award in Oshkosh, the Golden Daidalos Medal of the German Aeroclub and the OSTIV-Prize in France in 1997.[49]

Unmanned aerial vehicles[]

The NASA Pathfinder Plus electric-powered unmanned aerial vehicle

NASA's Pathfinder, Pathfinder Plus, Centurion, and Helios were a series of solar and fuel cell system–powered unmanned aerial vehicles (UAVs) developed by AeroVironment, Inc. from 1983 until 2003 under NASA's Environmental Research Aircraft and Sensor Technology program.[50][51] On September 11, 1995, Pathfinder set an unofficial altitude record for solar-powered aircraft of 50,000 feet (15,000 m) during a 12-hour flight from NASA Dryden. After further modifications, the aircraft was moved to the U.S. Navy's Pacific Missile Range Facility (PMRF) on the Hawaiian island of Kauai. On July 7, 1997, Pathfinder raised the altitude record for solar–powered aircraft to 71,530 feet (21,800 m), which was also the record for propeller–driven aircraft.[50]

On August 6, 1998, Pathfinder Plus raised the national altitude record to 80,201 feet (24,445 m) for solar-powered and propeller-driven aircraft.[50][52]

On August 14, 2001 Helios set an altitude record of 29,524 metres (96,863 ft) – the record for FAI class U (experimental/new technologies), and FAI class U-1.d (remotely controlled UAV with a mass between 500 and 2,500 kg (1,100 and 5,500 lb)) as well as the altitude record for propeller–driven aircraft.[53] On June 26, 2003, the Helios prototype broke up and fell into the Pacific Ocean off Hawaii after the aircraft encountered turbulence, ending the program.

The QinetiQ Zephyr is a lightweight solar-powered unmanned aerial vehicle (UAV). As of 23 July 2010 it holds the endurance record for an unmanned aerial vehicle of over 2 weeks (336 hours).[54] It is of carbon fiber-reinforced polymer construction, the 2010 version weighing 50 kg (110 lb)[55] (the 2008 version weighed 30 kg (66 lb)) with a span of 22.5 m (74 ft)[55] (the 2008 version had a 18 m (59 ft) wingspan). During the day it uses sunlight to charge lithium-sulphur batteries, which power the aircraft at night.[56] In July 2010 a Zephyr made a world record UAV endurance flight of 336 hours, 22 minutes and 8 seconds (more than two weeks) and also set an altitude record of 70,742 feet (21,562 m) for FAI class U-1.c (remotely controlled UAV with a weight between 50 and 500 kg (110 and 1,100 lb)).[57][58][59]

Light aircraft[]

The first commercially available, non-certified production electric aircraft, the Alisport Silent Club self-launching glider, flew in 1997. It is optionally driven by a 13 kW (17 hp) DC electric motor running on 40 kg (88 lb) of batteries that store 1.4 kWh (5.0 MJ) of energy.[60]

The first certificate of airworthiness for an electric powered aircraft was granted to the Lange Antares 20E in 2003. Also an electric, self-launching 20 m (66 ft) glider/sailplane, with a 42 kW (56 hp) DC/DC brushless motor and lithium-ion batteries, it can climb up to 3,000 m (9,800 ft) with fully charged cells.[61] The first flight was in 2003. In 2011 the aircraft won the 2011 Berblinger competition.[62]

In 2005, Alan Cocconi of AC Propulsion flew, with the assistance of several other pilots, an unmanned airplane named "SoLong" for 48 hours non-stop, propelled entirely by solar energy. This was the first such around-the-clock flight, on energy stored in the batteries mounted on the aircraft.[63][64]

The Boeing Fuel Cell Demonstrator (2008)

In 2007, the non-profit CAFE Foundation held the first Electric Aircraft Symposium in San Francisco.[65]

The Boeing-led FCD (fuel cell demonstrator) project uses a Diamond HK-36 Super Dimona motor glider as a research test bed for a hydrogen fuel cell powered light airplane.[66] Successful flights took place in February and March 2008.[66][67]

The Taurus Electro was the first two-seat electric aircraft to have ever flown,[68] while the Taurus Electro G2 is the production version, that was introduced in 2011. Powered by a 40 kW (54 hp) electric motor and lithium batteries for self-launching[69] to an altitude of 2,000 m (6,600 ft), after which the engine is retracted and the aircraft then soars as a sailplane. It is the first two-seat electric aircraft to have achieved series production.[70][71]

The Taurus G4 taking off from the Sonoma County Airport in California

The first NASA Green Flight Challenge took place in 2011 and was won by a Pipistrel Taurus G4 on 3 October 2011.[72][73][74]

In 2013 Chip Yates demonstrated that the world's fastest electric airplane, a Long ESA, a modified Rutan Long-EZ, could outperform a gasoline-powered Cessna and other aircraft in a series of trials verified by the Fédération Aéronautique Internationale. The Long ESA was found to be less expensive, have a higher maximum speed, and higher rate of climb, partly due to the ability of the aircraft to maintain performance at altitude as low air density does not impair engine performance.[75][76]

In 2017, Siemens used a modified Extra EA-300 acrobatic airplane, the 330LE, to set two new records: on March 23 at the Dinslaken Schwarze Heide airfield in Germany, the aircraft reached a top speed of around 340 km/h (210 mph) over 3 km (1.9 mi) and the next day, it became the first glider towing electric aircraft.[77]

Solar Impulse circumnavigation[]

In 2016, Solar Impulse 2 was the first solar-powered aircraft to complete a circumnavigation

Solar Impulse 2 is powered by four electric motors. Energy from solar cells on the wings and horizontal stabilizer is stored in lithium polymer batteries and used to drive propellers.[78][79] In 2012 the first Solar Impulse made the first intercontinental flight by a solar aircraft, flying from Madrid, Spain to Rabat, Morocco.[80][81]

Completed in 2014, Solar Impulse 2 carried more solar cells and more powerful motors, among other improvements. In March 2015, the aircraft took off on the first stage of a planned round-the-world trip, flying eastwards from Abu Dhabi, United Arab Emirates.[82] Due to battery damage, the craft halted at Hawaii, where its batteries were replaced. It resumed the circumnavigation in April 2016[83] and reached Seville, Spain, in June 2016.[84] The following month it returned to Abu Dhabi, completing its circumnavigation of the world.[85]

Research projects and proposals[]

NASA Electric Aircraft Testbed
NASA developed the X-57 Maxwell from a Tecnam P2006T

The NASA Puffin was a concept, proposed in 2010, for an electric-powered, vertical takeoff and landing (VTOL), personal air vehicle.[86]

The Sikorsky Firefly S-300 was a project to flight test an electric rotorcraft, but the project was put on hold due to battery limitations.[87] The world's first large-scale all-electric tilt-rotor was the AgustaWestland Project Zero unmanned aerial vehicle technology demonstrator, which performed unmanned tethered fights on ground power in June 2011, less than six months after the company gave the official go-ahead.[88]

The European Commission has financed many low TRL projects for innovative electric or hybrid propulsion aircraft. The ENFICA-FC is a project of the European Commission, to study and demonstrate an all-electric aircraft with fuel-cells as the main or auxiliary power system. During the three-year project, a fuel-cell based power system was designed and flown in a Rapid 200FC ultralight aircraft.[89]

The NASA Electric Aircraft Testbed (NEAT) is a NASA reconfigurable testbed in Plum Brook Station, Ohio, used to design, develop, assemble and test electric aircraft power systems, from a small, one or two person aircraft up to 20 MW (27,000 hp) airliners.[90] NASA research agreements (NRA) are granted to develop electric-propulsion components.[91] They will be completed in 2019 and the internal NASA work by 2020, then they will be assembled in a megawatt-scale drive system to be tested in the narrowbody-sized NEAT.[91]

NASA developed the X-57 Maxwell to demonstrate technology to reduce fuel use, emissions, and noise.[92] Modified from a Tecnam P2006T, the X-57 will have 14 electric motors driving propellers mounted on the wing leading edges.[93] In July 2017, Scaled Composites is modifying a first P2006T by replacing the piston engines with electric motors, to fly early in 2018, then will move the motors to the wingtips to increase propulsive efficiency and finally will install the high aspect ratio wing with 12 smaller props.[94]

Commercial projects[]

The Airbus CityAirbus is an electrically-powered VTOL aircraft demonstrator.[95] The multirotor aircraft is intended to carry four passengers, with a pilot initially and to become self-piloted when regulations allow.[95] Its first unmanned flight was scheduled for the end of 2018 with manned flights planned to follow in 2019.[96] Type certification and commercial introduction are planned for 2023.[97]

In September 2017, UK budget carrier EasyJet announced it was developing an electric 180-seater for 2027 with Wright Electric.[98] Founded in 2016, US Wright Electric built a two-seat proof-of-concept with 272 kg (600 lb) of batteries, and believes they can be scaled up with substantially lighter new battery chemistries. A 291 nm (540 km) range would suffice for 20% of Easyjet passengers.[99] Wright Electric will then develop a 10-seater, eventually an at least 120 passengers single aisle, short haul airliner and targets 50% lower noise and 10% lower costs.[100] Jeffrey Engler, CEO of Wright Electric, estimates that commercially viable electric planes will lead to around a 30% reduction in energy costs.[101]

On March 19, 2018, Israel Aerospace Industries announced it plans to develop a short-haul electric airliner, building on its small UAS electric power systems experience.[102] It could develop it in-house, or with a startup like Israeli Eviation, U.S. Zunum Aero or Wright Electric.[102]

By May 2018 almost 100 electric aircraft were known to be under development.[103] This was up from 70 the previous year and included 60% from startups, 32% from aerospace incumbents, half of them major OEMs and 8% from academic, government organizations and non-aerospace companies, mainly from Europe (45%) and the U.S. (40%).[27] Mostly (50%) and general aviation aircraft (47%), a majority are battery-powered (73%), while some are hybrid-electric (31%), most of these being larger airliners.[27]

Australia-based MagniX has developed an electric Cessna 208 Caravan with a 540 kW (720 hp) motor for flight durations up to an hour.[104] The company's Magni5 electric motor produces continuously 265–300 kW (355–402 hp) peak[clarification needed] at 2,500 rpm at 95% efficiency with a 53 kg (117 lb) dry mass, a 5 kW/kg power density, competing with the 260 kW (350 hp), 50 kg (110 lb) Siemens SP260D for the Extra 330LE.[104] By September 2018, a 350 hp (260 kW) electric motor with a propeller had been tested on a Cessna iron bird. The 750 hp (560 kW) Caravan was expected to fly by the fall of 2019 and by 2022 MagniX estimates electric aircraft will have ranges of 500 and 1,000 mi (800 and 1,610 km) by 2024.[105] The motor ran on a test dynamometer for 1,000 hours.[106] The iron bird is a Caravan forward fuselage used as a test bed, with the original Pratt & Whitney Canada PT6 turboprop engine replaced by an electric motor, inverter and a liquid-cooling system, including radiators, driving a Cessna 206 propeller.[106] The production motor will produce 280 kW (380 hp) at 1,900 rpm, down from the test motor's 2,500 rpm, allowing the installation without a reduction gearbox.[106]

A 560-kW (750-hp) MagniX electric motor was installed in a de Havilland Canada DHC-2 Beaver seaplane. Harbour Air, based in British Columbia, hopes to introduce the aircraft in commercial service in 2021, for trips under 30 minutes initially, until range increases as better batteries are introduced.[107] On December 10, 2019, it made its first flight of four minutes duration from the Fraser River near Vancouver. The normally-fitted Pratt & Whitney R-985 Wasp Junior piston engine of the six-passenger Beaver was replaced by a 135 kg (297 lb) magni500, with swappable batteries, allowing 30 minute flights with a 30 minute reserve.[108]

On 28 May 2020, the MagniX electric-powered nine-passenger Cessna 208B eCaravan flew on electric power,[109] towards commercial operation certification.[110]

By May 2019, the number of known electric aircraft development programmes was closer to 170, with a majority of them aimed at the urban air taxi role.[111] US/UK startup ZeroAvia develops zero-emissions fuel-cell propulsion systems for small aircraft, and tests its HyFlyer in Orkney supported by £2.7 million from the UK government.[107] A demonstrator for the German Scylax E10 10-seater should fly in 2022. It should be used by FLN Frisia Luftverkehr to connect East Frisian islands with its 300 km (160 nmi) range and 300 m (980 ft) short takeoff and landing distance.[107]

On 10 June 2020, the Velis Electro variant of the two-seat Pipistrel Virus was the first electric aircraft to secure type certification, from the EASA. Powered by a 76 hp (58 kW) electric motor developed with Emrax, it offers a payload of 170 kg (370 lb), a cruise speed of 90 kn (170 km/h), and a 50 min endurance. Pipistrel plans to deliver over 30 examples in 2020, to be operated as a trainer aircraft.[112]

On 23 September 2020, Gothenburg-based Heart Aerospace presented its ES-19 design, a 19-seat all-electric commercial aircraft planned to fly by mid-2026.[113] With a conventional aluminium airframe and wing, its planned range is 400 km (222 nmi) and expects to operate from runways as short as 800 m (2,640 ft).[113] Initially targeting airlines operating in the Nordic countries, Heart has received "expressions of interest" for 147 ES-19 aircraft worth about €1.1 billion or US $1.3 billion (€7.5 million or $8.8 million each) from at least eight airlines.[113] Backed by Swedish venture capitalist EQT Ventures, Nordic governments and the European Union, Heart was initially funded by the Swedish innovation agency Vinnova and is an alumnus of Silicon Valley start-up accelerator Y Combinator.[113]

On 22 March 2021, Toulouse-based Aura Aero announced the development of its ERA (Electric Regional Aircraft), a 19 passenger electric aircraft, planned to be certified in 2026.[114]

Applications[]

Drones[]

Main article: Drone (aircraft)

By far the majority of electric aircraft are unmanned drones. These vary from palm-sized to being comparable with a small manned type and are used in a wide variety of applications. For smaller drones, which are manufactured in the greatest numbers, the vertical takeoff quadcopter configuration is common. However Ingenuity, the drone which flew on Mars in 2021 to become the first extraterrestrial aircraft, has a single pair of coaxial rotors.

Drones are used in a wide variety of general, commercial and military applications and their use is expanding rapidly.

Fixed-wing aircraft[]

Currently, battery-powered manned electric aircraft have much more limited payload, range and endurance than those powered by conventional engines. Electric power is only suitable for small aircraft while for large passenger aircraft, an improvement of the energy density by a factor 20 compared to li-ion batteries would be required.[115] However, pilot training emphasises short flights. Several companies make, or have demonstrated, light aircraft suitable for initial flight training. The Airbus E-Fan was aimed at flight training but the project was cancelled. Pipistrel makes light sport electric aircraft such as the Pipistrel WATTsUP, a prototype of the Pipistrel Alpha Electro. The advantage of electric aircraft for flight training is the lower cost of electrical energy compared to aviation fuel. Noise and exhaust emissions are also reduced compared with combustion engines.

An increasingly common application is as a sustaining motor or even a self-launching motor for gliders. The most common system is the front electric sustainer, which is used in over 240 gliders. The short range is not a problem as the motor is used only briefly, either to launch or to avoid an outlanding. The advantage of an electric motor in this case comes from the certainty that it will start and the rapidity of deployment compared with reciprocating engines.

Rotorcraft[]

Solution F/Chretien helicopter

Although the Austro-Hungarian Petróczy-Kármán-Žurovec team flew an experimental tethered military observation helicopter in 1917 on electric power, they soon switched to using a gasoline engine and the use of electric power for rotor-borne flight was not explored further until recently.

The first free-flying electric helicopter was the Solution F/Chretien Helicopter, developed by Pascal Chretien in Venelles, France. It went from computer-aided design concept on September 10, 2010 to first flight in August 2011, in under a year.[116][117]

In February 2016, Philippe Antoine, AQUINEA and ENAC, Ecole Nationale Supérieure de l'Aviation Civile, successfully flew the first full electric conventional helicopter called Volta in Castelnaudary Airfield, France. Volta demonstrated a 15-minute hovering flight in December 2016. The helicopter is powered by two 40 kW (54 hp) permanent-magnet synchronous motors run from a 22 kWh (79 MJ) Lithium battery. Volta is officially registered by DGAC, the French Airworthiness Authority, and is authorized for flying in French civilian airspace.[citation needed]

In September 2016, Martine Rothblatt and successfully tested an electric-powered helicopter. The five minute flight reached an altitude of 400 feet (120 m) with a peak speed of 80 knots (150 km/h; 92 mph). The Robinson R44 helicopter was modified with two three-phase permanent magnet synchronous YASA Motors, weighing 45 kg (100 lb), plus 11 Lithium polymer batteries from Brammo weighing 500 kg (1,100 lb).[118][119][120] It later flew for 20 minutes in 2016.[121][122] On December 7, 2018, Tier 1 Engineering flew an electric, battery-powered R44 over 30 nmi (56 km) at 80 kn (150 km/h) and an altitude of 800 ft (240 m), setting a Guinness World Record for the farthest distance.[123]

See also[]

  • Electric vehicle
  • Emerging aviation fuels
  • List of electric aircraft
  • Solar energy

References[]

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Bibliography[]

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External links[]

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