An electric aircraft is a type of aircraft that uses electricity for power. These aircraft are considered a way to reduce the impact of flying on the environment, as they produce very few emissions and make less noise. Electricity can come from different sources, with batteries being the most common. Most electric aircraft use electric motors to turn propellers or turbines.

Electrically powered airships with people on board were used as early as the 19th century, and a tethered helicopter was tested in 1917. Model aircraft powered by electricity have been flown since at least 1957, before the development of small unmanned aerial vehicles (UAVs), also known as drones. Small unmanned aerial systems (UAS) can be used to deliver packages, while larger ones can be used for tasks like taking aerial pictures, monitoring areas, or providing communication services. The first crewed flight of an electric airplane, the MB-E1, happened in 1973. Most electric aircraft used by people today are still experimental models. The Lange E1 Antares was the first electric aircraft made in large numbers that could take off on its own and carry people. It received official approval from EASA in 2006 and had a special battery system built into its wings. It first flew in 1999, and more than 100 of these aircraft were delivered between 2004 and 2022, with over 165,000 hours of electric flight completed. From 2015 to 2016, the Solar Impulse 2 aircraft traveled around the world using only solar power. Electric vertical takeoff and landing (VTOL) aircraft or personal flying vehicles are being studied for use in city transportation. Electric airplanes used for commercial travel might help reduce costs for airlines.

History

By May 2018, about 100 electric aircraft were being developed. This number increased from 70 the year before. Of these, 60% were from new companies, 32% from established aerospace companies, half of which were major manufacturers, and 8% from academic, government, or non-aerospace organizations, mostly in Europe (45%) and the U.S. (40%). Most of the aircraft were urban air taxis (50%) or general aviation planes (47%). About 73% were powered by batteries, while 31% used hybrid-electric systems, with most of these being larger airliners. By May 2019, the number of electric aircraft development projects had grown to about 170, with most aimed at urban air taxis. By 2022, around 100 electric aircraft designs were under development worldwide. By 2023, up to 700 sustainable aircraft concepts, including electric and other types, were being developed.

Electric power for aircraft was first tested in the late 1800s during airship development. On October 8, 1883, Gaston Tissandier flew the first electric airship. The next year, Charles Renard and Arthur Krebs flew La France, which had a more powerful motor. However, the heavy batteries needed to store electricity limited the speed and range of these early airships.

Fully electric airships are expected to be available by the 2030s.

In 1909, an electric model aircraft reportedly flew for eight minutes, but this claim is disputed. In 1957, the first recorded flight of an electric radio-controlled model was achieved. Even small models faced challenges with power density.

NASA’s Pathfinder, Pathfinder Plus, Centurion, and Helios were solar and fuel cell-powered unmanned aircraft developed by AeroVironment from 1983 to 2003. On September 11, 1995, Pathfinder reached an unofficial altitude record of 50,000 feet (15,000 meters) during a 12-hour flight. After upgrades, it later set a new altitude record of 71,530 feet (21,800 meters) in 1997. In 1998, Pathfinder Plus reached 80,201 feet (24,445 meters). In 2001, Helios set an altitude record of 29,524 meters (96,863 feet), but the prototype crashed in 2003.

In 2005, AC Propulsion flew an unmanned plane named "SoLong" for 48 hours using solar energy stored in batteries. In 2010, the QinetiQ Zephyr, a solar-powered drone, set an endurance record of over two weeks (336 hours) and an altitude record of 70,742 feet (21,562 meters).

For tethered devices, power can be sent through a cable. In 1917, the Austro-Hungarian Petróczy-Kármán-Žurovec PKZ-1 helicopter used a ground-powered motor but failed after a few flights. In 1964, William C. Brown flew a model helicopter using microwave power.

The AgustaWestland Project Zero, the first large-scale electric tilt-rotor aircraft, performed tethered flights in 2011. The first free-flying electric helicopter, the Solution F/Chretien Helicopter, flew in 2011. In 2016, Martine Rothblatt and Tier1 Engineering tested an electric helicopter that flew 20 minutes and set a distance record in 2018.

In 2017, Airbus introduced the CityAirbus, an electric VTOL aircraft intended to carry four passengers. In 2021, NASA’s Ingenuity helicopter became the first aircraft to fly on Mars. A future mission, Dragonfly, plans to fly on Titan’s surface around 2034.

On October 21, 1973, the Militky MB-E1, powered by nickel-cadmium batteries, became the first electric aircraft to fly with a person on board. In the 1980s, human-powered aircraft stored energy for flight, such as the MIT Monarch and Aerovironment Bionic Bat.

The Boeing-led FCD project tested hydrogen fuel cells in a glider in 2008. The European Commission has supported many projects for electric or hybrid aircraft with low technology readiness levels.

Environmental effects of aviation

The environmental impact of aviation on climate change is a key reason for creating electric aircraft. Some teams are working to develop electric engines that produce no emissions. Aviation is responsible for 2.4% of all carbon dioxide emissions from burning fossil fuels. Between 2013 and 2018, emissions from air travel increased by 32%. Calculating aviation's effects on climate change beyond carbon dioxide is difficult, but nitrogen oxides and contrails may raise this total to 3.5%. Other advantages include reducing noise, which is a major issue in an industry that produces significant noise pollution.

Offboard power supply

Methods to supply electricity without storing it on a vehicle include:

• Solar cells use sunlight-absorbing materials to directly create electricity.
• Microwaves can send energy from a distant source to a vehicle.
• Power cables can connect to a ground-based electricity supply.

Solar cells change sunlight into electricity for immediate use or short-term storage. However, their power output is low, so many cells must be linked together. This limits their usefulness. Standard solar panels, which convert about 15–20% of sunlight into electricity, produce roughly 150–200 watts per square meter in direct sunlight. Their effectiveness is further limited because poorly performing panels reduce the power from all connected panels. All panels must face the sun at the same angle and avoid shadows to work efficiently.

Between 2010 and 2020, the cost of solar panels dropped by 90%, and prices continue to fall by 13–15% yearly. Solar cell efficiency has also improved, rising from 2% in 1955 to 20% in 1985. Some experimental systems now reach over 44% efficiency, though these are only tested in labs, not in large-scale production.

Sunlight is freely available, making solar power useful for high-altitude, long-duration missions. At higher altitudes, colder temperatures and less air interference increase efficiency. As altitude rises, temperature decreases by about 6.49°C per kilometer (or 1.98°C per 1,000 feet). At typical airplane cruising altitudes (around 35,000 feet), temperatures are much lower than at ground level.

For flights during nighttime or missions requiring 24-hour coverage, backup energy storage is needed. This storage is charged during the day using extra power and provides electricity at night.

Microwave energy beaming uses a ground-based power source to send energy to a vehicle. Unlike power cables, this method allows vehicles to move freely and reduces weight as altitude increases. However, this technology has only been tested on small models and needs further development for larger use.

For vehicles replacing tethered balloons, power cables can connect to ground-based supplies, such as generators or local power grids. At low altitudes, this avoids the need to carry batteries, as seen in the 1917 Petróczy-Kármán-Žurovec PKZ-1 aircraft. However, as altitude increases, the weight of the cable becomes heavier, limiting its usefulness at higher altitudes.

Power storage

Electric aircraft use different methods to store energy, including:

• Batteries that use chemical reactions to produce electricity, which can be reversed when the battery is recharged.
• Fuel cells that use fuel and an oxidizer in a chemical reaction to create electricity, requiring refueling, often with hydrogen.

Batteries are the most common way to store energy in electric aircraft because they can hold a large amount of energy. Early batteries powered airships in the 1800s, but lead–acid batteries were too heavy. Later, in the 1900s, other types like nickel–cadmium (NiCd) made batteries practical for heavier-than-air aircraft. Today, most batteries are rechargeable lithium-based types.

Lithium polymer batteries (LiPo), a type of lithium-ion battery (LIB), have been used in unmanned aircraft because they are lightweight and can be recharged. However, their energy density limits their use mainly to drones. Making larger aircraft with bigger batteries to increase flight time is inefficient because adding battery weight reduces the aircraft’s efficiency and range. There is also a trade-off between the number of passengers and flight range. Tools used to model these trends suggest a small electric aircraft (1500 kg) with average energy density (150 Wh/kg) could fly about 80 miles with one passenger, 60 miles with two, and less than 30 miles with three.

In 2017, batteries provided about 170 Wh/kg of energy, but only 145 Wh/kg after accounting for system efficiency. A gas turbine, by comparison, extracted 6,545 Wh/kg of energy from fuel with 11,900 Wh/kg of fuel energy. In 2018, lithium-ion batteries (including packaging) gave 160 Wh/kg, while aviation fuel provided 12,500 Wh/kg. At that time, battery energy storage was only 2% as efficient as aviation fuel. This 1:50 energy ratio makes electric propulsion unsuitable for long-distance flights. For example, a 500 nautical mile mission for a 12-passenger electric aircraft would require batteries with six times more energy density. However, electric motors are more efficient (~90%) than jet engines (~50%), and new battery technologies may improve this.

For electric aircraft to be practical, energy storage must improve. Energy density is the main challenge for zero-emission electric aircraft. Another issue is the discharge rate, as takeoff and landing require high power quickly. Electric aircraft also generate more heat and require special handling at the end of their lifespan, needing new thermal management and safety strategies.

By 2019, the best lithium-ion batteries achieved 250–300 Wh/kg, enough for small aircraft. A regional airliner would need batteries with 500 Wh/kg, and an Airbus A320-sized aircraft would require 2 kWh/kg. Electric power is only suitable for small aircraft, while large passenger planes would need batteries with 20 times more energy density than lithium-ion batteries.

Electric systems can lower operating costs for short flights. For example, the Harbour Air Beavers use electricity costing about $0.10 per kWh, compared to $2.00 per liter for gas, which provides 9.2 kWh of energy per liter. Jet fuel is cheaper, and large gas turbines are more efficient. In 2021, new battery technologies like solid-state batteries (lithium-sulfur and lithium-air) showed promise for better electric aircraft performance.

In 2018, the SAE International AE-7D committee was created to set standards for electric aircraft charging and energy storage. One early standard, AS6968, focuses on sub-megawatt charging for electric aircraft. The committee is also working on guidelines for megawatt-level charging. Some airports already have electric car charging stations that can also charge aircraft.

An ultracapacitor is a hybrid energy storage system that combines features of batteries and capacitors. It can charge and discharge faster than batteries and handle more charge-discharge cycles because its process involves both chemical and electrical reactions. However, its energy density is much lower (about 5 Wh/kg) and it is more expensive than batteries, even with a longer lifespan.

A fuel cell (FC) uses a chemical reaction between two substances, such as hydrogen and oxygen, to produce electricity. Unlike a rocket motor, which creates thrust, a fuel cell generates electricity in a controlled reaction. While the aircraft must carry hydrogen (with its own risks), oxygen can be taken from the air.

Propulsion

Most electric aircraft so far have used electric motors to power propellers that create forward motion or rotors that create upward lift.

Although batteries are heavier than the same amount of fuel, electric motors are lighter than traditional piston engines. In small planes used for short trips, this difference in weight can help balance the fact that batteries store less energy than gasoline. Electric motors also do not lose power at high altitudes, unlike traditional engines. This avoids the need for expensive and complicated systems, like turbochargers, that are used to help traditional engines maintain power at altitude.

The experimental Extra 330 LE uses a 260 kW (350 hp) Siemens SP260D motor that weighs 50 kg and a 37.2 kWh battery pack. The total weight of the plane is 1,000 kg. This replaces a 235 kW (315 hp) Lycoming AEIO-580 piston engine that weighs 202 kg. The piston-engine version of the Extra 330 weighs 677 kg empty, or 474 kg without the engine. The Lycoming engine uses 141 lb (64 kg) of fuel per hour when producing 315 hp (235 kW), or 0.27 kg of fuel per kWh. To produce the same 37.2 kWh of energy, it would need 10 kg of fuel.

In addition to the motor, an aircraft’s weight is affected by the energy it must carry. For example, a 19-seat plane must carry extra fuel for emergencies, such as 5% extra fuel for unexpected events, fuel to reach an alternate airport 100 nautical miles away, and fuel for 30 minutes of holding before landing. This requires 308 kg of fuel for a turboprop engine or 4,300 kg of batteries with 250 Wh/kg energy density. Electric systems also include a power inverter, while traditional fuel systems have their own fuel storage.

A 750 hp (560 kW) experimental magniX magni500 electric motor weighs 297 lb (135 kg), and a 729 hp (544 kW) certified Pratt & Whitney Canada PT6 A-114 engine also weighs 297 lb (135 kg). Both power the Cessna 208 Caravan.

Increasing the power of an electric motor, along with changes to the plane’s design, can help balance the weight of batteries by allowing the plane to carry more weight overall, including during landing. Planes that use fossil fuels are lighter when landing, which allows their structure to be lighter. With battery-powered planes, the weight remains the same, and the structure may need to be stronger.

A hybrid electric aircraft uses a system that combines electric and traditional power sources. It usually takes off and lands using electric power, which is quiet and clean, and uses traditional piston or jet engines for long-distance travel. This allows for longer flights while reducing carbon emissions. By May 2018, over 30 hybrid electric aircraft projects were underway, and short-haul hybrid-electric airliners were planned for 2032. Some advanced examples include the Zunum Aero 10-seater, the Airbus E-Fan X test plane, the VoltAero Cassio, a modified Bombardier Dash 8 by UTC, and the Ampaire Electric EEL prototype, which first flew on June 6, 2019.

In November 2018, engineers at MIT achieved the first free flight of a model aircraft with no moving parts, called the EAD Airframe Version 2. It moves by creating an ion wind using magnetohydrodynamics (MHD). MHD has been used before to create vertical lift, but only when the MHD system was connected to an external power source.