July 13, 2018
The Outlook of Electric Airplanes
Fueling with electricity offers some advantages not available in conventional internal combustion engine vehicles. Because electric motors react quickly, they are very responsive and have very good torque. While electric cars can replace conventional gasoline cars, why do not we replace conventional planes with electric planes for the same advantages? This question has stimulated many prominent aviation companies and startups to work on projects similar to those begun years ago, which led to the advent of electric cars.
An electric plane is a plane powered by electric motors. Electric planes have several advantages over conventional fuel planes since they make less noise pollution and emissions, they are mechanically efficient and may be cheaper to fly due to reduced fuel and maintenance costs. The challenges of flying electric planes are mostly due to the limitations of related technologies. One of the main obstacles to developing electric planes is battery technology. The energy density of existing batteries is not yet comparable with that of jet fuel. Although the efficiency of an electric motor is more than a fuel engine, this superiority would not cover the lower energy of batteries compared with fuel. In fact, 1kg of jet fuel contains 70 times as much energy as the best existing lithium-ion battery. This issue has made the range of electric planes limited to short flights (i.e. 30 minutes to 1.5 hours) and small planes (one to two passengers) whereas conventional planes can easily fly long distances and in huge sizes.
The other problem with batteries is about the weight. Although fuel engines are heavier than electric motors, in a conventional plane, the more fuel it burns the lighter it gets, but in electric planes, the batteries are a dead load for the whole trip.
Unfortunately, the pace at which battery technology is developing is not consistent with that of electric motors. These challenges have led many companies and startups to work on manufacturing prototypes of electric planes with one or two seaters and for short ranges until the battery technology helps them extend the range of electric planes. Since the nature of projects in aviation is different from that of projects on cars especially in terms of costs, many startups have to collaborate with big companies to cover the high costs of research and development. Some of these successful projects are introduced as follows:
Pipistrel company was founded in 1989 in Slovenia. This company specializes in manufacturing light electric planes weighting about 350 kilograms including batteries. Alpha Electro is the first fully electric plane manufactured by this company for training purposes with about 100,000 US dollars cost. It has a 60 kW motor that weighs 11 kilograms, and two 10 kWh batteries. It can fly for an hour and also half an hour more as a backup. It is worth noting that it takes 45 minutes for the batteries to get fully charged. For critical situations, a ballistic parachute is embedded on the roof of the plane, which can be activated by the pilot whenever regular landing is not possible due to system failure. It is worth noting that Pipistrel is collaborating with Uber on vertical takeoff and landing for urban trips. Pipistrel claims that the cost of running their plane is about a tenth of running a conventional plane with the same weight. Joshua Portlock who is the CEO at Electro aero says, “In electric planes, it does not matter how many times you start and stop the motor meaning it does not have to go through a major thermal cycle every time, it does not have hundreds of moving parts which is the one rotating part and direct drive no gearbox. So for short flights below one hour, electric planes are perfect since the batteries can already do it.”
The well-known German company, Siemens, has manufactured an electric plane named Extra 330LE, which is one of the most powerful among existing electric planes. The Extra 330LE is the fastest flying at a speed of 340 km/h (210 miles/hour) and can climb to 3000 meters above the ground just in 4 minutes. Weighing just 50 kilograms, the motor can produce 260 kW, which is equivalent to 348 horsepower. This plane is currently used for training purposes and to develop electric planes in the future.
Alice from Aviation Flight company is an Israeli startup aviation company. Alice is to be designed to carry up to nine passengers and travel a distance of 625 miles by 980 kWh lithium-ion batteries all combine at a total weight of 3.8 ton. Aviation Flight company has scheduled to release this project in 2019 with a price of 2.9 million dollars. Operating costs of this plane will be about $200 per hour, which is far less than the cost of $600-1000/hour for planes with a similar price.
Institute of aircraft design at the University of Stuttgart is working on an all-electric plane known as “E-Genius”. It was designed for a competition sponsored by NASA, the Green Flight Challenge. This plane can travel a 250-mile distance on one charge. This project is partly funded by Airbus. This plane has an 80 horsepower motor and a maximum speed of 100 mph.
Aero Electric is another company launching a fully electric plane called “Sun Flyer”. This model is manufactured for training purposes and the company claims that their plane can reduce the costs of flight by fuel counterparts from $45/hour to $1/hour in each flight. This plane has a 177 horsepower motor, the maximum speed of 140 mph and can fly for 4 hours.
HY4 is the first plane that can carry four people and is powered by hydrogen fuel cells and electric propulsion, which let this plane travel a greater distance. This plane has a 107 horsepower motor for the 2-seater model and a 141 horsepower motor for the 4-seater model, with a maximum speed of 120 mph and a range of 932 miles.
Wright Electric is collaborating with EasyJet, which is a low-fare British carrier. Wright Electric is working on a project with a vision to build an electric plane with 150 seats and a range of 300 miles. Here is what Jeff Engler, who is the CEO of Wright Electric, has told Ars Technica in an interview:
“The projected range of 335 miles is beyond the capabilities of today’s lithium-ion batteries and the lithium-ion battery technology may not improve quickly enough to achieve the goal within the next decade. The company is still in the early phases of designing its aircraft, and the company is considering a number of alternative approaches. We are looking at other battery technologies: lithium sulfur, aluminum air, and fuel cells.”
All the visions of these startups highly depend on battery technology. If battery technology does not progress to the level that these startups have planned their outcome, the visions will probably fail or at least be delayed. This means that the range will remain limited for a long time. This is similar to the case for electric cars. Some companies have introduced plug-in hybrid electric cars in which a gasoline engine is combined with a battery to extend the range of these cars and provide higher power. Hybrid electric planes have the same concept as hybrid electric cars. For example, in serial hybrid electric planes, several fans are installed along the wings that are powered by electricity from a battery charged by a gas turbine engine.
Hybrid electric planes could cover the disadvantages of all-electric planes. They can fly in medium distances for 2 to 4 hours. That is the reason a company called Zunum is working on hybrid electric planes. Zunum is planning to release its first commercial 10-50 passenger plane in 2020 with a range of 700 miles and the second plane with a range of 1000 miles by 2030. Likewise, the Airbus in collaboration with Rolls-Royce and Siemens are working on a hybrid electric plane called E-Fan X to release by 2020.
So far, it is obvious that electric planes are not going to replace existing planes in short term. It seems that for at least the medium term, conventional planes still dominate the skies, especially for medium and long-haul flights. Optimistically, in the medium term, electric planes may dominate short flights (under 2 hours or under 500 miles) and hybrid electric planes may dominate medium flights (2 to 4 hours) which account for a significant portion of flights around the world. The figure below shows the fuel economy of various US transport modes on short-haul (300-500 mile) trips. This figure indicates that planes are currently the most fuel-intensive transport option at about 43 passenger miles per gallon jet fuel. Replacing this amount of fuel with electricity could make a significant decrease in fuel consumption of US in short term.
It is worth noting that any leap in battery technology would expedite the process significantly. Whenever the new generation of super capacity batteries emerges, they can swap out older batteries and replace them with new super batteries to extend the range and power. If this is the case, in a long-term view, we can imagine that most of the current planes in the air will be replaced by fully electric planes that are much more environmentally friendly, make our cities quiet, and bring fuel security for future generations.