Making general aviation more environmentally friendly has in the past had an alternate fuels focus, but as batteries improve, all-electric aircraft are emerging in Europe. From Lange Aviation's Antares 20E in 2005 to this year's new entrant, the PC-Aero Elektra One, there is a growing European challenge to the likes of China's Yuneec and its E430 model that already has a sales office in the UK. But which is more likely to hold back worldwide industry for the electrification of private flight: technology or its regulation?

This week German company PC-Aero will unveil its battery-powered Elektra One at the Aero Friedrichshafen air show with the goal of having it fly by June and go on sale later this year. The single-pilot Elektra One follows Chinese company's Yuneec battery-powered E430 two-seater light sport aircraft, which flew in California last year.

As an all-battery electric two-seater that has already flown, it is a de facto market leader that Europeans need to challenge. According to Yuneec the E430 uses three lithium polymer (li-poly) battery packs to fly for 2h in an "optimum cruise" with two people on board. By increasing the battery packs to five, a single pilot can get 3h of flying time. Presented at Oshkosh last year, Yuneec's first prototype E430 undertook 22h of flying in Camarillo, California to be awarded its experimental certificate by the US Federal Aviation Administration so it could be demonstrated at the air show. Today Yuneec is aiming to sell its E430 from mid-2011.

E430 Yuneec
Yuneec, a Chinese company that flew its prototype in California last year, is the first to offer a battery-powered light sport aircraft. Picture: Yuneec

A mixture of prototype improvement and a need to create rules for certification has set the sales target date back from late 2010. The company could attempt to sell the E430 as an experimental aircraft in the USA, but would prefer to have certification for the light sport aircraft class. Certification would also aid Yuneec's plans to sell its all-battery propulsion system as a retrofit.

PC-Aero has no retrofitting plans, but it is working on a family of aircraft. Initially it wants to sell its Elektra One as an ultralight, as its mass is expected to be at the most 90kg (198lb). PC-Aero's chief executive Calin Gologan says: "For batteries you need a very light structure, very good aerodynamics and have to accept a slower speed."

His goal for Elektra One is for it to fly for 3h with a range greater than 400km (216nm). Gologan is looking to sell the Elektra One into the US ultralight market. The other aircraft in Gologan's family plan are two and four-seaters. For the two-seater, Gologan is aiming for sales in 2011, with serial production in 2012, selling it also as an ultralight in Europe, a class that he says has a 470kg mass limit. In the USA Gologan would sell it as a light sport aircraft (LSA), which he says has a mass limit of 600kg. But a problem with the US light sport class certification is that it does not include electric engines - an issue Yuneec is working to resolve.

Cell-powered aircraft
Boeing created this fuel cell-powered aircraft, but has no general aviation intentions. Picture: Boeing

Gologan is expecting the legal situation to be resolved by the time he is ready to sell his four-seat version in 2014. When that happens he says: "I give manufacturers [like Cessna] 10 years to survive after the four-seat electric aircraft reaches the market. Future emissions penalties for polluting technology mean electric has a future and the operating costs of electric will be a lot less."

In the near term PC-Aero has one advantage for its one- and two-seaters: Europe already has a certificated electric engine under its CS22 part h rule. The electric engine was certificated for Zweibrücken, Germany-based Lange Aviation's Antares 20E motor glider. The 20E's electric engine has been certificated by the European Aviation Safety Agency for the very light aircraft class, which has a maximum mass of 750kg and can carry two people. Since the start of production in 2005 the company has sold 72 Antares 20E motor gliders.

Like Lange, whose 20E is an electric evolution of its Antares 18S and 18T models, not everyone is ready to follow the lead set by Yuneec and PC-Aero in designing new aircraft. For German company Flight Design and its US counterpart in Colorado, Bye Energy, the key is to provide electric engines for existing internal combustion-powered models.

While Yuneec was presenting its E430 at Oshkosh in 2009, Stuttgart-based Flight Design unveiled its Hybrid Power Engine. Flight Design's hybrid system uses a lithium ion battery-powered electric motor in combination with a Rotax 914 engine, the development of which began more than three years ago. The purpose of the battery and electric motor is to boost power to enable take-off. The engine uses technology from the automotive sector, such as its electric motor controller electronics.

Flight Design has built a proof-of-concept engine, while ground test runs have been ongoing in 2009 and 2010. The company says the tests are delivering the desired results, but "we still have to complete the full variety of power levels and simulation of failure modes". The Stuttgart company expected to carry out flight tests in the second half of 2009, but they have been put back to this year's third quarter. "The current market situation made us more careful and has delayed the plan slightly," says Flight Design's technical director Oliver Reinhardt. The company's target market is the small four-seat aircraft, which it says "are typically powered by engines of the 160-200hp [120-150kW] class. Considering the weight and dimensional characteristics, we see a significant retrofit market," it says.

On the other side of the world in Colorado George Bye runs Bye Energy and he also sees the largest immediate market for electric as retrofitting the existing fleet. Like Flight Design, Bye is planning to offer a hybrid system for 200hp aircraft, but in the near term wants to offer an all-battery replacement for the piston engine. The future hybrid system will be a lithium ion battery with a "small auxiliary power unit", which is yet to be selected. Bye sees the hybrid system as a way of extending flight times, "for 1h or 2h, all-electric is fine, but for longer range you need extra power." Once back in the hangar Bye envisages solar panels on the roof or wind turbines generating the electricity to recharge the aircraft.

Like Flight Design, Bye is also planning a proof-of-concept flight for his all-battery replacement system later this year. This will involve the US Federal Aviation Administration and takes place at Denver, Colorado's Centennial airport. Bye says, "we don't talk about a particular plane for the trial as we don't want to give the impression that the technology is only for one market and one model". He expects the concept flight to prove his company's undisclosed projections for range and performance.

In the USA, Gologan's view of an all-battery electric future is shared by an organisation that works with NASA on advancing aviation technologies. "It would be transformative for general aviation," says Brian Seeley, the founder of the Comparative Aircraft Flight Efficiency (CAFE) Foundation, which works with NASA. Gologan's Elektra One is being entered into CAFE's 2011 Green Flight Challenge, a competition Bye would like to participate in as well.

NASA's innovative partnerships programme and CAFE created the Green Flight Challenge. It is a flight-efficiency competition for aircraft that can average at least 87kt (161km/h) on a 320km (175nm) flight while achieving greater than 322 passenger kilometres per 3.79 litres (1USgal). Seeley is looking forward to the inclusion of electric aircraft in the race. "In competitions we have only seen internal combustion engines before, using mogas, pump gas for cars, low lead gasoline, so this is about to change radically with pure battery electric and biofuels," he says.

Because of CAFE's role and work with NASA it was at the foundation's April 2008 Electric Aircraft Symposium that the Experimental Aircraft Association announced it had asked the FAA for regulatory exemptions to allow electric motors in ultralights and LSAs.

Seeley has watched battery development over decades, "I have followed [electric propulsion] as an interest for many years. I built a road legal electric car in 1973, a 2,000lb car, but 1,100lb of it was battery. It could do 70mph for 22 miles."

And for the all-electric products on the brink of worldwide sales, Seeley's view is that a range of issues will have to be tackled for aviation certification. They include battery maintenance, charging effectiveness and intelligent self-diagnosis. He adds: "They can't overheat, have to be waterproof, able to fly in rain and they need a good gauge, so you know how much time is left. That will have to be well done." Further out, Seeley envisages aircraft able to place conformable solar cells on the wings for in-flight energy supply.

Such is the expectation of a technological tipping point that the voluntary standards development organisation ASTM International is now drafting standards. ASTM International's committee F37, which focuses on the light sport aircraft class, is examining the issue of aircraft powered by electric propulsion. Yuneec's UK-based managing director for sales and marketing worldwide Clive Coote is working with ASTM on the standards.

Flight Design is also talking to the ASTM, "We are involved in the current activity of defining ASTM standards for all-electric LSA aircraft. The FAA has not yet been directly contacted. Following the very positive response of EASA, we decided to postpone this discussion for the time being."

The ASTM International work will be followed by an FAA team that in 2011 will examine what type of standards and rules would be needed. "This is all in the beginning stages. Our approach is to have the companies and industry prove the technology first and establish that the technology is viable under ASTM standards," the FAA says. "Then the FAA will examine how we will accommodate the aircraft from the regulatory and/or policy side."

EASA is taking a similar approach. "Sometimes people are asking for this [the certification of an electric engine], we have some companies in mind. We are open minded to new technology as long as they are safe enough," says EASA's general aviation design surveyor Stefan Ronig.

For hybrids the certification process could be simpler. "We have been talking already to EASA for the certification of the system. EASA was very much encouraging us to proceed," says Flight Design's Reinhardt. "The way of certification will be by means of supplementary type certificate to the existing engine certificate. The electric enhancement is designed in a way that does not affect the basic engine."

EASA's initial airworthiness rulemaking officer Boudewijn Deuss says: "The technology comes through certification. Rule-making comes after technology certification. You can certify an aircraft without having a whole set of rules but you have to develop rules for special conditions."

 Hybrid electric W445, Tim Brown

Flight Design's approach is to minimise the challenges for certification as much as possible. The company also sees the use of an electric propulsion system alongside an internal combustion engine as a route to an all-electric tomorrow. Reinhardt says: "It will significantly support future development of all-electric aircraft propulsion."

Fuel cells have been the future power technology for some time. The technology's theoretical energy density - more energy in the same volume - is far greater than that of today's batteries, but difficulties such as in-flight hydrogen fuel storage are still holding back a fuel cell-powered product.

Instead governments and large corporations have investigated the technology for auxiliary power units and unmanned air vehicles and 2008 saw two different projects fly. The German aerospace centre DLR worked with Lange on the Antares DLR-H2. The Lange Aviation Antares motor glider was the basis for the DLR-H2 aircraft that was used to test a fuel cell system provided by the DLR's Institute of Technical Thermodynamics. It was developed to test fuel cell technology for possible future APUs on board Airbus airliners. The DLR now intends to operate its Antares DLR-H2 for research purposes until 2017.

But Lange's chief executive Axel Lange is does not intend to take that experience and offer a fuel cell or battery-powered manned aircraft. Instead he is working on a fuel cell-powered UAV technology demonstrator with an undisclosed partner. The UAV, called H3, will be optionally manned to enable safe test flights and could pave the way for H4, a long-endurance fuel cell-powered UAV being planned by Lange. As for the prospects for battery-powered flight, Lange says: "When battery energy density doubles then I will be interested."

In March 2008, Boeing Research and Technology Europe flew a fuel cell-powered modified Dimona motor-glider for 20min at its Spanish test site. The US company ended the project after that flight and would only say that the fuel cell technology would be used for other unidentified projects. Last month Boeing announced it would work with a Japanese company on fuel cell APUs for 2016.

But in Europe fuel cell manned flight work has carried on. In June 2009 a modified Alpi Aviation Pioneer 300 ultralight powered with batteries made a successful flight, reaching a speed of 135kt (250km/h). Called Skyspark, the team behind it is planning a flight for 2011 to demonstrate take-off and cruise using only fuel cell power. The aircraft's development is supported through donations of equipment and people's free time. "We are looking for sponsors and are working on establishing some research projects," says the Skyspark project's leader, aeronautical engineer and former European Space Agency astronaut Maurizio Cheli.

How confident is an independent expert like Seeley that the technology and certification hurdles will be overcome for a new world of electric flight in this decade? "I am extremely confident, 99% or more, that in 10 years electric general aviation aircraft will be flying." And Lange might want to rethink his attitude towards manned electric flight. "At our conference this April a Dr Jaephil Cho from South Korea is promising an eightfold increase in [battery] energy density."

Electric aircraft

Source: Flight International