Electric aircraft are coming. But not as quickly as their backers predicted just a few years ago.
As this year’s Aero Friedrichshafen show rolls round, the pace of introduction has slowed as a combination of technical and regulatory factors have conspired to delay what its enthusiasts tout as near-silent, inexpensive flight.
Electric aircraft are undoubtedly “growing in popularity, just in the amount of technology we’re seeing coming forward”, says Experimental Aircraft Association (EAA) spokesman Dick Knapinski. A significant problem is persuading regulators to keep pace with that technology.
A particular difficulty is US Federal Aviation Administration regulations that insist on the use of reciprocating engines in certain classes of aircraft. These were formulated to prevent turbines from being fitted to light aircraft but have had the unintended consequence of severely limiting the use of electric motors.
“One of the big things right now is working with the regulators in the USA, making [electric propulsion] possible, allowing electric propulsion to be part of the ultralight and light sport aircraft categories,” says Knapinski. “We would like to open that up into other aircraft categories so that as the technology emerges, the regulatory environment here in the USA would be able to accept these products. That’s probably the most important hurdle.”
Knapinski believes that the FAA has taken on board the need for change. “They just have to work through all the legalities in changing the language.”
Brien Seeley, co-founder of the Comparative Aircraft Flight Efficiency (CAFE) Foundation, believes that the electric aircraft market needs some sort of stimulus to propel it from the fringes into mainstream use.
Chinese company Yuneec International has probably done most in this regard, he says.
Overall, the general aviation market has seen little innovation or investment in recent years, he says. Indeed, it has tended to be military-biased companies such as General Atomics or Northrop Grumman that have been looking most closely at electric power – for unmanned aerial systems, not light aircraft.
The problem of energy density – extracting enough power for sufficiently long periods – can be solved by using replaceable battery packs; like Knapinski at the EAA, Seeley believes the more intractable problem comes in the form of the regulatory regime.
“Research has shown that [a suitable power source] is already do-able, but as soon as you make the vehicle, you run into the question: ‘How will the FAA certificate the aircraft when currently there is no set of rules for doing so?’
“I think people see [electric aircraft] as the future, but it has not yet reached critical mass.” If electric aircraft are really to make an impact, he believes, there is no point in them simply replacing Cessnas and Pipers in what he describes as a saturated market; a revolutionary jump in capability is required.
That capability could come in the form of short take-off, ultra-quiet, autonomous “sky taxis”, he believes, although a halfway house would be a remote pilot overseeing the flight.
He sees these electrically-powered aircraft largely replacing the traditional owner-pilot model. A queue of waiting two-passenger sky taxis at small, secure airfields around towns and cities could deliver the swift transport that a time-pressed world demands. He believes that prototypes could exist by the end of the decade.
Seeley also cites the expense of bringing a new aircraft to market and jumping through the certification hoops, which can cost anywhere from $50 million to $100 million. This could be overcome, but it would require an act of will by governments to ease the regulatory burden.
On Flightglobal four years ago, Seeley said he was “extremely confident, 99% or more, that in 10 years, electric general aviation aircraft will be flying”. Lack of funding, he admits, has probably pushed that date four years downstream.
Although energy density issues are being solved for fixed-wing electric aircraft, they remain problematic for rotary-wing models. Sikorsky’s Firefly project involved taking a Schweizer S-300C light helicopter and replacing its Textron Lycoming HIO-360 D1A with an electric motor powered by lithium-ion battery cells. When Flightglobal reported on the project in July 2011, the helicopter was said to be just months away from its first flight. Almost three years later, that milestone has yet to arrive.
Firefly programme manager Jonathan Hartman says “the technology is sound and the vehicle is ready”. The problem: getting enough power from an electric power unit to cope with the particular stresses required by vertical take-off and landings.
“Sikorsky Innovations looks forward to incorporating and flying a future energy storage system that provides a meaningful amount of endurance,” says Hartman. “The most significant challenge for further development at present is finding an energy storage system (batteries, fuel cells, super capacitors as examples) with a sufficient balance of energy density, power density, safety and reliability to provide a compelling flight endurance for a VTOL application.” There is currently no indication when Firefly will take to the air.
A similar problem struck Colorado-based Bye Energy, which built an electrically-powered Cessna 172. “We went through the rigour of ground taxi and flight tests,” says founder George Bye. “It was very valuable research, but the energy density of the batteries wasn’t sufficient to make it a practical solution.”
Battery technology is advancing steadily and energy density has doubled in the past few years, which brings the prospect of commercially viable electrically-powered flight closer. For the moment, however, Bye’s company is focusing on unmanned designs aimed at the governmental or military markets, notably making use of solar energy cells embedded in the airframe.
Germany is in the vanguard of electrically-powered flight, with Lange Aviation having successfully obtained EASA certification for its Antares 20E motorglider (a larger version, the Antares 23E, is currently flying on a national permit, pending completion of the certification process). The fleet has so far flown around 80,000h without problems, says chief executive Axel Lange.
They derive their power from lithium-ion batteries from French company Saft. Positioned in the leading edges of both inner wings are two battery packs with a total of 72 cells. “I’m not allowed by Saft to say what the output is, but it’s a lot,” comments Lange. The batteries have a life of around 20 years and could give power for up to 4,500 cycles.
Lange Aviation has also developed, together with the German Aerospace Centre, or DLR, the Antares DLR-H2 testbed, which the company says is the world’s first piloted aircraft capable of performing a complete flight powered only by fuel cells.
This has performed flights of up to 500km (310 miles), from Zweibrücken to Berlin, with a maximum time aloft of around 3.75h. This is a pure research machine, says Lange. “You need a pilot who is also an engineer and another engineer to start the fuel cells. So, it’s not ready for the market. But it works.”
The H2 was designed to test fuel-cell systems that may one day fly in airliners, possibly replacing the auxiliary power unit and other subsystems. In the process, it also tests systems that will be incorporated into the company’s Antares H3, which is about 18 months from first flight, and for which a new type of fuel cell is currently being bench-tested.
This fuel cell is known as a “high-temperature PEM”, or proton exchange membrane, that is used in its design. The fuel cell can use either hydrogen as a fuel – giving up to 15h of endurance – or methanol. The latter is more difficult to work with, but could give a flying time of up to 50h and a range of up to 3,200nm (6,000km). Fuel and the fuel cells would be carried in four pods under the 23m (75ft) span wings, driving a pusher propeller mounted at the top of a T-tail.
The H3 will initially be a manned aircraft, but once these extreme flight durations are proven, unmanned operation then becomes the only real option, says Lange. The H3 could be used for tasks such as earth observation or surveying. Further German involvement in the sector comes from PC-Aero, which anticipates having its Elektra One certificated by the DULV by the end of summer.
The 11m span battery-powered aircraft has around 12kWh of power, giving endurance of around 3h. Economical cruising speed will be 70-80kt (130-150km/h), with a maximum speed of around 90kt and range of more than 400km, according to chief executive Calin Gologan.
PC-Aero designs and certificates the single-seat Elektra One, but will sell licences for others to build it, rather than constructing it itself.
It is also due to start work on a prototype two-seater Elektra Two in April or May, with the proof-of-concept aircraft due to take around a year to build. “I don’t want to go into too many details,” says Gologan. “We will be at Aero Friedrichshafen and there may be announcements there.” The Elektra Two would have a new, as yet unspecified, power unit.
Fellow German company Flight Design has gone down a different route, creating a hybrid powerplant that incorporates a lithium-iron-phosphate battery to power an electric engine that acts as a starter, generator and also provides additional power during take-off and the initial 5min of climb. It supplements a Rotax 914.
“The manufacturers see the advantage,” says chief executive Matthias Betsch, “but at the moment they have enough conventional projects and not enough capacity to take this additional project on board. But I think it will happen.”
The company that has come closest to making electrically-powered aircraft a regular feature on airfield aprons is China’s Yuneec International, manufacturer of what it describes as the world’s first commercially-produced electric aircraft, the two-seat e430.
This is currently undergoing certification with Germany’s DULV. Yuneec has already achieved DULV certification with its ESpyder electric ultralight. The e430 is an all-composite, V-tailed two-seat light sport aircraft, powered by lithium-ion batteries that allow 2h of flight with a maximum speed of 80kt and a stalling speed of 35kt.
In the USA, Yuneec uses its customer service and marketing division, California-based GreenWing International (GWI) as the conduit for its products. “The e430 is designed as a mainstream aircraft that can be flown cross-country or used for primary training,” said GWI’s US marketing and customer service manager Tony Settember.
He sees the e430 as appealing to two classes of customers: “People who want to own something that is cutting-edge, new and eco-friendly. It will be a niche market to begin with.” However, “In the USA, it won’t survive on the ‘wonder of flight’ factor. It will be the economics.”
Sharply-reduced operating costs compared with conventional aircraft will make it popular with training schools, believes Settember. “A Cessna 172 burns 8 gallons an hour, that’s $48 an hour in fuel. The e430 will burn $1-3 an hour in equivalent fuel costs,” he says. The electric motor is also designed to be virtually maintenance-free, he adds, whereas 2,000-3,000h on a Lycoming will require thousands of dollars worth of maintenance.
An e430 takes around 5h to fully recharge its battery, but that problem can be solved by the use of swappable battery packs. Flying schools will quickly realise, he believes, that even if they cannot do a full 40-50h training curriculum on the e430, undertaking the first 20h on it will still cut their costs significantly.
So, electric power remains on the horizon. But that horizon, in most cases, remains frustratingly distant.