August 2015 Issue
A Tilt Toward Hybrids
Pipistrel’s early-to-the-finish line Alpha Electro may be the first commercially viable e-airplane, but there are other projects on the developmental horizon. Judging their technical merit is an academic exercise, but the companies pursuing them obviously believe there’s a future in electrics, so these are worth a mention here.
If there’s any emerging trend in electric airplanes, last April’s Electric Aircraft Symposium in Santa Rosa, California, revealed it to be a tilt toward serious investment in hybrid-drive aircraft. Airbus has announced an ambitious project, Diamond has done the same and is partnering with Siemens AG, whose breakthrough super-efficient motors for electric aircraft were detailed at the symposium.
Another U.S. manufacturer, Aero Electric Aircraft Corp., is leveraging technology developed by PC Aero in Germany to produce what it hopes will be a certified solar electric trainer for delivery in 2017. AEAC has an order from Spartan Aeronautics reserving the first 20 of its Sun Flyers for the school’s long-established aviation program. We’re not sure how firm that commitment is.
Electric airplane development has been propelled mostly by small companies or startups. But the Airbus entry into the market with its proposed E-Fan project showed that larger players are at least interested in e-flight as showcase efforts. Although the $53 million Airbus has committed to its electric flight project is but a rounding error in the consortium’s $60-billion-plus business, it appears to be the largest above-ground electric development program to date and is certainly the most ambitious.
In a partnership with a handful of other companies, including Safran and Daher, Airbus formed a new subsidiary, Voltair SAS, to develop two aircraft. The E-Fan 2.0 is promised for 2017 and will be an all-electric, battery operated two-seat trainer powered by a pair of ducted fans.
The E-Fan proof of concept made its first flight in March of 2014 and was displayed at the recent Paris Airshow, where it completed its 100th flight. Performance details remain sketchy but from what Airbus has released, it’s similar to the Alpha Electro, with the longest flight lasting about 50 minutes. A flight across the English Channel is planned.
At EAS, Airbus’ Ken McKenzie revealed something interesting about the E-Fan 2.0: It taxis to the runway with chain-driven wheels rather than thrust from the propeller. He said Airbus found this to be more efficient. Despite relatively few test flights, Airbus has taken on 10 industrial partners and aims to go after the same market Pipistrel is: flight training in Europe. The company announced the E-Fan 2.0 will be manufactured in Bordeaux, in the south of France, with deliveries in 2017 planned.
“The battery technology continues to evolve and change. The important part for us is to lock down what technology to use; if you decide on one today and another one comes along tomorrow, you suddenly say, why did we do that?” McKenzie said. One of the technologies Airbus will have is what it calls an EFAC, a motor controller and electrical management system that can isolate individual battery cells, if necessary.
Even more ambitious is the E-Fan 4.0, a four-place hybrid that Airbus plans to aim at the U.S. GA market with aircraft certified and available before 2020 for both the training and the personal aircraft market. The 4.0 will be built and serviced in the U.S. “To give us the range that we want, the energy density for the batteries just isn’t there yet. So we’re going toward some kind of hybrid drive,” McKenzie told us. He didn’t offer details on this, but the other hybrids we know of—Diamond and Pipistrel—are serial hybrids that use a combination of a small engine driving a generator and a battery pack, with the batteries providing takeoff and climb burst power and the engine the cruise and battery recharge capability.
And that’s what Diamond Aircraft has in mind with its next electric hybrid project, its third such effort. Working with Siemens, the new aircraft will be based on the company’s DA40 airframe and will have two small electric motors in pods mounted on a canard.
Primary power will come from an Austro AE300 diesel driving a generator to both power the motors and charge the batteries, which will consume the airplane’s entire back seat, says Diamond CEO Christian Dries, rendering the hybrid a two seater.
But load carrying isn’t the point of the new project, Dries said, proof of concept and certification are. “This airplane is based on serial-production technology. Most likely this airplane will not come on the market,” Dries told us, “but this is a so-called certifiable program. That means in this airplane, we help the authorities set the standards for electric airplanes.”
The two motors weigh less than 30 pounds, but each deliver 85 kW or 114 HP. Battery weight totals 200 kg or 440 pounds, the heaviest battery payload of any small electric aircraft we know of. At typical cruise speeds of 110 to 120 knots, the airplane is expected to have a 10-hour endurance, burning about 1.8 GPH. Diamond has no specific timeframe on when the first flight will occur. “That depends on the authorities,” Dries said.
While Pipistrel is out front with its pure electric Alpha Electro, it’s also making a major investment in electric hybrid technology with its Panthera retrac. While the gasoline model suffers delays as the company reconceives it with a new engine, the hybrid version continues to advance. During our visit to Pipistrel’s Ajdovščina, Slovenia, factory, Vid Plevnik told us the Panthera hybrid may appear as early as next year’s Aero show in Friedrichshafen, although not in flyable form.
Like the Diamond and Airbus concepts, the Panthera is a serial hybrid using a small gasoline engine to drive a generator. Lithium-ion batteries in the wings provide burst power for takeoff and climb. Plevnik said for the first-generation hybrid, the Panthera will have a turbocharged Rotax 914 and batteries of lower energy density than those used in the Electro, but capable of much higher short-term discharge rate. Economy of flight isn’t the primary driver here, but the ability to operate unhindered by density altitude with the safety of a secondary power source.
At AirVenture last year, Aero Electric Aircraft Corp. showed a single-place electric trainer called the Sun Flyer, which leverages technology developed in Germany by PC Aero. It uses conventional lithium-ion batteries whose endurance is extended by solar cells on the wings. AEAC is developing a two-place version of the airplane which it plans to certify under the primary category for a price under $200,000.
From China, comes the Yuneec e340 pure-electric trainer which flew at AirVenture in 2010. Although the company’s website says the airplane continues in development, calls and e-mails to GreenWing International, its U.S. distributor, weren’t returned. The company says it’s also taking deposits on the eSpyder, a single-seat experimental electric.
Also from China is the RX1E developed by Shenyang Aerospace University. The company claims to have delivered its first customer aircraft in June and says it will have one at EAA AirVenture in July. Cost is $163,000 for a two-seat, sport/trainer type aircraft.