The whole concept of flying with nothing more than electric power seems somehow anathema to aviation.
It wasn't so many years ago when people used to say the same thing about cars. Up until a few years back, it was almost incomprehensible that electric power could ever be made reliable and efficient enough to power an automobile more than a few miles.
That was before the advent of such innovative technology as the Toyota Prius and Elon Musk's remarkable Tesla. The Tesla was one of the first to employ electric power in a luxury car, using either a 60 kWh or 85 kWh battery.
Now, we're looking at the possibility of electric airplanes, and that may be arriving just in time to help solve the coming pilot shortage.
Every indicator suggests the pilot shortage is real, and some people are convinced it will become even more acute in the near future. World air traffic is expected to grow by nearly 5% annually and, for that reason, Boeing estimates the industry will need about 500,000 new airline pilots in the next 20 years.
That means we'll need more pilots and more airplanes to train them. For that reason, the trainer market will have to expand in the near future. Fifteen years into the new millennium, there's really only one modern, dedicated trainer remaining on the market—Diamond's excellent DA20. Perhaps accordingly, Mooney recently announced plans to revive the Mooney M10, and Discovery Aviation has plans to put the on-again/off-again Liberty XL2 back into production. Piper, Cessna and Beech have apparently elected to steer clear of the two-seat trainer market altogether.
Meanwhile, a company in Nevada, Aero Electric Aircraft Corporation (AEAC), is determined to develop an electric airplane that would employ a series of Tesla batteries to provide as much as 4.0 hours endurance at max cruise. At this writing, Aero Electric, in conjunction with its partners, Bye Aerospace and PC-Aero, GmbH, of Germany, is flight-testing its Sun Flyer—a single-seat, fully electric, proof-of-concept aircraft flying out of Denver's Centennial Airport. The Sun Flyer design is based on the Elektra One developed by PC-Aero.
AEAC made its first flight on July 15 of last year and has been working toward developing this proof-of-concept airplane into a two-seat trainer in the near future.
As the name implies, the Sun Flyer employs electric power from an electric motor, batteries and solar cells mounted on the top surfaces of both wings. The Sun Flyer currently uses a single Tesla Li-Ion battery and 7.5 square meters of photovoltaic cells, but the planned two-seater could employ as many as three Tesla batteries and the aforementioned solar cells. Eventually, AEAC hopes to market the equivalent of a "flying Tesla" that might carry four people and a ballistic parachute.
Development of battery and photo voltaic technology is proceeding at an exponential pace, and the advantages of electric power from an operational point of view are already impressive. A battery-powered airplane has little need for cooling air, and that translates directly to a more aerodynamic cowling. This results in a significant reduction in flat-plate area and cooling drag. Similarly, the reshaped cowl means that blades on the variable-pitch, full-feathering prop can be larger and more efficient in contrast to a propeller on an aircraft with a reciprocating powerplant.
The airplane's 40 KW (54 hp) Geiger Engineering HPD-XXD motor isn't only smaller and more compact than any fossil fuel-burning mill, it's dramatically lighter, about 24 pounds total, partially because it has no magnetos, no alternator/generator, no starter and none of the other accessories associated with piston engines. A typical engine installation in a two-seat airplane such as a Cessna 150, Skipper or Tomahawk weighs close to 300 pounds.
The Sun Flyer itself is also remarkably light. Using high-tech carbon-fiber materials, the current single-seat technology demonstrator fuselage weighs only 30 pounds, and each wing weighs 44 pounds.
Using pure electric power also means you don't burn any oxygen, so the engine doesn't lose power as it climbs. In other words, it's not affected by high-density altitude. There's also little, if any, vibration. Imagine that your airplane is being powered by a perfectly balanced electric fan.
Add to that (or more accurately, subtract) the fact that the aircraft no longer needs to carry fuel in the wings or anywhere else, and the entire structure can be built lighter and more efficiently. True, an electric airplane needs to carry batteries, but they're a renewable resource that's typically located in the lower aft section of the fuselage. With no need to lean the mixture, the Sun Flyer uses a single lever to control power—basically a sliding rheostat. Managing the flow of electricity is essentially automatic.
Reliability should be excellent by general aviation standards, primarily because the Sun Flyer's electric motor has a total of one moving part. Depending upon frequency of usage and other factors, batteries will need to be replaced every 2,000 hours at a cost of only $2,000.
From a good neighbor standpoint, the acoustic signature of the current Sun Flyer is about 55 dB at 1,000 feet. George Bye of Bye Aerospace characterized the sound as "about as loud as a lawn mower 1,000 feet away." Similarly, there will be no CO2 emissions, since the electric motor burns no fossil fuels or any other type of liquid or synthetic fuel. There will be no heat signature, either—not too important for general aviation, but a point of interest for the military.
Preliminary specifications on the proposed two-seater include a gross weight of 1,320 pounds and an empty weight of about 700 pounds. (The 1,320-pound gross is the LSA maximum, but AEAC has since decided to certify the airplane with a Standard Airworthiness Certificate.) Four Tesla batteries weigh in at about 180 pounds, so equipped empty weight works out to 880 pounds. That leaves a payload of 440 pounds—pretty high for a two-seater. AEAC plans to certify the airplane in the normal category on a Standard Airworthiness Certificate. The cabin is planned for 49 inches across at the elbows.
Max endurance speed is 60 knots, and typical cruise has been set at 80 knots. Range is projected as 250 nm, though that may be a little irrelevant in the training mode. An AEAC spokesman commented that climb from sea level will be about 700 fpm (the wing won't be able to ignore density altitude) and will exact the most electrical power, so there's some interest in providing a limited fuel cell capability for the initial climb; when the aircraft reaches cruise altitude, it will switch to pure electric power.
Based on 800 hours' utilization a year, AEAC estimates operating costs for a two-seat Sun Flyer as $5/hr in contrast to $73/hr for a Skyhawk and $53/hr for a Diamond DA20. Keep in mind that this is a cost projection on an airplane that hasn't flown yet, so treat it accordingly.
As higher energy-density Li-Ion batteries are developed (and the success of Tesla will probably assure progressively more efficient batteries), the cost to fly electric will come down. AEAC has no price estimate for a certified two-place Sun Flyer, but the airplane will probably come standard with three Tesla batteries, good for an hour of endurance each, and the solar cells may contribute as much as an additional hour of flight time.
Who knows? In a few years, you may be driving your electric Tesla to the airport, pulling your electric Sun Flyer out of its hangar with an electric goat and flying away to do a day's business—all without burning a drop of carbon fuel.