Whenever you see the term proof-of-concept in front of an aircraft designation you need to think: extremely experimental, might never come to fruition, and of course, probably going to break. The two pilot-geniuses behind the Swiss Solar Impulse perpetual motion flying machine (I say that because frankly, it never has to stop flying), Bertrand Piccard and André Borschberg, have been holed up in Hawaii for months now with their proof-of-concept Solar Impulse airplane because they broke it on the five-day non-stop flight across the Pacific
from Nagoya, Japan, to Hawaii. That put their proof-of-concept flight around the globe on perpetual hold. New batteries had to be manufactured for the aircraft and the battery cooling system, which was determined to be inadequate for such a long flight, had to be completely redesigned and manufactured, as well.
It turns out the mission needed $20 million to make that happen, which meant funds needed to be raised, as well. Fundraising, however, is something Piccard and Borschberg’s idealistic group is quite good at. They have worked slowly over a couple decades, to date, to bring the experimental Solar Impulse program to life. In the process they’ve constructed and flown several aircraft that, by virtue of their electric engines, batteries and solar cells, can stay aloft essentially indefinitely. April 15, 2016 they announced that the airplane is ready to relaunch its mission. Next stop? Somewhere east of the California coastline. What are they waiting for? The perfect VFR day, or close to it. Yeah, there are still limitations. But remember, it’s just a proof-of-concept machine.
Once upon a time people delving into electric-powered flight were considered the outliers of experimental aviation. That is no longer true. At Sun ‘n Fun 2016, which concluded earlier this month, the CEO of the Colorado-based Aero Electric Aircraft Corporation (AEAC) announced that its all-electric powered two-place trainer, the Sun Flyer, was expected to fly within weeks. The Sun Flyer is powered by a single tried and true Emrax 268 electric motor putting out 100 kilowatts, which is basically 135 hp.
“Because the nose of this airplane is so sleek and narrow, however, the propeller is not blocked, giving you so much more power,” Bye explained to the Sun’n Fun crowd. “For instance, a typical Cessna 172 loses 30 percent of the power generated by the prop because it is blocked by the flat plate surface of the nose of the aircraft,” he said. “On the Sun Flyer 95 percent of the propeller energy can be used to convert torque to thrust. That’s how you get to an equivalent horsepower of more like 160 hp.”
The all carbon fiber construction of the Sun Flyer keeps it light, and South Korea’s LG’s chem batteries provide 260 watt-hours per kilogram of electricity for the engine, which adds up to three hours to empty. Except this airplane has regenerative energy capture technology in its propeller. What that means is that energy is recaptured when the airplane descends at more than 400 feet per minute. That energy recharges the batteries. This is how the Solar Impulse stays aloft each night, when its solar cells cannot capture light and turn it into energy. The pilot climbs in the late afternoon to 28,000 feet, and then descends all night long in parabolic arcs. It is proven technology, and AEAC’s Sun Flyer intends to use it to stay aloft for, well, who knows how long?
“It is certain that students who train in a Sun Flyer will have totally different fuel planning skills,” Bye chuckled. The Sun Flyer also sports solar cells on its upper wing surfaces, for recharging on the ground and in the air on sunny days. Bye stated that two days on a sunny ramp may be all a Sun Flyer needs to fuel up for its next sortie. In any case estimated operating costs, including maintenance and ground power refueling, is around $11 per hour. That compares to an average flight school Cessna 172’s estimated operating costs of $66 per hour in 2016 dollars.
AEAC intends to certify the Sun Flyer in 14 CFR Part 21. It will have a Standard Airworthiness certificate, a 1654 lbs max gross weight, two seats, a single engine, and a 45-knot stall speed. The payload will be 440 lbs, according to Bye. It’s sound footprint at 500 ft AGL? Nearly nil, at 55 decibels. If the upfront price tag is right (and there is all kinds of speculation there) it could revolutionize basic flight training, making it affordable for a larger swath of people, and more profitable for flight schools, all at once.
AEAC will have competition in the all-electric trainer market from Slovenian Pipenstrel, Chinese Yuneec and behemoth Airbus. Both companies are well into their two-seat electric airplane programs. Personally, I can’t wait to see what the flight training fleet looks like in 2025.