Electric Airplanes

Had an opportunity to attend a public presentation by George Bye about the upcoming Part 23 certified SunFlyer 2 and SunFlyer 4 electric airplanes (we also treated him to lunch after the presentation). Exciting stuff. I've been keeping a casual eye on electric airplanes, and have been sort of underwhelmed to date; e.g., the eFan 2.0's hour of flight time only made sense for the most rudimentary of training missions, and Pipistrel's decision to go LSA for the Alpha Electro was mind-boggling, given the fact there's no change to LSA definitions, which still require ICE. (All-electric propulsion is now an option under Part 23.) (Also, the weight limitation of light sport aircraft puts a serious limit on the kilowatt hours you can carry with you.)

I wasn't aware battery tech has advanced as aggressively as it has; they've gone from 100 Wh/kg to 260 Wh/kg in 5 years (and anticipate ~350 Wh/kg by the time the SunFlyers are certified). The SunFlyer 2 claims a 3.5 hour endurance at most efficient cruise (~60 knots), and a still respectable ~2.6 hours (plus reserves, not including regeneration via windmilling prop) at a more reasonable ~96 knots. Best cruise speed is 131 knots (Vne 160 knots). Recharge times are about 15 minutes per flight hour on a supercharger. It can be recharged on 110V or “household” 220V if you're patient (~17 hours recharge per hour of flight time on standard 110V).

The SunFlyer 2 is meant to be mostly a primary trainer, and it'll be day/night VFR. The SunFlyer 4 will be certified for IMC flight. Both will have G1000 panels.

The SunFlyers are 30 decibels quieter than a C172: https://www.nps.gov/subjects/sound/quietflight.htm

1150 fpm climb rate at gross weight. 46" wide cabin. 100 lbs thrust required vs. a C172 at 236 lbs. (10.8 vs. 18.9 L/D ratio, respectively). Good usable loads (440 lbs. for the SunFlyer 2, ~800 lbs. for the SunFlyer 4 - and remember, none of that gets eaten into by fuel). Another point - the prop and wings lose some efficiency, but an electric engine is developing as much power at 20,000' as at sea level, without turbocharging. (Duh, right?)

BRS (parachute) equipped.

The initial build of the “conformed design” airframe should be done by March, a production prototype built by the end of the year, and within 2 years they expect certification and production. They already have deposits down on 100 aircraft, and the first year of production has already been spoken for.

TBO of the engine is 10,000 hours. The batteries have a TBO of approximately 4,500 hours (1,500 cycles), and the costs are decreasing (the presentation above assumes $5/cell, but the prices are now approximately $3/cell). The FAA has agreed the trade-in criterial for battery cell replacement is 85% of capacity, allowing for significant industrial reuse. (Estimates suggest that, by the time the battery packs need replacing, the technology will have advanced such that drop-in replacements of the same size and weight will give the 'Flyer a 5 (vs. 3.5) hour endurance, etc.

$289,000 for the SunFlyer 2, $389,000 for the SunFlyer 4, are the projected price points. (Solar panels in the wings• are a $50,000 option...)

At lunch, we were teased with "not yet announced" details of another plane they intend to announce within a year, aimed squarely at the Cirrus market.

It's all still kinda vaporware for now, and the purchase price is definitely steep (though comparable to Diamond's DA20/DA40), but the costs of operation are projected to be significantly lower, the reduced noise and zero emissions (in the airport environment; I know electricity isn't necessarily free of emissions) should help with the NIMBY problem ... I'm excited.

(FYI, Bye Aerospace has also been brought on by the XTI Aircraft TriFan 600 project, a hybrid VTOL design.)

• Mostly a mechanism for on-the-ground recharging away from infrastructure, vs. a mechanism by which you get to fly forever. ;) Though in the proof of concept they tried, at slow cruise, in June, at lower latitudes, they were, periodically, generating more power than they were consuming. But that was in an eMotoGlider. http://byeaerospace.com/stratoairnet-solar-cell-wing-ground-test-successful/