Operating on only the Prius electric engine, with the small and efficient Prius auto engine providing recharging power ONLY would be VERY efficient. It also eliminates the issue with “twinning reduction gearboxes” and their associated complexity and weight–the electric motor is very reliable–and in the event of a stoppage of the small Prius engine, will be able to sustain flight for quite some time on battery power–it doesn’t take much power for cruise. It would be a spectacular short-field machine with that combined torque–and no action needed in the event of a power loss.
I don’t have it right in front of me now, but the combined weight of the two IO-520 engines plus prop would go a long way toward a “drop in” of the entire Prius engine, electric motor, and battery. The dry weight of an IO-520 “bare” (without accessories) is 405# each–PLUS the weight of starter, generator, vacuum pump, fuel injection, mags, exhaust–let’s just say 100#–plus the weight of 19 additional quarts of oil compared to the Baron–TIMES TWO makes it 1010 pounds–PLUS one prop & governor @ 100 pounds–PLUS the existing 2 batteries in the Baron–that’s about 1240 pounds saved–goes a long way toward the weight allowance for a Prius engine plus batteries. There also would not be a requirement to haul around 166 (or more) gallons of fuel.
The Prius battery weighs in at 99 pounds INCLUDING THE CONTROLLERS for the new HSD (the battery itself weighs 64 pounds)–(the first batteries and controllers weighed 167 pounds). The Aluminum block engine weighs 214#, and produces 95-148 hp (not that you need a lot of torque to spin a generator). That battery and engine weight is 278#–the weight savings over a Baron second engine would allow for 962# of batteries (substantial!)–not to mention that it doesn’t need nearly the fuel of the Baron.
Quiet–reliable–outstanding fuel efficiency–redundant propulsion–safe in the event of an engine failure–low cost to overhaul/replace–could be made to run on autogas, diesel, or jet fuel–uses automotive oil so no corrosion–it only spins the generator, so no main bearing propulsion issues (unlike other automotive conversions). It’s also “scaleable” for new construction.
Auto engine conversions in airplanes have not been very successful–but that’s largely because they are limited to a very low prop RPM–requiring reduction gearing, air cooling issues, and unique thrust issues with aero engine bearings. The Prius engine has been a reliable generator of electric charging power for years, and solves most of those problems. The redundancy of power and the use of automotive technology is a plus.
“Proven Prius Electric” hybrid? Sure. “Pure electric”? Pipe dream.