Zunum Aero, hybrid aircraft

https://spectrum.ieee.org/aerospace...c-airplane-aims-to-rejuvenate-regional-travel

https://zunum.aero/technology/

...Our series hybrid powertrain was designed for an eventual transition to fully electric, without requiring any mechanical retrofitting. Designing with batteries at 12 to 20% of total weight, we’ve future-proofed our aircraft for 15 to 20 years, enabling us to embrace future technologies...Our batteries and range extenders are sized specifically for regional distances, with an optimized system that balances the depletion of batteries and use of range-extenders in-flight...

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Parallel hybrid makes a LOT more sense for aircraft, both from an efficiency and safety point of view.

I have been searching for details, simply because this has interested me for a long time. I found one small obscure reference to the auxiliary engine being a gas turbine. It is definitely small, and aircraft designers are very familiar with a centrifugal-compressor "Auxiliary Power Unit" (APU). It has a compressor that is similar to a turbocharger, and in fact, turbocharger parts have been used to make "toy" jet engines by a company called AMT (Advanced Micro Turbines). The exhaust "power turbine" is an axial.

Such an APU can run off of just about any flammable fuel, and they are most commonly powered by a low-smoke kerosene called "Jet-A".



To be clear, this pic above is a random APU from the web, and I am only speculating that the Zunum hybrid generator is powered by something similar. Mostly because any 'new' power unit would have to pass extensive FAA testing, so...there are dozens of affordable and existing designs that are readily available from reliable suppliers.

spinningmagnets said:

Mostly because any 'new' power unit would have to pass extensive FAA testing, so...there are dozens of affordable and existing designs that are readily available from reliable suppliers.

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Well, except the FAA has different categories for powerplants (i.e. engines) vs accessories (i.e. APU's.) So they'd have to do the work to uprate it.

But again, it would make a lot more sense to make this a parallel system. Take a layout like the Falcon 50, keep the center engine, add a much more powerful starter/generator and replace the two outboard engines with electric fans. That way you get the greater takeoff power you want - and you still have the center engine if the electrical power transfer system takes a dump. (And your batteries need only supply takeoff power and a small amount of cruise.)

I'm of the impression a rotory engine would be used, due to efficiency of designs. Primary drawbacks for Wankel designs, high exhaust temps and narrow band of efficient RPM. Heat transfer at altitude shouldn't be a problem, and the hybrid system would easily be 'tuned' for max efficiency RPM.
The only turbines I know of that have high efficiency, are natural gas power generators which use the exhaust gas to heat a boiler. Piston engines are more efficient, complex, and heavy. While ceramic apex seals for the Wankel have revolutionized power output and durability.
Just my 2cent, from a general engine design perspective.

I have been saying for years, in several public forums, that we should build fuel-cell powered Un-Ducted Fan (UDF) airliners, using the fuel cells from the transit busses and hydrogen cracked by wind-power. In terms of safety, a pilot could jettison fuel rapidly in an emergency, eliminating the risk of fire or explosion after a crash. Turbine/generators are a complex answer to a simple question.

These hybrid airliners would be quiet (GASP!), with sustainable and low emission fuel. Both the fuel cells and the UDFs are proven technologies.
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I'm not familiar with UDF airliners but in powered paragliding the noise from the "noisy" 2 stroke motor is peanuts compared to the roar of the propeller itself.

parajared said:

I'm not familiar with UDF airliners but in powered paragliding the noise from the "noisy" 2 stroke motor is peanuts compared to the roar of the propeller itself.
https://flyoverppg.com/wp-content/uploads/2017/07/beach1_640xx.jpg

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parajared,

Most prop noise comes from the blade tips, running at or near supersonic airspeeds. A lot of the noise that you hear is the sonic shock waves from the fast tips. Try swinging a much larger prop (and that may require a gear reduction) and your paramotor would run much quieter in the sky. That change would need a bigger fan cage, et c. so I doubt anybody would opt for less noise.

The Un-Ducted-Fan engine has lots of short fat blades, rather than long thin blades, and so the blades run much slower, at the tips. I saw a video of a fly-by at the roll-out of the UDF. They first had a conventional airliner, roaring past the cameras. Then came the UDF airliner, and it just whispered past the cameras, with a low buzzing noise. Bear in mind, that UDF was powered by a GE turbine (like a 747 engine, which is a Ducted Fan). I believe that an electric UDF would make a lot less noise, and the fuel cells would produce a lot less pollution. All IMHO, of course. 8)

Holy shit, a Kasper Wing! Fledge pilot here, back in the day, then Pterodactyls.....

Since I got my plugin Prius, every time I make a big descent in my plane I can't help but think of all that energy just being pissed away, then again, a hybrid plane with regen while in a glide would have a horrible glide ratio, no free lunch I guess.

craneplaneguy said:

Holy shit, a Kasper Wing! Fledge pilot here, back in the day, then Pterodactyls.....
Since I got my plugin Prius, every time I make a big descent in my plane I can't help but think of all that energy just being pissed away, then again, a hybrid plane with regen while in a glide would have a horrible glide ratio, no free lunch I guess.

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craneplaneguy,

Close . . . Actually, Klaus helped me to install the new Fledgling-3 rudders on my Fledgling-2, and yeah, it was truly one-of-a-kind, then. Very easy to see a KasperWing in flight there, no doubt. I did fly "chase" for lots of flight hours, back when the KasperWings were being developed. Amazing design. Now somewhere in the upper MidWest, somebody is building the KasperWings again.
https://www.kasperwing.com/

These guys are building electric flyin' machines:
http://www.electraflyer.com/

We now return you to our regularly scheduled mayhem. 8)