3) electric might also solve the problems of long shaft and balance issues if installing pusher propeller at the very back of the aircraft
-or twin pushers, or placing propellers at any position really.
I think also that the real benefit is for turbine power that cannot easily be run economically at different power settings. A hybrid turbine will beat a huge 350 hp diesel in every aspect I would think?
Imagine how much cheaper shockload inspection gets if you can simply replace a smallish electric motor 
A hybrid turbine will beat a huge 350 hp diesel in every aspect I would think?
Yes, especially in fuel consumption… double at least. A diesel engine with a generator would be ideal for GA. The smartest design is from Zoche in my opinion but it’s far from materialising. Their last iteration switched from driving a propeller through a shaft to having an integrated generator.
I have been peripherally involved in some vehicle technology in the past and the case for hybrid where a gas turbine is used to charge batteries hangs entirely on the turbine running at a constant power, whereas the vehicle runs at very variable power and often in a stop/start manner.
If the “vehicle” is running at a constant power then the benefit of doing a hybrid drive train is a second order thing.
Motor efficiency and power to weight ratio can be improved by using ever more exotic materials, closing up the air gaps, and using better drive electronics. Normal industrial 3 phase motors are pretty crap, and very heavy for the power output. But in most industrial apps the weight doesn’t matter.
Note the solution adopted by BMW for the i8 and i3. It’s a fairly small petrol engine in these cars yet the i8 is very impressive in bursts of power, much as would be required for takeoff in an aircraft.
I don’t think any hybrid power train is any good for planes, due to the relatively high minimum power required to maintain even slow flight.
A car “functions” at ~20% of max power. A 130mph car will probably do about 50mph at 20% power.
But a plane operating at 40% power will be only just staying up. That sort of power level is specified in the POH as a “holding” power and anything below that will put you on the back of the curve where things go downhill rapidly.
So a small battery charging engine is no good. Maybe for a simplified type of flight training it might be OK but recent experience seems to suggest that planes designed minimalistically for the training market tend to fail to sell anything – perhaps because there won’t be any self fly hire usage.
I think there are a lot of “publicity” projects being done around the place. The media are desperate for stories – it’s very hard to come up with any content in an era where people get so much free via the internet. And some “green” project is just the ticket.
replace two seats with 200 kg of batteries
The issue is that, today, 200 kg of batteries cannot store that much energy. Even with higher efficiency of all electric design. And high energy density batteries tend to be “temperamental” when mistreated (not that avgas is harmless). Metal-air cells (say Lithium-air) are indeed interesting as energy density goes.
I think also that the real benefit is for turbine power that cannot easily be run economically at different power settings. A hybrid turbine will beat a huge 350 hp diesel in every aspect I would think?
Are you sure? Small turbines are not known for high efficiency. And airplanes in cruise tend to present rather constant load. Hybrid systems typically make sense for load balancing – e.g. in a city car, that frequently accelerates and brakes.
A car “functions” at ~20% of max power. A 130mph car will probably do about 50mph at 20% power.
Relative numbers are not very useful. Maintaining 130 km/h, depending on aerodynamics and other factors, can take maybe 30-35 kW. Whether the engine is rated at 100 kW peak or 350 kW peak. That’s just ballpark figure from memory. PS: But the point is valid, relatively little power is required to maintain such speeds. And piston engines don’t exactly fancy this.
I will add a little bit:
So a small battery charging engine is no good.
There is another way to go about this. Let’s say you would like 150 kW for cruise. So you design a generator that can produce 150 kW plus anything needed for accessories etc. effectively. And you put in 350 kW electric engine and enough batteries to give you, say, 10 minutes of full (take-off, if you will) power operation. Of course, question is what will be the generator. What kind of peak power you could get from it and at what efficiency. Nonetheless, hybrid system will give you more freedom in design.
Note the solution adopted by BMW for the i8 and i3. It’s a fairly small petrol engine in these cars yet the i8 is very impressive in bursts of power, much as would be required for takeoff in an aircraft.
Yes, I thought so too when they gave it to me for 5 days… 250hp out of a 3 cylinder 1500cc engine — a miracle! Incredible reactions everywhere, not what you get with a Lambo etc., people really like the car. Had a 80 year old guy on the crossing give me thumbs up. Most desirable car I’ve ever driven (now my i3 in the garage will be jealous!).
I don’t think any hybrid power train is any good for planes, due to the relatively high minimum power required to maintain even slow flight.
The engine can run at 75% BHP all the time. The huge advantage is that it can sit in the fuselage at the best position and the props can be anywhere and in any quantity. And please not the “car engines cannot run at 75% BHP, they would break in no time, only aero engines can do it” again, that is a myth! With some excess power it can charge boost batteries which give additional HP for takeoff and in case you need it. Makes a lot of sense. BTW, just like the i8. You can charge the battery for the 135hp e-motor externally or you can switch to sport mode and it will use the petrol engine to charge the battery and keep that energy available when you need a boost.
I think no proof will ever be enough that auto engines can maintain way beyond 75% rated power continuously. Even if all the planes would be powered by Austro / Technify kit I bet we’d still hear “no car engine is able to maintain be it 65% power as MCP”
