I’m at a loss to understand how a hybrid drive train in an aeroplane makes any significant sense. Normally the advantage is that when an internal combustion engine is regularly varying its rpm wildly e.g. in stop-go urban traffic, when the engine is on it can immediately go to its most efficient rpm and stay there until the battery is charged. This makes for a potentially significant improvement in the efficiency of the engine.
In an aircraft, once it is at cruising speed/altitude the rpm is almost constant and mixture adjusted for most economical use for any given circumstance. So, what use is lugging around enormous battery as well as the internal combustion engine, all its necessary complex ancillary systems, fuel et cetera?
The whole idea sounds a bit like the answer to a question that has not been asked.
On the other hand a fully electric aircraft makes huge sense although obviously currently only for relatively short journeys.
Perhaps someone who actually knows what they’re talking about can enlighten me…?