Don’t conflate airplanes with rockets.

On an airplane, most of the energy in cruise is spent overcoming parasitic drag, not induced drag. It’s spent pushing the airmass out of the way as it moves forward, not creating lift to stay aloft.

For that reason, a change in weight does not significantly change cruise fuel usage.

Weight is still precious, but that’s because airplanes’ load are more often weight constrained than volume constrained, and capital and operating costs are such that you want to maximize the load.

> you're carrying all that dead weight for the rest of the flight

If you're recharging the batteries for extra go-arounds during landing, they are as dead weight as the fuel you would otherwise reserve for that purpose. And if you have 30% more efficient engines, meaning less fuel and smaller engines, it's possible you could come out ahead, weight-wise.

> what if you need two go-arounds

I assume that a go-around requires less sustained power output than a full climb from takeoff, so you will probably get more than one go-around anyway, and we don't know how much over-capacity they're designing for. In any case, any design will require tradeoffs in safety, and having more engine-out capabilities might improve safety enough to overcome the higher risk with go-arounds.

Not saying this project is will work out or that you're even wrong necessarily (this could be the equivalent of a concept car for Pratt & Whitney).

Energy density of liquid fuels cannot be beat by batteries, so this is not competitive if you are looking to maximize cargo. However, there are plenty of short haul flights: private jets, island hopping, regional routes where you need to move little mass.

Exactly. A hybrid passenger car can tolerate unpredictable power output that may come with an auxiliary power setup that may or may not be available when stronger dynamics are called for.

A plane doesn’t have this luxury and needs predictable output. The fossil fuel engine either needs a sacrificial “overboost” mode for emergencies (at the cost of wear/long-term longevity), or has to be sized for full power at the ultimate cost of efficiency.

On anything but very short flights most of the fuel is spent on cruising.

Valid.

Perhaps it's not all negative: the electric portion could give a pilot a bit more glide than the gas portion dies.

The Prius uses a planetary gear set to blend power of the engine with that of the two motor-generators.

Both the engine and motors are used at all speeds. Particularly during highway acceleration the entire assembly rotates in the same direction.

The Prius is in series, or something like it.