I keep banging on about this in other threads for aviation in general. But it makes extra muchness of sense for helicopters. And until batteries are where they need to be, a hybrid solution is very interesting.
Let's toy with the idea for a second.
Brushless motor or motors run the main rotor and anti-torque. You have small battery that can power heli at full power for about 10 minutes. You have turbine APU that runs a brushless gen that recharges the batteries during the flight and/or can directly power the brushless motors. Look at the benefits:
1. No gearbox needed, direct drive on the shaft. Weight savings, reliability improvements.
2. Brushless motors give more power per weight than any other engine (easily about 8-10Kw/kg - beat that gas turbines), which saves weight further.
3. Anti torque is direct driven by a dedicated brushless and rpm only, no complicated shafts, no blade actuation.
4. Brushless motors are pretty much only limited by bearing life, so maintenance should become very cheap.
5. APU gen set can be made cheaper and to lesser standards and be overhauled less frequently because if it should fail, you have 10 minutes on battery power to get safely down.
6. For HEMS and other time critical operations, startup and shutdown would be a 10 second affair. Just power up and go on battery power, then start the APU when you're airborne. That time could save lives.
7. No over temps, no over-torques, no cool downs, no altitude penalties, no shock cooling, no performance losses from tail, no LTE, etc.
8. Much less noisy.
9. Training could be done on batteries alone that get swapped and recharged, which would dramatically lower the cost of training. At least at the home field.
10. Fadecs and governing becomes a piece of cake, as all brushless motors keep the rpm you tell them to keep, regardless of load. That's how you drive them electronically. It's literally a $10 circuit.
I was thrilled to hear about Sikorskys 300CB that they converted to electrics and flew before Oshkosh. It can only fly for 15 minutes at the moment at full power, but it's a great start. Battery capacity has steadily increased over the years and with the new nanowire silicon batteries in development with 10 times more capacity, it could be all over for fossil fueled aviation much quicker than we think. Mind you, I'm no environmental nut, I just welcome all the benefits of electric power. It has virtually no drawbacks and is perfectly suited for aviation.
But let's say one of the big manufacturers presented such a ship tomorrow, the certification processes are not in place. It's going to take FAA and EASA decades before they get on the ball, is my suspicion. That's probably going to be the funnel.