Folks, stop me if i'm going too far off Rotorheads territory.
Brett,
For passenger carrying the motor and all systems would have to be developed/tested for the 1E-9 loadcases. As with airframes this would not always guarantee 100% failsafe.
Dave,
Motors are certainly getting to the point where direct drive is possible, but i wouldn't reject the humble gearbox until you have done a good concept study of
ALL the available systems. Axial flux or "pancake" motors are the best way to minimise the flux return paths (ie steel), but RPM is the best way to achieve power/weight. Besides epicyclic gearboxes are compact and reliable, and package very well in a motor housing.
The big problem is going to be the power source for some time to come. You can couple a turboshaft to a generator (turbogenset had a good direct drive concept before they went bust). The question is why would you want to cost in a generator & motor when a driveshaft is just as effective? In the case of high disk loading ducted fans, i was proposing the use of motors only to overcome the inherent lack of autorotation during engine failure. To my mind the solution has to be fuel cell that will operate on kerosine. This sounds far fetched but think about what it has to replace. Turboshafts are:
1. Cost effective.
2. Reliable.
3. Efficient.
4. Low weight
5. Infrastructure supported.
6. Durable.
7. Improving by development.
This means that the successor has a lot to live up to to be commercially accepted. In the long run i believe this is practical, but you will see it on the road long before you see it in the air. The main reason for this is convenience, since service will be well in excess of the 100+ hours between service that folks now expect from their car.
If you just want to be in Guinness, then stick with LiMH battery packs. For a short duration it will pack a good enough punch to get airborn. Ultracaps are being developed primarily as a means of regenerative braking, but offer no real advantage in a heli.
Mart