The thread is still in Rotorhead territory but it is sliding off topic.
Brett,
Thanks for mentioning a couple of potential problems.
Do you happen to know if any of the RC electric motors use a Halbach array? The reason for asking is that, in addition to their performance advantage, all the Halbach array magnets are tightly abutting the adjacent magnets. This may give better battery fixation than the conventional surface mounting or the embedding of the magnet in the rotor's epoxy.
Theoretically, the failure of a controller or battery pack will not be critical. It will only reduce the available continuous-power.
Mart,
"RPM is the best way to achieve power/weight."
From the motors perspective ~ yes. However, in this application I wonder. A gearbox requires a minimum of two reductions and one of them must be a right angle set. Perhaps if Sikorsky gets their face gear patent to work, the proceeding statement may be a lie.
The use of an axial flux (pancake, disk) motor conjures up the possibility of locating it in the rotor hub. By adding electrical blade pitch to the rotor, the power train and the flight controls, as we now know them, will ceases to exist.
DESIGN OF AXIAL-FLUX PERMANENT-MAGNET LOW-SPEED MACHINES AND PERFORMANCE COMPARISON BETWEEN RADIAL-FLUX AND AXIAL-FLUX MACHINES
"Ultracaps are being developed primarily as a means of regenerative braking, but offer no real advantage in a heli."
I wonder. The ultra capacitor will offer a high power/weight ratio but a low power/volume ratio. These two ratios suggest that the capacitors could be located in the tail boom. The small amount of power that they would hold could be used to supplement the batteries during takeoff and high maneuvering, plus with regeneration they could provided the power for an autorotation landing flare.
Energy Storage in Advanced Vehicle Systems
Dave