manofsan,
Differential rotor speeds -will- rotate the aircraft, but will that turn
the aircraft, in level flight, or just rotate the aircraft in yaw? The
hard part about differential rotor speeds is not in yawing the aircraft.
The hard part is NOT yawing the aircraft, constantly. Gyros might do the
job of balancing rotor speeds for you (with *more* expense and complexity),
but you would still lose the safety advantages of simplicity, and
maintaining control if one motor fails. The spider gears and one motor
might not maintain altitude, but you could still move forward and steer as
you descend slowly, to select a good place for the BRS deployment. In a
deployment situation, one motor could still be used for a last-minute burst
of power, to soften the parachute landing.
Recovering energy by auto-rotation would mean a lot of weight and
complexity for very small gains. Aircraft are like boats, always fighting
drag, and if aircraft could get anything back on descent, they would have
to expend a lot more energy to do the climb, first. You can never win
against drag, so at best, we just try to cut our losses, up front.
I hear Boeing is working on a single-engine plane using a fuel cell and an
electric motor to provide propellor thrust, so that technology seems
realistic. New hydrogen storage systems can derive their hydrogen "fuel"
from other liquids, rather than highly pressurized hydrogen gas, which
would need strong and heavy tanks.
The WaveCrest motor idea looks good, too.
--
(Replies *will* bounce, unless you delete
the letter A from my email address)
Cheers,
Red

wrote:

Hi red, thanks for the great ideas.

Hmm, I read about how a coax design can use differential rotation speed
between the 2 rotors for the purpose of turning the aircraft. That'd be
pretty easy to do with a wheelmotor for each rotor.

Here's a link to a new kind of wheelmotor which is attracting
attention:

http://www.wavecrestlabs.com

The company is headed by General Wesley Clark, former NATO commander.
Regarding portable fuel cell for propulsion, here's another link:

http://www.intelligent-energy.com/in...6&artID=3 709

And hydrogen is a lightweight fuel too, for lower fuel load.
But suppose you want some extra juice sometimes, for more
maneuvering/lifting power. Then use the new Toshiba battery:

http://www.dpreview.com/news/0503/05...sh1minbatt.asp

It can apparently discharge and absorb energy at a very high rate. This
might be useful for using regenerative braking to recover energy from
your rotor when you're reducing airspeed/altitude, since a wheelmotor
can convert torque/rpm back into electricity. Once you've landed,
regenerative braking would allow you to quickly bring the rotors to a
stop while recovering energy from them.

I'd also imagine the electric motors would be quieter too, so your
eardrums don't take a beating.