Hi Dave,
Not worried about topic, as long as thread is constructive.
"Why could not a reasonably large diameter, linear induction disk motor be an integral part of a special rotor hub, which is shaped like a very large Frisbee?"
Why not, but aerospace motors and generators run at 80'000 rpm regardless of shape. Any less and you are just introducing unecessary weight.
"It might have thousands of poles (with 50% or 33% of them activate at one time) and air bearings to maintain the gap."
Why not. Sounds unecessarily complex to me though and doesnt get around the torque/mass limitation. You are just packing more copper into the 1 Tesla mag flux.
"The weight will be kept down by the preceding integration, composite construction and the elimination of the gearbox."
Nope. You still need an iron return circuit, which is the cause of the 1 Tesla limit. Careful design can just about get up to 2 Teslas. Nano carbon fibre promises room temp superconductivity, but you won't be able to buy 'em for quite a while.
"To double the motor's speed on coaxial helicopters, the motor could be located between the rotors, with the 'armature' connected to one rotor and the 'stator' to the other rotor."
Sounds draggy. Why not just use an epicyclic reduction gearset (lowest mass for given torque) and run the motor at 80'000 rpm, or whatever is centrifugally achievable? Why not use a gas turbine...
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"What if triple redundancy was applied to all facets of the drive."
Then, as long as pilot (or more likely operator) has common sense to ground aircraft on single failure, the crew only crash and die during a triple failure. What if a +ve lightning strike over the north sea wipes out all of the redundancy?
"The large electrical force and its large moment arm should be able to maintain rotor inter-phasing..."
Agreed, but so should gears. My concern comes from the fact that the best motor will likely be a brushless DC requiring power electronics, unless you want all the wear and reliability problems of a brush. The power electronics, although reliable, do go wrong and never when you want them too. You are talking about aerospace motors which will have to run at high rpm and are going to be expensive. When was the last time you drove a hybrid car? I drive a diesel.
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"Just a demented idea."
My concern comes from the fact that the idea comes from a false premise (assuming you are trying to avoid driveshafts in SBS tandems). Tail rotors in themselves are not bad things, but counter-rotating rotors offer better potential for aircraft flexibility.
The main problem with ANY rotorcraft is the retreating portion of the rotor. In a conventional heli the retreating portion of the rotor limits top speed. In a counter-rotating heli the retreating portion can still introduce unecessary power loss, through distorted downwash distribution. Intermeshers will suffer vortex spill blade slap, and interleavers will still have to operate retreating tip at higher than ideal AOA. Either work at highest aerodynamic efficiency with outboard advancing.
Why not just accept the loss and just use root/tip control to perfectly feather the retreating blade? If you do this the Stepniewski rotation intermesher wins hands down, and ANY other configuration is just unecessary complexity.
Unicopter, with a tandem instructor seat, is a good design concept - why not just stick with it?
Mart
[Edit: typos]