Dave Jackson said:
Mechanical independent root and tip pitch controls should be possible today.
I see challenges with this. That torque tube has a lot of potential windup over the span of a blade. And, even those rigid rotors generally aren't all that rigid. So, it's not like the torque tube is going to have a nice straight tunnel to ride in as the blade whirls around. This will induce bending, chafing, and honest to God fatigue cycles.
Dave's website says:
The skin of the blade is firmly attached to the spar at all locations along the span. The skin and the spar twist in unison. The root of the blade is controlled by the root pitch horn. The tip of blade is controlled by the tip pitch horn. The tip and the tip pitch horn are connected by a torque tube, which is located in the middle of the spar.
You already have a strong piece of structure absolutely required that can serve duty as a torque tube. It's called the spar. Why wouldn't you use that as your torque tube, secure the airfoil to the tip, and have seperate pitch horns inboard, one for the spar and one for the airfoil. That reduces the parts count by one. Of course, the same problems with chafing and bending will still be present.
Vfrpilotpb said:
To do this would need sophisticated computer controlled switchgearing to translate from the pilots hand controls to electronically produced twist inputs at the blade.
The sophisticated computer controlled switchgearing is the easy part. You can find somebody to write all the equations (or do it yourself if that's your thing) to define mixing to the active twist. The tricky part is getting that fly by wire stuff from the pilot's hand in the fixed frame to the rotorhead in the rotating frame, and with enough redundancy and reliability that you are reasonably sure you'll go home everyday after flying it. I think the other tricky part is basic blade stability with this scheme.
slowrotor said:
Rotor blades are probably the most torsionally stiff structures ever designed to prevent flutter.
That's part of what I was trying to say in my original post.
I may come across as too negative in this little open source rotor design community. But, I think that what we are talking about is tommorow's technology, not todays. In the immortal words of Igor Sikorsky, "To invent a flying machine is nothing. To build it is little. To make it fly is everything."
-- IFMU