Flying an R22 has rekindled my interest in helicopter design. Serious thanks Andy - looking forwards to next w/end
. Lots of "sofa flying" already planned to get that coordination sorted...
Dave,
Please bear in mind that i have to fit in PPRUNE postings between other time consuming activities, this often leads to revision "B" and "C" releases of my postings. Also i often have to reiterate technical points, since i am not convinced they have been properly understood. However, i will endeavor to moderate my enthusiasm
Consider that i do not believe a computer to be necessary to implement a "FBW" control system. This is particularly true if it is based on a mechanical primary system. Also consider that if you spin on a rotating office chair with your eyes shut you will soon lose all sense of rotational velocity - this is also true of flying in cloud, indicating the limit of the human balance system. A gyro system can be designed using analogue feedback, rather like a HiFi amplifier, to give pilot direct control over aircraft roll and pitch rotational velocities with cyclic position correction for airspeed (ie longitudinal and lateral dihedral). Since i have tried and failed to suggest the mechanical means of achieving this (Lockheed system), then the electronic means is by electric servos with the control/gyro difference signal actuating a mechanical mixer. This is all just 2nd year degree stuff, and i remember Nick commenting that such a system would cost between $2000 to $10000 per aircraft. The only reason to go digital is when the control laws became too complicated for a simple feedback model.
You have persuaded me that it is possible to significantly improve the flying qualities of a helicopter by aerodynamic only means. You have not persuaded me that this can be accomplished in a cost effective design, since two rotor heads and additional driveshafts will increase cost to achieve the same reliability. The best compromise is a Flettner rotation rigid rotor intermesher, although aerodynamic efficiency will be marginally compromised. Even this system will not offer dihedral stability, so does not achieve the holy grail of hands free hover.
What i propose is a compromise, like so much of engineering, taking the best features of all solutions. For example: A Flettner rotation intermesher could have the stability augmented by a reasonably simple 21st century modification to the control system. There is nothing to stop this system affecting a conventional helicopter, but i too am interested in designs that increase the operational capability of the rotorcraft (retreating blade stall). This generic approach is already being implemented by Sikorsky in the X2, which is why i believe it will be a very versatile basis for future helicopters.
Mart