• I think that the rotors' RPMs and the propeller's RPM will now be fixed.
• Rotor. Consider; DESIGN: UniCopter ~ Rotor - Disk - Large Chord & Low Tip Speed
• Use("controllable-pitch propeller" OR "variable pitch propeller") and Continuously Variable Transmission to the rotors?
• Propeller: Without a differential in the power-train, the propeller may work reasonably well with only a disengagement clutch and a feathering system.
• Rotors: The range of horsepower to be transmitted by the rotors will be large, but their rotational speed change will be relatively small. Might a Continuously Variable Transmission serve the rotors? Any small slippage can be compensated for by the central processing unit. This assumes that the friction loss, additional weight and complexity of the CVT is not significant. For CVT for High Torque Applications see; (http://cvt.com.sapo.pt/MCVT/MCVT.htm)
• Vibration:
• The propeller must not be the cause of vibration at any frequency from zero speed to full speed.
• "Each propeller has its own set of natural frequencies of resonance which is predetermined by the blade's length, thickness and weight distribution."
• "These vibrations may be decrease by use of the proper airfoils and tip design."
• "Mechanical vibrations are generated by the power pulses in a piston engine and are considered to be more destructive in theire effect than aerodynamic vibrations." The use of an electric motor or turbine should help.
• Can more blades and/or static and dynamic balancing eliminate this concern?
• Variable Speed v.s. Variable Angle of Attack:
• " The most desirable angle of attack is between two and four degrees, with any angle above 15-degrees being in effective. (Airfoils stall at about 15-degress angle of attack.)". Work out the angle of attack at various operational free air speeds and propeller rpm
• For data on propeller see DESIGN: UniCopter ~ Pusher Prop - Variable Speed Rotors and Prop - Propeller and DESIGN: UniCopter ~ Pusher Prop - General - Pusher Prop Assist
• 40 degree pitch ??? perhaps make maximum speed 2400 rpm
• Diameter/Pitch 60/34 ???
• Circumference of 11.79 ft at 75% radius and a pitch angle of 40º gives a pitch of 0.643 * 11.79 = 7.58 ft.

• Failure:
• A breakdown of the vari-speed device must not have a serious effect on other components.
• If the thrust of the propulsor is inline with the fuselage's center of drag, will the sudden loss of thrust cause the craft to pitch down?
• Self-Excited Vibration:
• If the rotor speed is variable then here is better speculation. "In conventional helicopter flight operations, the rotor speed is designed to operate at a fixed value. A constant rotor speed is chosen to avoid a host of dynamic conditions that would increase rotor vibration and blade loads. Rotors that operate over a wider range of angular velocities will surely encounter more diverse dynamic conditions as changes in centrifugal stiffening modify blade structural mode frequencies and increase (hingeless) bending moments. While the design of the rotor must account for the dynamic conditions, there may still exist in the flight envelope dynamic conditions that result in unacceptable loads. " From ~ OPTIMAL AEROELASTIC TRIM FOR ROTORCRAFT WITH CONSTRAINED, NON-UNIQUE TRIM SOLUTIONS

• For a rotorcraft to achieve significantly faster forward speeds, and have an efficient Figure of Merit in hover, the rpm of the rotor must be slower during cruise than it is during hover.
• In addition, the propeller must be delivering high thrust during cruise and no thrust during hover.
• The following concept is a proposed means of achieving the above; in a controlled and progressive manner.
• In other words; infinitely variable power distribution between;-
• Hover: 100% of the power going to the rotors and 0% going to the propeller.
• Cruise: 50% (⁺/_-) of the power going to the rotors and 50% (⁺/_-) to the propeller. The objective probably being that;
• The rotors are edge on to the free airflow and the thrust is just sufficient to maintain level flight. ~ or ~
• The rotors are contributing slightly to forward thrust and thereby possible contributing to the speed stability.

• There is no need for a variable pitch propeller; with it's sophisticated gearing and control.
• The propeller will not be rotating when the helicopter is hovering or on the ground.
• Yaw control can be achieved by having two propellers, complete with their own independent Speed Controller.

• United States Patent Application, 20060269414, Variable speed transmission for a rotary wing aircraft, Sikorsky
• This application shows on Fig. 2B shows a box entitled 'Tail Drive Output ~ Speed Varies' (item 30), however it give no information as to what is inside this box that provides a variable speed.
• United States Patent Application, 20060269413, Rotor drive and control system for a high speed rotary wing aircraft, Sikorsky Have hard copy
• United States Patent Application, 20060266883, Split torque gearbox for rotary wing aircraft with translational thrust system. , Sikorsky
• United States Patent Application, 20070125907, Filed: December 2, 2005, Variable speed gearbox with an independently variable speed tail rotor system for a rotary wing aircraft. , Sikorsky. This is by Nick Lappos. See PPRuNe post http://www.pprune.org/forums/showthread.php?t=245168&page=3 below; Technically, this patent is very conflicting and poorly done, which is probably the result of the lawyer, since Nick had left Sikorsky before the application was filled.
• Patent 7,434,764 was granted October 14, 2008

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