Perhaps Nick has the answer.
He was involved with the
patent application 20070125907 ~ Variable speed gearbox with an independently variable speed tail rotor system for a rotary wing aircraft.
Item 18' is shown as a blank box. It transmits power for primary forward thrust during a high speed flight. However, the patent does not show what is inside this box. Could it be a box of corn flakes?
OK, so much for corny jokes.
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Speculation;
- The center of lift, and perhaps the centers of drag, percussion and mass etc. etc., have been moved further out the blades then they were on the earlier ABC. This will have increased the length of the moment arms and thereby increased the loads on the transmission.
- 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
CEFOSKEY you don't have to say what the problem is. Just node to the left for 1. or node to the right for 2.
Dave