Where the rubber meets the road.
Many years ago Nick mentioned that Sikorsky does 90% of its helicopter development after the prototype has been built and is in testing. Some might suggest that most of the development should take place after the craft meets the notepad, not after it meets the helipad.
But then, who would dare question The Big Sikorsky?
The full technical information on the performance of the X2 may involve a long wait. Or it may never be made public, since this is a privately funded project. For the fun of technical speculation, and perhaps discussion, the following is put forth.
The blades on the X2 have a reverse taper. Presumably, this is done so that the airfoil portions of the blades are subjected to minimal reverse airflow during fast forward flight. However, this will result in disadvantages. The reverse taper will increase the induced velocity in the outer regions of the two overlaid rotor disks but reduce the induced velocity in their inner regions; as compared to today's conventional rotors. Actuator Disk Theory and Bernoulli's principle assumes that the aerodynamic loading is distributed uniformly over the disk.
During hover; ~ One disadvantage may be the reduction in the Figure of Merit; particularly when considering that
Dr. Gordon Leishman has said;-
"... it had taken the industry sixty years to realize a helicopter with an average increase in rotor hovering efficiency (figure of merit or FM) of only 13%".
During cruise; ~ Another disadvantage may be the reduced Lift/Drag Ratio. In addition, the aft-located propeller (pusher configuration) will probably strip away some of the lift that is generated by the coaxial rotors. Consider the remark by
Carson "...on average, the maximum L/D of the helicopter has only increased by less than 10% in the last 30 or more years."
If the above concerns are valid, can the X2 be a viable contender in the field of VTOL craft?
Dave
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Bravo73,
The earlier XH-59A ABC had a two-speed transmission. To my recollection, a variable speed transmission for the X2 has been inferred but never stated outright.