Mart, you said;
My guess is that the Sikorsky engineers puzzled over the problem.....
The initial and the follow-up technical documents on the XH-59A ABC clearly show the difficulties that Sikorsky faced when calculating the specifications for the craft. This was because their existing knowledge base was predominantly about single-rotor helicopters.
An example of this limitation is 'disk area'. Even to this day there is no consensus as to what constitutes the
'disk area' of the various twin-rotor configurations. 'Disk area' is probably the most fundamental parameter. It is next to impossible to optimize the other parameters when they are based on a nebulous 'disk area'. The difficulty is obvious when seeing the large usage of various K-factors (fudge factors) throughout the calculations.
Those who think that there are difficulties understanding the aerodynamics of a single rotor might want to consider the greater difficulties understanding aerodynamically interacting twin-rotors, particularly as this interaction radically changes with the changes in flight mode.
However;
Just think how much more advanced rotorcraft would be today if the research and development over the past 60 years had been built upon the superior German twin-rotor helicopter configurations.
Just think how much more advanced 'Advancing Blade Concept' rotorcraft would be today if Sikorsky had been able to develop the ABC on the shoulders of an existing twin-rotor knowledge base.
Dave
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Last May, I sent a letter to the editor of the American Helicopter Society's quarterly magazine Vertiflite. It was related to this very subject. It was not published in either of the last two issues. Interestingly, 5-years earlier they saw fit to published a letter of mine that indirectly addressed the relatively simplistic subject of 'a helicopter in every garage'.
Yesterday, the letter was e-mailed again, with a 'Request Read Receipt'. Should there be no response, the letter may be placed on PPRuNe. Members may then wish to suggest reasons as to why it was not published.
