Charles Darwin to Intelligent Design
Symmetry has an aesthetic beauty, but more importantly, it has a functional beauty. Virtually all mobile life forms are bilaterally symmetrical. The fish in the ocean, the animals on the land and the birds in the air all share this characteristic. The logic of this 'survival of the fittest' is unquestionable. In addition, man's technological developments are founded in nature. It is therefore not coincidental that all vehicles are bilaterally symmetrical. All that is, except for a very few temporal exceptions; such as helicopters with tail-rotors, with tandem-rotors and even those with coaxial-rotors.
How did this anomaly come about? At the dawn of helicopter flight, the leading country in this field was Germany. It developed effective craft using bilaterally symmetrical configurations. In fact, the Intermeshing Flettner FL-282 and the Side-by-side Focke Fa-223 were the world's first production helicopters. The Flettner FL-282 was comparable to the Sikorsky R-4B, but it out performed the R-4B in all primary areas. In fact, it was said "At an AHS dinner meeting where Flettner and Sikorsky were both present, Igor was taken aback by the technological advancements shown in an 8mm film of the Intermeshing Flettner FL-282."
What went so wrong and why has there been sixty years of tail-rotor dominance? At the risk of irritating some, I suggest that the Germans, plus the Russians and the Europeans lost the Second World War, economically, whereas the United States was the major winner. The ideas that were prevalent in the United States at that time became the predominant configuration. The well connected and financially endowed went with the single rotor, and 'simply' offset its torque with a horizontal fan. I suspect that the problems confronting the rotor aerodynamists were formidable and the early American developers resisted compounding these problems by having to deal with two main rotors. Unfortunately, this configuration with a tail rotor created a new set of problems that can never be adequately overcome. In addition, the early Western aerodynamicists appear to have underestimated the thrust-to-power advantage of twin main rotors.
If the expertise and money, which was devoted to the fan-on-tail helicopters, had been applied to improving the twin-rotor configurations, I suspect that some of the current concerns of the V-22 would now be little more than historical footnotes. This sixty years of wandering in the wilderness should have been spent improving the lift/drag ratio of the main-rotors, by developing features such as active blade twist and high-rate pitch change.
Volume production is the primary means of cost reduction. A craft with twin main rotors becomes an ironic means of halving the research and development costs and significantly reducing the production costs, per rotor.
The Tilt-rotor configuration probably represents the first salvo in the evolution of Generation II Rotorcraft. A revived and improved Coaxial-ABC may represent the second salvo. However IMHO, the greatest salvo will be the modern Intermeshing, Interleaving and PropRotor configurations that are founded in intelligent design.