Bilateral
Symmetry
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.
Bilateral Symmetry
List of Successful Asymmetric Aircraft