A STUDY OF DESIGN AND ECONOMICS OF ROTARY WING GLIDERS

Since the advent of the helicopter toward the end of World War II, there has been a marked increase of interest in the uses of rotary-wing aircraft in technical as well as in non-technical circles. A promising future for the helicopter was predicted in both military and commercial services. Although its predecessor, the autogiro, receded into oblivion, apparently because of its inability to hover, many new combinations of hovering rotary-wing machines have been since proposed and tried. It seems that the search for an "ideal" aerial vehicle was only intensified by the birth of the helicopter. Among the new machines with indisputable advantages, and promising future, are the gyrodyne, the convertoplane, and a number of other "all-purpose" and "special-purpose" machines. To their list must be added rotary-wing gliders, which were also conceived and successfully developed within the recent past. Although the rotor operation in rotary-wing gliders is essentially identical to that of an autogiro, the advantages of this type of craft did not become apparent until it was designed specifically as a glider and judged on its own functional merits. The first outstanding feature of the rotary-wing glider is its unusually low-empty weight. The average empty weight of fixed-wing gliders is 50-60 per cent of the gross weight, while rotary-wing machines readily achieve a much lower figure of 20-30 per cent. As a good approximation, it may be conservatively stated that a rotary-wing glider will lift twice the payload of its fixed-wing counterpart, based on the same gross weight. By the same rule, it lifts three times the payload of a helicopter of equal gross weight. Reasons for this will become apparent in the subsequent discussion.