A Study of the Attainable Range of Helicopters

A study has been made of the effects of parasite drag, mean rotor lift coefficient, and mean rotor blade tip Mach number on the maximum lift-drag ratio and range that can be achieved with large helicopters. The best (L/D) ratio occurred at the highest value of mean rotor blade lift coefficient investigated, at the edge of the retreating blade stall range. It has been determined that a gross reduction in parasite drag will not result in a range improvement of similar magnitude. There appears to be no large range penalty in operating at mean blade tip Mach numbers as high as .6. There is, however, a considerable drop in the achievable (L/D) ratios between tip Mach numbers of .6 and .7. The effects of empty weight reduction have also been reviewed. The results indicate that a, significant improvement in maximum range may eventually be possible, but that it will be necessary to improve all the significant parameters, i. e., (L/D ) ratio, specific fuel consumption, and weight empty ratio.