Total Parasite Drag
Figure 4.27, taken from reference 4.24, presents the state of the art of parasite drag of both helicopters and airplanes with several levels of aircraft cleanliness. This plot can be used to make first estimates of the drag of a helicopter in the early stages of the preliminary design. Table 4.3 lists published drag breakdowns for three typical helicopters, which can also be used to guide first estimates. (Note of caution: I have never known of an airplane or a helicopter drag estimator who was pleasantly suprised by flight test results showing that he had overestimated the drag of the aircraft. The estimating methods outlined in this chapter must be considered to produce minimum estimates and thus are suitable for the wishful – thinking phases of proposals and sales brochures. For realistic engineering estimates, I recommend that at least another 20% be added to the total to include those items that were not initially included or that will grow during the normal development of the helicopter.)
Source: Rosenstein & Stanzione, “Computer-Aided Helicopter Design,” AHS 37th Forum, 1981.
Total Drag Breakdown, Equivalent Flat Plate Area