Effects Of Parasite Drag On Rotor Performance And Dynamic Response

A five-degree-of-freedom coupled aeroelastic analysis is used to compute the rotor response of a typical helicopter. The effect of drag on rotor dynamic loadings, bending moment distributions, blade section angle of attack, rotor power and hub shears is shown over a range of forward flight speeds and typical rotor loading conditions. It can generally be concluded that increased drag substantially increases rotor power required, blade tip angles of attack and vibratory hub shears. Blade vibratory bending moments are not necessarily increased with increased drag. Until recently, parasitic drag of utility type helicopters was of secondary importance in design considerations. Drag was cons i dered important only as it affected performance. Drag, however, can increase vibration, causing the design to be more complex, thereby increasing the structural and weight requirements. With the advent of the more advanced aeroelastic analyses, it is now possible to investigate the effects of drag on rotor vibration. This paper reports the results of such a study, where a coupled aeroelastic analysis used to study the effect of changes in equivalent flat plate area of a typical helicopter. The effect of drag on rotor dynamic loadings, load distributions, blade section angle-of-attack variations, rotor power requirements and control requirements is discussed. As helicopter drag affects loadings, it also affects blade response, blade bending moments and hub vibration. Knowledge of these parameters are very important to designers attempting to build structurally sound rotors. It is, therefore, necessary to impress on designers that drag not only increases fuel consumption and reduces maximum forward speed, but it also can seriously affect vibratory loads in helicopter structures.