Nó đi để trang trải các chủ đề nâng cao hơn trong khí động học máy bay trực thăng, bao gồm dòng chảy cánh, khí động học không ổn định, gian hàng năng động, và cánh quạt đánh thức, và khung máy bay tương tác khí động học rotor, với các chương cuối cùng về autogiros và các phương pháp tiên tiến của máy bay trực thăng phân tích khí động học. | 58 AERODYNAMICS OF THE HELICOPTER After substituting equations 17 and 18 equation 16 becomes dT b ị p íìr 2a y ớ - dr 19 Integrating equation 19 over the blade radius assuming the blade chord c constant the thrust of the rotor is _ b R3 - Ị - c 20 Equating this equation to the expression for thrust as given by equation 11 an expression for the rotor thrust coefficient is obtained. T b pữ2a 6 - C R2p ữR 2 Cr ỉ ịW -rì 21 4 7TK The term solidity will now be introduced. The solidity r of a rotor having rectangular blades1 may be defined as the ratio of the total blade area to the rotor disk area. Thus _ bcR be ttR 22 Substituting a ốc tiT into equation 21 the expression for CT becomes Cr a ớ -0 23 Equation 23 expresses the thrust of an ideally twisted constant-chord blade. EXPRESSION FOR TORQUE. By referring again to Fig. 3-5 it can be seen that the drag of the blade element is composed of two parts 1 the profile drag and 2 the induced drag which consists of the components of lift in the plane of rotation arising from the tilt of the lift vector caused by the inflow velocity. Inasmuch as the torque about the axis of rotation resulting from the drag on the element is dD times r then dg bịp ữr 2c cdo ỘC r dr 24 1 The calculation of the solidity of a rotor having blades of any plan form will be considered in a later section of this chapter. AN INTRODUCTION TO HOVERING THEORY 59 Before this equation can be integrated the variation of with r must be known which in turn requires a knowledge of the variation of ar with r. The variation of ỘC is known because ideal twist was assumed. The expression for the blade-section angle of attack for an ideally twisted blade is a fi - ột 1 ô - Ộ 25 Because the angle of attack of the element varies with the spanwise position of the element the profile-drag coefficient will do likewise unless the blade section characteristics are such that the variation of cdo with ar is relatively small over the operating range of the blade. The .
