Sự phát triển của máy bay quay-Wing Giới thiệu về các máy bay trực thăng Giới thiệu về Di Lý thuyết Di và Phân tích Hiệu suất chuyến bay theo chiều dọc Các yếu tố ảnh hưởng đến Di và Hiệu suất Vertical-Flight Autorotation trong Descent dọc | 286 AERODYNAMICS OF THE HELICOPTER oscillation which also results in a moment due to damping in roll. This moment has an important effect on the oscillation. Examine the position of the helicopter shown in Fig. 11 10c. At this instant the helicopter has a counterclockwise angular velocity which causes a small clockwise tilt Fig. 11-10 Oscillation of a helicopter following an angular displacement in hovering damping neglected . b of the rotor cone from that shown with damping neglected. The actual configuration of the rotor with damping considered is as shown in Fig. 11-11. As can be seen from this figure the angular velocity of the helicopter causes the rotor cone to lag behind the position it would have if no damping were present. Thus far the separate effects resulting from an angular displacement in attitude of the helicopter have been examined. It has been seen that the result of the displacement is an oscillation and it will now be shown that stability with speed and damping in pitch or roll are most HELICOPTER STABILITY 287 important in influencing the period of the oscillation. The factors that influence the divergence or convergence of the oscillation are indicated subsequently herein. In order to examine the combined effects of stability with speed and damping in roll the motion following an angular displacement of a hovering helicopter is examined in successive steps. For the sake of clarity stability with speed and damping in roll are assumed to act Fig. 11-11 Position of rotor cone with and without damping for helicopter of Fig. 11-lOc. successively although their effects actually occur simultaneously. Each of the following cycles of events should therefore be considered as occurring over a very short interval of time. Also the moment of inertia of the fuselage is assumed to be negligible for the immediate discussion. Consider a hovering helicopter displaced in roll or in pitch to an attitude shown in Fig. 11 12a. Although no moment is produced about .