时间:2011-04-05 11:32来源:蓝天飞行翻译 作者:航空 点击:次
To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. Axis-of-Rotation—The imaginary Tip-Path Plane—The imaginary line about which the rotor rotates. circular plane outlined by the It is represented by a line drawn rotor blade tips as they make a through the center of, and perpen-cycle of rotation. dicular to, the tip-path plane. BLADE PITCH ANGLE The pitch angle of a rotor blade is the angle between its chord line and the reference plane containing the rotor hub. [Figure 2-4] You control the pitch angle of the blades with the flight controls. The collective pitch changes each rotor blade an equal amount of pitch no matter where it is located in the plane of rotation (rotor disc) and is used to change rotor thrust. The cyclic pitch control changes the pitch of each blade as a function of where it is in the plane of rotation. This allows for trimming the helicopter in pitch and roll during forward flight and for maneuvering in all flight conditions. ANGLE OF ATTACK When the angle of attack is increased, air flowing over the airfoil is diverted over a greater distance, resulting in an increase of air velocity and more lift. As angle of attack is increased further, it becomes more difficult for air to flow smoothly across the top of the airfoil. At this point the airflow begins to separate from the airfoil and enters a burbling or turbulent pattern. The turbulence results in a large increase in drag and loss of lift in the area where it is taking place. Increasing the angle of attack increases lift until the critical angle of attack is reached. Any increase in the angle of attack beyond this point produces a stall and a rapid decrease in lift. [Figure 2-5] Angle of attack should not be confused with pitch angle. Pitch angle is determined by the direction of the relative wind. You can, however, change the angle of attack by changing the pitch angle through the use of the flight controls. If the pitch angle is increased, the angle of attack is increased, if the pitch angle is reduced, the angle of attack is reduced. [Figure 2-6] Aircraft Pitch—When referenced Aircraft Roll—Is the movement of to a helicopter, is the movement of the helicopter about its longitudithe helicopter about its lateral, or nal, or nose to tail axis. Movement side to side axis. Movement of the of the cyclic right or left causes the cyclic forward or aft causes the helicopter to tilt in that direction. nose of the helicopter to move up or down. LIFT MAGNUS EFFECT |