直升机教员手册 Helicopter Instructor’s Handbook
时间：2014-11-10 08:35来源：FAA 作者：直升机翻译 点击：次
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To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. For example, in steady state flight, the aircraft is maintaining a constant airspeed and constant altitude. The aerodynamic forces are balanced. Although the helicopter is moving, it is not accelerating or climbing. [Figure 3-6] Any time opposing forces become unequal (unbalanced), acceleration results in direction of the greater force. If lift is greater than weight the helicopter climbs. If thrust is greater than drag, the helicopter moves horizontally. Point out that thrust can occur in any or all directions. For example, if the helicopter is moving sideways or backwards, thrust is in the direction that it is moving. [Figure 3-7] Airfoil Define and discuss the different types of airfoils with the student and stress the importance of using standardized terminology. An airfoil is a curved surface body or structure designed to produce a lift or thrust force when subjected to an airflow. An instructor can check the student’s understanding of airfoils and the terminology used to describe them by having the student draw and label the parts of an airfoil. [Figure 3-8] Refer to the Pilot’s Handbook of Aeronautical Knowledge and the Helicopter Flying Handbook (FAA- 8083-21) for definitions and illustrations of airfoil design. Blade Twist Explain to the student that the rotor blade of a helicopter is designed with a twist to relieve the stresses on the blade and distribute lifting force more evenly along the blade due to the lift differential along the blade. Blade twist provides greater pitch angles at the blade root where velocity is low and smaller angles at the tip where blade velocity is higher. This increases the induced air velocity and blade loading near the inboard section of the blade. Rotor Blade and Hub Definitions The CFI must be familiar with the following basic terms and be able to explain them to the student. 1. Hub—the attachment point of the rotor blades. 2. Tip of the blade—the farthest outboard section of the rotor blade. 3. Root of the blade—the section of the blade closest to the hub and where the attachment point is located. 4. Twist—the change in blade angle with respect to the angle at the hub outward to the tip. 5. Taper—the change (decrease) in blade chord with radial distance. These terms related to the rotor hub and blades are best discussed in the classroom and identified on the aircraft during a preflight. Airflow and Reactions in the Rotor System When introducing and describing the airflow in a rotor system, the instructor must first identify the types of relative wind. By defining and explaining the various air movements in a rotor system [Figure 3-9] and the relationship of air movement to an airfoil, the instructor establishes a foundation for more detailed discussions of aerodynamic principles. . The movement of a rotor blade through the air creates relative wind. Relative wind moves in a parallel but opposite direction to the movement of the rotor blade. . The flow of air parallel to and opposite the flightpath of an airfoil is rotational relative wind. It always meets the airfoil at a 90° angle. . The component of the total relative wind velocity created by forward flight velocity/airspeed is airspeed relative wind. . Induced flow (downwash) is a downward component of air that is added to the rotational relative wind. . Resultant relative wind is the airflow from rotation (rotational relative wind) that is modified by induced flow. . Up flow (inflow) is airflow approaching the rotor disk from below as the result of some rate of descent. Up flow also occurs as result of blades flapping down or an updraft. A demonstration of the airflow in the following instances helps the student understand the concept of relative wind: . Airfoil moving in one direction . Rotating rotor blades . Advancing blade . Retreating blade . Relative winds are the same for tail rotor Rotor Blade Angles Angle of incidence is the acute angle between the chord line of the airfoil and the plane of rotation (tip path plane) or the angle between the chord line of a blade and the relative wind. Sometimes, this is referred to as the blade pitch angle. The angle is changed through rotation of the rotor blade around its spanwise axis, which is known as feathering. [Figure 3-10] An instructor can use training aids to discuss the angle of incidence in the classroom, but it is best demonstrated at the aircraft. Show the student how the angle of incidence is changed on all blades (except tail rotor) simultaneously by using the collective pitch control. Define this action as collective feathering and explain how it affects the overall lift of the rotor system. Demonstrate how the cyclic pitch control causes a differential change in the angle of individual blades (except tail rotor) and define it as cyclic feathering. Stress to the student that cyclic feathering changes the attitude of the rotor system but does not change the amount of lift. [Figure 3-11] Point out how the angle of incidence for the tail rotor is changed on all tail rotor blades simultaneously by using the antitorque pedals. . Stress that angle of incidence is a mechanical angle. [Figure 3-12] . Remind the student that the AOA is the acute angle between the chord line of an airfoil and the resultant relative wind. It can change with no change in the angle of incidence due to blade flapping and up/down drafts. . Stress that angle of attack is an aerodynamic angle. [Figure 3-12] Discuss lift at different AOAs. With the use of diagrams, an instructor can explain how the AOA affects the amount of lift. An easy demonstration of how the AOA affects lift is to remind the student of what happens if an arm is extended out of the window of a moving vehicle. Using guided discussion and demonstration, ask the student what happens when the palm of the hand is parallel to the ground and when it is rotated forward. Show the student how the hand rises until reaching the point at which it stalls and is just pulled rearward. Emphasize the following principles: |
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