Up flow also occurs as result of blades flapping down or an updraft.Ī demonstration of the airflow in the following instances helps the student understand the concept of relative wind: Up flow (inflow) is airflow approaching the rotor disk from below as the result of some rate of descent.Resultant relative wind is the airflow from rotation (rotational relative wind) that is modified by induced flow.Induced flow (downwash) is a downward component of air that is added to the rotational relative wind.The component of the total relative wind velocity created by forward flight velocity/airspeed is airspeed relative wind.It always meets the airfoil at a 90° angle. The flow of air parallel to and opposite the flightpath of an airfoil is rotational relative wind.Relative wind moves in a parallel but opposite direction to the movement of the rotor blade. The movement of a rotor blade through the air creates relative wind.By defining and explaining the various air movements in a rotor system and the relationship of air movement to an airfoil, the instructor establishes a foundation for more detailed discussions of aerodynamic principles. When introducing and describing the airflow in a rotor system, the instructor must first identify the types of relative wind. Airflow and Reactions in the Rotor System These terms related to the rotor hub and blades are best discussed in the classroom and identified on the aircraft during a preflight. Taper-the change (decrease) in blade chord with radial distance.Twist-the change in blade angle with respect to the angle at the hub outward to the tip.Root of the blade-the section of the blade closest to the hub and where the attachment point is located.Tip of the blade-the farthest outboard section of the rotor blade.Hub-the attachment point of the rotor blades.The CFI must be familiar with the following basic terms and be able to explain them to the student. This increases the induced air velocity and blade loading near the inboard section of 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.
Elements of an airfoil.Įxplain 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. Refer to the Pilot’s Handbook of Aeronautical Knowledge and the Helicopter Flying Handbook (FAA- 8083-21) for definitions and illustrations of airfoil design. 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. An airfoil is a curved surface body or structure designed to produce a lift or thrust force when subjected to an airflow. Define and discuss the different types of airfoils with the student and stress the importance of using standardized terminology.
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