Aerodynamics Flashcards
Give definitions of the following according to how they affect aircraft: Lift, Gravity, Thrust, and Drag.
Lift- Opposes gravity and the force produced by the airfoil of the aircraft’s wings. Gravity- Force by which an aircraft is attracted toward the earth. Thrust- Forward force created by the aircraft’s power plant engines. Drag- Resistance caused by the disruption of the airflow over the aircraft’s structure.
What two theories are used to explain how airfoils produce lift, give brief explanation of both.
Newton’s Third Law: of action and reaction-the action of pushing a mass of air downward produces a reaction force causing the airfoil to move upward. Bernoulli’s Principle: the relationship between pressure and the velocity of moving fluids. As air flows over the upper surface of an airfoil, the speed will increase, while the pressure decreases.
What is the angle of attack?
Formed between the relative wind striking the airfoil and the chordline of the airfoil. Angle changes when fixed wing aircraft nose up/down and helos change blade angle.
What is a stall and what causes it to occur?
Smooth flow of air breaks away from the upper surface of air airfoil, resulting in turbulent airflow and decreases the amount of lift. Caused by too great of an angle of attack.
What is torque effect? ***
Reaction of helicopter to the turning of the main rotor. If planes turn clockwise, reactionary torque effect would rotate the helicopter counterclockwise.
What are the two purposes of a tail rotor?
Counteract torque effect of main rotor, and give directional control (yaw.)
What is the difference between the advancing and retreating blades?
Advancing blade- when the blade is moving forward. Retreating blade- when the blade starts to move aft.
What is dissymmetry of lift?
When there is a differnce between the speed of the advancing half of the rotor and the retreating half of the rotor.
What is blade flapping and what causes it?
Blades moving up and down as they rotate, caused by dissymmetry of lift.
What is autorotation?
State of flight where the main rotor system is being turned by the action of the relative wind passing up through the blades rather than by the engine power.
