4 Terminology Airfoils Camber An airfoil or airfoil section may be defined as any surface designed to obtain lift. It has been found that the most suitable shape for producing lift is a curved or cambered shapeCamberThe camber is the curvature of the upper and lower surfaces of an airfoil. Usually the upper surface has a greater camber than the lower
6 Terminology Cont’d Equilibrium When two forces are equal and opposite, the aircraft is said to be in a state of “equilibrium”. Therefore, the aircraft will continue to move forward at the same uniform rate of speed.LiftWeightIf Lift = Weight, then the aircraft is notclimbing or descending, therefore, it is saidto be in “equilibrium”ThrustDragIf Thrust = Drag, then the aircraft is notaccelerating or decelerating, therefore,it is said to be in “equilibrium”
7 Terminology Cont’d Centre of Gravity Centre of Pressure The point on the aircraft where all the weight acts throughCentre of PressureThe point on the aircraft where all the lift acts throughBIG NOTE: NOT ALWAYS THE SAME POINT
8 Terminology Cont’d Couples When two equal forces act in opposite directions separated by a distance, that is said to form a couple“Every couple has it’s moment” Moment!WLWL
9 Terminology Cont’d Relative Airflow A term used to describe the direction of the airflow with respect to the wingIs created by the motion of the airplane through the air.RelativeAirflowDirection oftravel
10 Terminology Cont’d Streamlining Is a device by which a body is so shaped that drag is minimized as the body moves forward through the air.
11 Terminology Cont’d Lift and Drag Curves Lift to Drag Ratio The forces of “Lift” and “Drag” are dependent on:The shape of the airfoil (CL or CD)The plan area of the airfoil “S”The square of the velocity (true airspeed) “V2”Density of the air “ρ”Lift to Drag RatioUsed to express the relation between lift and drag and is obtained by dividing the lift coefficient by the drag coefficient
12 Lift and Drag Curves Lift = CL · ½ · V2 · S · ρ Drag = CD · ½ · V2 · S · ρ