Theory of Flight 6.05 Lift and Drag References: Transport Canada Study and Reference Guide Glider Pilot, FTGU pages 91-98

6.05 Lift & Drag Bernoulli’s Principle Lift Airfoil terms Angle of Attack versus Lift Angle of Incidence Types of airfoils Drag Types of Drag Wingtip Vortices Streamlining

Bernoulli’s Principle An increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy

Bernoulli’s Principle Speed Pressure Speed Pressure

Bernoulli’s Principle Airfoils are shaped in a way to manipulate air pressure based on Bernoulli’s principle Air moves faster over the upper surface compared to the lower surface there by causing a difference in pressure Decreased pressure on the upper surface and increased pressure on the lower surface

Lift Lift is the force perpendicular to the relative airflow or relative wind

Airfoil Terms Relative Airflow Angle of Attack (AoA) Centre of Pressure (CoP)

Relative Airflow The direction of the air flowing with respect to the wing and in some causes the whole aircraft Created by the movement of the aircraft as well as the movement of air (updrafts, downdrafts, turbulence) Opposite to the flight path

Angle of Attack (AoA) The angle between the chord line of the aerofoil and the relative airflow Or, simply the angle at which the airfoil meets the relative airflow

Centre of Pressure Is the average or sum of the distributed pressures on an airfoil acting through a single straight line Moves forward on an airfoil as the angle of attack is increased

Centre of Pressure

AoA versus Lift Lift Increases Drag Increases Now we know how we get lift but how much can we get? One factor affecting lift is Angle of Attack As the angle of attack increases, what happens to lift? BUT… As the angle of attack increases, what happens to drag? Lift Increases Drag Increases

AoA v. Lift Lift / Drag Angle of Attack

Angle of Incidence (AoI) The angle between the mean aerodynamic chord of the wing and the longitudinal axis of the aircraft The AoI impacts forward visibility, takeoff and landing characteristics, and drag in level flight

Types of Airfoils An Airfoil is two-dimensional surface designed to obtain a reaction from the air through which it moves The shape and design of an airfoil will affect how air flows over the wing

Types of Airfoils What are some functions of airfoils? Create lift for flight Create thrust, used in propeller and rotor designs Attachment point for the control surfaces, flaps, slots, slats, external stores House fuel tanks, instrument components, retractable landing gear Added to effect stability

Drag Drag is the force parallel to the relative airflow The resistance an aircraft experiences when moving through the air

Types of Drag There are 2 main types of drag Parasite Drag which breaks down into Form Skin Friction Interference Induced Drag

Parasite Drag Drag of all those parts of an aircraft which DO NOT contribute to lift This drag increases the square of the speed so effort is taken to minimize its affect

Parasite Drag Skin Friction is the tendency of air smoothly flowing over the aircraft’s surface. The air tending to cling to its surface and its resistance to the motion of the aircraft (increases with accumulation of ice, dirt, or any contamination) Form drag is caused by the shape of the aircraft and attached components (Landing gear, Antennas, Struts) Interference drag is how smooth the air can flow around the attachment points of the different components

Induced Drag Is caused by those parts of an aircraft which are active in producing lift Cannot be eliminated Lift Drag

Induced Drag Low aspect ratio – high induced drag and low parasite drag High aspect ratio – low induced drag and high parasite drag

Due to the pressure changes Wing Tip Vortices Airflow over the top of the wing flows inward Airflow under the bottom of the wing flows outward Due to the pressure changes This creates a swirling motion off the wing tip called a vortex, this is the induced drag

Wingtip Vortices

Streamlining Streamlining is important and is a design by which a body is shaped to minimize drag The less drag… The futher and or faster you can fly In a glider you can fly further In an aeroplane you use less power so less fuel

Confirmation Check

Confirmation Check 1. Label where the high and low pressure areas are 2. ________ is the angle at which the airfoil meets the relative airflow ________ is the angle at which the airfoil and fuselage are attached ________ is the average of the pressure on an airfoil

Confirmation Check 3. Lift acts 90o to the ____________ 4. Bernoulli’s principle states that an _(increase/decrease)_ in the speed of a fluid occurs simultaneously with a _(increase/decrease)_ in pressure or a _(increase/decrease)_ in the fluid's potential energy 5. As lift increases the drag ________ 6. Label the diagram