LIFT

The Airfoil

Leading edge Trailing edge

Top

Bottom

Airfoil CharacteristicsRounded Leading Edge – to split the airSharp Trailing Edge – to reduce turbulenceFlat Bottom Declining Top

Air Flow

Air flow is caused by both:1. the motion of the wing moving forward and2. natural wind

The air is split in half where it meets the leading edgeThe air recombines at the trailing edge

Air on top of the airfoil moves faster than air on the bottom , but why?

Venturi Effect

As a fluid (air) is compressed it moves faster

The effect of compressing fluids

Air is evenly distributed normally

Half a Venturi

The asymetric shape of the air foil causes the air on top to be compressed while the air on the bottom is hardly moved

So the air on top of the air foil moves FASTER

Why is this important?

Bernoulli’s Principle: The pressure air exerts as it moves decreases as the speed of the air increases

The faster I make my airfoil go, the

more I decrease the air pressure on top

of my airfoil

How does this help?

Aircraft on the ground

Pressure on top and bottom are equal

Aircraft moving forward Pressure on top is less than pressure on bottom

Lift

Calculating Lift

L = (1/2) d v2 s CL•L = Lift, which must equal the airplane's weight in pounds •d = density of the air. This will change due to altitude. These values can be found in a I.C.A.O. Standard Atmosphere Table. •v = velocity of an aircraft expressed in feet per second •s = the wing area of an aircraft in square feet •CL = Coefficient of lift , which is determined by the type of airfoil and angle of attack.

Which parts does the pilot control???

Velocity (speed) and Density (altitude)

How can I use this when flying?Imagine you are flying and you are having trouble keeping the aircraft from losing altitude.

What should you do?

Things to know

Lift is always perpendicular to the wing (airfoil)

Ground

Things to know

• Lift must equal aircraft total weight for aircraft to fly level– Weight exceeds Lift will cause aircraft to descend– Lift exceeds weight will cause aircraft to climb

Explore

• If you were an aircraft designer how would you design an airfoil for:– A passenger airliner– A fighter

Memory Check

What is the Venturi effect?

Memory Check

Where does the Venturi effect occur on the Airfoil?

Memory Check

Describe the sequence of events that leads to lift using a thinking map

How lift is created

Aircraft moves

forward

Air moves around

wing

Air on top compresses

Air pressure on

top decreases

Air on top moves faster

Pressure differences create lift

Venturi Bernoulli