Lift Flashcards
2 components of total reaction
Lift and drag
How is total reaction created
Surface pressure differentials over the area of aerofoil.
Lift force equation
Lift=qxsxCl
Or
Lift= 0.5x rhox V*2 xS x Cl
Lift coefficient
Dimensionless number which describes how effective the aerofoil is at producing lift for a given airflow speed and surface area.
What factors affected lift coefficient
Angle of attack
Camber
Thickness
Effect of angle of attack
Up to a certain angle an increase in AOA causes the airflow over the upper surface to travel faster. Pressure is reduced over upper surface.
What is Cl max
Maximum value of the coefficient of lift for a particular aerofoil. Achieved at the stalling angle or critical angle which is the highest AOA the wing does not stall at.
What happens to lift at angles greater than the stalling angle
The coefficient of lift reduces rapidly because the wing is stalled.
Effect of Aerofoil Thickness
As thickness increases
Cl max increases (lifting ability much greater)
Stalling angle of attack increases
Rate at which Cl increase with angle of attack is approximately the same.
Camber Aerofoil compared to Symmetrical Aerofoil
Cambered aerofoil produces lift even at 0% AOA
Greater lifting ability Cl max higher.
Stalling angle remains in the same approximate region.
Rate at which Cl increases with AOA is approximately the same.
Zero lift angle of attack is negative.
The effects of Flaps
Camber has significant effect on production of lift.
Trailing edge flaps increase Camber.
Camber is distance between chord line and mean camber line.
Cl max increases
Stalling AOA reduces.
Relationship between Lift Speed and Cl
If speed doubles lift increases fourfold.
For level flight the Cl has to be reduced by 1/4. Inverse relationship.As Camber and thickness are fixed only variable that can be changed is AOA.
