Aerodynamics of the Airfoil
Fineness Ration is a term used to describe the overall shape
of a streamlined body. It is described as the ratio of length to maximum width
of the streamlined body.
bodies that are short in length and fat in width has a low fineness ratio, but
those bodies that are long in length and less in width has higher fineness
Experiments show that for higher ratios of fineness ration less drag
Lift is depend on the shape of
the airfoil and its surface area. According to speed range different types of
airfoils are made. Nowadays NACA series Airfoils are used for best results.
Different Types of terms are used
to define an airfoil shape. For example Mean chamber line, Mean chord line, Mean
aerodynamic chord, Center of pressure etc.
Mean Camber Line:-
An imaginary line on the cross
section of a symmetrical airfoil that is drawn from leading edge to trailing
edge dividing upper and lower chambers in equal parts.
MEAN Chord Line:-
It is defined as a straight line
joining the leading edge to the trailing edge.
For symmetrical wings mean camber
line and mean chord line are same but differ in an un- symmetrical wings. For
un- symmetrical wing chord line shown in blow picture.
The Mean Aerodynamic Chord (MAC)
is a point on a wing where all aerodynamic and gravitational forces act upon.
This point is used as a reference for different types of gravitational and
Center Of Pressure:-
Center of pressure (CP) is the point on chord line of an
airfoil at which all aerodynamic forces cancelled each other’s effect. Its
depending direction shows in picture.
Angle of Attack:-
Angle of attack (AOA) is the
angle between the chord line and direction of relative wind. Within the limits
an increase in the angle of attack increases lift, this limit is 15°to 20°. After
this limit wing will be stall.
Wash In and Wash Out:-
Both are the terms describing the
angle of incidence of the wing tip versus the wing root.
Wash-in is the twist in wing that
increase its angle of incidence near tip in this case tip will stall. On the
other hand wash-out is the twist that decreases the angle of incidence near the
wing tip and root will stall.
In a flight thrust, weight and
their aerodynamic resultant are co-related each other’s. For example when
thrust increases the amount of lift required to keep the aircraft in level
decreases so as a result of this weight will decreases.