Airfoil Design – Structure of the Airfoil in Aviation

In our previous lesson on Airfoil design, we discussed about the Bounday Layer. In this lesson we will take a deeper look at the structure of the airfoil.

What is an Airfoil ?

The airfoil is any shape that derives lift force from the relative airflow for a minimal penalty of drag. The lift produced by an airfoil is the result of the shape and its angle of attack to relative airflow.

Structure of the Airfoil

There are some basic terms associated with an airfoil, they are :

1.Leading Edge Radius and Trailing Edge : the radius of curvature of the leading edge is called the leading edge
radius. The point at the end of the airfoil is the trailing edge.

2.Relative Airflow :the apparent movement of air with respect to the aircraft’s flightpath,relative airflow
has 3 qualities :-
a.Direction – the air is parallel and in opposite direction to the flight path of the aircraft.
b.Condition – air is close to and unaffected by the presence of the aircraft
c.Magnitude – the magnitude of the Relative airflow is the TAS (True Air Speed)

3.Chord : is that line on the airfoil that joins the leading edge to the trailing edge

4.Angle of Attack : the angle between the chord and the relative airflow.

5.Mean Camber Line : is that line that divides the airfoil into two equal halves.Remember that the chord and the
mean camber line are both different, chord is a line that joins the leading edge to the trailing edge.

6.Camber : the space between the chord and the mean camber line is called camber.The word camber refers to curvature .Usually,the upper camber of an airfoil is greater than the lower surface,also greater the camber more the lift .Adding camber doesn’t necessarily increase lift. It depends on the airfoil shape, if too much camber is added,the flow over the airfoil may not stay attached to the wing even at an angle of attack of zero, as we discussed earlier in the boundary layer lesson.

7.Thickness : the distance between the upper and lower surface of an airfoil.

8.Angle of Incidence : or Rigger’s angle is the angle between the chord-line at the wing root and set to the fuselage with respect to its reference line. Its usually at 4 degrees positive, this is because at this angle an airfoil will give best lift / drag ratio.We will take a closer look at lift/drag ratio in the lessons to come.

Now we know the basics of the airfoil.In this lesson remember the definitions and the diagrams they make understanding easier,Why is it required to know all this? Because every part of your airplane is interconnected and related to another, change or modify any one of its parameters and you have a different profile of flight. Aviation as a subject has just too much to cover, we are breaking it down and giving you what is required.