Total Drag

Total drag is the sum of all forces working parallel to but opposed to thrust. Although there are numerous of factors affecting total drag it is common to subdivide these factors into 2 main factors, namely:

- induced drag (drag which is associated with the production of lift)
- parasite drag (drag which is not associated with lift production but mainly depends on aircraft shape or skin friction for example and is also known as zero lift drag)

Thereby, the boundary layer (figure 1.1) plays a significant role in how much drag is produced at different airspeeds. How these forces act in different flight phases are explained in the following chapters.

 Figure 1.1 Wing boundary layer

Figure 1.2 shows the variation of the total drag with the indicated airspeed (IAS) and is made up of the two components mentioned above. From this graph we are able to see that parasite drag varies as the square of the IAS while induced drag varies with the inverse of the square of the IAS. From this total drag curve we can specify a point known as the minimum drag speed and as such is the most efficient speed.

 Figure 1.2 - Total drag curve

The shape of the total drag curve changes as certain conditions change. For example when the weight increases the minimum drag speed will also increase and vice versa. We'll get into more detail with induced and parasite drag in the next chapters and how they are related to eachother.