## Types of drag

 Drag - Wikimedia

### Drag:-

Drag is one of the four aerodynamic forces that act on a plane. For more information on aerodynamic forces click here. Drag is a restrictive force which opposes the motion of an aircraft. There are various types of drag depending upon their sources

### Types of drag

• Parasite drag
• Form drag or pressure drag
• Skin friction drag
• Profile drag
• Interference drag
• Lift induced drag
• Wave drag
ADetailed explanation of each type of drag is given below

1. Parasite drag
Parasite drag is a drag produced due to the motion of an object through a fluid. With respect to aviation, the object is an aircraft and the fluid is the atmospheric air. Parasite drag occurs due to air molecules. Parasite drag is classified as form drag or pressure drag, skin friction drag and interference drag.

2. Form drag or pressure drag
 Form drag - Wikimedia
Form drag is produced due to the shape of the object moving through the fluid. It depends on the cross section of an object. An object with a larger cross section and blunt shape will have a larger form drag whereas an object with a smaller cross section area and a sharper shape will have a lesser form drag.

How is form drag reduced?
It can be reduced using smaller cross section area for making wings and by using aerodynamic shape for an aerofoil.

3. Skin friction drag
Skin friction drag is a drag produced due to friction between an object (aircraft) & fluid (atmospheric air). The rough surface will have high skin friction drag and conversely a smooth surface will have less skin friction drag.

How is skin friction drag reduced?
Making the aircraft skin smooth will reduce skin friction.

4. Profile drag
Profile drag is a sum of the form drag & skin friction drag.

5. Interference drag
Interference drag is produced due to the interference of two or more airflows having different speeds. And this drag is produced by the interference of different aircraft parts, that is, due to a mixture of airflow around wing and the airflow around the fuselage.

How interference drag is reduced?
This can be reduced by keeping the angle between these two below 90 degrees

6. Lift Induced drag

 Lift induced drag
Lift is another aerodynamic force. It is a force which keeps an aircraft in the air and its magnitude is equal to the weight of the aircraft during stable flight. The direction of lift is perpendicular to the oncoming airflow towards the aircraft. Lift induced drag, as the name suggests, is a drag produced due to lift. At slower speed & higher angle of attack, aircraft will have more lift. But as the angle of attack increases, the air pushes the aircraft in the backward direction. This backward push is the induced drag. Technically speaking change in a vector direction of lift of the aircraft results in the formation of this type of drag.

Other types of induced drag are due to a mixture of airflow above and below the wing. The air flow mixes at the tips of the aircraft. We know that speed of airflow above the wing is higher than the speed of an airflow below the wing. Want to know the reason? Check here!

At the wing tips, these two air flows with variable speed, get mixed with each other which produces vortices at wing tips. The Reason for production of vortices is that high-pressure airflow gets pulled toward low-pressure airflow.

How is lift induced drag reduced?

Using winglet or shark-lets at wing tips.

 Winglets - Wikimedia

8.Wave drag

Wave drag is generally produced at transonic speed (speed almost equals to speed of sound) & Supersonic speed (speed greater than speed of sound). Due to high speed of airflow, shock waves are produced. Shockwaves are nothing but the disturbance in the air. This disturbance increases drag of the aircraft known as wave drag.

How wave drag is reduced?
 NASA F-15 - Wikimedia
Shock wave drag is one of the reason that at present time there are no supersonic passenger aircraft. Hence scientists are looking for the way to reduce shock wave drag. NASA is trying to reduce the shock wave drag by making aircraft noses sharp.  NASA's quite spike  F-15 is aircraft somewhat reduced the shockwave drag.

Drag Curve
 Drag Curve - Wikimedia
This drag curve shows the variation of different types of drag with respect to airspeed.