Do you know how the different types of drag affect performance?

But First... What Exactly Is Drag?

When two masses are in contact, they resist each other's motion. In the case of an airplane, air resists the forward motion of the airplane. So when it comes to flying, drag is the resistance of an aircraft's movements through air. Drag opposes thrust.

1) Interference Drag

Interference drag is generated by the mixing of airflow streamlines between airframe components. For example, the wing and the fuselage, or the landing gear strut and the fuselage. As air flows around different aircraft components and mixes, a localized shock wave is formed, creating a drag sum greater than the drag that components would have by themselves.

2) Skin Friction Drag

Skin friction drag is the result of the aircraft's surface being rough. Olympic swimmers wear swim caps on their heads, so hair doesn't create extra drag and they can swim faster through the water. This same principle can be applied to most aircraft, where a smooth skin reduces skin friction drag, improving performance and fuel efficiency.

3) Form Drag

Form drag is the result of an object's general shape in relation to the relative wind. Have you ever stuck your hand out the window of the car, first tilting it flat, and then vertical, into the wind? When your hand is horizontal like an airfoil, it's easy to stick outside the window. But when you open your hand into the wind, your hand flies backwards, and requires a lot more force to hold it position. That's the easiest way to understand form drag.

4) Induced Drag

As the air (and vortices) roll off the back of your wing, they angle down, which is known as downwash. Downwash points the relative wind downward, so the more downwash you have, the more your relative wind points downward. That's important for one very good reason: lift is always perpendicular to the relative wind.

Check out the diagram below. You can see that when you have less downwash, your lift vector is more vertical, opposing gravity. When you have more downwash, your lift vector points back more, causing induced drag. On top of that, it takes energy for your wings to create downwash and vortices, and that energy creates drag.

As you get close to the ground, your downwash is reduced and your vortices are reduced, which means your induced drag is reduced as well. Click here to learn everything you need to know about ground effect.

5) Flying Supersonic? You'll Get Wave Drag.

Wave drag is caused by the formation of shock waves around the aircraft in transoni or supersonic flight. As air flows from the supersonic region in front of the shockwave, to the subsonic region behind the shockwave, it separates and becomes turbulent. As the shockwave becomes stronger, more airflow separation occurs, known as wave drag.