system
Given the following post, respond as if you're commenting on Reddit:
human
Why aren't any planes covered in dimples, yet every golfball is?
gpt
Masters in Aerospace here.

There is a characteristic of the airflow that is called turbulence. Turbulence represents the amount of rotation in air molecules as they move through the air. Turbulent flows are more energetic, because in the addition to the kinetic energy from moving with the stream, they contain rotational energy as well. 

Turbulence can occur at various scales and various strengths. You can have large vorticies, and you can have very small ones. As it happens, the vorticies that one would find in the general air through which the golf ball flies happen to be very weak - observe the smoke from a match in a room without the AC blowing. You will see very slow rotation. 

The second part of this is aerodynamic drag. There are two major sources of drag - skin friction drag (air friction), and pressure drag. The latter is what you experience when you attempt to move a large sheet of wood through the air - the pressure on one side is a lot from the molecules bunching up, and the air behind the sheet is for the most part stagnant at the start, thus creating a pressure difference which causes a force in the opposite direction of movement. In fact, the energy you exert to move the sheet goes into the creation of vorticies as the air flows quickly around the edges of the sheet. 

And that situation is unfavorable for you because you want the majority of the energy going towards the propulsion of your object, not the creation of vorticies that do you no good. This is when people figured out what it means to have an aerodynamic shapes.

Well, a golf ball is a smooth shape, so it should be fine, right? Nope, this is where the interesting effect of turbulence comes in. You see, the smoothness of the golf ball is enough for it to avoid the creation of vorticies, but because the initial strength of the vorticies in the ambient air is so low, you get something thats called separation - the flow does not have enough energy to go to the back of the ball, leaving you with pressure drag. 

So what the dimples do is they create micro vorticies, with significant strength. The higher energy flow has the energy to expand to the low pressure area behind the ball, thus increasing the pressure there.   The downside to this is that the vorticies cause more skin friction drag then before (the energy from the motion goes into the creation of the vorticies), but the decrease in pressure drag is greater then that. Therefore the ball flies further. 

For airplanes, for the most part, the wing shape prevents separation because it channels the flow smoothly from front to back. Also, the skin friction creates micro vorticies as well, that serve to keep the flow "attached" to the wing, preventing separation. (Golf ball without dimples does create some, however because it flies relatively slow compared to the aircraft, and the area exposed to the air is much smaller, they are much, much weaker then the aircrafts, and are not able to punch through the low pressure area).  

However, to improve performance at low speeds, some aircraft add transverse strips on the top part of the wings towards the front to create artificial turbulence to aid with keeping the flow attached to the wing. 

In the end though, you don't want turbulence - if you can find a way to keep the flow very laminar (i.e. turbulence free), you don't have to expend energy into creating these vorticies. Remember, the faster you go, the higher strength vorticies you create with skin friction, the more energy you expend. So if you look at something like an F-104 Starfighter jet, you have short stubby wings to minimize the area of affect. The wings were also very, very thin - in fact, you could cut your finger on the leading edge. This design keeps the flow laminar, and avoids the separation bubbles. The downside is you have to be going very fast for this, because your short wings do not provide enough lift at slow speeds, which means that at slow speeds you have to pitch up to increase lift, and your sharp edge starts creating vorticies way more then a conventional smooth wing of a passenger aircraft.