Streamlining Question

[kuranes]

The dimples one sees on the surfaces of golf balls are supposed to make them fly through the air with less impediment. Why is it that the surfaces of jets are smooth as can be, then, for supposedly the same reason ? The speed at which they travel changes the principles at work ?

[Jack Flak]

Originally Posted by kuranes

The dimples one sees on the surfaces of golf balls are supposed to make them fly through the air with less impediment. Why is it that the surfaces of jets are smooth as can be, then, for supposedly the same reason ? The speed at which they travel changes the principles at work ?

Many aircraft surfaces (esp. wings) use similar techniques as golf balls. I don't have all the data on hand though.

Motorcycle helmets too.

[CaptainChick]

Taken from Golf ball - Wikipedia, the free encyclopedia

When a golf ball is hit, the impact which lasts less than a millisecond, determines the ball’s velocity, launch angle and spin rate, all of which influence its trajectory (and its behavior when it hits the ground).

A ball moving through air experiences two major aerodynamic forces, lift and drag. Dimpled balls fly farther than non-dimpled balls due to the combination of two effects:

Firstly, the dimples delay separation of the boundary layer from the ball. Early separation, as seen on a smooth sphere, causes significant wake turbulence, the principal cause of drag. The separation delay caused by the dimples therefore reduces this wake turbulence, and hence the drag.

Secondly, backspin generates lift by deforming the airflow around the ball, in a similar manner to an airplane wing. This is called the Magnus effect. Backspin is imparted in almost every shot due to the golf club's loft (i.e. angle between the clubface and a vertical plane). A backspinning ball experiences an upward lift force which makes it fly higher and longer than a ball without spin. Sidespin occurs when the clubface is not aligned perpendicularly to the direction of swing, leading to a lift force that makes the ball curve to one side or the other. Unfortunately the dimples magnify this effect as well as the more desirable upward lift derived from pure backspin. (Some dimple designs are claimed to reduce sidespin effects.)

[LostInNerSpace]

Originally Posted by kuranes

The dimples one sees on the surfaces of golf balls are supposed to make them fly through the air with less impediment. Why is it that the surfaces of jets are smooth as can be, then, for supposedly the same reason ? The speed at which they travel changes the principles at work ?

There's a company developing a kind of skin with nano technology for use on aircraft wings. I seem to recall it being composed of what looked like nono cogs which moved as the wind passed over the surface. It is supposed to decrease drag and in the process increase fuel efficency and decrease cabin noise.

[ygolo]

I understand the dimples on a golf ball make it go farther, so why aren't there dimples on an airplane wing? - Yahoo! Answers

The answer you've been waiting for:

Since Laminar Flow and Induced drag have been addressed already: I will add my $0.02 about structure and substructure. A golfball and a wing are two different animals.

A wing is a stressed skin design which supports all imposed loads on its skin. Think of an aluminum coke can. You can stand on it slowly and it won't bend, but if it's dimpled even a little bit, you can bend it with one hand. This holds true even for our modern semi-monocoque wings with sub-structures.

Now a golfball is not a stressed skin design. The skin is not responsible for holding the shape of the golfball. This is true because golfballs bend like Beckham's soccer balls when whacked with a kinetic titanium club. I've seen slow-mo videos about it and I don't even consider GOLF a sport.

As Lt. Commander Data would say: "Theoretically it is possible." So theoretically if a wing were made of a solid core of fiberglass or styrofoam or even carbonfiber (like an RC plane) then you could put dimples in it because it's not the skin that's holding it up. But even RC planes are mostly stressed skin designs.

Now if you did have a dimpled wing; what would be the consequences? Well; assuming the dimples are placed on the top surface to speed laminar flow over the top of the wing, you gotta make sure that airplane never goes inverted. If it does, that plane will make a bee-line for the ground like a rock.

OK , so what? So I'll just keep it right side up! OK , but then how're you gonna certify the aircraft with the FAA? What about stall and spin recovery? If you're recovering from a spin, it already takes a coupla thousand feet; but with dimpled wings in a spin or an inverted spin, it's gonna take a lot of altitiude to recover (if at all) . ooooh, I doubt the FAA will certify the aviation equivalent of a dribble-glass! They have really dry wooden senses of humor those dudes...

[kuranes]

Originally Posted by LostInNerSpace

There's a company developing a kind of skin with nano technology for use on aircraft wings. I seem to recall it being composed of what looked like nono cogs which moved as the wind passed over the surface. It is supposed to decrease drag and in the process increase fuel efficency and decrease cabin noise.

Hmmm. I'll check it out. I'm kind of interested in Nano.

Originally Posted by ygolo

I understand the dimples on a golf ball make it go farther, so why aren't there dimples on an airplane wing? - Yahoo! Answers

Aha!

[entropie]

Look this is what happens with dimples pointing to the outside

+ "Traumtor" via YouTube