Hummm? Fairings

[mraf]

Fairings

 

For those of you who are interested in history, here's where the word "Fairing" comes from.

Early in the development of aviation, it was realized that the important thing for an airplane was to have a lot of lift and very little drag. An enormous amount of drag happens if you lose laminar flow - that is, if instead of smoothly following the surfaces on the airplane, when the air breaks away from the surface it will form spinning vortices which tumble around and wreck the airflow all over the place. This is called turbulence. The exact same problem was known from laying out the keels of ships, for water flow around a ship hull is a lot like air flow around the skin of an airplane. This problem was analyzed by mathematicians. They learned something: they could predict the points at which the air flow (or water flow) would break away from the surface and start to become turbulent.

A curve which has no breaks in it is called "Continuous" by mathematicians. A curve which has no sharp corners in it is called "smooth" by mathematicians. Smooth means the first derivative of the curve is continuous. At any given point, a curve has a radius of curvature. If there are no sudden jumps in the radius of curvature, the curve is called "Fair." A Fair curve has a continuous second derivative. It was learned that turbulent flow always starts at a point on the skin where the curve has an abrupt change in the radius of curvature, that is a point where the curve is not fair, or a point where the second derivative is discontinuous. So, you can't just stick a wing onto an airplane fuselage - the sharp corner where they meet is not even smooth, much less fair. The designers found they had to locate places like this on the aircraft skin and cover them with some smoothly curved sheet metal. These pieces of sheet metal are called "Fairings." http://www.calsci.com/motorcycleinfo/Images/dc3.jpg

Notice the fairings on the wing-fuselage joint of this DC-3.

I jumped out of one of these once, and it was working just fine at the time.

In the '70's, when gas mileage became important, automotive companies quickly hired some aircraft designers to help them make their cars have less drag. Shortly after that, the automotive companies started putting pressure on the computer programmers to make certain that all the curves on an automotive body were fair. Some companies became quite obsessed with this: honda at one point announced that they had determined that surfaces which had a continuous fifth derivative were most pleasing to the eye, so they wanted their cad/cam systems to only design curves which were smooth, fair, and also had three more levels of derivative continuity. I don't think they got very far, as very few programmers can handle the mathematics of c5 continuous surfaces.

Of course, until about 1970, there basically was no such thing as computer aided design. To lay out the curves for the hulls of ships and large bombers, boeing many years ago built a building with an unbroken wooden floor which was bigger than a football field. They would clear this building, and draw a coordinate graph on the floor. Then, the designers would tell them exact points where they wanted the hull skin or aircraft skin to be. The engineers would hammer nails into the floor at these points. They would then take very long, very thin strips of oak, soak them in water, and tie the oak strips to the nails. The oak will naturally form a shape of least energy, which happily enough is a shape which is both smooth and fair. The engineers would wait for the oak to dry, then trace the lines on the floor of the building. This then became the master drawing for the bulkheads. The thin strips of wet oak were called "splines," which is why today curves in mcdraw and autocad are called splines, although essentially none of the programmers know this either. Most of our bombers and battleships in WW II were laid out in this building, because this was what we had. In General Relativity, Einstein assumed that the universe itself was curved, but in a smooth and fair fashion. His reasoning: anything else would have been mathematically ugly, and he didn't believe God did ugly things. Since then, several people have made alternative theories of gravity where the universe does not have to be smooth and fair. None of them have worked worth beans, however. It seems God does in fact have a sense of aesthetics. Later, it was pointed out to Einstein that his theory included the possibility of points where the universe was neither smooth nor fair. These points are called singularities, or more popularly black holes. Not all scientists believe in black holes, and Einstein was skeptical.

[Yammer Dan]

And I thought they were just the Plastic junk that held the shield on my bike!!

[1BigDog]

Fairings??? whew...I thought he said Fairies!!!!!!

[Sylvester]

I for one found this very informative. Although I don't understand the total concept, it is interesting that we have the mathematicians, engineers and bean counters to make this all happen.

 

[Mel]

I wonder----- do pieces of restored farm equipment get retrofit with fairings??? Just asking.

[slick97spirit]

I love this stuff. It's so cool to see/hear the history of how these things were developed and how they overcame obstacles.

 

Thanks for posting this.

[Cougar]

A very cool plane to jump out of. I did the same thing

about 20 years ago. really fun!

[Guest PlaneCrazy]

While it's a very interesting history on aviation and aerodynamics in general, the actual verb "fair", adjective "faired" and the noun "fairing" were developed much earlier then aviation. Sources vary, but the earliest dates are around 1819 or so (Websters "...to join so that the external surfaces blend smoothly") and Oxfords says "mid 19th century". These terms came about for ship building, which actually uses the same principles of aerodynamics (air has has much of the same properties as liquids).

 

You know what they say... "There's nothing new under the sun"