June 2008 Issue

Smoothing The Bumpy Ride

Learning to anticipate where turbulence will occur and how “enthusiastic” it might be is just as important as knowing what to do when you fly into it.

Nothing can spoil a nice trip on a good-weather day like bumpy air. Like most other things in meteorology, it’s somewhat possible to predict turbulence. But unlike most other things in meteorology, as well as in life itself, there is something you can do about it. Altitude, time of day, tall—and not-so-tall—buildings and the relative flatness of the terrain over which we’re flying can all combine to make what should have been a smooth, relaxing flight into your (or your passengers’) worst nightmare. Sometimes, those are the cards you’re dealt. Most of the time, though, it doesn’t have to be that way. The air that supports our aircraft is a fluid subject to the laws of physics. Ignoring the local influence of the sun and obstructions for a moment, when the wind blows, its flow is laminar—all air moves together smoothly. Even though that air might be moving rapidly it will be pretty smooth. If you upset the laminar flow of that wind, things can get interesting in a hurry. The upset can be something physical like a mountain or just a different air flow. The result on the nice days is just a slight change to the laminar flow of the wind. On bumpy days, though, the result is air in the boundary between the laminar flow and the upsetting influence is not smooth at all. In fact, there are often eddies and backflows, same as you get aft of an airfoil that’s just at or past the its critical angle of attack. Depending on the strength of the wind and the opposing forces, those eddies and backflows can be slight or quite severe, with the corresponding flight through them being either a little jittery or enough to separate wing from fuselage.

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