April 26, 2000

It is characteristic of a young bull to charge directly at any sort of challenge or opportunity. The old bull, having survived his youth, is inclined to take a few more chomps of grass before committing himself to a specific course of action. Permit me to fancy that the old bull takes a moment to philosophise upon the situation, to take the time to observe a bit more and to ask WHY more frequently. Back in the bad old days (which maybe weren't so bad after all), that's why draftees were young men.

My solitary ride each night is, in many ways, a young bull's challenge. There are a lot of aspects of the job that beg the question WHY, but resist easy answers. Most of the young bulls move on to pastures that aren't so steep, but there are some old bulls who have found satisfactory answers to their questions. Old enough to know better, I entered this job with a youngster's experience.

Difficult weather can be found in any season, but cutting our year into lopsided halves we could generalize it into winter and summer. Summer has thunderstorms, winter has ice and in between you can have some... or none... of either. Last week, riding out the tail end of the icing season, I amused myself with some casual observations.

I am sure that you can recall that there was an abundance of moisture last week. It rained every day from Sunday to Sunday, starting out cold, warming, and then returning to cold again. For the most part, it was more winter than summer although there was no snow or ice. Not too far above the ground though, the clouds dripped with liquid water, chilled below 32 degrees, but not so cold that it would freeze without some sort of provocation.

We all learn that freezing is 32 degrees, and for the most part, that is sufficient information for the daily fare. We observe water dripping off of a snowy roof on a sunny 20 degree day, but we can readily understand that the sun has warmed the roof enough to melt the snow despite the surrounding cold. Occasionally we notice things that aren't so readily explained and we just ignore them, or think that we must have seen them wrong.

A bottle of pop, left in the car on a cold night might still be liquid when we first get in the car, but by the time we leave the driveway, we notice that it is full of ice crystals. We have observed one of the exceptions that exist in the narrow band of temperatures near freezing; water needs an excuse to freeze at temperatures that are just below 32 degrees. The pop didn't freeze until it was jostled. Similarly, the moisture in a cloud chilled to the upper twenties won't freeze until something- like an airplane- jostles it.

Clouds can be a real threat to airplanes in the winter, causing ice to build up on all of the forward- facing parts of the structure; the wings, tail, landing gear, struts, antennas, propeller blades, windshield, and engine air intakes. The ice adds weight to the airplane, and its rough surface creates extra drag. By far the worst problem though, is the way that it alters the shape of the wing, causing a drastic reduction in its efficiency. Ice attacks from four directions, reducing lift and reducing engine power while adding drag and adding weight.

The news isn't all bad though. Some clouds are dryer than others, and all clouds become dryer as they get colder. By the time that the temperature has fallen to 15 degrees, most clouds have become harmless because such cold air is generally incapable of holding enough moisture to pose a threat. Moreover, the water droplets in such a cold cloud have likely been turned to harmless ice crystals. Surprising to many, flight through snow, and even snow - filled clouds, is seldom icy.

Six months ago I had never seen these things, but earlier this week I found myself musing about the past winter, as I watched nature play a fickle game of physics outside of my airplane. The temperature was just barely below freezing, according to both of the airplane's thermometers, but no ice was forming. My passage through wet clouds was causing water droplets to stream back along the windshield, the wing strut and the wing, but it did not freeze. Gradually, as I watched, it appeared as though a ridge of rock candy was forming at the crest of the wing's leading edge.

The air striking the airplane was being heated because the airplane compresses it slightly as it moves it aside. It was no longer cold enough to freeze the water, but once the air started over the top of the wing, it passed into a low pressure area. Just as compressing the air causes it to heat, releasing the pressure causes it to cool. As the air started past the very leading edge of the wing, its temperature dropped below freezing and its moisture froze there.

It was a night for playing. I had flown my nightly schedule through the cold and dark of the "R months" and successfully outmaneuvered the ice devil each time it threatened. This night had the capacity for creating severe ice problems, but I knew that the safety of warmer air was just below me. I sat and watched while nature took its course, and fancied that someday I could become one of the old bulls that can consistently outflank the daring young bulls.

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