Tuesday, March 22, 2011
There’s No Such Thing As Tailwinds
Why is it that we always only remember headwinds?
But assume the wind isn’t directly on the nose or tail. You’ll still lose slightly more speed in headwinds than you’ll gain in tailwinds. Assume your magnetic course with the same 200-knot airplane is 90 degrees (and variation is 0), and the 20-knot wind is from 60 degrees in the headwind direction, 30 degrees off the nose; and the same on the tailwind leg, 30 degrees off the tail. With the headwind, your speed will be 189 knots, an 11-knot loss. In the opposite direction, plan on 209 knots, only a nine-knot gain.
The same thing happens when the wind is 60 degrees off the nose or tail. The loss to the headwind isn’t compensated for by the tailwind. In fact, a direct 90-degree crosswind will resolve to a small headwind. Not fair, is it?
Finally, there’s the psychological aspect. We all tend to remember the frequent, horrible headwinds, but we often dismiss anything but those rare, spectacular tailwinds with a, “Well, it’s about time.” In this age when avgas costs more than reasonably priced Chablis, most of us need to fly as efficiently as possible. To that end, you often can minimize the damage by careful planning. When you have the option, one trick is to fly headwind legs in the early morning when winds tend to be lighter, and tailwind trips in the afternoon when the winds are woofing. You can also fly lower on headwind legs, then aviate the return leg as high as possible to take maximum advantage of the breezes.
Flying higher may be a mixed blessing, however, and it may not apply to everyone. You’ll need to climb longer, burning more fuel and possibly having to don an oxygen mask if the sky is going your way and you hope to benefit from the atmospherics. For that reason, this may not pay off except in airplanes with blowers under the bonnet.
The airlines and some smart long-distance fliers also minimize the effect of negative winds by flying pressure patterns, seeking out tailwinds even if it extends the total trip distance. Remember, a Great Circle may be the shortest distance between two points, but you’re looking for the shortest time.
I’m no different from most pilots. I assume I’ll have headwinds all the time, and that must be a self-fulfilling prophecy, because most of the time, I do. The only good news about that attitude is that every once in a while, not very often, I’m pleasantly surprised with a slight tailwind.
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