AN ILLUSION. In a nondirect headwind, you’ll lose slightly more speed than you’ll gain in tailwinds.
I know what some of you may be thinking. Bill Cox has finally gone off his rocker.
Well, yes and no. I was reflecting a while back during an allegedly quickie delivery of a Seneca IV from Oakland, Calif., to Cleveland, Ohio, that God doesn’t seem to hand out headwinds and tailwinds equitably. By all accounts, that should have been a tailwind trip. It didn’t work out that way. Most other trips don’t either, and therein lies the rub.
As I reflect on several years of delivering airplanes to destinations both domestic and foreign, it seems there have been more headwinds than tailwinds, so many more that I sometimes wonder if I’ve EVER had tailwinds. (Of course I have. They’re just hard to remember.)
Logic and Las Vegas odds suggest you should have tailwinds on half your flights, on the premise that you always fly out-and-backs (for the now $250 hamburger). Sorry, it just doesn’t work that way. My semi-educated SWAG estimate is that you’ll only experience tailwinds around 25% of the time, and here’s why.
Like many of you, I’ve seen the occasional freakish tailwind that shoved me along ridiculously faster than book. The best I’ve flown was in a Cheyenne III, predictably up high on an Atlantic crossing from St. Johns, Newfoundland, Canada to Shannon, Ireland. We had a welcome 130 knot push at FL270.
(Several years later, returning home to Los Angeles on a Qantas 747 after delivering a new Mooney Ovation to Sydney, Australia, I watched the readout on the flight-information monitor creep up to 1,100 kph at 37,000 feet. That’s almost a 600 knot groundspeed. My seatmate had probably just read the book Yeager; he knew I was a pilot, and when he saw the speed, he immediately exclaimed, “Good Lord, we’re traveling faster than Mach 1.” I shook my head, but no, I didn’t bother to explain it to him.)
Contrary to the title above, big tailwinds obviously do happen, but almost never on round-trips, and almost never in the bottom 10,000 feet of sky.
There are several reasons for this. One is that, in many instances, there simply isn’t much wind below 10,000 feet where most normally aspirated singles spend the majority of hours. The simple friction of the Earth’s atmosphere with the ground often results in light and variable for the first 5,000 feet. Above that height, however, wind can make or break a flight, and it’s more likely to break it than make it.
If you fly many trips in the mountains, the issue becomes more confused. As mentioned above, any irregularity on the Earth’s surface would seem to maximize friction between sky and ground, but mountains make their own rules. Wind speed tends to increase because of Venturi effect, the same phenomenon that produces lift on a wing. Funnel wind thru a narrow opening, and it inevitably speeds up.
In fact, a combination of geographic features can sometimes produce spectacularly dangerous winds in the mountains. Little 6,300-foot Mount Washington in New Hampshire, barely a hill by the standards of the 14,000-foot Rockies and Sierra Nevada, has experienced winds of more than 200 knots. The winds are so consistently ferocious that the government weather station at the top regularly records wind chills below -100 degrees F, not that dissimilar to conditions at the South Pole.
Turbulence is another factor that universally kills lift and causes airplanes to fly slower. While updrafts may impart a temporary increase in airspeed (assuming you maintain altitude), a downdraft can cause a dramatic drop in speed. I flew a Caravan to Seoul, Korea, last year, and as I left the Sea of Japan and crossed the Korean coast at Pusan, I watched airspeed slide back and forth from 140 to 75 knots for the next 200 miles because of spectacular up and down drafts that plague the area in winter.
In the Midwest and other regions where the wind really does come whipping down the plain, the sky can deliver surprising surface gusts that may tempt a pilot to fly low to take advantage of the free speed. Not a good idea, as those gusts can become violent and ruin more than your day.
Sadly, even when mid-altitude winds are glycerine-smooth and consistent, they most often won’t help you on a two-way flight. You’ll always lose more time in headwinds than you’ll gain in tailwinds, simply because headwinds act on the aircraft longer than tailwinds. Crunch some numbers on your flight computer, and you’ll see this to be the case. If you fly an airplane with a 200-knot true airspeed on a 400 nm out-and-back trip, and there are 20-knot winds directly on your course line, you’ll need 2+13 in the headwind direction and 1+49 for the return flight. That’s two minutes longer than if you flew both legs in no-wind conditions. The situation gets even worse as the trip gets longer.
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.