July 31, 2014
By Barry Schiff
One of the most popular cross-country flights from the Los Angeles Basin is, not surprisingly, across the Mojave Desert to Las Vegas. Convective turbulence, though, can make it a rough flight. It was during such a flight with my mentor, Paul Blackman, in his North American Navion, that he taught me in the summer of 1956 a useful technique that I have used in turbulence ever since.
The roughness during this flight began in earnest as we passed over Barstow, California. During the updrafts, I would lower the nose so as to maintain altitude and reduce power to prevent an excessive increase in airspeed. Upon entering a downdraft, I would add power and raise the nose to continue maintaining altitude. This is the most common method of coping with convective turbulence. As I fought through the thermals, Paul just sat there in the right seat, his arms folded across his chest and a knowing smile on his face. He slowly shook his head in a disapproving manner.
“What’s the matter?” I asked. “Am I doing something wrong?”
“There’s a better way to do this,” he said. “Something we learned crossing the deserts of North Africa during the war.”
I was all ears. Paul had been a command bomber pilot in B–24 Liberators and was a marvelous instructor. When he spoke, it was wise to listen.
“When you hit an updraft,” he began, “use it to your advantage. Allow the airplane to gain altitude. Don’t fight it. For just as night follows day, downdrafts follow updrafts.” The idea, he explained, is to have surplus altitude available to sacrifice when transitioning from an updraft to a downdraft.
“When you enter the downdraft,” he continued, “simply allow the airplane go down with it. Don’t fight that, either.
“In terms of aircraft performance,” he yelled over the air and engine noise, “thermals can be beneficial. They give you something for nothing. So don’t fight it. Go with it. When in the surging updraft, just hold a constant attitude [not altitude], leave the power alone, and allow the airplane to rise.”
He explained that lowering the nose to maintain altitude is counterproductive. It results in increased airspeed and less time spent in the rising air to take advantage of the free lift.
Sounds simple enough, I thought.
Paul then added, “Raising the nose in a downdraft is similarly counterproductive. The reduced airspeed causes you to remain longer in the sinking air. When you hit a downdraft, apply the same technique that you used in the updraft. Hold a constant attitude, leave the power alone, and allow the airplane to descend, sacrificing the altitude gained in the thermal. Increasing power at reduced airspeed to attempt maintaining altitude in a downdraft—especially in the heat of the summer—can result in an overheated engine.”
None of this is earthshaking to sailplane pilots. They are adept at maximizing en route performance by decreasing airspeed and climbing in rising air. They allow their aircraft to lose altitude and increase airspeed in sinking air, which lessens their exposure to it. The idea in both airplanes and sailplanes is to spend more time in updrafts and as little time as possible in downdrafts. This technique is suitable only when flying VFR.
This technique also is good practice in severe or extreme turbulence, occasions when maintaining a more-or-less constant attitude is strongly recommended. This is structurally safer than imposing the damaging G loads that could result from attempting to maintain altitude during such turbulence (when IFR or VFR). It goes without saying, of course, that airspeed should kept at or below the minimum maneuvering speed (VA) when the degree of turbulence calls for it.
Another method of improving en route performance involves envisioning the wind as it flows over mountainous or hilly terrain, and then altering course so as to fly within rising air as much of the time as possible. For example, when the wind is blowing across a valley, fly along the downwind side to take advantage of the rising air usually found there. Depending on the nature of the terrain, such a ride is often smooth. At such a time, simply lower the nose to prevent climbing and enjoy picking some extra knots in the process. It’s like creating your own tailwind.
Cruising on the other side of the valley would be in sinking air that might not even be noticeable except that you might begin wondering why your airplane doesn’t seem to be performing as well as it should.
It’s all a matter of knowing the direction of the wind and using it to advantage. The difference in flight time can be significant.
Barry Schiff writes for AOPA Pilot from Southern California.
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