AOPA Pilot Magazine - May 2012 - 32

LICENSETOLEARN

BY ROD MACHADO

Mythconceptions

veryone believes in a myth at one time or another. This is especially true for those convinced that the world will expire on December 21, 2012,

flight. This is where applying flaps in a turn from base to final approach could bite you in the empennage. Let’s say that you’re in a descending turn from base to final approach in an airplane whose flaps generate a nose-up pitching moment when deployed (partially or fully). As you extend the flaps in the turn, the airplane’s nose pitches up along a diagonal, from your toes to your nose (as seen from the cockpit). You compensate for this motion because the Mayan calendar abruptly ends on by applying forward elevator pressure to sustain that date. Isn’t it possible, however, that the masthe desired nose-down attitude to maintain your Rod Machado is sive, five-by-seven-foot stone calendar simply approach speed. an active flight fell on the guy doing the carving before he could The problem is that flap deployment in a turn instructor and finish the job? That was the original meaning of results in both a horizontal and vertical compoaviation speaker. getting stoned. nent of nose movement, instead of pure vertical Pilots occasionally believe in myths, too. One motion of the nose as experienced in wings-level such mythtake revealed itself at a local FAA safety flight. Therefore, you don’t see the nose pitch up seminar when an attendee mentioned that he never extends vertically toward the horizon by the same amount it does when flaps in a turn for fear of stalling. When I asked how this applying flaps in wings-level flight. Without the obvious vertimight happen, he simply sat there dumbstruck, never having cal pitch movement toward the horizon, some pilots simply thought the idea through. I playfully reminded him that he fail to apply sufficient forward elevator pressure to sustain needed to respond before December 21 of this year, while we their approach airspeed. Ultimately, this can lead to airspeed were still around to hear the answer. decay and eventually a stall. No, extending flaps while turning from base to final There is an additional factor that increases an unwary approach won’t cause you to stall—unless you let it cause you pilot’s potential for stalling as flaps are applied in a turn. The to stall. Flaps aren’t the culprit here. It’s your reaction (or lack increase in elevator back-pressure necessary to sustain your of it) to flap extension while turning that causes you to stall, attitude in a descending turn at steeper banks often masks which is often accompanied by a personal introduction to Ah changes in elevator pressure resulting from flap application. Uuc Ticab, the Mayan god of the Earth. In many airplanes, applying flaps moves the center of lift forExtending flaps allows you to maintain a particular angle ward and increases the downwash on the tail. The result is of attack at a lower nose-down attitude. Flap extension also often a change in elevator control forces that helps remind creates drag, requiring a lower nose-down attitude to sustain you to adjust your attitude and maintain your approach airthe target airspeed during a descent. While it’s easy to see how speed. The aft elevator pressure that you’re already applying in much the nose should be lowered in wings-level flight (lower the descending turn, however, might mask this flap-induced the nose by eight degrees, for instance), it’s much more dif- change in elevator force. The net result is that you could miss ficult to determine this value in a descending turn, especially a valuable clue (a change in elevator pressure) that reminds or as flaps are deployed. prods you to maintain the correct approach speed. During a descending turn to final approach, changing your Ultimately, it’s a myth to believe that applying flaps in a turn pitch attitude moves the airplane’s nose along some diago- results in a stall. On the other hand, it’s absolutely true that a nal to the horizon. The angle of the diagonal depends on the pilot who doesn’t understand how flap application in a turn degree of bank you’re using at the time. The net result of any affects an airplane is more likely to stall. So, during a descendpitch change is that the nose moves a little in the horizontal ing turn, glance out your left window and compare the wing direction and a little in the vertical direction. In a 45-degree chord to ground movement for an approximate assessment bank, the nose moves horizontally as much as it does verti- of your angle of attack. And be especially cognizant of your cally. If you could sustain a 90-degree bank (request a landing attitude in a descending turn, making a special effort to adjust clearance from Ah Uuc Ticab Tower, first), any pitch change it immediately to maintain the right approach airspeed. That’s would result in only horizontal movement of the nose—there how to fly stall-free when applying flaps in a descending turn. would be no vertical movement whatsoever. It’s also how to keep your lifespan calendar from getting The takeaway point here is that changing your pitch atti- rocked and ending abruptly. tude in a descending turn doesn’t provide the same vertical displacement of the nose that you experience in wings-level Visit the author’s blog (www.rodmachado.com). 32 • MAY 2012

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AOPA Pilot Magazine - May 2012

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