More is not always better
For all the romance in the language of an airplane’s pieces and parts—ailerons, empennage, fuselage, nacelle—there’s one component that somehow got left out in the cold when they were handing out interesting names: Flaps.
“Flaps” may be an adequate description of what they do—one of the earliest recorded definitions of the word is “something that hangs down”—but how we go from sultry-sounding ailerons to the purely perfunctory flaps is a mystery.
Maybe it has something to do with the complex function of flaps compared with other control surfaces. Flaps increase lift, at least in the initial stages of extension. Beyond that they become drag devices. And in many airplanes extending the flaps significantly will alter pitch.
When extended, flaps increase wing camber (curvature of the airfoil) and the wing’s angle of attack. Fowler-type flaps, which slide back and down, also increase wing area. The effect of extending flaps completely on final approach to landing is to increase lift and drag for a steeper, slower approach. Deploying flaps lowers stall speed, so the use of flaps on approach provides an additional margin of safety when the airplane is low and getting lower and slow and getting slower.
It’s the subtle transition from flaps being primarily lift producers to primarily drag producers that can be confusing, and leads some to figuratively throw up their hands and abandon flexibility and choice—using only the amount of flaps necessary for a particular approach—in favor of a rigid policy of deploying all of the flaps all of the time.
Several factors have conditioned me to use only partial flaps on approach and landing, although that is far from a hard and fast rule. One is that the airplane I currently fly has hydraulically actuated flaps that can be extended to any position between stowed and fully down. In other words, there are no detents for, say, quarter- and half-flaps. That gives me an infinite number of choices for selecting a flap position best suited to the specific conditions of airplane weight, balance, and speed in conjunction with prevailing weather on the approach.
One other big influencing factor is that any extension of this airplane’s relatively large flaps causes the nose to pitch up sharply. If I don’t anticipate the pitch-up and proactively apply considerable forward pressure on the yoke, the airplane balloons and gains altitude.
The manufacturer acknowledges this strong nose-up tendency in the airplane’s POH, and recommends that flaps be extended by pulsing the flap handle—push down for a second or two, return the handle to the neutral position, push down again for a few more degrees of extension, neutral position again, and so on—until the flaps are extended to the desired position. Using this pulse technique allows me to keep up with the trim changes necessary to control pitch attitude and prevent an undesirable change in altitude.
Air traffic control is another reason I often use only partial flaps on approach. The trip I fly most often has me overflying an airline airport when returning to home base. ATC usually keep me at 2,000 feet agl or higher until I’m just a few miles from my destination. Consequently, I have little distance and time to slow down and come down, especially to a speed that allows for full flap deployment on anything but short final. (I try to avoid deploying flaps until well below recommended flap-extension speeds because it reduces stress on the airframe.)
Finally, using only partial flaps allows me to make my approaches at higher indicated airspeeds, which helps keep traffic moving in the high-density areas I typically frequent. Coming up on a slow-mover in a busy final approach path is like encountering someone exiting an expressway at city-street speed—it’s legal, but boy, can it create a big hairball in the normal flow of things.
Mark Twombly is a writer and editor who has been flying since 1968. He is a commercial pilot with instrument and multiengine ratings and flies a Piper Aztec.
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