Plane & Pilot
Tuesday, April 9, 2013

The Logic Of Flaps


Flaps make pilots’ lives easier—for those aviators who know how to use them


You'll typically extend flaps upon entering the pattern. Make it a point to do that with wings level rather than in a turn. Asymmetric flap deployment is rare, but if you're turning hard left and have only the left flap deploy, you could be in for an unpleasant surprise.

Similarly, don't make it a habit to extend gear and flaps at the same time. If both systems are operated electrically, you could overtax the alternator and pop a circuit breaker. That's not exactly an emergency, but it's one less thing to worry about if you've just entered a busy pattern.

If there's any major crosswind blowing, be cautious about extending full flaps in one swell foop. Try using half on downwind and the last half on base or 1/3 at a time on downwind, base and final, respectively. The FAA used to recommend no flaps for strong crosswind landings, but now, even they agree that full flaps should be used on practically every landing. Best to introduce them a little at a time, however, rather than all at once.

If you're a little high with flaps full down and power full off, think twice about using a full flap slip. Though slips may not be a problem on some aircraft, others don't react kindly to fully cross-controlled maneuvering at low altitude. The problem is often blanking the airflow across the tail and essentially nullifying elevator control. Some Cessna flight manuals warn against such antics.

If you do decide to try it in an aircraft that allows the maneuver, keep careful watch over airspeed. Full-flap slips can bleed off airspeed in a hurry, so you may need considerable forward yoke or stick to preserve your approach speed.

If the runway is short and there's a need to plant it on and stop it short, consider raising the flaps immediately upon touchdown to place more weight on the main gear and enhance braking action. If you have considerable time in the airplane and fully understand its landing characteristics, you might even try what some Mooney pilots call "autoland". Once you're established in the flare a foot or so above the ground, trip the flaps full up and be ready to cushion the touchdown with plenty of back elevator. If you do it right, you can generate greasers practically every time. Do it wrong, and you may not be happy with the result. As mentioned above, this trick is only for highly experienced pilots with plenty of hours in type.

Flaps are just one more tool in a pilot's bag of tricks. In conjunction with wing design, they have varying effects in different aircraft. Most of the time, they allow pilots to fly approaches slower. Fast may be better at cruise, but when it comes to landing, slower is safer.



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