Plane & Pilot
Tuesday, April 9, 2013

The Logic Of Flaps

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

By any measure, flaps have almost no downside, but they're perhaps the least appreciated component of an aircraft. They help determine one of the least glamorous but most essential speeds in an airplane—how slow it can fly. High Mach numbers may be more romantic, but they rarely have as much effect on safety. Aircraft rarely crash because they couldn't fly fast enough. They do crash when they're not flown slowly enough.

In that respect, Cessna pilots have a leg up on the rest of the flight training world. I'm not sure what percentage of aviators learn to fly in the little high-wing airplanes from Wichita, but it has to be a big number. Whatever it is, those lucky prospective aviators benefit from some of the most effective flaps in general aviation—huge barn-door surfaces that provide dramatic reductions in stall speed and impressive short-field performance. By definition, pilots trained in the marquee's products receive an education on the usefulness and effectiveness of flaps.

Sadly, not every airplane manifests the same advantages. I learned to fly in a variety of trainers, everything from an Aeronca Champ to a Piper Colt, and none of my trainers had flaps. If you didn't learn to control airspeed and master the slip, you might have a tough time putting an airplane down on a short runway.

Part of that learning process in the last century was in a Globe Swift with among the industry's quickest ailerons, most effective elevator and least effective flaps. I dearly loved that little Swift, but the Globe GC-1B had a pair of short-span/narrow-chord flaps that improved the pilot's view of the runway but didn't do much else.

Perhaps for that very reason, there were only two positions, full up or full down, and the latter setting required only two seconds to set. A final joke: The flap-position selector was shaped like a wheel and the landing-gear position knob was shaped like a flap. Go figure.

No matter how effective they are (or in the case of the Swift, aren't), flaps make a pilot's job exponentially easier in virtually all respects. They deploy from the trailing edge of the wings and increase the camber or curvature of the airfoil, improving the lift coefficient in the process. This allows the wing to develop the same lift at a lower speed, effectively increasing drag, reducing the stall speed and allowing the aircraft to approach at a slower velocity. This can significantly reduce landing roll, a valuable benefit for short field operation.

Some aircraft designs specify flaps for takeoff and landing, others for landing only. Using flaps during the takeoff run allows the aircraft to lift off sooner and use less runway. Many general aviation designs and practically all commuter and large airliners require flaps for both departure and arrival.


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