Flight Training - September 2012 - 26

SLATS are a leading-edge device.

FLAPS are a trailing-edge device.

THE SWEPT WING ON AIRLINERS is great for high cruise speeds, but terrible for low-speed handling. So airliners use both flaps and slats to be able to make approaches at reasonably sized runways.

to accommodate the hardware without sacrificing fuel capacity or taking on extra weight); or by economics, if not all of the above. Flaps, though, are mechanical, and like anything mechanical, they can break. When a flap motor burned out on a Cessna that I was flying, I learned that I needed to be able to confidently land without flaps. So, I started practicing landing in various configurations. Starting with full flaps, I did a number of landings in each configuration, and then I would slowly decrease the amount of flaps—going from 40 to 30 to 20 to 10 degrees, and eventually none at all. Going from full flaps to half did relatively little to affect the behavior of the airplane, but the change in pitch and speed was noticeable. It became noticable when the flaps were in the 10- to 20-degree range. Lift was a much greater part of the equation than drag, and the approach profile needed to be changed as well. One of the biggest differences was the need to close the throttle much earlier on final to allow for a longer float to the runway. The starkest difference came with a zero-flap landing, which requires quite a bit of advanced planning. You also need to be aware of the zero-flap stall speed of your bird. My home airport was 2,900
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feet with a displaced threshold, and the change in landing distance was considerable. If you are considering practicing these exercises— and you should—you should start with a fairly long runway. With zero flaps, plan on using a slip to lose altitude quickly and safely without gaining too much speed. Flaps, like any other system, often have limitations. Cessna has long advised against performing slips with flaps extended all the way in several models; check your airplane’s POH to see if it advises against this practice. The reason is that the airflow can cause harmful vibrations to the tail assembly of the airplane. It also became widely recognized that conducting a go-around with flaps at 40 degrees in a Cessna 150 could be dangerous if not done properly. In any airplane, proper energy management during a go-around is critical, and the flaps play an integral role in that process. Most limitations on flaps are related to speed. There are extension speed limits (to prevent undue aerodynamic pressure on the drive motors or jackscrews; the CRJ 50 became notorious for flap-fail events that led to numerous modifications to the extension speeds), and on larger aircraft, there usually are limits on minimum speeds based on the weight and associated stall speed of the airplane. It is easy to take flaps for granted, but they are a wonder of aerodynamic flexibility, and a lack of understanding can lead to less-than-desirable consequences. Know the limitations of your bird, and use them properly—you will find it to be an uplifting experience.

Chip Wright has been flying since 1990, has been a CFI since 1994, and is an ATP and a Canadair Regional jet captain for Comair.

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Flight Training - September 2012

Table of Contents for the Digital Edition of Flight Training - September 2012