What Flaps are used for?

Let’s imagine the following situation, there is a group of airline pilots, standing on an airport hall, talking about different matters, then a kid appears and after saying “hello”, comes with the following question:     – can you please tell me why an airplane flies?    You will probably see the guys slowly disappear, smile, make an exclamation like … Oh!  And,  finally a courageous one will take the challenge of an explanation.

Well, this is happening to me, and I can’t run, at first because she is my daughter and second she is not a kid anymore, she is becoming a glider pilot and she has thousands of questions!  Yesterday question was what flaps are used for?  And, I wondered myself about an article here about…. FLAPS.

Flaps are movable surfaces mounted on the trailing or leading edge of an airplane’s wing.  Flaps, when extended, increase the wing camber and the maximum coefficient of lift (L) generated by the wing for a given speed, allowing lower speeds for takeoff, approach and landing.  In most aircraft flaps are graduated in degrees of deflection, like 1, 2, 5, 10, 15, 25, 30, 40 (e.g. Boeing 737), or simply have intermediate positions like Up, Approach and Landing, (e.g. Beechcraft King Air).

Main purpose of these high lift devices during takeoff is to help the wing generate the necessary amount of lift to get the aircraft airborne at a determined speed.  Although a certain selection of flaps will allow us to reduce the required take off distance, we will sacrifice initial rate of climb during second segment of take off.   Flap up takeoff configuration is mostly used on low wing turboprops because in case of the critical engine failure at V1 the aircraft cannot achieve a positive rate of climb during the second segment.   On landing flaps have a dual purpose, up to a certain selection they actuate as high lift devices and beyond that selection they are used as air brakes to increment the angle of descent without increasing airspeed, on certain aircrafts beyond a certain extension of flaps, also ailerons lower altogether with them (e.g. Twin Otter).

These are the most common types of flaps:

Types of Flaps - (Wikipedia)

Types of Flaps – (Wikipedia)










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