PHAK Chapter 6-15 Secondary Flight Controls

Secondary Flight Controls

Secondary flight control systems may consist of wing flaps, leading edge devices, spoilers, and trim systems.

 

Flaps

Flaps are the most common high-lift devices used on aircraft. 

 

These surfaces, which are attached to the trailing edge of the wing, increase both lift and induced drag for any given AOA. 

 

Flaps allow a compromise between high cruising speed and low landing speed because they may be extended when needed and retracted into the wing’s structure when not needed. 

 

There are four common types of flaps: plain, split, slotted, and Fowler flaps.

 

The plain flap is the simplest of the four types. 

 

It increases the airfoil camber, resulting in a significant increase in the coefficient of lift (CL) at a given AOA. 

 

At the same time, it greatly increases drag and moves the center of pressure (CP) aft on the airfoil, resulting in a nose-down pitching moment. 

 

The split flap is deflected from the lower surface of the airfoil and produces a slightly greater increase in lift than the plain flap. 

More drag is created because of the turbulent air pattern produced behind the airfoil. 

 

When fully extended, both plain and split flaps produce high drag with little additional lift.

 

Secondary Flight Controls

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