Straight Elliptical Tapered Delta Sweptback axis. Wing flaps acts symmetrically about the longitudinal  axis producing no rolling moment; however, both lift and drag  increase as well as a pitching moment about the lateral axis.  Lift is a function of several variables including air density,  velocity, surface area, and lift coefficient. Since flaps increase  an airfoil’s lift coefficient, lift is increased.  [Figure 11-3] As flaps are deflected, the aircraft may pitch nose up, nose  down or have minimal changes in pitch attitude. Pitching  moment is caused by the rearward movement of the  wing’s center of pressure; however, that pitching behavior  depends on several variables including flap type, wing  position, downwash behavior, and horizontal tail location.  Transition to a complex airplane, or a high-performance  airplane, can be demanding for most pilots without previous  experience. Increased performance and complexity both  require additional planning, judgment, and piloting skills.  Transition to these types of airplanes, therefore, should be  accomplished in a systematic manner through a structured  course of training administered by a qualified flight instructor. Aifoil with flap extended Angle of attack  C$_{L}$ C$_{L, }$max flapped C$_{L, }$max normal Stalled airfoil Normal airfoil Simple flapped airfoil Mean camber line Increased camber Flaps work primarily by changing the camber of the airfoil  which increases the wing’s lift coefficient and with some  flap designs the surface area of the wing is also increased.  Flap deflection does not increase the critical (stall) angle of  attack (AOA) and, in some cases, flap deflection actually  decreases the critical AOA. Deflection of a wing’s control  surfaces, such as ailerons and flaps, alters both lift and drag.  With aileron deflection, there is asymmetrical lift which  imparts a rolling moment about the airplane’s longitudinal  Figure 11-2.  Coefficient of lift comparison for flap extended and  retracted positions. Since an airfoil cannot have two different cambers at the same  time, one of two things must be done. Either the airfoil can  be a compromise, or a cruise airfoil can be combined with  a device for increasing the camber of the airfoil for low- speed flight. Camber is the asymmetry between the top and  the bottom surfaces of an airfoil. One method for varying  an airfoil’s camber is the addition of trailing-edge flaps.  Engineers call these devices a high-lift system. Airplanes can be designed to fly through a wide range of  airspeeds. High speed flight requires smaller wing areas and  moderately cambered airfoils whereas low speed flight is  obtained with airfoils with a greater camber and larger wing  area.  [Figure 11-1]  Many compromises are often made by  designers to provide for higher speed cruise flight and low  speeds for landing. Flaps are a common design effort to  increase an airfoil’s camber and the wing’s surface area for  lower speed flight.  [Figure 11-2] Figure 11-1.  Airfoil types. Function of Flaps 11-2