L =  $^{1 }$pV  2  SC$_{L}$ 2 L = Lift produced P = Air density V = Velocity relative to the air S = Surface area of the wing C$_{L}$ = lift coefficient which is determined by the camber of the airfoil used, the chord of the wing and AOA Plain flap Split flap Slotted flap Fowler flap Figure 11-4.  Four basic types of flaps. Figure 11-3.  Lift equation.  Consequently, pitch behavior depends on the design features  of the particular airplane. Flap deflection of up to 15° primarily produces lift with  minimal increases in drag. Deflection beyond 15° produces a  large increase in drag. Drag from flap deflection is parasite drag  and, as such, is proportional to the square of the speed. Also,  deflection beyond 15° produces a significant nose-up pitching  moment in most high-wing airplanes because the resulting  downwash increases the airflow over the horizontal tail. Flap effectiveness depends on a number of factors, but the  most noticeable are size and type. For the purpose of this  chapter, trailing edge flaps are classified as four basic types:  plain (hinge), split, slotted, and Fowler.  [Figure 11-4] The plain or hinge flap is a hinged section of the wing. The  structure and function are comparable to the other control  surfaces—ailerons, rudder, and elevator. The split flap is  more complex. It is the lower or underside portion of the  wing; deflection of the flap leaves the upper trailing edge  of the wing undisturbed. It is, however, more effective  than the hinge flap because of greater lift and less pitching  moment, but there is more drag. Split flaps are more useful  for landing, but the partially deflected hinge flaps have the  advantage in takeoff. The split flap has significant drag at  small deflections, whereas the hinge flap does not because  airflow remains “attached” to the flap. deflections are much like the slotted flap. Fowler flaps are  most commonly used on larger airplanes because of their  structural complexity and difficulty in sealing the slots. It would be impossible to discuss all the many airplane design  and flap combinations. This emphasizes the importance of the  Federal Aviation Administration (FAA) approved Airplane  Flight Manual and/or Pilot’s Operating Handbook (AFM/ POH) for a given airplane. While some AFM/POHs are  specific as to operational use of flaps, others leave the use  of flaps to pilot discretion. Hence, flap operation makes pilot  judgment of critical importance. Since flap operation is used  for landings and takeoffs, during which the airplane is in close  proximity to the ground where the margin for error is small.  The slotted flap has a gap between the wing and the leading  edge of the flap. The slot allows high-pressure airflow on  the wing undersurface to energize the lower pressure over  the top, thereby delaying flow separation. The slotted flap  has greater lift than the hinge flap but less than the split flap;  but, because of a higher lift-drag ratio, it gives better takeoff  and climb performance. Small deflections of the slotted flap  give a higher drag than the hinge flap but less than the split.  This allows the slotted flap to be used for takeoff. Since the recommendations given in the AFM/POH are  based on the airplane and the flap design, the pilot must  relate the manufacturer’s recommendation to aerodynamic  effects of flaps. This requires basic background knowledge  of flap aerodynamics and geometry. With this information,  a decision as to the degree of flap deflection and time of  deflection based on runway and approach conditions relative  to the wind conditions can be made. The Fowler flap deflects down and aft to increase the wing  area. This flap can be multi-slotted making it the most complex  of the trailing-edge systems. This system does, however, give  the maximum lift coefficient. Drag characteristics at small  11-3 Operational Procedures Flap Effectiveness