However, because lift is required during low speed flight  and is characterized by high AOA, flaps or other high lift  devices are needed to either change the camber of the airfoil,  or delay the boundary level separation. Plain and split flaps  [Figure 4-12]  are most commonly used to change the camber  of an airfoil. It should be noted that with the application of  flaps, the aircraft will stall at a lower AOA. For example,  if the basic wing stalls at 18° without flaps, then with the  addition of flaps to the C$_{L-MAX}$ position, the new AOA that  the wing will stall is 15°. However, the value of lift (flaps  extended to the C$_{L-MAX}$ position) produces more lift than lift  at 18° on the basic wing. Fowler  Delaying the boundary layer separation is another way to  increase C$_{L-MAX}$. Several methods are employed (such as  suction and use of a blowing boundary layer control), but the  most common device used on general aviation light aircraft  is the vortex generator. Small strips of metal placed along  the wing (usually in front of the control surfaces) create  turbulence. The turbulence in turn mixes high energy air from  outside the boundary layer with boundary layer air. The effect  is similar to other boundary layer devices.  [Figure 4-13] Slotted  Most small airplanes maintain a speed well in excess of 1.3  times V$_{SO}$ on an instrument approach. An airplane with a  stall speed of 50 knots (V$_{SO}$) has a normal approach speed  of 65 knots. However, this same airplane may maintain 90  knots (1.8 V$_{SO}$) while on the final segment of an instrument  approach. The landing gear will most likely be extended at  the beginning of the descent to the minimum descent altitude,  or upon intercepting the glideslope of the instrument landing  system. The pilot may also select an intermediate flap setting  for this phase of the approach. The airplane at this speed has  good positive speed stability, as represented by point A on  Figure 4-11 . Flying in this regime permits the pilot to make  slight pitch changes without changing power settings, and  Aircraft are usually slowed to a normal landing speed when  on the final approach just prior to landing. When slowed to  65 knots, (1.3 V$_{SO}$), the airplane will be close to point C.  [Figure 4-14]  At this point, precise control of the pitch and  power becomes more crucial for maintaining the correct speed.  Pitch and power coordination is necessary because the speed  stability is relatively neutral since the speed tends to remain  at the new value and not return to the original setting. In  addition to the need for more precise airspeed control, the pilot  normally changes the aircraft’s configuration by extending  landing flaps. This configuration change means the pilot must  be alert to unwanted pitch changes at a low altitude. accept minor speed changes knowing that when the pitch is  returned to the initial setting, the speed returns to the original  setting. This reduces the pilot’s workload. Figure 4-13.  Vortex generators. Figure 4-12.  Plain and split flaps. Small Airplanes Uncontrolled Turbulence  Controlled Vortices  Plain  Split  4-9