Figure 5-71.  Control surfaces.  differential type, they extend further on one side and retract  on the other side. If they are the non-differential type, they  extend further on one side but do not retract on the other side.  When fully extended as speed brakes, the non-differential  spoilers remain extended and do not supplement the ailerons.  To obtain a smooth stall and a higher AOA without airflow  separation, the wing’s leading edge should have a well- rounded almost blunt shape that the airflow can adhere to  at the higher AOA. With this shape, the airflow separation  starts at the trailing edge and progresses forward gradually  as AOA is increased.  The pointed leading edge necessary for high-speed flight  results in an abrupt stall and restricts the use of trailing edge  flaps because the airflow cannot follow the sharp curve  around the wing leading edge. The airflow tends to tear loose  rather suddenly from the upper surface at a moderate AOA.  To utilize trailing edge flaps, and thus increase the C$_{L-MAX}$,  the wing must go to a higher AOA without airflow separation.  Therefore, leading edge slots, slats, and flaps are used to  improve the low-speed characteristics during takeoff, climb,  and landing. Although these devices are not as powerful as  trailing edge flaps, they are effective when used full span in  combination with high-lift trailing edge flaps. With the aid  of these sophisticated high-lift devices, airflow separation is  delayed and the C$_{L-MAX}$ is increased considerably. In fact, a  50 knot reduction in stall speed is not uncommon.  5-50  737 Control Surfaces  727 Control Surfaces  Takeoff Flaps  Flaps Retracted  Landing Flaps  Aileron  Leading edge slat  Leading edge flap  Foreflap  Midflap  Aftflap  In bo ar d  w i n g  O u t b o a rd  wi n g  In bo ar d  w i n g  O u t b o ar d  w i n g  Foreflap  Midflap  Aftflap  Aileron  I n bo ar d  w i n g  O u t b o ar d  w i n g  Aileron  Rudder  Elevator  Tab  Stabilizer  Inboard flap  Flight spoilers  Ground spoiler  Outboard flap  Tab  Aileron  Leading edge slats  Leading edge flaps  Stabilizer  Elevator  Control tab  Upper rudder  Anti-balance tabs  Control tab  Inboard aileron  Leading edge flaps  Lower rudder  Vortex generators  Pitot tubes  Ground spoilers  Inboard flaps  Flight spoilers  Outboard flap  Balance tab  Outboard aileron  Slats  Fence 