PHAK 5-50

Figure 5-71. Control surfaces. 737 Control Surfaces 727 Control Surfaces Takeoff Flaps Flaps Retracted Landing Flaps Aileron Leading edge slat Leading edge flap Foreflap Midflap Aftflap I n b o a r d w in g O u t b o a r d w i n g I n b o a r d w i n g O u t b o a r d w i n g Foreflap Midflap Aftflap Aileron I n b o a r d w i n g O u t b o a r 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 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 CL-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 CL-MAX is increased considerably. In fact, a 50 knot reduction in stall speed is not uncommon.