Summary of Boeing 737 Flight Control Systems Overview
Boeing 737 Flight Control Systems: Overview for Students
Introduction
The flight control systems of an aircraft keep it at the required attitudes and enable safe and efficient maneuvering. This guide explains the primary and secondary flight controls used on the Boeing 737 family (737-600/700/800/900) in clear, digestible sections with practical examples and comparisons.
Definition: Flight controls are the movable surfaces and their associated systems that change an aircraft's attitude and aerodynamic forces during flight.
Overview of Flight Control Categories
Flight controls are divided into two main categories:
Primary Flight Controls
Primary controls move the airplane about the three principal axes:
- Lateral axis (pitch) — controlled by the elevator
- Longitudinal axis (roll) — controlled by the ailerons
- Vertical axis (yaw) — controlled by the rudder
Components (typical for 737 family):
- Ailerons (2)
- Elevators (2)
- Rudder (1)
Definition: Primary flight controls are the surfaces whose direct movement changes the aircraft’s orientation about its axes.
Secondary Flight Controls
Secondary controls adjust lift, drag, and handling qualities to optimize performance during takeoff, climb, cruise, approach, and landing.
Components (typical for 737 family):
- Leading edge devices (12)
- Trailing edge flaps (4)
- Spoilers and speedbrakes (12)
- Horizontal stabilizer (trim)
Definition: Secondary flight controls are devices that modify the aerodynamic characteristics of the wing and empennage to assist the pilot and improve flight efficiency.
How Each Control Works (Digestible Parts)
Ailerons (Roll control)
- Located near the outboard trailing edge of each wing.
- Move differentially: one up while the other goes down to create rolling moment.
- Example: During a left roll input, left aileron up (reduces lift), right aileron down (increases lift) producing left bank.
Elevator (Pitch control)
- Mounted on the trailing edge of the horizontal stabilizer.
- Both elevator surfaces move together to change the pitching moment.
- Example: Pulling the control column back raises the elevators, increasing tail-down force and raising the nose.
Rudder (Yaw control)
- Mounted on the vertical stabilizer.
- Deflects left or right to create yawing moment.
- Often used for coordinated turns and to counter adverse yaw.
Leading Edge Devices
- Slats or leading edge flaps extend forward/down to increase wing camber and delay flow separation at high angles of attack.
- Used during takeoff and landing to increase lift at lower speeds.
Trailing Edge Flaps
- Increase wing area and camber to produce more lift and drag.
- Multiple settings: takeoff, approach, landing.
- Example: Flaps 1, 5, 15, 30 (values vary by model) increase lift progressively while adding drag.
Spoilers and Speedbrakes
- Spoilers reduce lift and increase drag when deployed; used for roll assist and descent rate control.
- Speedbrakes are large spoiler panels used symmetrically to increase descent rate without increasing airspeed.
- Example: On touchdown, spoilers deploy to dump lift and transfer weight to landing gear for braking.
Horizontal Stabilizer (Trim)
- Adjustable-stabilizer or trim changes the tailplane incidence to trim out control forces.
- Trim is used to maintain a set pitch attitude without continuous control input.
Definition: Trim is a means to relieve control forces and maintain desired attitude by changing a control surface’s neutral setting.
Control System Types and Interfaces
- Mechanical linkages: control wheels, cables, pulleys for direct feel (partially used historically).
- Hydraulic actuators / PCUs (Power Control Units): provide force augmentation for large surfaces.
- Flight control computers (FCC): process inputs for systems like autopilot (A/P) and flight augmentation.
Table: Primary vs Secondary Controls
| Aspect | Primary Controls | Secondary Controls |
|---|---|---|
| Purpose | Direct |
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Aircraft Flight Controls
Klíčová slova: Aircraft Flight Controls
Klíčové pojmy: Primary controls: ailerons, elevator, rudder control roll, pitch, yaw, Secondary controls: slats, flaps, spoilers, stabilizer trim modify lift and drag, Ailerons move differentially to produce roll, Elevators move symmetrically to produce pitch, Rudder produces yaw and coordinates turns, Flaps and leading edge devices increase lift at low speed, Spoilers act for roll assist and lift dump on landing, Stabilizer trim relieves control forces for hands-off flight, PCUs and hydraulic actuators provide force augmentation, FCCs and autopilot command controls during automated flight, Inspect actuators, PCUs, and hydraulics for maintenance, Use spoilers asymmetrically or rudder to manage certain failures