Summary of Aircraft Flight Controls and Forces

## Introduction A clear understanding of aircraft flight controls is essential for any pilot, mechanic, or aviation enthusiast. This material explains the components, functions, and practical considerations of primary, secondary, and auxiliary flight control systems, plus cable systems and surface condition effects that influence aircraft handling and safety. > **Definition:** Flight controls are the movable surfaces and systems on an aircraft that the pilot uses to control attitude and flight path. ## 1. Flight control groups Flight controls are commonly divided into three groups based on their function and importance. ### Primary flight controls - **Purpose:** Directly control the aircraft's attitude. - **Members:** **Elevators**, **ailerons**, **rudder**. > **Definition:** Primary flight controls are control surfaces that the pilot uses to control roll, pitch, and yaw directly. ### Secondary flight controls - **Purpose:** Modify aerodynamic characteristics to improve performance during specific flight phases (takeoff, climb, cruise, landing). - **Members:** **Wing flaps**, **speed brakes**, **spoilers**, **slats**, **leading edge flaps and slots**. > **Definition:** Secondary flight controls change wing lift/drag characteristics for performance and handling, but are not used for basic attitude control. ### Auxiliary flight controls - **Purpose:** Assist the pilot by reducing control forces or trimming the aircraft to maintain a steady attitude. - **Members:** **Trim tabs**, **spring tabs**. > **Definition:** Auxiliary controls reduce pilot workload by trimming out control forces or assisting primary control movement. ## 2. How specific controls affect flight ### Ailerons (roll) - Move opposite directions on each wing to create differential lift and produce roll. - Used for coordinated turns and roll control. ### Elevators (pitch) - Located on the tailplane, elevators control pitch by changing camber of the horizontal tailplane. - Directly affects angle of attack of the main wing and climb/descent attitude. ### Rudder (yaw) - Controls yaw about the vertical axis, used for coordination during turns and to counter adverse yaw. ### Flaps (secondary control example) - Flaps increase wing camber and lift allowing slower approach speeds and steeper glide paths for landing. - Practical effect: with flaps extended, an aircraft can fly slower without stalling and descend at a steeper angle while maintaining lift. > **Definition:** Flaps are high-lift devices on the wing trailing edge that increase lift and drag when extended. Fun fact: Extending flaps increases both lift and drag, which is why pilots often reduce power during flap deployment to maintain desired descent profile. ## 3. Control cable systems: materials, connections, and maintenance ### Materials used for flexible control cables - Typical materials: **carbon steel coated with tin or zinc**, or **corrosion-resistant steel**. > **Definition:** Flexible control cables transmit pilot control inputs to moving surfaces using wire rope made of high-strength metallic strands. ### Cable end connections - Ends of two cables are normally equipped with **swaged** or **threaded terminals**, and the pair is joined using a **turnbuckle** to adjust length and tension. ### Fairleads and pulleys - **Fairlead:** a guide that keeps a cable aligned in a straight line through or between structural members; it should not deflect a cable more than 3 degrees from straight. > **Definition:** A fairlead is a cable guide that preserves proper cable alignment and reduces wear where cables pass through structure. - Cable breakage most commonly occurs where cables pass over **pulleys** and through **fairleads** because of repeated bending and abrasion. ### Automatic tension regulators - Large airplanes often use automatic tension regulators for control cables because temperature changes (and structural contraction of materials like aluminum) can change cable tension in flight; the