Flight Control Systems Review

Vocabulary flashcards covering primary and secondary flight controls, aerodynamic balance techniques, trim systems, and fly-by-wire computer architectures based on the lecture notes.

Longitudinal Axis

An axis extending lengthwise through the fuselage from nose to tail around which roll movement occurs, controlled by the ailerons.

Lateral Axis

An axis extending crosswise from wingtip to wingtip around which pitch movement occurs, controlled by the elevators.

Normal Axis (Vertical Axis)

An axis passing vertically through the aircraft center of gravity around which yaw movement occurs, controlled by the rudder.

Center of Gravity (CG)

The point representing the center of an airplane total weight, through which all three axes of rotation pass.

Primary Flight Control Surfaces

Control surfaces responsible for maneuvering the aircraft about its three axes, consisting of the ailerons, elevator, and rudder.

Ailerons

Primary flight control surfaces located on the outboard trailing edge of each wing that move in opposite directions to control roll about the longitudinal axis.

Adverse Yaw

An airplane natural tendency to turn its nose in the opposite direction of a roll, caused by higher lift and induced drag on the rising wing with the downward-deflected aileron.

Differential Ailerons

An aileron control design where the up-deflecting aileron moves a greater distance than the down-deflecting aileron to equalize drag and reduce adverse yaw.

Frise-Type Ailerons

Ailerons hinged on an offset axis so that the leading edge of the raised aileron projects below the lower wing surface into the airflow, creating drag to counteract adverse yaw.

Flaperons

Control surfaces managed by a mixer that combine the banking functions of ailerons with the lift-enhancing lowered movement of flaps.

Coupled Ailerons and Rudder

A control arrangement linked via rudder-aileron interconnect springs that automatically deflects the rudder when ailerons are moved to correct for adverse yaw.

Drooping Ailerons

A design feature where both ailerons deflect downward symmetrically when flaps are extended to increase overall wing lift and improve low-speed performance.

Elevator

A primary control surface hinged to the trailing edge of the horizontal stabilizer that moves the aircraft around the lateral axis to control pitch and angle of attack.

Elevator Down Spring

A mechanical spring that supplies a nose-down load to the elevator to lower the nose and prevent a stall if trim fails or aft center of gravity causes inadequate tail efficiency.

Stabilator

A one-piece horizontal tail surface that pivots around a central hinge point to perform the functions of both a horizontal stabilizer and an elevator.

Elevons

Combined elevator and aileron control surfaces used on tailless aircraft to provide both pitch and roll control.

Rudder

A primary control surface hinged to the trailing edge of the vertical stabilizer operated by foot pedals to provide directional control around the vertical axis.

Rudder Ratio Changer

A gear change system in the rudder control system that provides smaller or decreasing rudder deflection for full pedal movement as airspeed increases.

Ruddervator

Movable surfaces on a V-tail empennage that operate simultaneously for pitch control or differentially for yaw control via a mixing mechanism.

Hinge Moment

The aerodynamic moment acting about a control surface hinge line, expressed as force times distance ($\text{Hinge moment} = F \times d$).

Stick Force

The physical force required from a pilot on the control column or rudder pedals to overcome and balance the control surface hinge moment.

Static Balance

The tendency of a control surface or object to remain stationary when supported from its own center of gravity.

Underbalance

A static out-of-balance condition (plus condition) where the trailing edge of a control surface moves downward below horizontal on a balance stand.

Overbalance

A static out-of-balance condition (minus condition) where the trailing edge of a control surface moves upward above horizontal on a balance stand.

Dynamic Balance

The distribution of balance weights along the span of a control surface to maintain balance and eliminate vibration while in motion during flight.

Inset Hinge

An aerodynamic balancing method where the hinge line is positioned aft closer to the surface center of pressure, creating a countering moment to reduce stick force.

Horn Balance

An aerodynamic balance projection located forward of the hinge axis at the tip of a control surface that creates an assisting moment against main hinge resistance.

Internal Balance

An enclosed aerodynamic balance chamber inside the rear airfoil section that uses pressure differentials to oppose hinge moment without increasing external drag.

Flutter

An uncontrolled and uncommanded vibration of a control surface, typically occurring at high airspeeds when the center of gravity is well aft of the hinge axis or cable tension is low.

Secondary Flight Control Systems

Auxiliary devices—including wing flaps, leading-edge devices, spoilers, and trim systems—that improve performance characteristics and relieve pilot control forces.

Trim Tabs

Small secondary surfaces set into trailing edges of primary flight controls that statically balance the aircraft and maintain desired flight attitudes without continuous control pressure.

Balance Tabs

Auxiliary tabs coupled to primary control linkages that automatically move in the opposite direction of the main surface to reduce required pilot control force.

Servo Tabs

Dynamic trailing-edge tabs directly linked to flight deck controls that deflect to aerodynamically drive primary control surfaces that are otherwise too heavy to move manually.

Anti-servo Tabs

Tabs on stabilators that move in the same direction as the surface trailing edge to increase stick force feedback and de-sensitize controls against overcontrolling.

Spring Tab

An auxiliary tab incorporating a spring in its linkage that activates to assist control surface deflection only when control forces become high at elevated speeds.

Adjustable Stabilizer

A pitch trim arrangement where a motor- or cable-driven jackscrew pivots the entire horizontal stabilizer about its rear spar.

Flaps

Trailing-edge high-lift devices that alter wing camber and area to increase lift, permitting the aircraft to operate at lower flight speeds during takeoff and landing.

Leading-edge Flaps

High-lift surfaces on the forward edge of a wing that extend forward and down to increase wing camber and lift at low airspeeds.

Slots

Permanent openings in the wing leading edge that allow air to flow through over the upper surface, delaying boundary layer separation and increasing the critical angle of attack.

Slats

Movable aerodynamic surfaces on the leading edge that extend forward to create a gap, directing air over the wing to enhance lift and delay stalls.

Roll Spoilers (Spoilerons)

Upper wing spoilers deployed asymmetrically on one wing only to assist ailerons in banking the aircraft while minimizing adverse yaw.

Flight Spoilers

Wing spoilers extended symmetrically on both wings during flight to act as speedbrakes, allowing the aircraft to descend rapidly without increasing airspeed.

Ground Spoilers

Wing spoilers that automatically deploy upon touchdown to dump remaining wing lift, transferring weight to the wheels to maximize tire braking efficiency.

Air Brakes

Movable aerodynamic drag devices mounted on the fuselage or tail designed to increase drag during descent with little change to wing lift.

Reversible Flight Control System

A manual flight control system where air pressure loads on the control surfaces are transmitted backward to provide natural feel at the cockpit controls.

Irreversible Flight Control System

A fully powered flight control system where loads applied to the control surface cannot move the cockpit controls, requiring artificial feel units.

Fly-By-Wire (FBW)

A flight control system that replaces mechanical control linkages with electrical signals sent from cockpit transducers through computers to hydraulic actuators.

Elevator Aileron Computer (ELAC)

A flight control computer in Airbus Fly-By-Wire systems responsible for controlling the ailerons, elevators, and horizontal stabilizer.

Spoilers Elevator Computer (SEC)

A flight control computer in Airbus Fly-By-Wire systems that manages upper wing spoiler surfaces and standby elevator/stabilizer operation.

Flight Augmentation Computer (FAC)

A flight control computer in Airbus Fly-By-Wire systems responsible for electrical rudder control, yaw damping, and trim functions.