Flight Control System

Flashcards covering primary and secondary flight controls, high lift devices, trim systems, aerodynamic/mass balancing, feel systems, transmitting mechanisms, FBW/FBOW, and rigging based on the lecture transcript.

What are the primary flight control surfaces of an aircraft?

Ailerons, elevators, rudders, and (on some aircraft) spoilers.

Which aircraft axes do ailerons, elevators, and rudders control movement around?

Ailerons control lateral roll around the longitudinal axis, elevators control pitch around the lateral axis, and rudders control yaw around the vertical (normal) axis.

What is the purpose of differential aileron control?

It minimizes adverse aileron yaw by deflecting the upward-moving aileron further than the downward-moving aileron, balancing induced drag with parasite drag.

How does pulling the control column rearward affect the elevator and aircraft attitude?

Pulling the control column back moves the elevator upward, which increases tail downforce and causes the aircraft nose to pitch upward.

What is a stabilator, and how does its anti-servo tab function?

A stabilator is a one-piece, all-moving horizontal tail surface combining stabiliser and elevator functions. Its anti-servo tab moves in the same direction as the control surface trailing edge to decrease control sensitivity.

What movement occurs when the pilot pushes the right rudder pedal forward?

The rudder moves to the right, which deflects airflow to the right, yaws the tail to the left, and moves the aircraft nose to the right.

What is the operational distinction between flight spoilers and ground spoilers?

Flight spoilers operate in flight to assist roll control or reduce lift. Ground spoilers deploy only after touchdown to destroy wing lift and increase drag to slow the aircraft down.

What is the primary function of trim tabs?

They are small auxiliary control surfaces hinged to trailing edges that adjust primary surfaces aerodynamically in the opposite direction, relieving continuous control pressure for the pilot.

For what flight condition is a fixed trim tab effective?

A fixed trim tab is effective at correcting an out-of-trim condition for a single airspeed only.

What factors can cause an aircraft to develop flying faults or out-of-trim conditions?

Changes in weight, shifts in center of gravity, uneven fuel consumption, passenger/cargo disposition, flap operation, or improper de-icing boot deflation.

How does a servo tab operate to move a primary control surface?

The servo tab is directly moved by the control linkage in the opposite direction of the desired control movement, generating aerodynamic forces that deflect the main control surface.

How does a spring tab provide aerodynamic assistance as control forces increase?

At low loads, the spring acts as a rigid link; under high aerodynamic loads, the spring compresses or extends, allowing the tab to move in the opposite direction of the surface and provide aerodynamic assistance.

What is the main aerodynamic purpose of trailing-edge flaps?

To increase wing camber and surface area, thereby increasing the lift coefficient ($C_L$) for takeoff and landing at lower speeds.

How do leading-edge slots combined with trailing-edge flaps alter the lift characteristics of an aerofoil?

Slots increase the stalling angle of attack (from $13^\circ$ or $15^\circ$ up to $23^\circ$), while combining slots and flaps yields a significantly higher maximum lift coefficient ($C_L$).

How do leading-edge slots delay wing stall at high angles of attack?

High-pressure air from beneath the wing is ducted through a converging gap to the upper surface, accelerating the airflow over the top surface, re-energizing the boundary layer, and delaying airflow separation.

Where are Krueger flaps typically located, and what is their function?

Krueger flaps are located on the inboard wing leading edge, hinging forward and down to increase camber and area, raising low-speed lift.

Why is mass balancing applied to primary control surfaces?

It redistributes the mass of the surface relative to its hinge line to prevent flutter, achieve satisfactory inertia characteristics, and keep the center of gravity within calculated limits.

What are the three principal methods of aerodynamic balancing used on manual primary control surfaces?

Horn balance, inset hinge, and pressure balancing (balance panel).

How does a horn balance reduce pilot stick forces?

A portion of the primary control surface projecting ahead of the hinge line extends into the airflow when deflected, creating an aerodynamic force that assists movement in the desired direction.

How does a balance panel generate force to assist aileron movement?

When the aileron moves upward, increased airflow velocity under the panel causes reduced pressure below it; higher pressure above the panel pushes down, aiding rotation about the hinge.

What is the function of an artificial 'Q' feel system in powered flight control systems?

It provides control column resistance proportional to dynamic air pressure ($Q \propto V^2$) to simulate lost aerodynamic forces and prevent the pilot from overstressing the airframe.

What do the designations $7 \times 7$ and $7 \times 19$ indicate regarding aircraft control cables?

They specify cables constructed of 7 strands, each strand containing 7 wires or 19 wires, respectively.

What is the maximum allowable wear on outer cable wires before replacement is required?

Maximum allowable wear is $50\%$ of outer wires (indicated by a fully polished appearance on approximately 6 wires per outer strand or hairline cracks).

What types of swaged end fittings are commonly used on aircraft control cables?

Fork, eye, chain, inner thread, ball, and outer thread fittings.

Why are cable tension regulators required in flight control systems?

They maintain constant cable tension by compensating for unequal thermal expansion/contraction and airframe flexing between steel cables and the aluminum airframe.

How do cable quadrants and cable drums differ in converting mechanical motion?

Cable quadrants convert limited linear cable movement into rotary movement (or vice versa), while cable drums transform continuous rotary motion into linear cable travel using circumferential grooves.

How are control push-pull rods adjusted for length?

Length is adjusted using external threaded end fittings or spherical eye bearings at the rod terminals.

What devices protect flight control surfaces from wind damage while the aircraft is parked?

Internal or external ground gust locks for ailerons and elevators, and a hydraulic damper for the rudder.

What are three key advantages of Fly-By-Optical-Wire (FBOW) over Fly-By-Wire (FBW)?

Higher data transmission capacity, faster transmission speed, lighter weight, and complete immunity to electromagnetic interference (EMI).

Name three protections provided under Normal Law in an Electrical Flight Control System (EFCS).

Load factor limitation (G-limits), high angle of attack (AOA) / stall protection, high speed protection, and pitch/bank angle limits (e.g., maximum bank angle of $67^\circ$).

What is the purpose of a rudder 'Q' limiter or travel limitation unit?

It restricts maximum rudder deflection as airspeed increases to prevent structural damage from excessive aerodynamic loads.

How does a pneumatic stall warning system function on light aircraft?

As angle of attack increases, an inlet slot in the wing leading edge moves into a low-pressure region, drawing air through a cabin reed/horn assembly to alert the pilot.

What additional forces of control can Active Control Technology (ACT) provide beyond traditional moments?

Direct Lift Force and Direct Side Force.

How do automatic lift dumpers operate upon landing?

Weight-on-wheels switches on the landing gear trigger hydraulic actuators to deploy upper-surface wing panels, spoiling remaining lift and transferring aircraft weight fully onto the wheels for maximum braking efficiency.

What is the main objective when rigging an aircraft flight control system?

To ensure cockpit controls and control surfaces align simultaneously in neutral, move in the correct sense, achieve specified maximum travel, and operate within friction limits.

What is the function of the No. 1 or master rigging pin during control system rigging?

It secures the cockpit controls in the exact neutral position (in conjunction with the neutral setting bar) while the rest of the control run is aligned and pinned.

How are breakout force and running friction distinguished during control system friction testing?

Breakout force (static friction) is the initial force measured on a spring balance needed to start control movement from rest, whereas running friction is the lower force required to keep the control moving.

In a synchro servo-control system, how is surface position controlled using CX and CT units?

The control transmitter (CX) converts input position into electrical signals sent to a control transformer (CT), which compares the input with actual surface position and produces an error signal that drives the servo-motor until the error is zero.