module 5

Aircraft Systems Overview

Aircraft systems include hydraulic

ATA Chapters

Standardized classification of aircraft systems such as ATA-27 (Flight Controls)

More Electric Aircraft

Aircraft architecture trend replacing hydraulic/pneumatic systems with electrical systems to reduce weight and increase efficiency

Hydraulic System Purpose

Converts small pilot inputs into the large forces needed for landing gear

Hydrostatic Principle

Hydraulic systems transmit force via static pressure using p = F/A

Hydraulic System Pressure

Typical commercial aircraft operate at 3000 psi

newer systems like A380/B787 use 5000 psi

Hydraulic Pumps

EDP provides continuous power

EMP provides backup/supplemental pressure and starts automatically when needed

Hydraulic Accumulator

Stores pressure

Hydraulic Reservoir

Stores hydraulic fluid

Hydraulic Actuator

Converts hydraulic pressure into linear motion

includes balanced and differential cylinders

Primary Flight Controls

Ailerons

Secondary Flight Controls

Flaps

Hinge Moment

Aerodynamic load resisting control-surface movement

Fly-By-Wire System

Electrical control system replacing mechanical linkages with computers and sensors

Actuator Types

HMA

High-Lift Systems

Flaps and slats that increase lift for low-speed takeoff and landing performance

Landing Gear Functions

Enable taxi

absorb loads

retract to minimize drag

Landing Gear Configurations

Includes tricycle (most common)

Shock Strut

Oleo-pneumatic unit using nitrogen and hydraulic fluid to absorb vertical landing loads

Steering System

Nose landing gear steering using mechanical

Braking System

Uses carbon brakes with hydraulic actuation

Avionics Definition

Aviation electronics including navigation

Federated Avionics

Architecture with independent LRUs for each function

simple but heavier

Integrated Modular Avionics

Architecture combining functions into shared modules to reduce weight and wiring

Navigation System Functions

Determine aircraft position and provide guidance

Flight Management System

Provides navigation

Pitot-Static System

Measures static and total pressure to compute airspeed and altitude

includes heated probes

VHF Communication

Short-range line-of-sight radio communication used for ATC exchanges

HF Communication

Long-range communication over oceanic and remote regions

affected by weather and ionosphere

Transponder

Responds to radar interrogation with coded aircraft information including identification and altitude

Auto-Flight System

Includes autopilot

Hydraulic Power System

Provides and transmits fluid power to high-load consumers such as flight controls and landing gear

Engine-Driven Pump (EDP)

A pump driven by the engine accessory gearbox providing continuous hydraulic pressure whenever the engine runs

Electric Motor Pump (EMP)

electrically powered pump used for backup

Hydrostatic Pressure Equation

Defined as p = F/A where pressure equals force divided by area

Hydraulic Flow Rate

Flow rate Q = A * v where v is piston speed and A is piston area

Hydraulic Fluid Properties

Includes flammability

Mineral Oil Hydraulic Fluid

Used mainly on military aircraft

good lubrication but lower fire resistance

Phosphate Ester Hydraulic Fluid

Used on commercial aircraft

high fire resistance (e.g.

Skydrol)

Hydraulic Reservoir Pressurization

Prevents pump cavitation and ensures fluid delivery at altitude

Hydraulic System Losses

Pressure drops caused by pipe length

Triple Hydraulic System

Many aircraft use 3 independent hydraulic systems (Green

Hydraulic PTU

Power Transfer Unit transferring hydraulic power between systems without fluid mixing

Ram Air Turbine (RAT)

Deployable turbine providing emergency hydraulic or electrical power

Aileron Function

Primary flight control surface controlling roll by differential deflection

Elevator Function

Primary flight control surface controlling pitch via symmetric deflection

Rudder Function

Primary flight control surface controlling yaw via left/right movement

Spoilers

Surfaces used for roll control

Trim System

Adjusts small surfaces to relieve pilot control force and maintain attitude

Hinge-Moment Coefficient

Describes how aerodynamic forces at a control surface hinge scale with speed

Pilot Input Transmission

Movement transferred from cockpit to surfaces via mechanical

Fly-By-Wire Feedback

Computers simulate artificial feel to replace natural aerodynamic feedback lost in electronic systems

Hydro-Mechanical Actuator (HMA)

Actuator using mechanical pilot input combined with hydraulic power assistance

Electro-Hydraulic Servo Actuator (EHSA)

Hydraulic actuator controlled electrically

used in modern fly-by-wire systems

Electro-Hydrostatic Actuator (EHA)

Self-contained hydraulic actuator powered electrically without central hydraulic supply

Electrical Backup Hydraulic Actuator (EBHA)

Hybrid actuator operating normally with hydraulics but capable of electrical backup mode

Electro-Mechanical Actuator (EMA)

Fully electric actuator used in more-electric aircraft

High-Lift Slats

Leading-edge devices extending forward to increase wing camber and delay stall at low speed

High-Lift Flaps

Trailing-edge devices increasing wing area and lift for takeoff/landing

Flap Power Drive Unit (PDU)

Central gearbox and motor assembly distributing mechanical power to flap actuators

Ballscrew Actuator

Converts rotational motion into linear movement for flap and slat mechanisms

Landing Gear Strut (Oleo)

Shock absorber using nitrogen and hydraulic fluid to absorb vertical landing loads

Torque Links

Hinged links maintaining alignment between inner and outer strut cylinders to prevent rotation

Uplock

Mechanical system securing landing gear in retracted position

Downlock

Mechanism ensuring landing gear locks into extended position

Nose Wheel Steering

Allows aircraft to turn on the ground using hydraulically or electrically powered actuators

Anti-Skid System

Prevents wheel lockup by modulating brake pressure for maximum braking efficiency

Brake-By-Wire

Electronic braking control using sensors and brake control computers

Tire Construction

Uses multiple plies and bead bundles to withstand high loads

Tire Failure Types

Include blowouts

Avionics Functions

Include navigation

Federated Architecture

Avionics architecture where each function resides in an independent LRU with dedicated wiring

Integrated Modular Avionics (IMA)

Architecture combining functions onto shared processing modules to reduce weight and wiring

ARINC Data Bus

Aviation standard digital data bus for communication between avionics units

AFDX

High-speed deterministic Ethernet-based avionics network used in aircraft such as A380 and B787

Air Data Computer

Processes inputs from pitot/static sensors to compute speed

Pitot Tube Function

Measures total (dynamic + static) pressure used for airspeed calculation

Static Port Function

Measures ambient atmospheric pressure used for altitude and vertical speed

Radar Altimeter

Provides precise height above ground using radio waves

GPS System

Satellite-based navigation providing accurate global position for navigation and flight management

VHF NAV System

Provides navigation aids such as VOR and ILS for approach and enroute guidance

HF Radio

Long-range communication used for oceanic and remote operations

SELCAL

System that alerts crew when a ground station is calling

Transponder Modes

Mode A (ID)

Autopilot System

Automatically controls aircraft pitch

Flight Director

Displays visual guidance cues for the pilot to manually follow desired flight path

Auto-Throttle

Automatically adjusts engine thrust to maintain desired speed or power setting

Electrical Power System

Provides AC/DC power for avionics

AC Power Source

Generated by engine-driven generators producing alternating current (often 115V/400Hz)