Aircraft Hydraulics System - Des

AE 415

Presented by: DESIREE C. CAPUNO BS AeE - IV

AgendaIntroduction Advantages of a Hydraulic System Hydraulic System Components and Design Hydraulic Power Components Hydraulic System Interfaces Conclusion

Introduction1 As airplanes grow in size, so do the forces needed to move the flight controls thus the need to transmit larger amount of powerAir Turbine Pump

5 Hydraulic power is generated mechanically, electrically and pneumatically

2 Hydraulic system transmits and controls power from engine to flight control actuatorsPilot Inputs

Electric MotorpumpRam Air Turbine Pump

Hydraulic Storage/Conditioning

Electric Generator Engine Pump

Flight Control Actuators

3 Pilot inputs are transmitted to remote actuators and amplified

4 Pilot commands move actuators with little effort

IntroductionHydraulics is based on the fact that liquids are incompressible. Hydraulic system is a system where liquid under pressure is used to transmit energy. In it, a hydraulic pump converts mechanical power to hydraulic power. An actuating cylinder converts hydraulic power to mechanical power.

AdvantagesLighter weight Ease of installation Simplification of inspection Minimum maintenance requirements Dead beat Fire Hazard, not a Shock Hazard Develops practically unlimited force

Why use Hydraulics?Effective and efficient method of power amplificationSmall control effort results in a large power output

Precise control of load rate, position and magnitudeInfinitely variable rotary or linear motion control Adjustable limits / reversible direction / fast response

Ability to handle multiple loads simultaneouslyIndependently in parallel or sequenced in series

Smooth, vibration free power outputLittle impact from load variation

Hydraulic fluid transmission mediumRemoves heat generated by internal losses Serves as lubricant to increase component life

Principles of OperationGoverned by Pascals law The oil is in contact with both sides of the piston head but at different pressures. High pressure oil may be pumped into either side of the piston head. The selector valve determines to which side of the actuating cylinder the high pressure oil (red colored side) is sent.

EVOLUTION OF THE HYDRAULIC SYSTEM

A basic hydraulic system consists of a supply of hydraulic fluid, a pump, an actuator, and a selector valve.

A double-acting actuator allows the actuator to be powered in both directions. A two-way valve allows selection of either side of the actuator.

A Simple Hydraulic System

Hydraulic Fluidmust be able hydraulic liquidsof the lines with a minimum also called to flow through all of opposition which power is transferred medium by must be incompressible in hydraulic machinery must have good lubricating properties to prevent wear in based on mineral oil or water. the pump and valves must inhibit corrosion and not chemically attack any of the seals in the system must not foam in operation

HYDRAULIC SYSTEM COMPONENTS AND DESIGN

Function

Property Low compressibility(high bulk modulus) Fast air release Low foaming tendency Low volatility Good thermal capacity and conductivity

Medium for power transfer and control

Medium for heat transfer Sealing Medium

Adequate viscosity and viscosity index Shear stabilityViscosity for film maintenance Low temperature fluidity Thermal and oxidative stability Hydrolytic stability / water tolerance Cleanliness and filterability Antiwear characteristics Corrosion control Proper viscosity to minimize internal leakage High viscosity index

Lubricant

Pump efficiency Special function Environmental impact Functioning life

Fire resistance Friction modifications Radiation resistanceLow toxicity when new or decomposed Biodegrability Material compatibility

Characteristics considered when selecting a liquid for a system viscosityViscosity is internal resistance to flow Saybolt universal viscosimeter- instrument commonly used by engineers [reading: SSU (seconds, Saybolt universal)]

chemical stabilitythe ability of the liquid to resist oxidation and deterioration for long periods

flash pointthe temperature at which a liquid gives off vapor in sufficient quantity to ignite momentarily (flash) when a flame is applied

fire pointthe temperature at which a substance gives off vapor in sufficient quantity to ignite and continue to burn when exposed to a spark or flame

TYPES OF HYDRAULIC FLUID

Type

Vegetable-base Mineral-baseCastor oil & alcohol

Mixture

Dye Compatible color seals (MIL-H-7644)Blue

CleanserAlcohol

Flammab le

Vegetable-base (MIL-H-7644) Mineral-base (MIL-H-5606)

(MIL-H-5606)Red

Natural rubber

Synthetic Fluid

Kerosene type petroleum

(Sky-drol)

Neoprene seals

Naptha, Varsol, Stoddard solvent

Synthetic Fluid (Sky-drol)

Non-petroleum Light base / purple phosphate-ester base

Natural & Synthetic Fiber

trichlorethylene

Typical Users of Hydraulic PowerLanding gearExtension, retraction, locking, steering, braking

Primary flight controlsRudder, elevator, aileron, active (multi-function) spoiler

Secondary flight controlshigh lift (flap / slat), horizontal stabilizer, spoiler, thrust reverserLanding Gear

Utility systemsCargo handling, doors, ramps, emergency electrical power generationSpoiler Actuator HYDR. MOTOR Flap Drive

GEARBOX

TORQUE TUBE Nosewheel Steering

Sources of Hydraulic PowerMechanicalEngine Driven Pump (EDP) - primary hydraulic power source, mounted directly to engines on special gearbox pads Power Transfer Unit mechanically transfers hydraulic power between systems

ElectricalPump attached to electric motors, either AC or DC Generally used as backup or as auxiliary power Electric driven powerpack used for powering actuation zones Used for ground check-out or actuating doors when engines are not running Ram Air TurbineEngine Driven Pump

PneumaticBleed Air turbine driven pump used for backup power Ram Air Turbine driven pump deployed when all engines are inoperative and uses ram air to drive the pump Accumulator provides high transient power by releasing stored energy, also used for emergency and parking brake

AC Electric Motorpump Power Transfer Unit

Maintenance-free Accumulator

ReservoirFUNCTIONS Holds reserve supply oil to account for normal leakage, emergency supply of oil, volume changes, thermal contraction of oil Provides pressure head on the pump, a place to remove air or foam from liquid, air space for expansion of the oil due to temperature changes TYPES Integral In-line

HYDRAULIC POWER COMPONENTS

PumpsFUNCTION

is to move fluid through the system transmitting hydraulic powerTYPES Hand pump Powered pump

Example of a hand pump

Powered PumpsFUNCTION Is to change mechanical horsepower to hydraulic horsepower TYPES Gear pumps: move fluid based upon the number of gear teeth and the volume spacing between gear teeth. Piston pumps: move fluid by pushing it through the motion of the pistons within the pump

Powered PumpsPRINCIPLES OF GEAR PUMPSThe liquid from the reservoir is pushed between the gear teeth. The oil is moved around to the other side by the action of the drive gear itself and sent through the pressure line.

Powered PumpsPRINCIPLES OF RECIPROCATING PISTON PUMP As the cylinder block rotates, space between the block and the pistons increase, letting in more oil. As the block rotates from bottom dead center, the reverse occurs and the pistons push oil out through the outlet

ValvesTYPES Flow controlSelector valves Check valves A flow-control valve selects the route of Sequence valves flow of the fluid through the system, and is not Priority valves normally concerned with the pressure. Quick-disconnect Relief valves

Pressure controlPressure regulator Pressure-control valves, on the other Pressure reducer hand, adjust, regulate, or limit the amount of pressure in the system, or in any portion of the system.

AccumulatorsUSES Absorbs the shocks due to rapid pressure variations in a hydraulic system Helps maintain a constant pressure within the hydraulic system Helps the hydraulic pump under peak pressure loads It is an emergency source of power Spherical shape is preferred for accumulators

PRINCIPLE Gas valve lets in compressed gas at system pressure Diaphragm pops up & oil is sent through system When system pressure>accumulator pressure, diaphragm deploys

ActuatorThe function is to take the pressure & hydraulic fluid flow & change them into linear or rotary motion. Single piston double rod is an equal displacement cylinder used in aileron system or automatic guidance system Double piston-double rod actuating cylinder used in bomb bay doors

How does a simple hydraulic system works?

Principal System InterfacesDesign ConsiderationsElectrical System Flight ControlsFlow under normal and all emergency conditions priority flow when LG, flaps are also demanding flow

Electric motors, Solenoids Power on Demand Electrical power variations under normal and all emergency conditions

Hydraulic System

Power on Demand Hydraulic power from EDP

Nacelle / EnginePad speed as a function of flight regime idle to take-off

AvionicsSignals from pressure, temperature, fluid quantity sensors Signal to solenoids, electric motors

Landing GearFlow under normal and all emergency conditions retract / extend / steer

Aircraft Hydraulic ArchitecturesComparative Aircraft Weights10,000,000 1,000,000MTOW - lbWIDEBODY

SINGLE-AISLE

100,000

LARGE BIZ / REGIONAL JETS MID / SUPER MID-SIZE BIZ JETS / COMMUTER TURBO-PROPS

10,000

VERY LIGHT / LIGHT JETS / TURBO-PROPS GENERAL AVIATION

1,000

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Increasing Hydraulic System Complexity

Conclusions Aircraft hydraulic systems are designed for high levels of safety using multiple levels of redundancy System complexity increases with aircraft weight