Aircraft Hydraulic System Design pptx

Introduction As airplanes grow in size, so do the forces needed to move the flight controls … thus the need to transmit larger amount of power Ram Air Turbine Pump Hydraulic Storage/

Aircraft Hydraulic System Design

Peter A Stricker, PE

Product Sales Manager

Eaton Aerospace Hydraulic Systems Division

August 20, 2010

Purpose

design principles for civil aircraft

architectures on common aircraft

electric” and “all electric” architectures

Conclusions

Introduction

As airplanes grow in size, so

do the forces needed to move the

flight controls … thus the need to

transmit larger amount of power

Ram Air Turbine Pump

Hydraulic Storage/Conditioning

Engine Pump

Electric Generator

Electric Motorpump

Flight Control Actuators

Air Turbine Pump

Hydraulic system

transmits and controls

power from engine to

flight control actuators

2

Pilot inputs are transmitted to remote actuators and amplified

pneumatically

5

Pilot Inputs

Introduction

aerodynamic forces that drive control surface size and loading

• A380 – 1.25 million lb MTOW – extensive use of hydraulics

• Cessna 172 – 2500 lb MTOW – no hydraulics – all manual

Controlling Aircraft Motion

Primary Flight Controls

Definition of Airplane Axes

1 Ailerons control roll

2 Elevators control pitch

1

Controlling Aircraft Motion

Secondary Flight Controls

• Flaps (Trailing Edge), slats (LE Flaps)

increase area and camber of wing

• permit low speed flight

Flight Spoilers / Speed Brakes: permit steeper

descent and augment ailerons at low speed

when deployed on only one wing

Ground Spoilers: Enhance deceleration on

ground (not deployed in flight)

Trim Controls:

• Stabilizer (pitch), roll and rudder (yaw) trim to

balance controls for desired flight condition

Example of Flight Controls (A320)

REF: A320 FLIGHT CREW OPERATING MANUAL CHAPTER 1.27 - FLIGHT CONTROLS

PRIMARY SECONDARY

Why use Hydraulics?

• Effective and efficient method of power amplification

• Small control effort results in a large power output

• Precise control of load rate, position and magnitude

• Infinitely variable rotary or linear motion control

• Adjustable limits / reversible direction / fast response

• Ability to handle multiple loads simultaneously

• Smooth, vibration free power output

• Little impact from load variation

• Hydraulic fluid transmission medium

• Extension, retraction, locking, steering, braking

• Primary flight controls

• Rudder, elevator, aileron, active (multi-function)

spoiler

• Secondary flight controls

• high lift (flap / slat), horizontal stabilizer, spoiler, thrust

Landing Gear

Nosewheel Steering

Sources of Hydraulic Power

Ram Air Turbine

AC Electric Motorpump

Maintenance-free Accumulator Engine Driven Pump

• Pump 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

Pneumatic

• Bleed 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

Key Hydraulic System Design Drivers

• High Level certification requirement per aviation

regulations:

Maintain control of the aircraft under all normal and

anticipated failure conditions

• Many system architectures * and design approaches exist to meet this high level requirement – aircraft

designer has to certify to airworthiness regulators by analysis and test that his solution meets requirements

Arrangement and interconnection of hydraulic power sources and consumers in a manner that meets requirements for

controllability of aircraft

Considerations for Hydraulic System Design

to meet System Safety Requirements

• Redundancy in case of failures must be

designed into system

• Any and every component will fail during life of

aircraft

• Manual control system requires less

redundancy

Fly-by-wire (FBW) requires more redundancy

• Level of redundancy necessary evaluated per

methodology described in ARP4761

• Safety Assessment Tools

• Failure Modes, Effects and Criticality Analysis –

computes failure rates and failure criticalities of

individual components and systems by

considering all failure modes

• Fault Tree Analysis – computes failure rates

and probabilities of various combinations of

failure modes

• Markov Analysis – computes failure rates and

criticality of various chains of events

• Common Cause Analysis – evaluates failures

that can impact multiple components and

systems

• Principal failure modes considered

• Single system or component failure

• Multiple system or component failures occurring simultaneously

• Dormant failures of components or subsystems that only operate in emergencies

• Common mode failures – single failures that can impact multiple systems

• Examples of failure cases to be considered

• One engine shuts down during take-off – need

to retract landing gear rapidly

• Engine rotor bursts – damage to and loss of multiple hydraulic systems

• Rejected take-off – deploy thrust reversers, spoilers and brakes rapidly

• All engines fail in flight – need to land safely without main hydraulic and electric power sources

Civil Aircraft System Safety Standards

(Applies to all aircraft systems)

Failure

Criticality Failure Characteristics

Probability of Occurrence

Design Standard

Minor Normal, nuisance and/or possibly requiring

emergency procedures

Reasonably

Major Reduction in safety margin, increased crew

workload, may result in some injuries

Hazardous Extreme reduction in safety margin, extended

crew workload, major damage to aircraft and possible injury and deaths

Extremely remote P ≤ 10-7

Catastrophic Loss of aircraft with multiple deaths Extremely

improbable P ≤ 10-9

Examples

Minor: Single hydraulic system fails

Major: Two (out of 3) hydraulic systems fail

Hazardous: All hydraulic sources fail, except RAT or APU (US1549 Hudson River A320 – 2009)

Catastrophic: All hydraulic systems fail (UA232 DC-10 Sioux City – 1989)

System Design Philosophy

Conventional Central System Architecture

• Multiple independent centralized power

systems

• Each engine drives dedicated pump(s),

augmented by independently powered

pumps – electric, pneumatic

• No fluid transfer between systems to

maintain integrity

• System segregation

• Route lines and locate components far

apart to prevent single rotor or tire burst

from impacting multiple systems

• Multiple control channels for critical

functions

• Each flight control needs multiple

independent actuators or control

surfaces

• Fail-safe failure modes – e.g., landing

gear can extend by gravity and be

locked down mechanically

EMP

EMP RAT

ROLL 2 PITCH 2 YAW 2 OTHERS

EMP

ROLL 3 PITCH 3 YAW 3 LNDG GR

EMRG BRK NORM BRK

NSWL STRG ADP

OTHERS

System Design Philosophy

More Electric Architecture

• Two independent centralized power

systems + Zonal & Dedicated

Actuators

• Each engine drives dedicated pump(s),

augmented by independently powered

pumps – electric, pneumatic

• No fluid transfer between systems to

maintain integrity

• System segregation

• Route lines and locate components far

apart to prevent single rotor or tire burst

to impact multiple systems

• Third System replaced by one or more

local and dedicated electric systems

• Tail zonal system for pitch, yaw

• Aileron actuators for roll

• Electric driven hydraulic powerpack for

emergency landing gear and brake

• Examples: Airbus A380, Boeing 787

LEFT ENG.

SYSTEM 1

RIGHT ENG SYSTEM 2

ROLL 1 PITCH 1 YAW 1 OTHERS

EMP

GEN1 RAT

ROLL 2 PITCH 2 YAW 2 OTHERS

EMP

ROLL 3

ZONAL PITCH 3 YAW 3

NORM BRK

EMRG BRK LNDG GR

NW STRG

GEN2

EDP Engine Driven Pump EMP Electric Motor Pump

GEN Electric Generator

RAT Ram Air Turbine Generator

Electric Channel

OTHERS

ELECTRICAL ACTUATORS

LG / BRK EMERG POWER

System Design Philosophy

All Electric Architecture

“Holy Grail” of aircraft power distribution ….

capable of high power / high power density generation,

running at engine speed – typically 40,000 rpm

• Electric power will replace all hydraulic and pneumatic power for all flight controls, environmental controls, de-icing, etc.

• Flight control actuators will like remain hydraulic, using

Electro-Hydrostatic Actuators (EHA) or local hydraulic

Fly-by-Wire (FBW) Systems

Fly-by-Wire

• Pilot input read by computers

• Computer provides input to electrohydraulic flight control actuator

• Control laws include

• Enhanced logic to automate many functions

• Artificial damping and stability

• Flight Envelope Protection to prevent airframe from exceeding structural limits

• Multiple computers and actuators provide sufficient redundancy – no manual reversion

Conventional Mechanical

• Pilot input mechanically connected to flight control

hydraulic servo-actuator by cables, linkages, bellcranks, etc

• Servo-actuator follows pilot command with high

force output

• Autopilot input mechanically summed

• Manual reversion in case of loss of hydraulics or

Principal System Interfaces

Electrical power variations

under normal and all

demanding flow

Avionics

Signals from pressure, temperature, fluid quantity sensors

ir 200

Learj

et 45

BAe Jetstre

Gulfstream

G650

s A321

Boein

g 757-300Airbu

s A330-300

Boein

g 777-300ER

Boein

g 747-400E

RAirbu

s A380

Aircraft Hydraulic Architectures

Comparative Aircraft Weights

Increasing Hydraulic System Complexity

Aircraft Hydraulic Architectures

Example Block Diagrams – Learjet 40/45

Flight Controls: Manual

Key Features

• One main system fed by 2 EDP’s

• Emergency system fed by DC electric pump

• Common partitioned reservoir (air/oil)

• Selector valve allows flaps, landing gear,

nosewheel steering to operate from main or

• All Power-out: Manual flight controls; LG extends by

gravity with electric pump assist; emergency flap

extends by electric pump; Emergency brake energy

stored in accumulator for safe stopping

Mid-Size Jet

Aircraft Hydraulic Architectures

Example Block Diagrams – Hawker 4000

Flight Controls: Hydraulic with manual reversion

exc Rudder, which is Fly-by-Wire (FBW)

Key Features

• Two independent systems

• Bi-directional PTU to transfer power between

systems without transferring fluid

• Electrically powered hydraulic power-pack for

Emergency Rudder System (ERS)

Safety / Redundancy

• All primary flight controls 2-channel; rudder has additional backup powerpack; others manual reversion

• Engine-out take-off: PTU transfers power from system #1 to #2 to retract LG

• Rotorburst: Emergency Rudder System is located outside burst area

• All Power-out: ERS runs off battery; others manual;

LG extends by gravity

Super Mid Size

REF.: EATON C5-38A 04/2003

Aircraft Hydraulic Architectures

Example Block Diagrams – Airbus A320/321

MTOW (A321): 206,000 lb

Flight Controls: HydraulicFBW

Key Features

• 3 independent systems

• 2 main systems with EDP

1 main system also includes backup EMP &

hand pump for cargo door

3rd system has EMP and RAT pump

• Bi-directional PTU to transfer power between

primary systems without transferring fluid

Aircraft Hydraulic Architectures

Example Block Diagrams – Boeing 777

LEFT SYSTEM

Wide Body

RIGHT SYSTEM CENTER SYSTEM

MTOW (B777-300ER): 660,000 lb

Flight Controls: Hydraulic FBW

Key Features

• 3 independent systems

• 2 main systems with EDP + EMP each

• 3rd system with 2 EMPs, 2 engine bleed

air-driven (engine bleed air) pumps, + RAT pump

Safety / Redundancy

• All primary flight controls have 3 independent

channels

• Engine-out take-off: One air driven pump and

EMP available in system 3 to retract LG

• Rotorburst: Three systems sufficiently

segregated

• All Power-out: RAT pump powers center

system; LG extends by gravity

REF.: AIR5005 (SAE)

Aircraft Hydraulic Architectures

Example Block Diagrams – Airbus A380

Wide Body

Flight Controls: FBW (2H + 1E channel)

Key Features / Redundancies

• Two independent hydraulic systems+ one electric system (backup)

• Primary hydraulic power supplied by 4 EDP’s per system

Conclusions

• Aircraft hydraulic systems are designed for

high levels of safety using multiple levels of

redundancy

• Fly-by-wire systems require higher levels of

redundancy than manual systems to maintain same levels of safety

• System complexity increases with aircraft

weight

Suggested References

Federal Aviation Regulations

FAR Part 25: Airworthiness Standards for

Transport Category Airplanes

FAR Part 23: Airworthiness Standards for

Normal, Utility, Acrobatic, and Commuter

Category Airplanes

FAR Part 21: Certification Procedures For

Products And Parts

AC 25.1309-1A System Design and

Analysis Advisory Circular, 1998

Aerospace Recommended Practices (SAE)

ARP4761: Guidelines and Methods for

Conducting the Safety Assessment

Process on Civil Airborne Systems and

Equipment

ARP 4754: Certification Considerations for

Highly-Integrated or Complex Aircraft

Systems

Aerospace Information Reports (SAE)

AIR5005: Aerospace - Commercial Aircraft Hydraulic Systems

Radio Technical Committee Association (RTCA)

DO-178: Software Considerations in Airborne Systems and Equipment Certification (incl Errata Issued 3-26-99) DO-254: Design Assurance Guidance For Airborne Electronic Hardware

Text

Moir & Seabridge: Aircraft Systems – Mechanical, Electrical and Avionics Subsystems Integration 3rd Edition, Wiley 2008