Download - MS2-IEEE Hyd Systems Presentation
© 2008 Eaton Corporation. All rights reserved.
Aircraft Hydraulic System Design
Peter A. Stricker, PEProduct Sales Manager
Eaton Aerospace Hydraulic Systems Division
August 20, 2010
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Purpose
• Acquaint participants with hydraulic system design principles for civil aircraft
• Review examples of hydraulic system architectures on common aircraft
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Agenda
• Introduction• Review of Aircraft Motion Controls• Uses for and sources of hydraulic power• Key hydraulic system design drivers• Safety standards for system design• Hydraulic design philosophies for conventional, “more
electric” and “all electric” architectures • Hydraulic System Interfaces • Sample aircraft hydraulic system block diagrams• Conclusions
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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
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Pilot inputs are transmitted to remote actuators and amplified
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3
Pilot commands move actuators with little effort
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Hydraulic power is generated mechanically, electrically and pneumatically
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Pilot Inputs
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Introduction • Aircraft’s Maximum Take-Off Weight (MTOW) drives
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
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Controlling Aircraft MotionPrimary Flight Controls
Definition of Airplane Axes
1 Ailerons control roll
2 Elevators control pitch
3 Rudder controls yaw
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3 2
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Controlling Aircraft MotionSecondary Flight Controls
High Lift Devices:
►
• 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
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Example of Flight Controls (A320) REF: A320 FLIGHT CREW OPERATING MANUAL
CHAPTER 1.27 - FLIGHT CONTROLS
PRIMARY
SECONDARY
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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• Independently in parallel or sequenced in series
• Smooth, vibration free power output• Little impact from load variation
• Hydraulic fluid transmission medium• Removes heat generated by internal losses • Serves as lubricant to increase component life
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HYDR. MOTOR
TORQUE TUBE
GEARBOX
Typical Users of Hydraulic Power• Landing gear
• 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
reverser• Utility systems
• Cargo handling, doors, ramps, emergency electrical power generation
Flap DriveSpoiler Actuator
Landing Gear
Nosewheel Steering
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Sources of Hydraulic Power
Ram Air Turbine
AC Electric MotorpumpMaintenance-free
Accumulator
Engine Driven Pump
• Mechanical • Engine Driven Pump (EDP) - primary hydraulic power source,
mounted directly to engines on special gearbox pads• Power Transfer Unit – mechanically transfers hydraulic
power between systems• Electrical
• 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
Power Transfer Unit
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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
* Hydraulic System Architecture: Arrangement and interconnection of hydraulic power sources and consumers in a manner that meets requirements for controllability of aircraft
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Considerations for Hydraulic System Designto 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 redundancyFly-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
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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 probable
NA
Major Reduction in safety margin, increased crew workload, may result in some injuries
Remote P ≤ 10-5
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)
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System Design PhilosophyConventional 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
LEFT ENG.
SYSTEM 1
SYSTEM 3 RIGHT ENG.
SYSTEM 2
EDP EDP
ROLL 1
PITCH 1
YAW 1
OTHERS
EMP
EMP RAT
PTU
ROLL 2
PITCH 2
YAW 2
OTHERS
EMP
ROLL 3
PITCH 3
YAW 3
LNDG GR
EMRG BRKNORM BRK
NSWL STRG
ADP
EDP Engine Driven Pump
EMP Electric Motor Pump
ADP Air Driven Pump
PTU Power Transfer Unit
RAT Ram Air Turbine
Engine Bleed Air
OTHERS
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System Design PhilosophyMore 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
EDP EDP
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 BRKLNDG 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
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System Design PhilosophyAll Electric Architecture
“Holy Grail” of aircraft power distribution ….• Relies on future engine-core mounted electric generators
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 systems, consisting of
• Miniature, electrically driven, integrated hydraulic power generation system
• Hydraulic actuator controlled by electrical input
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Fly-by-Wire (FBW) SystemsFly-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
autopilot malfunction
BOEING 757 AILERON SYSTEM
PILOT INPUTS
AUTOPILOT INPUTS
LEFT WING
RIGHT WING
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Principal System InterfacesDesign Considerations
Hydraulic System
Hydraulic power from EDP
Nacelle / Engine
Pad speed as a function of flight regime – idle to take-off
Landing Gear
Power on Demand
Flow under normal and all emergency conditions – retract / extend / steer
Electric motors, Solenoids
Electrical System
Electrical power variations under normal and all emergency conditions (MIL-STD-704)
Flight Controls
Power on Demand
Flow under normal and all emergency conditions – priority flow when LG, flaps are also demanding flow
Avionics
Signals from pressure, temperature, fluid quantity sensors
Signal to solenoids, electric motors
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1,000
10,000
100,000
1,000,000
10,000,000
Cessna
172
Pheno
m 100
KingAir 2
00
Learj
et 45
BAe Jets
tream
41
Learj
et 85
Hawke
r 400
0
Challen
ger 6
05
Falcon
F7X
Global X
RS
Gulfstre
am G65
0
Embraer
ERJ-195
Boeing
737-7
00
Airbus
A321
Boeing
757-3
00
Airbus
A330-3
00
Boeing
777-3
00ER
Boeing
747-4
00ER
Airbus
A380
MT
OW
- lb
LARGE BIZ / REGIONAL J ETS
SINGLE-A ISLE
WIDEBODY
MID / SUPER MID-SIZE B IZ J ETS /
COMMUTER TURBO-PROPS
VERY LIGHT / LIGHT J ETS / TURBO-PROPS
GENERAL AVIATION
Aircraft Hydraulic Architectures Comparative Aircraft Weights
Increasing Hydraulic System Complexity
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Aircraft Hydraulic ArchitecturesExample Block Diagrams – Learjet 40/45
MAIN SYSTEM EMERGENCY SYSTEMMTOW: 21,750 lb
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 emergency system
• All primary flight controls are manual
Safety / Redundancy
• Engine-out take-off: One EDP has sufficient power to retract gear
• 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
REF.: AIR5005A (SAE)
Mid-Size Jet
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Aircraft Hydraulic ArchitecturesExample Block Diagrams – Hawker 4000
MTOW: 39,500 lbFlight 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
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Aircraft Hydraulic ArchitecturesExample Block Diagrams – Airbus A320/321
MTOW (A321): 206,000 lbFlight Controls: Hydraulic FBWKey Features• 3 independent systems • 2 main systems with EDP
1 main system also includes backup EMP & hand pump for cargo door3rd system has EMP and RAT pump
• Bi-directional PTU to transfer power between primary systems without transferring fluid
Safety / Redundancy• All primary flight controls have 3 independent
channels• Engine-out take-off: PTU transfers power from
Y to G system to retract LG• Rotorburst: Three systems sufficiently
segregated• All Power-out: RAT pump powers Blue; LG
extends by gravity
Single-Aisle
REF.: AIR5005 (SAE)
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Aircraft Hydraulic ArchitecturesExample Block Diagrams – Boeing 777
LEFT SYSTEM
Wide Body
RIGHT SYSTEMCENTER SYSTEMMTOW (B777-300ER): 660,000 lbFlight Controls: Hydraulic FBWKey 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 pumpSafety / 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)
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Aircraft Hydraulic ArchitecturesExample Block Diagrams – Airbus A380
Wide Body
MTOW: 1,250,000 lbFlight 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• All primary flight controls have 3 channels
– 2 hydraulic + 1 electric• 4 engines provide sufficient redundancy
for engine-out cases
REF.: EATON C5-37A 06/2006
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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
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Suggested References
Federal Aviation RegulationsFAR 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
TextMoir & Seabridge: Aircraft Systems –
Mechanical, Electrical and Avionics Subsystems Integration 3rd Edition, Wiley 2008