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AST 473 Cessna Citation II Hydraulic Power System

AST 473 Cessna Citation II Hydraulic Power System. Dr. R. Kurt Barnhart. Hydraulic System. One Pump per engine Operates: Landing gear Speedbrakes Thrust reversers (optional). Hydraulic System Operation. Open Center- no pressure buildup- bypasses unused output back to reservoir

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AST 473 Cessna Citation II Hydraulic Power System

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  1. AST 473 Cessna Citation IIHydraulic Power System Dr. R. Kurt Barnhart

  2. Hydraulic System • One Pump per engine Operates: • Landing gear • Speedbrakes • Thrust reversers (optional)

  3. Hydraulic System Operation • Open Center- no pressure buildup- bypasses unused output back to reservoir • System Pressurized upon component activation • Electric firewall shutoff valves- cockpit • Reservoir pressurized to provide adequate pressure at altitude

  4. Hydraulic System Operation • Fluid filtered: • Prior to reservoir • Prior to sub-system (landing gear, etc.) Annunciator lights: -low fluid level- reservoir -low pressure -when system pressurized

  5. Hydraulic System Operation • Reservoir (figure 13-1): • Located in tailcone on engine carry through beam • Pressurized to 15 – 16 psi via hyd. Pressure- small piston in reservoir neck. • When system not under pressure- internal spring gives 2.7 – 4.0 psi pressure.

  6. Hydraulic System Operation • Visual indicator on reservoir: • Full- .5 Gal. Fluid • Overfull- .65 Gal. • Refill- .2 Gal.- Illuminates amber “HYD LEVEL LO” annunciator • Relief valve- on top of reservoir opens @30 psi to prevent overpress.- can be manually activated for system maintenance

  7. Hydraulic System Operation • Pumps- constant volume gear driven- accessory section rated at 3.25 gpm. Ea. Operates when engine on- either pump can operate all sub-systems • System Bypass valve- spring loaded open- routes pump output to return line- valve energized closed (electric) to produce system pressure- valve fails open • Mechanical relief valve- in parallel w/ bypass valve opens @ 1,500 psi as a backup.

  8. Hydraulic System Operation • Firewall Shutoff Valves: • Installed in supply line of ea. Pump.- electric- controlled by ENG FIRE switchlights • Normally open valve- closed for fire or mx. • Position indicated by respective F/W SHUTOFF annunciators

  9. Hydraulic System Operation • Filters- 3; 2 for fluid leaving pumps/1 filters return fluid prior to reservoir return.- Each has a bypass valve- opens @ 100 psi if clogged- no cockpit indication • Flow Switches- in ea. Pump press. Line- controls the HYD PRESS (or FLOW) LO L/R. Limits: • .35 - .55 gpm- Light on • 1.33 gpm- Light off • Check valve prevents backflow into pump

  10. Hydraulic System Operation • Operation: • When No demand- bypass valve open- to rtn. • HYD FLOW LOW annunciators extinguish on eng. Start. • Upon any demand- bypass valve closes- HYD PRESS ON annunciator illuminates- system press. Limited to 1,500 psi by relief valve • When operation completed pressure builds- bypass valve opens (spring)- system depressurizes- HYD PRESS ON annunciator extinguishes

  11. Hydraulic System Operation • Loss of a pump indicated by the HYD PRESS LOW annunciator

  12. Thrust Reversers • Optional- most have;- target type- assist in deceleration on landing. • Deployed and held in position by system pressure • Upon stowing- hyd. Press. Is isolated and they are held in stow by an overcenter condition of the operation mechanism

  13. Thrust Reversers • Protection- Solenoid lock in throttle quadrant- prevents power application during reverse until full reverser deployment • Throttle feedback system moves FCU lever and throttle to idle during inadvertent deploy • Reverser operation limited to gnd. Op only via the left squat switch. • After inadvertent deploy- mx. Check needed to determine cause and check linkage rigging

  14. Thrust Reversers • Control- via reverser levers piggy-backed on throttles- 3 positions • Full fwd. (stow) • Reverse idle (detented) • Full aft. (reverse) • When lever moved to reverse idle- solenoid lockout mechanism prevents further aft lever movement until reverser fully deployed.

  15. Thrust Reversers • Microswitch in throttle quadrant gives electrical control. • Switch closed- when reverser moved from stow applying power to: • Close hydraulic bypass valve and pressurize system • Open hydraulic isolation valve to provide pressure to reverser system • Energize reverser control valve to deploy position provided either squat switch is closed (ground).

  16. Thrust Reversers • Each Reverser- 3 lights on glareshield • ARM- circuit completed by pressure switch = hyd. Press. Available to reverser control valve • UNLOCK- circuit completed by microswitch- closes when reverser mechanism initially moves from (mechanically) locked stowed pos. • DEPLOY- incicates reverser door mechanism has reached fully deployed pos. • Electrical power- left reverser- left. Ext. bus, rt. Reverser- rt. Crossover bus.

  17. Thrust Reversers • Operation- After lndg.- throttles idle- nosewheel on ground: • Raise thrust reverser levers to idle deploy detent • ARM and HYD PRESS ON lights come on • Closely followed by UNLOCK then DEPLOY lights • Reverser lever solenoid lock- release

  18. Thrust Reversers • Next: • Reversers can be moved aft to accel. Engine directly via fuel control- thrust levers held @ idle by mechancal interlock in pedestal • During reverse thrust- ARM, UNLOCK, DEPLOY, and HYD PRESS ON lights all stay on

  19. Thrust Reversers • As 60 KIAS go to idle reverse- maintain this position as needed for drag and thrust attenuation • To stow reverser: • Reverser levers fully forward and down- energizes control valve to “stow” (directs hyd. Pressure to stow side of reverser actuators • DEPLOY light goes out followed by UNLOCK, ARM, and HYD PRESS ON lights- indicates Stow position.

  20. Thrust Reversers • Caution: DO NOT attempt re-stow on Takeoff if reversers inadvertently deploy- throttle linkage damage may occur- loss of power • Caution: Reverser deployment @ higher than normal lndg. Speeds causes nose up pitching tendency- counter w/ yoke or else may porpoise & damage nose wheel.

  21. Thrust Reversers • EMER STOW- bypasses normal sequencing system used for: • Inadvertent deployment • Normal Stow failure

  22. EMER STOW OPERATION • 2 position switch- ea. Reverser- inboard of reverser lights- labled “STOW SW” • EMER- closes hydraulic bypass valve and energizes control valve to stow position • NORMAL

  23. EMER STOW OPERATION • If reversers deployed when EMER STOW selected: • HYD PRESS ON light comes on & reverser lights extinguish in sequence: • DEPLOY • UNLOCK • (HYD PRESS ON and ARM lights stay on in stow position- reverser held in stow position with continuous pressure as overcenter lock may be inop.- mx. check before next flight)

  24. EMER STOW OPERATION • If either ARM or UNLOCK comes on in flight- MCAW system triggers • NOTE: If fire switch light pushed (test or eng. Fire)- isolation valve de-energizes closed & hydraulic reverser operation not possible.

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