AST 473 Cessna Citation II Hydraulic Power System
- Slides: 24
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 buildupbypasses unused output back to reservoir • System Pressurized upon component activation • Electric firewall shutoff valves- cockpit • Reservoir pressurized to provide adequate pressure at altitude
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
Hydraulic System Operation • Reservoir (figure 13 -1): – Located in tailcone on engine carry through beam – Pressurized to 15 – 16 psi via hyd. Pressuresmall piston in reservoir neck. – When system not under pressure- internal spring gives 2. 7 – 4. 0 psi pressure.
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
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 subsystems • System Bypass valve- spring loaded open- routes pump output to return line- valve energized closed (electric) to produce system pressurevalve fails open • Mechanical relief valve- in parallel w/ bypass valve opens @ 1, 500 psi as a backup.
Hydraulic System Operation • Firewall Shutoff Valves: – Installed in supply line of ea. Pump. - electriccontrolled by ENG FIRE switchlights – Normally open valve- closed for fire or mx. – Position indicated by respective F/W SHUTOFF annunciators
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
Hydraulic System Operation • Operation: – When No demand- bypass valve open- to rtn. – HYD FLOW 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
Hydraulic System Operation • Loss of a pump indicated by the HYD PRESS LOW annunciator
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
Thrust Reversers • Protection- Solenoid lock in throttle quadrantprevents 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
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.
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).
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.
Thrust Reversers • Operation- After lndg. - throttles idlenosewheel 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
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
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.
Thrust Reversers • Caution: DO NOT attempt re-stow on Takeoff if reversers inadvertently deploythrottle 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.
Thrust Reversers • EMER STOW- bypasses normal sequencing system used for: – Inadvertent deployment – Normal Stow failure
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
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 positionreverser held in stow position with continuous pressure as overcenter lock may be inop. - mx. check before next flight)
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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