Cessna Citation IIPowerplant Dr. Barnhart
Introduction • Powerplant systems include: • Engines • Lubrication • Fuel distribution • Ignition • Engine instrumentation • Engine power control • Engine starting • Engine synchronization
Powerplant General • 2 aft fuselage mounted turbofans • Pratt & Whitney JT15D-4 • 2,500 lbs. thrust- standard conditions
Powerplant Sections • Intake • Compressor • Combustion • Turbine • Exhaust • Accessories
Powerplant Intake • T(1) probe in inlet • Anti-iced by bleed air • Intake- becomes 2 concentric ducts aft of fan. • Outer duct- bypass • Inner duct- core engine air
Powerplant- Fan • Fan assembly: • Nose cone (continuously anti-iced by bleed air when engine operating) • Fan stage • Single axial compression stage • 2 sets of stator vanes (anti-iced when “Eng Anti-ice- ON”)
Compressor • 2 stages: Low press./High press. • Low Press.- Non-geared fan and booster stage- axial flow; compresses and accelerates air rearward. • Outer span of Fan- speeds a high volume of air at relatively low velocity into bypass duct. • Inner span of Fan- accelerates air to booster stg.
Compressor ctn. • Booster stg.- extends to primary (core) air only and incr. air press. then directs it to high press. compressor. • Bypass ratio- diff. in air mass flow btn. Bypass duct and eng. Core- 2.7:1 in this eng. • Fan = 2/3 of total thrust at sea lvl.
Compressor ctn. • High press. Compr.- single stage centrifugal compr. Which receives airflow under pressure from booster stg.- Increases press. Further & directs it rearward.
Combustion • Annular- reverse flow chamber- 12 fuel nozzles, 2 igniter plugs- directs expanding/accelerating gas rearward to turbine scn.
Turbine Section • Single high press. Stg. • 2 low press. Stgs. • HPT connected to HPC via shaft • HPT- extracts energy from combustion gasses to drive the HPC and accessory scn. • HPC/T together = High press. Spool- N(2)
Low press. Turbine- LPT • 2 stg.- connected to LPC by shaft which runs inside the HP shaft • Low press. Turbine- extracts sufficient energy from comb. Gasses to drive LPC and Fan.
Exhaust section • 2 sections- Primary duct and bypass duct • Primary- tapered cone and struts • Combination of primary exhaust and bypass flow produces a total propulsive force for the A/C.
Accessory scn. • A gear assy. Encased and mounted beneath the compressor. • Driven by tower shaft and bevel gear. • Drives: • Oil pump • Hydraulic pump • Fuel control unit (FCU) and pump • Tach. generator- N(2)
Powerplant Operation • Nacelle inlet directs air to eng. Inlet. • Outer fan span- compresses and accelerates a larger volume of air at low vel. To full length bypass duct. • Inner fan span- compresses/accelerates air to axial compr. Stg. • Air press. Increased by booster stage & directed to the HPC which accelerates air & directs it through a diffuser.
Powerplant Operation ctn. • Diffuser- changes kinetic energy to static energy (velocity to press. By slowing) • Low volume of the core air flows through combustion chamber- fuel added- ign. Occurs. • Combustion process- produces expansion & acceleration • Remaining core compressed air- cooling and bleed functions.
Powerplant Operation ctn. • HPT- extracts energy to drive HPC and accessory scn. • LPT- extracts energy to drive LPC (fan/booster). • Remaining flow- directed to exhaust scn;- joins w/ bypass flow to provide thrust.
Engine Systems • Oil system • Fuel system • Ignition system • Instrumentation • Power control • Synchronization • Thrust reversing
Oil system • Fully automatic- cooling/lub.of engine and accessory brgs. • Tank- integral part of compressor intermediate case- contains filler and dipstick assy. For servicing (ensure fully engage after svc. Or inspn.- check qty. 10 min. after shutdown. • Max. allowable consumption 1 qt. ea. 4 hrs. over a 10 hr. period. • Different Oil brands not normally mixed
Oil system ctn. • Pump- engine driven (1 pressure, 2 scavenge elements)- mounted on accessory scn. • Oil cooling- FCOC- fuel cooled oil cooler- heat exchanger or radiator. • Filter- removes solid contaminants and combustion by products- no indication of bypass feature in cockpit.
Oil system ctn. • Oil press.- eng. Oil press maintained by a mechanical relief valve. • Indication- sensed by dual transmitters. • Press. Transducer sends input to dual vert. tape gauges in IP.- gauge calibrated in psi- a pr. Sw. activates an L or R OIL PRESS LO light. On annunciator panel.
Oil press. Ctn. • Oil press. Indicating sys.- powered from main DC elec. System.- Red OFF flag appears @ top when D.C. not avail. • Oil press. Sw.- also senses oil press.- if oil press at or below 35 psi- contacts close and L or R OIL PRESS LO light comes on.
Oil Temperature • Sensed by a resistance bulb- transmitted to a dual-scale vertical tape gauge on center IP- calibrated in deg. C and require main D.C. power- Red OFF flag at top when D.C. not avail.
Fuel System • Components: • Engine driven pump] • Fuel filter • Fuel control unit (FCU) • Step modulator • Flow divider • Emergency shutoff valve • 2 fuel manifolds • 12 fuel nozzles
Fuel System ctn • Fuel pump- receives fuel at tank pump pressure & delivers high press. Fuel to FCU • Not a suction pump- must receive pressure- if eng. Pump fails- engine flames out- PERIOD!
Fuel System- FCU • FCU- hydromechanical- 3 scns: 1. computing, 2. governing, 3. metering. • Computing section senses 5 parameters: • P(3)- compressor discharge press. • P(A)- Ambient press. • T(1)- compressor inlet temp. • N(2)- RPM • Throttle position
FCU- ctn • Governing section- senses both N(2) rpm and throttle position then modifies the signals sent by the computing section to the metering system. • The result of this process determines the position of the fuel metering valve which controls the volume of fuel delivered to the combustion chamber.
FCU- step modulation • A step modulator on the FCU increases fuel scheduling whenever the ignition system is operating ensuring engine acceleration performance. • Step modulation performance may be checked through ITT and N(1) for an increase when ignition is on
Fuel System- Flow Divider • Flow divider- divides metered fuel between the primary and secondary manifold (supplies fuel nozzles). • Flow divider also prevents fuel flow to nozzles until sufficient fuel press. Present. • Primary nozzles- used during eng. Start and low power.- Both nozzles at high pwr. • Residual manifold- collects residual fuel during shutdown- fuel flows back to the respective tank on next startup.
Emergency Fuel Shutoff Valve • Primary and secondary fuel from the flow divider pass through a N.O. shutoff valve • Valve activated mechanically by aft movement of the LPC shaft .070 inch. • Valve automatically shuts off fuel (i.e. failure of the LPC shaft- shaft would move aft); This prevents overspeed of N(1) turbines.
Fuel Nozzles • 12 Duplex nozzles- produce a precise atomized spray pattern conducive to combustion • Primary- operates continuously when eng. On- secondary only for high power settings.
Fuel indication system • Flow meter- senses metered flow downstream of the FCU; displays pph (100 – 2,000) on vertical tape gauges in main I.P. • Flowmeter power- main D.C. thus a red off flag indicated no D.C. avail.
Ignition System • Dual high energy ignition system: • 2 engine mounted ign. Exciters (older models had one exciter box per engine • Shielded cables • 2 igniter plugs in the comb. Chamber provide redundancy only (only 1 is needed for normal operations). • Ignition divided into 2 phases: 1) automatic, 2) selective
Ignition System ctn. • Automatic ign.- avail. During starting- terminated automatically when start sequence is terminated- also ign. Is automatic when eng. Anti-ice is ON. • Selective ign.- continuous operation selected by pilot • Remember- when ign. Circuit powered- step modulation is also activated
Ignition System Control • Ign. Controlled by an IGNITION sw. for ea. Eng. On the pilot’s sw. panel. Sw. is labeled: ON and NORM. • *NOTE: Ign. Should be ON for T/O and Lndg. And during heavy precip., heavy turbulence, stalls, or emerg. Descents.
Ignition System Control ctn. • In NORM- ing. Is automatic when START button is depressed AND associted throttle is moved from the cutoff position. • Power comes from the hot batt. Bus through the throttle microswitch. • Ign. And starter operation both terminated by the speed sensor switch on the starter generator.
Ignition System Control- ctn. • When ign. Sw. in ON ign. Is continuous regardless of throttle pos. • In this case, left eng. Ign. Power is supplied by rt. X-over bus and the rt. Eng. Ign. Pwr supplied from left ext. bus. • CB’s on pilot’s CB panel. • Remember- Ign. Also activated when ANTI ICE is ON.
Ignition indication • Ign. Operation indicated by a grn. Light near the ign. Sw. whenever pwr. Avail. To exciter. DOES NOT indicate exciter is operating or plug is firing
Engine Instrumentation • Horizontal row of gauges @ top of center I.P. • From Left to Right: N(1) or fan rpm, ITT, N(2) or HPC rpm called “turbine”, oil temp., oil pressure.
Engine Instrumentation ctn. • N(1)- supplied from a Tach generator located on top side of compr. Case. Driven by LPC rotor shaft. • Tach. Gen. output is then amplified and output displayed on the dual tape guage calibrated in % rpm- 3 digit lighted display also below ea. Gauge.
Engine Instrumentation- ctn • N(1) is the primary thrust indicator for the JT15D-4- and is the ref. for all pwr. Settings. • Gauge powered via main D.C.- when elec. Pwr. Not avail. The lighted display inop. • Also, loss of D.C. means loss of the amplifier circuit. The vertical tape still receives tach. Gen. output and provides accurate information when engines are above 50% N(1).
Engine Instrumentation ctn. • ITT- a computed synthetic readout. EGT is sensed by 6 thermocouples in the exhaust aft of the turbine. • Also, temp rise across the fan sensed by 4 T(1) probes (1 in front of fan and 3 @ aft end of bypass duct). • A trim resistor in the thermocouple system is test-cell adjusted.
ITT ctn. • The ITT readout is the result of adding 3 times the temp. rise in the bypass duct to the trimmed value of the thermocouple output- provides an accurate indication of eng. Combustion temp. under all flight conditions. • Computed temp displayed on vert. tapes calibrated in deg. C. OFF flag when D.C. not avail.- pwr. Source same as for N(1).
HPC rpm N(2) • H.P.C. rpm supplied via a tach. Gen. driven by the accessory scn- displayed in % rpm by dual lighted digital displays on the turbine gauge • Pwr. Failure results in loss of lighted display. • Red light under ea. Display will come on (and digital read will flash) when N(2) exceeds 96%. Pwr. Supply same as N(1)
Engine Power Control • Via throttle or “power levers” travel from full aft or “cut off” to full fwd. or “max. thrust” position. • A cutoff stop prevents inadvertent selection of cutoff. A latch must be raised before eng. Can go into idle cutoff. • Thrust reversers “TR’s” are piggyback mounted on ea. Throttle- throttle is mechanically connected to a pwr. Lever on FCU • Friction adjustment on side of pedestal
Engine Starting • 2 types of engine starts: • Ground- further divided into battery starts, generator assists, and External pwr. Starts. • Air- divided into starter-assist, and windmilling starts. • Starter operation covered in chap. 2 (elec.) • Perform all airstarts I.A.W. the airstart envelope (Fig. 7-11).
Engine Synchronization (Sync) • Ea. Eng. Has both a fan and/or turbine has • master/slave rpm synchronizer controller • An actuator • A control sw. • An indicator light • Left eng. Is master- rt. is slave.
Engine Synchronization (Sync) • System adjusts rt. Eng. Rpm to that of left- eliminates the out-of-sync. “beat” of engs. • Operates in a very narrow rpm band to prevent rt. Eng. Spool down if left fails • Manually sync. To 1.5% prior to engaging the system using N(1) fan or N(2) turbine. • System should be off for: pwr. Changes, T/O & lndg., and for single eng. Ops.
Engine Synchronization (Sync) • Sync cntrol- 3 pos. rotary sw. labeled “ENGINE SYNC FAN-OFF-TURB” • OFF permits sync. Controller to position the actuator (in rt. Nacelle) to a “null” or center pos. • FAN or TURB selection permits sync. Of N(1) or N(2) as desired- Fan for pax. Turb. For pilots.
Engine Synchronization (Sync) • When ENNGINE SYNC sw. is in FAN or TURB- the amber ENGINE SYNC light is on. • System activated by pilot following T/O • Tach. Generators (turb. And fan) supply signals to sync. Controller. Controller computes error diff. of selected inputs and transmits an output to actuator (rt.) which then adjusts rt. FCU to sync. R Eng. to left.