Powerplant Flashcards
What are the typical engines on the 200? B200?
PT6A-41
PT6A-42
What is the horsepower capabilities?
850 shaft HP, 903 ESHP
What are the seven sections of the engine?
Air intake section
Compressor section
Combustion section
Turbine section
Exhaust section
Reduction gear section
Accessory drive section
Where is the air intake at?
By the air scoop under the nacelle
Where does the intake air first flow to?
The gas generator compressor
How many stages are in the compressor section?
4 - 3 axial stages, 1 centrifugal stage
What’s the function of the compressor?
Compress and supply air for combustion, cooling, pressurization, and pneumatic services
What is provided to prevent compressor stalls in the centrifugal stage?
Compressor bleed valves
When are compressor bleed valves most effective at preventing compressor stalls?
Low N1 rpm ranges
At what percent N1 do the compressor bleed valves close? What happens if they were to stick closed below this value?
90%, a compressor stall would occur
What would happen if one or both compressor bleed valves were to stick open?
ITT increase with a torque decrease while the N1 rpm remained constant
How many fuel nozzles are in the combustion chamber?
14
How many igniter plugs are in the combustion section?
2
How many reaction turbines does the PT6A use? What are they?
Free, two-stage axial propeller(power) turbine and a single-stage compressor turbine
What does the two-stage power turbine do?
Extracts energy from the combustion gases to drive the propeller and its accessories through the planetary reduction gears. This is Np.
What does the single stage compressor turbine do?
It extracts energy from the combustion gases to drive the gas generator compressor and the accessory gear section. This is N1.
What is the type of reduction gearing?
Two-stage, planetary type
What’s the purpose of the reduction gear section?
To reduce the high rpm of the free turbine to the value required for propeller operation.
It’s also used for torquemeter operation and includes drive sections for the prop governor, overspeed governor, and the prop tachgenerator.
What section forms the aft portion of the engine?
The accessory section
What is accessory section driven by?
The compressor turbine through a shaft that extends aft through the oil tank to the accessory gearbox
What’s the function of the accessory gearbox?
Drive the FCU and high pressure fuel pump, lubricating pump, N1 tachgenerator, DC starter generator, low pressure fuel boost pump, refrigerant compressor (right engine only)
What type of oil system does it have?
A dry-sump system
Where is the oil tank located?
Between the aft end of the compressor inlet and the forward end of the accessory gearbox
Where is engine oil pressure sensed?
In the pressure pump outlet line
What type of power does the engine oil pressure and oil temperature gauge require?
DC power
Where the magnetic chip detectors located?
The bottom of each reduction gearbox
Explain the operation of the oil system.
Oil pressure is drawn via a pump from the tank through various filters to engine bearings, accessory and reduction gears, prop governor, and torquemeter system.
What is oil pressure regulated by?
A relief valve
What type of pump returns the gear case oil to the tank through the oil-fuel heater? From the reduction gear case?
A scavenge pump
The fuel control system on a PT6A engine is essentially a _____ governor that increases or decreases ___ ___ to the engine to maintain selected engine operating speed.
Fuel; fuel flow
How is the low pressure boost pump driven?
By the engine
What’s the purpose of the low pressure engine driven boost pump?
Provides sufficient fuel head pressure to the high-pressure pump to maintain proper cooling and lubrication
How does the oil-to-fuel heat exchanger maintain a desired fuel temperature at the fuel pump inlet?
By using warm engine oil, uses automatic sensors
Where does fuel enter the engine fuel system through?
The oil-to-fuel heat exchanger
After flowing through the oil-to-fuel heat exchanger, where does the fuel flow?
Into the high pressure engine-driven fuel pump and then into the FCU
What will vary the flow rates through the high pressure engine-driven pump?
The gas generator (N1) RPM
What’s the primary purpose of the high pressure engine-driven fuel pump?
Provide sufficient pressure at the fuel nozzles for a good spray pattern at all modes of engine operation
At what PSI does the high pressure pump provide fuel at? Where does it provide it at?
800PSI - the fuel side of the FCU
What valve is between the FCU fuel valve and the engine combustion chamber?
Minimum pressurizing valve
What’s the purpose of the minimum pressurizing valve? How many psi is required to open it?
It cuts off fuel flow during starts until fuel pressure builds sufficiently to maintain a proper spray pattern in the combustion chamber
About 70 psi is required to open it
What maintains the high pressure to the minimum pressurizing valve?
The engine driven high-pressure fuel pump
What would happen to the valve and the engine if the high pressure engine driven pump were to fail?
The minimum pressurizing valve would close and the engine would flameout
What valve does the condition levers control?
The fuel cutoff valve
When the engine is starting, where does fuel initially flow through?
The flow divider to the primary fuel spray nozzles in the combustion chamber.
When shutting down the engine, what forces the remaining fuel in the manifold out?
Purge tank pressure
What’s the main purpose of the FCU?
To meter the proper fuel amount to the nozzles in all modes of engine operation
How does the FCU regulate fuel to the engine fuel nozzles?
Compares gas generator (N1) speed with the power lever setting
What does the condition lever adjust?
The N1 speed from LOW IDLE to HIGH IDLE.
How do the power levers control fuel to the engine?
Adjusting the governor position, which repositions the fuel - metering valve in the FCU
How does the FCU control engine power?
Maintains the requested N1 rpm through the N1 governor
What governor protects against power turbine overspeed?
The fuel topping governor
What does the fuel topping governor do to reduce fuel flow if the propeller goes beyond 106%?
Vents air
With the props in reverse, what percent is the fuel-topping governor restricting fuel flow to?
95% of requested propeller rpm
What are the 2 divisions of the ignition system?
Starting ignition and auto ignition
Starting position has 3 positions - ON - OFF - STARTER
What does is it do when it’s ON?
What does it do when it’s on STARTER?
ON - provides engine cranking and ignition operation
STARTER - provides for engine motoring, igniters do not function here
When auto ignition is armed, when will the system kick in?
If engine torque drops to 400 ft-lbs or less
It prevents flameout if loss of power was caused by a momentary fuel or air interruption
What indications should be on to show that they igniters are receiving power?
Green annunciations of L & R IGNITION ON
What is unfeathering and reversing controlled by?
Hydraulic (engine oil) pressure developed by a high-pressure oil pump
Three conditions of a propeller governor:
Onspeed
Overspeed
Under speed
What is onspeed?
Selected rpm and actual rpm are the same
What is overspeed?
Actual rpm is greater than selected rpm
What is under speed?
Actual rpm is less than selected rpm
What is rpm controlled by? How does it work?
The propeller governor, it balances two forces - speeder spring force and fly weight force
What is the speeder spring force adjusted by?
The propeller control lever
What is flyweight force controlled by?
The propeller rpm through a reduction gear section
If the speeder spring force is greater than flyweight force, the propeller would be in a under speed condition
If the flyweight force is greater than speeder spring force, the propeller would be operating in an overspeed condition
If speeder spring and flyweight force is equal, propeller is in onspeed on condition.
What’s the normal rpm range of the primary governor?
1,600-2,000 rpm
What’s the purpose of the overspeed governor?
For if the primary governor failed to limit rpm to 2,000(100%) it would limit the rpm to 2,120 (106%)
When the prop governor switch is moved to TEST, what is the new value of the overspeed governors range?
1,830-1,910rpm
If a propeller were to have a mechanical failure & lock or stick, it would not respond to oil pressure. What is used as a countermeasure to adjust the blade angle in the case this occurs?
The fuel topping governor
What does the FTG (fuel topping governor) do?
Reduces fuel flow, which in turn reduces propeller rpm
Which governors flyweights must still be operating to let the fuel topping governor work?
The primary governors
What is the maximum allowable propeller speed in reverse?
1,900rpm
What part of the engine is the condition levers connected to?
The FCU
What percent N1 is low idle with the condition levers? High idle?
Low - 61% N1
High - 70% N1
What are the torque limits?
2,368-2,447 ft lbs
How does the torque limiter work?
It bleeds off and changes the pneumatic servo pressures in the FCU, which reduces metered fuel flow and gas generator power to the preset limit of the torque limiter
Does the torque limiter stop the pilot from exceeding the max torque of 2,230?
No, it’s just protecting the nose gearbox and reduction gearing from excessive torque
What causes a propeller to move to higher pitch?
Low oil pressure, and the centrifugal counterweights and spring forces
How does autofeather work?
It opens a solenoid on the affected propellers overspeed governor and dumps out all of the oil. Counterweights and feather springs feather the prop.
When arming the autofeather, what N1 is required to make the switches close?
90% N1
When will the autofeather annunciation illuminate?
When the engines torque is over 400 ft-lbs
How many torque sensitive switches are there for each engine within the autofeather system?
2
When do the torque sensitive switches close in the autofeather system?
At 400 ft-lbs of torque and then the second switch on each engine closes at 200 ft-lbs
For autofeather operation, at what torque setting will the dump valve on the overspeed governor open and dump oil to produce feather?
Falling between 200 ft-lbs
When will the autofeather light extinguish?
When the propeller goes into feather from torque falling below 200 ft-lbs
When testing the autofeather, what should be the indications you’re looking for?
When reducing power below 400 ft-lbs on one engine, the opposite engine autofeather light should extinguish. As power is continued to decrease through 200 ft-lbs, the other autofeather light extinguishes then will begin to flash as the feather/unfeather cycle begins.
Does the propeller fully feather during autofeather test?
No because the engine is still producing torque
Why would autofeather not be able to reduce torque below 200 ft-lbs if condition levers aren’t in LOW IDLE?
Engine still producing more than 200 ft-lbs
Where does the oil get dumped to during the autofeather sequence?
The reduction gear case
