Powerplant Flashcards
What type of engine is provided?
PT6A-21 free shaft turbine rated at 550SHP
What are the type of propellers provided?
4 bladed, full-feathering, reversing, variable-pitch
What do the propellers do when the engines are shutdown?
They go into a full feather
How is engine power measured on turboprops?
Equivalent shaft horsepower (ESHP) and shaft horsepower (SHP)
How is SHP determined?
By propeller RPM and torque applied to turn the propeller shaft
What is ESHP?
It is the total power delivered, including the jet thrust
PT6A-21 specs
Page 140
What is N1?
Gas generator rpm is percent of turbine speed
N2
Propeller rpm
Nf
Power turbine rpm - not indicated on engine instruments
P3
Air pressure at station 3 (bleed air source)
ITT
Interstage turbine temperature in degrees of temperature at station 5
How many turbine sections are there? What are they?
2, compressor turbine and the power turbine
What does the compressor turbine do?
Drives the engine compressor and accessories
What does the power turbine do?
Drives the power section and the propeller
Is the power turbine and compressor physically connected?
No
How are the turbines mounted?
On separate shafts and are driven in opposite directions by the gas flow across them
What does “reverse flow” refer to?
Refers to airflow through the engine
Where does air enter the engine?
At the aft end of engine
Where is the exhaust released?
At the front of the engines
How many fuel injection nozzles are there in the combustion chamber?
14
How does the power turbine drive the propeller?
Through a reduction gearbox
What is ITT?
The temperatures of air between the compressor turbine and the power turbine at engine station 5
When is bleed air taken off the engine?
After the centrifugal compressor stage and prior to entering the combustion chamber
How many modules is the engine divided into? What are they?
2, a gas generator section and a power section
What does the gas generator section do?
Draws air into the engine, adds energy in the form of burning fuel, and produces necessary gases to drive the compressor and power turbine
What is the power sections job of the engine?
Converts gas flow from the gas generator into mechanical action to drive the propeller - which is done through a planetary gearbox
What does the planetary gearbox do in the power section of the engine?
Converts high speed and low torque to low speed and high torque to the propeller. The reduction ratio from the power turbine shaft rpm to propeller rpm is 15:1.
What’s the purpose of the compressor bleed valve?
Prevent compressor stalls and surfers in the low N1 rpm range (75%-80% N1)
When is the compressor bleed valve opened? When does it close?
It is open when N1 is low. It closes when at takeoff and cruise N1 rpm, above approximately 80%.
If it sticks closed, a compressor stall will occur. If it sticks open, ITT will be noticeably higher as power is advanced above 80% N1.
What are the positions of the igniters?
ON, OFF, and STARTER ONLY
What does the ON position do on the starters?
It activates both the starter and the igniters
What does the STARTER ONLY position do on the starter?
It only provides motoring to clear the engine of unburned fuel. No ignition occurs in this position.
How many igniters does the combustion chamber have?
2, but it only starts with 1 just in-case one is open or shorted, the remaining igniter will continue to function
What happens to the igniters once the engine is started?
They de-energize since combustion is self-sustaining.
What is the backup function for emergencies that the ignition system offers?
Auto ignition.
If engine torque falls below 400 ft-lb, the igniter will automatically energize, attempting to restart the engine. The IGNITION ON annunciator will be illuminated
What does the spark ignition system consist of?
Ignition-exciter & 2 spark igniters
What are the 2 functions of the lubrication system?
Cool and lubricate the engine bearings and bushings, and provide oil to the propeller governor and propeller reversing control system
What is the capacity of the engine oil system?
3.5 gallons, including the 2.3 gallon oil tank
Max oil consumption: 1 qt. every 10 hours
Normal oil consumption: 1 qt every 50 hours of operation
What does the magnetic chip detector do?
It alerts the pilot of oil contamination. It will pop up on the annunciation panel of L CHIP DETECT or R CHIP DETECT
If you get the CHIP DETECT annunciation, what do you need to do?
Shut off the engine to prevent serious internal damage
What are the components of the engine fuel system?
Electric low pressure boost pump, oil to fuel heat exchanger, high pressure fuel pump, fuel control unit, fuel cutoff valve, flow divider, and dual fuel manifold with 14 simplex nozzles
What would happen to the minimum pressurizing valve in the fuel control unit should the high pressure pump fail?
The valve will close and the engine will flame out
While starting the engine, fuel initially flows through the __________ to the 10 primary fuel nozzles in the combustion chamber. As the engine accelerates through ____ %N1, fuel pressure is sufficient to open the flow divider to the secondary _______ fuel nozzles.
Flow divider, 40%, 4
What does the primary and secondary fuel nozzle operation provide?
Cooler starts
What is there a noticeable increase of when the secondary nozzles are activated?
ITT
What’s the primary purpose of the FCU (fuel control unit)?
To meter proper fuel amounts to the fuel nozzles in all modes of operation
What does the prop lever adjust?
The prop governor to the desired prop speed
How does the prop governor maintain a set speed?
Varying the blade angle
What is torque controlled by?
The power lever acting on the N1 governor
What happens when the power lever is advanced?
The N1 governor causes the FCU to increase fuel flow, resulting in increase in engine speed
What limits the engine at cold temperatures or low altitude?
What limits the engine at hot temperature or high altitude?
Torque limits power
ITT limits power
*Whichever limit is reached first, determines the available power
What is the normal operating ITT range?
400-695 c
What is the max ITT starting temperature?
1,090 c limited to 2 seconds
What is the max permissible sustained torque?
1315 ft-lb
What is the transient torque limit?
1,500 ft-lb, limited to 2 seconds
What does the N1 gas generator tachometer measure?
The rotational speed of the compressor shaft in percent of RPM, based on 37,500 at 100%
What is the max continuous generator speed?
38,100 percent which is 101.5% on the N1.
Transient: 102.6%, 38,500 rpm, is time limited to 2 seconds
What are the 3 ranges the power levers have?
Flight, beta (ground fine), reverse
On the condition levers, what is the gas generator (N1) speed at low idle?
51%
What is the N1 speed at high idle?
70%
What is the normal governing range for the propellers?
1,800-2,200 RPM
Why do the props feather when the engine is shut down?
Loss of oil pressure in the dome
At any N1 below 70%, what is the ITT idle restriction?
660 C, if it is observed, then the generator load need be reduced and N1 speed increased before reintroducing a load on the engines
At N1 speeds above 70%, the 660 C restriction is removed, as airflow is sufficient through the engine
What is propeller pitch controlled by?
Engine oil pressure boosted through a governor pump integral within the propeller governor
What moves the propeller blades toward high pitch and into the feathered position?
Centrifugal counterweights and feathering springs
What would happen without the oil pressure to counteract the counterweights and feathering springs?
The propeller would move into feather
How is the low pitch propeller position determined?
By the primary low pitch stop, which is a mechanically actuated hydraulic stop
What controls the propeller rpm?
Two governors: A primary governor and a backup overspeed governor
What does the overspeed governor limit the propeller RPM to if the the primary governor malfunctions?
2,288rpm
What is the advantage of having 4 bladed propellers?
They have lower tip speeds, which generates less noise
What is the purpose of the primary governor?
Converts a variable-pitch propeller into a constant speed propeller
What is the range of the primary governor?
1,800-2,200RPM
What is the overspeed condition? How is it adjusted to the on speed condition?
Airplane trimmed down with no decrease in power, the airspeed increases. The blade angle of the propeller is decreased, creating less drag, increasing its rpm.
The governor increases blade angle to a higher pitch, which slows it back to the on speed condition.
What is the under speed condition? How is it fixed to go back to the onspeed condition?
Airplane goes from cruise to climb without a increase in power, the propeller rpm will decrease.
It will fix by decreasing the blade angle to a lower pitch, allowing the rpm to increase back to the original value.
Give an example of when the primary governor can’t maintain the selected RPM.
What stops the propeller blades from selecting blade angles too low for safety?
Airplane approaching to land with the governor set at 1,900rpm. As power and airspeed are reduced, the under speed condition will exist which will cause the governor to decrease blade angle to restore the on speed condition.
A low pitch stop. When it’s reached, the blade angle becomes fixed and cannot continue to a lower pitch. Therefore; the governor is incapable of restoring the onspeed condition and the propeller rpm falls below the selected governor rpm setting.
What are the functions of the primary governor?
Can select any constant prop rpm and can feather the propeller
If the flyweights are slow, how is the pilot valve positioned?
Lower
If the flyweights are spinning fast, how is the pilot valve positioned?
Raises
What does the pilot valve do?
Determines the amount of oil pressure that’s being sent to the propeller pitch mechanism
What does it mean when the propeller rpm is below the selected governor rpm?
The prop blade angle is at the low pitch stop
What is the low pitch stop also know as?
The “Beta” valve
What is the low pitch stop controlled by?
The power lever, bringing the power lever aft of idle progressive repositions the stop to lesser blade angles
Before reversing can take place, where must the propeller be?
On the low pitch stop
What is the ground fine range?
+12 to +3, and the engines compressor speed (N1) remains at the value it had when the power lever was at IDLE
What does the low pitch stop use to control propeller blade angle?
Mechanical linkage
When the power lever is moved from idle to reverse range, what happens to the beta valve?
It is positioned to direct governor oil pressure to the propeller piston, decreasing the blade angle through 0 into a negative range
When feathering occurs, what does the pilot valve do?
It rises, allowing all oil pressure to be released from the propeller pitch mechanism allowing it to move to feather
Can the prop be feathered during engine operation? Why?
Yes because the prop shaft and N1 shaft are not connected
What is the max N1 reverse?
88%
What does the overspeed governor do?
Provides protection against excessive propeller speed in the event of primary governor malfunction
If an overspeeding propellers speed reaches 2,288 rpm, the overspeed governor would control the __ ______ and the _______ to prevent the rpm from continuing its rise.
Oil pressure and pitch
What condition could occur if the primary governor failed?
An overspeed condition
What is the fuel topping governor?
It is a fail safe for an overspeed condition - it will limit prop rpm by decreasing the pneumatic pressure to the FCU, reducing fuel flow and engine speed as means of controlling prop rpm
What is the stipulation for the fuel topping governor working?
Will only prevent an overspeed if the primary governors flyweights are still operational
What does the auto feather system provide?
A means of immediately dumping oil pressure from the prop hub, thus enabling the feathering spring and counterweights to start the feathering action of the blades in the event of an engine failure
When is autofeather armed?
When both power levers are advanced above 90% N1
When is the systems use designed for?
Takeoff, climb, and missed approach - should be turned off during cruise
When else will the autofeather take place?
If the oil pressure drops below a selected amount
What is the type of prop sync?
Type 2
