Engines- Study Questions Flashcards
Why are liquid lubricants the best type for use in gas turbine engines
they effectively dissapate heat
What is the designation of the most common synthetic oil used by the military?
The most common synthetic oil used by the military is
MIL-L-23699
what is the main advantage of a dry sump system?
The main advantage of a dry sump system (from the book)
temperature/viscosity can be better regulated
instructor also mentioned that another advantage is that the dry sump system can still function when upside down, banked turns
What does an oil reservoir contain to ensre a constant oil supply during all flight altitudes and G loads?
weighted swivel outlet assembly
what are the two functions of pumps used in the lubrication system?
the two functions of pumps
to supply oil under pressure and to scavenge oil
Where is oil pressure monitored? Why?
monitored after the oil pump. it can indicate an oil pump malfunction
Where is the oil temperature regulator valve located and what does it do?
the oil temperature regulator valve is located at entrance of the fuel-oil heat exchanger.
It directs flow of oil either through or past the heat exchanger
Where is oil temperature monitored?
oil temperature is monitored prior to entrance to the engine bearing compartments
Where would you find the hottest air: the high or low pressure compressor?
you would find the hottest air at the high pressure compressor
Why do you want the starter to remain engaged after you’ve reached self-accelerating speed?
you want the starter to remain engaged to decrease the potential of an abnormal start by reaching normal idle RPM
How does a gas turbine produce thrust?
a gas turbine produces thrust by rapidly compressing, heating, and accelerating a large quantity (mass) of air and fuel
What happens to the velocity of the gasses as they pass through the compressor section? The burner section? The turbines?
The velocity of gasses
remains constant in the compressor
increases in the burner and turbine sections
when is gross thrust equal to net thrust?
gross thrust = net thrust when the aircraft is in a static position and standard day conditions
What is the optimum cruise altitude?
why?
36,000 ft
this is the altitude where the thrust availble plus low fuel flow and diminished drag combine to provide optimum performance for many engines
*36,000 ft is the isothermal layer
Why do rotor and stator vanes within an axial compressor decrease in length from the front to the rear of the compressor?
the cross sectional area decreases within the compressure to allow the velocity to remain fairly constant as the pressure increases. Therefore, the rotor and stator length will decrease
What are the criteria for a good burner section?
a good burner section will:
minimize pressure loss
high combustion efficiency
constant flame (doesn’t burn out)
contain the total combustion process
what is the purpose of the turbine?
to turn the compressor and accessories
What controls the amount of thrust augmentation an afterburner will produce?
fuel
the more fuel is introduced the more thrust is produced
What type of nozzle is used on an afterburner equipped aircraft?
variable exhaust nozzle
Other than mechanical malfunctions, what causes most stalls?
Airflow distortions
what determines the AOA on a compressor blade
the angle between the chordline of the rotors and the relative wind.
Relative wind is comprised of the compressor RPM and the inlet airflow
What automatically compensates for acceleration and deceleration schedules to help prevent stalls?
FCU
What should be done if a stall can not be controlled?
Execute engine failure procedures
What two ways may the fan be driven in a turbofan engine?
Free power turbine or through the gas generator turbine
How much thrust is produced by the fan on a turbofan?
gas generator?
fan: 30%-60%
gas generator: 40%-70%
What component produces the majority of thrust in a turboprop?
90% of thrust is produced by the prop
What is a free power turbine?
A turbine that is not mechanically connected to the compressor and aft of the gas generator turbines
Changing the position of the selector valve will have what effect on the movement of fluid in the hydraulic system?
it will reverse the flow of hydraulic fluid, changing the direction of travel to the actuator
What provides a constant rotational input to the generator regardless of engine rpm?
Constant Speed Drive
Which bus provides power to safety of flight components?
Essential bus
What is the main provider of power to the AC Busses?
AC Generator
What bus charges the battery?
DC essential bus
How does temperature change volitility? flashpoint?
temperature increases volitility
Trick question! It doesn’t change the flash point…. that is always set.
How does the pilot communicate with the Fuel Control Unit?
Through the PCL
What does the FCU monitor to ensure the proper amount of fuel is delivered to the combustion section?
PCL input
Compressor inlet temperature
ITT
RPM
What does the FCU do during engine start?
the FCU sends a signal to close the dump valve at engine start
What is the position of the pressurizing and dump valve during an engine start? normal operation? shutdown?
engine start: both closed
normal operation: dump valve closed, pressurizing valve open
shutdown: dump valve open, pressurizing valve closed
