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Terms in this set (52)
1. What is the relation between static and dynamic pressure?
a. Static pressure + Dynamic pressure = Total pressure
b. If static pressure decreases, dynamic pressure increases
2. Bernoulli's theorem?
a. Any incompressible fluid passes through a convergent opening is velocity increases and pressure decreases
3. Brayton's principle?
a. Consists of 4 events occurring simultaneously: intake, compression, combustion, and exhaust
4. Convergent Openings
a. Subsonic - velocity increases, pressure decreases
b. Supersonic - velocity decreases, pressure increases
5. Divergent openings
a. Subsonic - velocity decreases, pressure increases
b. Supersonic - velocity increases, pressure decreases
6. Effect of altitude on thrust?
a. With an increase in altitude, rate of thrust decreases because a pressure drop is greater than the thrust increase resulting from a temperature drop
7. How is SHP (shaft horsepower) read?
1. What does the inlet duct do?
a. Increase pressure, while decreasing velocity of incoming air
b. Deliver uniform turbulence free air to the first stage of the compressor
2. What does a variable geometry inlet duct allow?
a. Change the shape of the inlet duct as the aircraft speed varies between subsonic and supersonic
b. At subsonic speeds will be divergent
c. At supersonic speeds will be convergent/divergent
d. Attempts to increase pressure while decreasing velocity
3. What does the burner section do?
a. Contains the combustion chamber, and provides the means for proper mixing of the fuel and air to assure good combustion
b. 25% of the air is mixed with fuel for combustion
4. How much energy goes to thrust in a gas turbine engine?
a. 75% used in the turbine section, 25% used for thrust by accelerating gases out the exhaust section
5. What does the Fir tree design do?
a. Prevents the thin metal blades from cracking at the attachment points by allowing them to expand or creep when heated
6. What is the job of the exhaust section?
a. To direct the flow of hot gases rearward to cause a high exit velocity to the gases while preventing turbulence
b. Convergent for subsonic engines
c. Convergent/Divergent for supersonic engines
7. What does the flame holder do?
a. Provides a region in which airflow velocity is reduced and turbulent eddies are formed to allow proper fuel air mixing in the afterburner section
8. What are screech liners and what do they do?
a. Generally corrugated and perforated with thousands of holes that allow the liner to reduce pressure fluctuations and vibrations by acting as a form of shock absorber.
b. Cannada - shock absorber for violent pressure fluctuations and cyclic vibrations
1. Factor(s) causing a compressor stall?
a. When AOA of compressor blades is too high, causing them to no longer be able to create a pressure differential
i. This is the AOA between the relative wind and the chord line of the rotor blade.
b. Airflow distortions and mechanical malfunctions
c. Abrupt change in aircraft altitude
d. Air turbulence
e. Deficiency of air velocity or volume, caused by atmospheric conditions
f. Rapid throttle movement
2. What are the indications of a compressor stall?
a. Engine pulsations
b. RPM decay
c. Interstage turbine temperature rise
d. Possible loud noises
3. What are the 4 mechanical functions that cause a compressor stall?
a. Variable inlet guide vane and stator vane - fail to change AOA
b. Fuel control unit - too much/too little fuel
c. Foreign Object Damage
d. Variable exhaust nozzle
1. What parts make a turbojet?
a. Simplest form of gas turbine engine. Constructed by the addition of an inlet of an exhaust section to the basic gas generator.
2. What engine does cargo planes use and why?
a. Turbofan, higher bypass rate gives it a lower TSFC; using less fuel for the same amount of thrust
3. To produce the same amount of thrust, does a turbofan or turbojet use more fuel?
a. Turbojet's lower bypass rate gives it a higher thrust specific fuel consumption
1. How is a turboprop moving us forward?
a. Imparts a small amount of acceleration to a large mass of air
2. How is pitch changed on a turboprop?
a. Moving the PCL
b. Pitch change/dome assembly
3. What does the Reduction Gear Box do?
a. Prevents propeller blades from reaching supersonic speed. Converts high RPM/low torque from the gas generator to low RPM/high torque necessary for efficient propeller operation
b. Slows rotation around to a manageable level - 12000RPM to 2000RPM
4. How much propulsive force is produced from a turboshaft's exhaust?
1. What does a hydraulic system do for us?
a. Provide extra power and mechanical advantage over control surfaces
2. What is Pascal's Law on force applied to a liquid?
a. Pressure applied to a confined liquid is transmitted equally in all directions without the loss of pressure and acts with equal force on equal surfaces.
3. What is the main purpose of the hydraulic system?
a. To multiply force
4. What are the different systems in the hydraulic system?
a. Power control system (flight controls)
b. Utility system (flaps, gear, wheel brakes)
c. Each system consists of a reservoir, pump, and distribution lines
6. What does the check valve do during shut down?
a. Works with the accumulator to maintain system pressure
7. What does the accumulator do?
a. Shock absorber for the hydraulic system - air nitrogen mixture
b. Dampen pressure fluctuations
c. Supplement pump output when the pump is under pressure
d. Enough fluid is held under pressure for one time emergency use
1. What are the sources of AC power?
a. AC generators/ alternators
2. What does a turbojet and turbofan use to ensure steady voltage output?
a. Constant speed drive - ensures there is constant rotational/voltage input regardless of PCL input
3. What transforms AC current into DC current?
a. Transformer rectifier
1. What fuel is safe for use onboard naval ships?
a. JP-5 - very high flash point, very low volatility (ability to vaporize)
2. What are the design considerations for modern aircraft?
a. High rate fuel flow - main concern
b. Also consider
i. Low atmospheric pressure
ii. Piping system complexity
iii. Weight and size constraints
iv. Vapor loss resulting in decreased range
v. Cold weather starting
3. What does a boost pump do?
a. Prevents aeration of the fuel supply at altitude
b. Ensures adequate supply of fuel
4. What is the FCU and what does it work off of?
a. Fuel control unit
b. Pilot input through PCL
i. Compressor inlet temp
ii. RPM - compressor speed
iii. Turbine temp
5. What is the fuel flow meter?
a. How many lbs/hr are you burning - delivers the information to the fuel flow gauge
b. Located before the fuel oil heat exchanger
6. What does the Fuel-oil cooler do?
a. Pre-heats fuel to eliminate ice crystals increase volatility to facilitate efficient fuel ignition
7. What is the Afterburner control unit?
a. Meters fuel to the afterburner spray bars
1. What is viscosity?
a. Resistance to flow
2. What does the weighted swivel outlet assembly do?
a. Gravity keeps it submerged during maneuvers and G-loads to ensure oil pick up is always immersed in the oil
3. What does the oil pressure release valve do?
a. Limit max pressure in pressure line
b. Bypasses oil back to the pump inlet
4. What does the oil temperature regulator valve do?
a. Thermostatically operated to direct flow of oil either through or past the heat exchanger
b. If the oil is not hot enough for the heat exchanger it is bypassed to the reservoir
5. What does the breather pressurizing valve do?
a. Maintain pressure at 29.92 in the scavenge system and oil tank, open at sea level conditions
1. What are the types of bleed air?
a. Low, high, interstage
2. What is interstage bleed air used for?
a. Compressor stability
b. Ducted overboard to prevent compressor stalls during low thrust operations
3. What is the purpose of the starter?
a. Accelerate the engine until the turbine is producing enough power to accelerate the engine itself
4. What are the four starter errors?
a. Hot, wet, hung, false
5. What is the most dangerous starter error?
a. Wet - fuel oil mixture does not ignite initially, but has the capability to ignite eventually
b. Excess fuel in combustion chamber prior to ignition
6. What are the types of ignitors?
i. Annular gap - plug protrudes slightly into the combustion chamber liner - most common
ii. Constrained gap - plug slightly outside of combustion chamber - arc jumps beyond chamber line for ignition - works at cooler temp
This set is often in folders with...
HATLEY - SMALL ENGINES - COOLING SYSTEM
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