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ASA POWERPLANT ORALS FINAL EXAM
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ASA POWERPLANT ORALS FINAL EXAM
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ASA POWERPLANT ORALS FINAL EXAMWhat is the main advantage of a horizontally opposed engine over a radial engine for
powering modern aircraft? - ANSWER smaller frontal area and easier to streamline.
How many throws are there in the crankshaft of a six-cylinder horizontally opposed
engine? - ANSWER six
What kind of connecting rod arrangement is used in a radial engine? - ANSWER a
master rod connects the single throw of the crankshaft with a piston. all other pistons
are connected to the master rod with link rods
Of what material are most piston rings made? - ANSWER grey cast iron
What is the reason for using hydraulic valve lifters in an aircraft engine? - ANSWER
keep all of the clearance out of the valve operating mechanism, decreases wear of
valve train components
At what speed does the camshaft turn, relative to the crankshaft speed in a
horizontally opposed engine? - ANSWER camshaft is one half the speed of
crankshaft
What kind of main bearings are used in a horizontally opposed engine? - ANSWER
steel backed lead alloy bearings
On what stroke is the piston of a reciprocating engine when the intake valve begins
to open? - ANSWER exhaust
On what stroke is the piston of a reciprocating engine when the exhaust valve begins
to open? - ANSWER power
Why are both the hot and cold valve clearances given for most radial engines? -
ANSWER hot clearance is for valve timing. timing adjusted with valves in cylinder 1
set with hot clearance then adjusted to cold clearance
What is meant by a cam-ground piston - ANSWER A piston that is not perfectly
round. . When the piston reaches operating temperature, the metal expands enough
that the piston becomes perfectly round.
Where is the piston in a reciprocating engine when the ignition spark occurs? -
ANSWER before top dead center on the compression stroke
What is meant by a full-floating wrist pin? - ANSWER pin not clamped in either
piston or connecting rod
Why do most aircraft reciprocating engines use more than one spring on each valve?
- ANSWER for different frequencies/rpms
,Would excessive valve clearance cause the valves to open early or late? - ANSWER
open late close early
What is the purpose of valve overlap in a reciprocating engine? - ANSWER Valve
overlap allows the inertia of the exhaust gases leaving the cylinder to help the fresh
induction charge start flowing into the cylinder.
What type of piston rings are installed on the pistons of an aircraft reciprocating
engine? - ANSWER compression, oil control, oil wiper
Why are some exhaust valves partially filled with metallic sodium? - ANSWER The
metallic sodium melts at engine operating temperature It picks up heat from the
valve head and transfers it into the valve stem, so it can be transferred to the
cylinder head through the valve guide
What causes detonation in an aircraft engine? - ANSWER Excessive heat and
pressure in the engine cylinder , the mixture explodes rather than burns.
Why is a compression check important for determining the condition of an aircraft
reciprocating engine? - ANSWER to check condition of seals between piston ring
and cylinder wall and valves and thier seats
What is meant by the compression ratio of a reciprocating engine? - ANSWER ratio
of volume of cylinder with piston at bottom vs piston at top
What are the two basic sections of a turbine engine? - ANSWER hot and cold
What are the two basic types of compressors that are used in aircraft turbine
engines? - ANSWER axial flow and centrifugal
What is the purpose of the stators in an axial-flow compressor? - ANSWER convert
velocity energy to pressure energy and change direction of air
What are three types of combustors used on aircraft turbine engines? - ANSWER
can, annular, can-annular
How many igniters are there normally in an aircraft turbine engine? - ANSWER two
What is the main purpose of the turbine nozzle in an aircraft turbine engine? -
ANSWER direct gasses as they leave combustors so they will turn turbine wheel
with maximum efficiency
What is meant by a free-turbine turboshaft engine - ANSWER A turboshaft engine
that has a turbine wheel, that is not used to drive the compressor of the gas
generator section of the engine. This free turbine drives the propeller in a turboprop
engine or the transmission and rotor of a helicopter.
Why do some axial-flow turbine engines have more than one set of turbines and
compressors - ANSWER A two-spool turbine engine has a low-pressure and a high-
, pressure compressor, each driven by its own turbine. The two independent systems
operate at the speed at which they are most efficient.
What kind of bearings are used to support the rotor shaft of an aircraft turbine engine
- ANSWER anti fiction, ball, roller
What is meant by a turbofan engine - ANSWER An axial-flow turbine engine in
which the first stage of compressor blades are lengthened, so they can force air
around the outside of the gas generator portion of the engine.
11. Where can you find the limits of repair allowed for the compressor blades of an
aircraft turbine engine? - ANSWER manufacturer service manual
Why is it important that a turbojet engine be allowed to cool before it is shut down
after it has been operated at a high power setting? - ANSWER If the engine is shut
down while it is hot, there is a possibility that the shroud will contract around the
turbine wheel and seize the rotor.
13. What is meant by a hung start in a turbine engine? - ANSWER A start in which
ignition occurs, but the engine does not accelerate to proper speed
What is meant by a hot start in a turbine engine? - ANSWER A start in which ignition
occurs, but the internal temperatures are too high
What is meant by creep of the turbine blades? - ANSWER permanent elongation of
the turbine blades. caused by the high temperatures and the high centrifugal loading
How is the compressor of a turbine engine cleaned? - ANSWER emulsion-type
cleaner is sprayed through the engine while it is being motored by the starter or
operated at a low speed. The wash is followed by a clean water rinse. .More
vigorous cleaning is done by injecting a mild abrasive, such as ground-up apricot pits
or walnut shells, into the engine while it is operating at low speed
Where is water injected into a turbine engine for cooling purposes? - ANSWER
compressor inlet & diffuser case
At what point in a turbine engine is the temperature the highest? - ANSWER inlet to
high pressure turbine
What is the function of the interconnect tubes between the cans of a turbine engine
that uses can-type combustors? - ANSWER These tubes allow the flame to travel
from the cans that contain the igniters to all of the other cans when the engine is
being started.
What are two types of thrust reversers that are used on turbojet engines? -
ANSWER mechanical blockage, aerodynamic blockage
What is meant by trimming a turbojet engine? - ANSWER Adjusting the fuel control
to get the correct idling and maximum-thrust RPM.
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