ASA Powerplant Orals Exam 2024 | ASA
Power Plant Orals Exam Update Latest
2024 Questions and Correct Answers
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What is the main advantage of a horizontally opposed engine over a
radial engine for powering modern aircraft? -ANSWER-The
horizontally opposed engine has a much smaller frontal area and is
easier to streamline than a radial engine
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 of the other pistons are connected to the master rod
with link rods
Of what material are most piston rings made? -ANSWER-Gray cast
iron
What is the reason for using hydraulic valve lifters in an aircraft
engine? -ANSWER-Hydraulic valve lifters keep all of the clearance out
of the valve operating mechanism. This decreases the wear of the
valve train components
At what speed does the camshaft turn, relative to the crankshaft
speed in a horizontally opposed engine? -ANSWER-The camshaft
turns at one half of the crankshaft speed
,What kind of main bearings are used in a horizontally opposed
engine? -ANSWER-Steel-backed, lead-alloy bearing inserts
On what stroke is the piston of a reciprocating engine when the intake
valve begins to open? -ANSWER-On the exhaust stroke
On what stroke is the piston of a reciprocating engine when the
exhaust valve begins to open? -ANSWER-On the power stroke
Why are both the hot and cold valve clearances give for most radial
engine? -ANSWER-The hot clearance is given for valve timing
purposes. The timing is adjusted with the valves in cylinder number
one, set with the hot clearance. When the timing is set, all of the
valves are adjusted to their cold clearance.
What is meant by a cam-ground piston? -ANSWER-A piston that is
not perfectly round. Its dimension parallel with the wrist pin is several
thousandths of an inch less than its dimension perpendicular to the
wrist pin. When the piston reaches operating temperature, the metal in
the piston pin boss expands enough that the piston becomes perfectly
round
Where is the piston in a reciprocating engine when the ignition spark
occurs? -ANSWER-About 30 degrees of crankshaft rotation before the
piston reaches top center on the compression stroke
What is meant by a full-floating wrist pin? -ANSWER-A wrist pin that is
not clamped in either the piston or the connecting rod. Full-floating
wrist pins are kept from scoring the cylinder walls by soft metal plugs
in their ends
,Why do most aircraft reciprocating engines use more than one spring
on each valve? -ANSWER-By using more than one spring and having
the wire diameter and pitch of the springs different, valve float is
minimized. The springs have different resonant frequencies, so at
least one spring will always be exerting a force on the valve
Would excessive valve clearance cause the valves to open early or
late? -ANSWER-Excessive clearance will cause the valve to open late
and 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 rings, oil control rings,
and oil wiper rings
Why are some exhaust valves partially filled with metallic sodium? -
ANSWER-The metallic sodium melts at engine operating temperature
and sloshes back and forth inside the hollow valve. 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 causes the fuel-air mixture to
reach its critical pressure and temperature. Under these conditions,
the mixture explodes rather than burns. This explosion is called
detonation
, Why is a compression check important for determining the condition of
an aircraft reciprocating engine? -ANSWER-A compression check can
determine the condition of the seal between the piston rings and the
cylinder walls, and the seal between the intake and exhaust valves
and their seats
What is meant by the compression ratio of a reciprocating engine? -
ANSWER-The ratio of the volume of the cylinder with the piston at the
bottom of its stroke to the volume with the piston at the top of its
stroke
What are the two basic sections of a turbine engine? -ANSWER-The
hot section and the cold section
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-The stators convert some velocity energy into pressure
energy and change the direction of the air so it is proper for the next
stage of rotors
What are three types of combustors used on aircraft turbine engines?
-ANSWER-Can-type, annular-type, and can-annular-type
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-The turbine nozzle directs the hot gases as they
leave the combustors so they will turn the turbine wheel with
maximum efficiency
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