ASA Powerplant Oral Exam Questions with Correct Answers 100% Verified By Experts| Latest
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What is the main advantage of a horizontally opposed engine over a radial engine for powering
modern aircraft? 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?
Six
What kind of connecting rod arrangement is used in a radial engine? 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? Gray cast iron
What is the reason for using hydraulic valve lifters in an aircraft engine? 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? The camshaft turns at one half of the crankshaft speed
What kind of main bearings are used in a horizontally opposed engine? Steel-backed, lead-
alloy bearing inserts
On what stroke is the piston of a reciprocating engine when the intake valve begins to open?
On the exhaust stroke
On what stroke is the piston of a reciprocating engine when the exhaust valve begins to open?
On the power stroke
,Why are both the hot and cold valve clearances give for most radial engine? 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? 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? 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? 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? 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? Excessive clearance
will cause the valve to open late and close early
What is the purpose of valve overlap in a reciprocating engine? 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?
Compression rings, oil control rings, and oil wiper rings
,Why are some exhaust valves partially filled with metallic sodium? 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? 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? 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? 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? The hot section and the cold section
What are the two basic types of compressors that are used in aircraft turbine engines? Axial-
flow and centrifugal
What is the purpose of the stators in an axial-flow compressor? 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? Can-type, annular-
type, and can-annular-type
How many igniters are there normally in an aircraft turbine engine? Two
, What is the main purpose of the turbine nozzle in an aircraft turbine engine? The turbine
nozzle directs the hot gases as they leave the combustors so they will turn the turbine wheel
with maximum efficiency
What is meant by a free-turbine turboshaft engine? A turboshaft engine that has a turbine
wheel, or stage of turbine wheels, 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?
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? Anti-
friction bearings, such as ball bearings or roller bearings
What is meant by a turbofan engine? 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
Where can you find the limits of repair allowed for the compressor blades of an aircraft turbine
engine? In the FAA-approved service manual issued by the manufacturer of the engine
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? If the engine is shut down while it is hot, there is a
possiblity that the shroud will contract around the turbine wheel and seize the rotor
What is meant by a hung start in a turbine engine? A start in which ignition occurs, but the
engine does not accelerate to a self-sustaining speed
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What is the main advantage of a horizontally opposed engine over a radial engine for powering
modern aircraft? 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?
Six
What kind of connecting rod arrangement is used in a radial engine? 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? Gray cast iron
What is the reason for using hydraulic valve lifters in an aircraft engine? 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? The camshaft turns at one half of the crankshaft speed
What kind of main bearings are used in a horizontally opposed engine? Steel-backed, lead-
alloy bearing inserts
On what stroke is the piston of a reciprocating engine when the intake valve begins to open?
On the exhaust stroke
On what stroke is the piston of a reciprocating engine when the exhaust valve begins to open?
On the power stroke
,Why are both the hot and cold valve clearances give for most radial engine? 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? 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? 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? 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? 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? Excessive clearance
will cause the valve to open late and close early
What is the purpose of valve overlap in a reciprocating engine? 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?
Compression rings, oil control rings, and oil wiper rings
,Why are some exhaust valves partially filled with metallic sodium? 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? 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? 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? 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? The hot section and the cold section
What are the two basic types of compressors that are used in aircraft turbine engines? Axial-
flow and centrifugal
What is the purpose of the stators in an axial-flow compressor? 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? Can-type, annular-
type, and can-annular-type
How many igniters are there normally in an aircraft turbine engine? Two
, What is the main purpose of the turbine nozzle in an aircraft turbine engine? The turbine
nozzle directs the hot gases as they leave the combustors so they will turn the turbine wheel
with maximum efficiency
What is meant by a free-turbine turboshaft engine? A turboshaft engine that has a turbine
wheel, or stage of turbine wheels, 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?
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? Anti-
friction bearings, such as ball bearings or roller bearings
What is meant by a turbofan engine? 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
Where can you find the limits of repair allowed for the compressor blades of an aircraft turbine
engine? In the FAA-approved service manual issued by the manufacturer of the engine
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? If the engine is shut down while it is hot, there is a
possiblity that the shroud will contract around the turbine wheel and seize the rotor
What is meant by a hung start in a turbine engine? A start in which ignition occurs, but the
engine does not accelerate to a self-sustaining speed
