ASA Powerplant Oral Study Guide (All
Questions)33
What is the main advantage of a horizontally opposed engine over a radial engine for powering
modern aircraft? - ANSWERS-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? -
ANSWERS-Six.
What kind of connecting rod arrangement is used in a radial engine? - ANSWERS-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? - ANSWERS-Gray cast iron.
What is the reason for using hydraulic valve lifters in an aircraft engine? - ANSWERS-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? - ANSWERS-The camshaft turns at one half of the crankshaft speed.
What kind of main bearings are used in a horizontally opposed engine? - ANSWERS-Steel-
backed, lead-alloy bearing inserts.
On what stroke is the piston of a reciprocating engine when the intake valve begins to open? -
ANSWERS-On the exhaust stroke.
,On what stroke is the piston of a reciprocating engine when the exhaust valve begins to open? -
ANSWERS-On the power stroke.
Why are both the hot and cold valve clearances given for most radial engines? - ANSWERS-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? - ANSWERS-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? - ANSWERS-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? - ANSWERS-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? -
ANSWERS-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 a valve.
Would excessive valve clearance cause the valves to open early or late? - ANSWERS-Excessive
valve clearance will cause the valve to open late and close early.
,What is the purpose of valve overlap in a reciprocating engine? - ANSWERS-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? -
ANSWERS-Compression rings, oil control rings, and oil wiper rings.
Why are some exhaust valves partially filled with metallic sodium? - ANSWERS-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? - ANSWERS-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? - ANSWERS-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? - ANSWERS-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? - ANSWERS-The hot section and the cold
section.
What are the two basic types of compressors that are used in aircraft turbine engines? -
ANSWERS-Axial-flow and centrifugal.
, What is the purpose of the stators in an axial-flow compressor? - ANSWERS-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? - ANSWERS-Can-type,
annular-type, and can-annular type.
How many igniters are there normally in an aircraft turbine engine? - ANSWERS-Two.
What is main purpose of the turbine nozzle in an aircraft turbine engine? - ANSWERS-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? - ANSWERS-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? -
ANSWERS-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? -
ANSWERS-Anti-friction bearings, such as ball bearings or roller bearings.
What is meant by a turbofan engine? - ANSWERS-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.
Questions)33
What is the main advantage of a horizontally opposed engine over a radial engine for powering
modern aircraft? - ANSWERS-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? -
ANSWERS-Six.
What kind of connecting rod arrangement is used in a radial engine? - ANSWERS-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? - ANSWERS-Gray cast iron.
What is the reason for using hydraulic valve lifters in an aircraft engine? - ANSWERS-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? - ANSWERS-The camshaft turns at one half of the crankshaft speed.
What kind of main bearings are used in a horizontally opposed engine? - ANSWERS-Steel-
backed, lead-alloy bearing inserts.
On what stroke is the piston of a reciprocating engine when the intake valve begins to open? -
ANSWERS-On the exhaust stroke.
,On what stroke is the piston of a reciprocating engine when the exhaust valve begins to open? -
ANSWERS-On the power stroke.
Why are both the hot and cold valve clearances given for most radial engines? - ANSWERS-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? - ANSWERS-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? - ANSWERS-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? - ANSWERS-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? -
ANSWERS-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 a valve.
Would excessive valve clearance cause the valves to open early or late? - ANSWERS-Excessive
valve clearance will cause the valve to open late and close early.
,What is the purpose of valve overlap in a reciprocating engine? - ANSWERS-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? -
ANSWERS-Compression rings, oil control rings, and oil wiper rings.
Why are some exhaust valves partially filled with metallic sodium? - ANSWERS-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? - ANSWERS-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? - ANSWERS-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? - ANSWERS-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? - ANSWERS-The hot section and the cold
section.
What are the two basic types of compressors that are used in aircraft turbine engines? -
ANSWERS-Axial-flow and centrifugal.
, What is the purpose of the stators in an axial-flow compressor? - ANSWERS-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? - ANSWERS-Can-type,
annular-type, and can-annular type.
How many igniters are there normally in an aircraft turbine engine? - ANSWERS-Two.
What is main purpose of the turbine nozzle in an aircraft turbine engine? - ANSWERS-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? - ANSWERS-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? -
ANSWERS-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? -
ANSWERS-Anti-friction bearings, such as ball bearings or roller bearings.
What is meant by a turbofan engine? - ANSWERS-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.
