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ASA POWERPLANT ORALS FINAL EXAM 2025
UPDATED ACTUAL EXAM WITH CORRECT
SOLUTIONS.
What is the main advantage of a horizontally opposed engine
over a radial engine for powering modern aircraft? - correct
answer- smaller frontal area and easier to streamline.
How many throws are there in the crankshaft of a six-cylinder
horizontally opposed engine? - correct answer- six
What kind of connecting rod arrangement is used in a radial
engine? - correct 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? - correct answer-
grey cast iron
What is the reason for using hydraulic valve lifters in an aircraft
engine? - correct answer- keep all of the clearance out of the
valve operating mechanism, decreases wear of valve train
components
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At what speed does the camshaft turn, relative to the
crankshaft speed in a horizontally opposed engine? - correct
answer- camshaft is one half the speed of crankshaft
What kind of main bearings are used in a horizontally opposed
engine? - correct answer- steel backed lead alloy bearings
On what stroke is the piston of a reciprocating engine when the
intake valve begins to open? - correct answer- exhaust
On what stroke is the piston of a reciprocating engine when the
exhaust valve begins to open? - correct answer- power
Why are both the hot and cold valve clearances given for most
radial engines? - correct 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 - correct answer- A
piston that is not perfectly round. . When the piston reaches
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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? - correct answer- before top dead center on the
compression stroke
What is meant by a full-floating wrist pin? - correct answer- pin
not clamped in either piston or connecting rod
Why do most aircraft reciprocating engines use more than one
spring on each valve? - correct answer- for different
frequencies/rpms
Would excessive valve clearance cause the valves to open
early or late? - correct answer- open late close early
What is the purpose of valve overlap in a reciprocating engine?
- correct answer- Valve overlap allows the inertia of the exhaust
gases leaving the cylinder to help the fresh induction charge
start flowing into the cylinder.
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What type of piston rings are installed on the pistons of an
aircraft reciprocating engine? - correct answer- compression, oil
control, oil wiper
Why are some exhaust valves partially filled with metallic
sodium? - correct 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? - correct 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? - correct 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? - correct answer- ratio of volume of cylinder with piston
at bottom vs piston at top
ASA POWERPLANT ORALS FINAL EXAM 2025
UPDATED ACTUAL EXAM WITH CORRECT
SOLUTIONS.
What is the main advantage of a horizontally opposed engine
over a radial engine for powering modern aircraft? - correct
answer- smaller frontal area and easier to streamline.
How many throws are there in the crankshaft of a six-cylinder
horizontally opposed engine? - correct answer- six
What kind of connecting rod arrangement is used in a radial
engine? - correct 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? - correct answer-
grey cast iron
What is the reason for using hydraulic valve lifters in an aircraft
engine? - correct answer- keep all of the clearance out of the
valve operating mechanism, decreases wear of valve train
components
,2 | Page
At what speed does the camshaft turn, relative to the
crankshaft speed in a horizontally opposed engine? - correct
answer- camshaft is one half the speed of crankshaft
What kind of main bearings are used in a horizontally opposed
engine? - correct answer- steel backed lead alloy bearings
On what stroke is the piston of a reciprocating engine when the
intake valve begins to open? - correct answer- exhaust
On what stroke is the piston of a reciprocating engine when the
exhaust valve begins to open? - correct answer- power
Why are both the hot and cold valve clearances given for most
radial engines? - correct 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 - correct answer- A
piston that is not perfectly round. . When the piston reaches
,3 | Page
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? - correct answer- before top dead center on the
compression stroke
What is meant by a full-floating wrist pin? - correct answer- pin
not clamped in either piston or connecting rod
Why do most aircraft reciprocating engines use more than one
spring on each valve? - correct answer- for different
frequencies/rpms
Would excessive valve clearance cause the valves to open
early or late? - correct answer- open late close early
What is the purpose of valve overlap in a reciprocating engine?
- correct answer- Valve overlap allows the inertia of the exhaust
gases leaving the cylinder to help the fresh induction charge
start flowing into the cylinder.
, 4 | Page
What type of piston rings are installed on the pistons of an
aircraft reciprocating engine? - correct answer- compression, oil
control, oil wiper
Why are some exhaust valves partially filled with metallic
sodium? - correct 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? - correct 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? - correct 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? - correct answer- ratio of volume of cylinder with piston
at bottom vs piston at top
