AMT-P Powerplant Oral Questions and
Answers
What is the main advantage of a horizontally opposed engine over a radial engine
for powering
modern aircraft - answerThe horizontally opposed engine has a much smaller
frontal area & is
easier to streamline than a radial engine.
How many throws are there in the crankshaft of a six-cylinder horizontally opposed
engine -
answerSix.
What kind of connecting rod arrangement is used in a radial engine - answerA
master rod
connects the single throw of the crankshaft with the piston. All of the other pistons
are connected
to the master rod with link rods.
Of what material are most piston rings made - answerGray cast iron.
What is the reason for using hydraulic valve lifters in an aircraft engine -
answerHydraulic 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 - answerThe camshaft turns at one half of the crankshaft speed.
What kind of main bearings are used in a horizontally opposed engine -
answerSteel-backed,
lead-alloy bearing inserts.
,On what stroke is the piston of a reciprocating engine when the intake valve begins
to open -
answerOn the exhaust stroke.
,On what stroke is the piston of a reciprocating engine when the exhaust valve
begins to open - answerOn the power stroke.
Why are both the hot & cold valve clearances given for most radial engines -
answerThe 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 - answerA 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 -
answerAbout 30 degrees of crankshaft rotation before the piston reaches top
center of the compression stroke.
What is meant by a full-floating wrist pin - answerA 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
- answerBy using more than one spring & having the wire diameter & pitch of the
spring 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 -
answerExcessive valve clearance will cause the valve to open late & close early.
What is the purpose of valve overlap in a reciprocating engine - answerValve
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 -
answerCompression rings, oil control rings, & oil wiper rings.
Why are some exhaust valves partially filled with metallic sodium - answerThe
metallic sodium
melts at engine operating temperature & sloshes back & forth inside the hollow
valve. It picks up
heat from the valve head & 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 - answerExcessive heat & pressure in
the engine
cylinder causes the fuel-air mixture to reach its critical pressure & 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 - answerA compression check can determine the condition of the seal
between the piston
rings & the cylinder walls, & the seal between the intake & exhaust valves & their
seats.
What is meant by the compression ratio of a reciprocating engine - answerThe 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.
In what position should the crankshaft be when a magneto is being timed to the
engine -
answerThe piston in cylinder no. 1 should be in the correct position for ignition to
occur. This is
normally about 30° before top center on the compression stroke.
What is the purpose of a cold cylinder check - answerA cold cylinder check
determines which
cylinder is not firing. Run the engine for a few minutes at the speed, and on the
magneto, at which
Answers
What is the main advantage of a horizontally opposed engine over a radial engine
for powering
modern aircraft - answerThe horizontally opposed engine has a much smaller
frontal area & is
easier to streamline than a radial engine.
How many throws are there in the crankshaft of a six-cylinder horizontally opposed
engine -
answerSix.
What kind of connecting rod arrangement is used in a radial engine - answerA
master rod
connects the single throw of the crankshaft with the piston. All of the other pistons
are connected
to the master rod with link rods.
Of what material are most piston rings made - answerGray cast iron.
What is the reason for using hydraulic valve lifters in an aircraft engine -
answerHydraulic 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 - answerThe camshaft turns at one half of the crankshaft speed.
What kind of main bearings are used in a horizontally opposed engine -
answerSteel-backed,
lead-alloy bearing inserts.
,On what stroke is the piston of a reciprocating engine when the intake valve begins
to open -
answerOn the exhaust stroke.
,On what stroke is the piston of a reciprocating engine when the exhaust valve
begins to open - answerOn the power stroke.
Why are both the hot & cold valve clearances given for most radial engines -
answerThe 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 - answerA 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 -
answerAbout 30 degrees of crankshaft rotation before the piston reaches top
center of the compression stroke.
What is meant by a full-floating wrist pin - answerA 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
- answerBy using more than one spring & having the wire diameter & pitch of the
spring 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 -
answerExcessive valve clearance will cause the valve to open late & close early.
What is the purpose of valve overlap in a reciprocating engine - answerValve
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 -
answerCompression rings, oil control rings, & oil wiper rings.
Why are some exhaust valves partially filled with metallic sodium - answerThe
metallic sodium
melts at engine operating temperature & sloshes back & forth inside the hollow
valve. It picks up
heat from the valve head & 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 - answerExcessive heat & pressure in
the engine
cylinder causes the fuel-air mixture to reach its critical pressure & 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 - answerA compression check can determine the condition of the seal
between the piston
rings & the cylinder walls, & the seal between the intake & exhaust valves & their
seats.
What is meant by the compression ratio of a reciprocating engine - answerThe 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.
In what position should the crankshaft be when a magneto is being timed to the
engine -
answerThe piston in cylinder no. 1 should be in the correct position for ignition to
occur. This is
normally about 30° before top center on the compression stroke.
What is the purpose of a cold cylinder check - answerA cold cylinder check
determines which
cylinder is not firing. Run the engine for a few minutes at the speed, and on the
magneto, at which
