ASA POWERPLANT ORALS FINAL EXAM

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ASA POWERPLANT ORALS FINAL EXAM

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 1 / 4

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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 2 / 4

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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

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