Powerplant - Reciprocating Engines Questions and Answers Well Solved

Powerplant - Reciprocating Engines Questions and Answers Well Solved 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 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 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 the valve. Would excessive valve clearance cause the valves to open early or late? - Answers Excessive 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 gasses 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.