Aircraft Systems

broken or shorted wires between the magneto and the plugs, Reciprocating engines use either a wet-sump or a dry-sump or improperly timed firing of the plugs. It should be noted oil system. In a wet-sump system, the oil is located in a sump that “no drop” in rpm is not normal, and in that instance, the that is an integral part of the engine. In a dry-sump system, aircraft should not be flown. the oil is contained in a separate tank and circulated through the engine by pumps. [Figure 7-17] Following engine shutdown, turn the ignition switch to the OFF position. Even with the battery and master switches The main component of a wet-sump system is the oil pump, OFF, the engine can fire and turn over if the ignition switch which draws oil from the sump and routes it to the engine. After is left ON and the propeller is moved because the magneto the oil passes through the engine, it returns to the sump. In requires no outside source of electrical power. Be aware of some engines, additional lubrication is supplied by the rotating the potential for serious injury in this situation. crankshaft, which splashes oil onto portions of the engine. Even with the ignition switch in the OFF position, if An oil pump also supplies oil pressure in a dry-sump the ground wire between the magneto and the ignition system, but the source of the oil is located external to the switch becomes disconnected or broken, the engine could engine in a separate oil tank. After oil is routed through accidentally start if the propeller is moved with residual fuel the engine, it is pumped from the various locations in the in the cylinder. If this occurs, the only way to stop the engine engine back to the oil tank by scavenge pumps. Dry-sump is to move the mixture lever to the idle cutoff position, then systems allow for a greater volume of oil to be supplied to have the system checked by a qualified AMT. the engine, which makes them more suitable for very large reciprocating engines. Oil Systems The oil pressure gauge provides a direct indication of the oil The engine oil system performs several important functions: system operation. It ensures the pressure in pounds per square • Lubrication of the engine’s moving parts inch (psi) of the oil supplied to the engine. Green indicates • Cooling of the engine by reducing friction the normal operating range, while red indicates the minimum and maximum pressures. There should be an indication of • Removing heat from the cylinders oil pressure during engine start. Refer to the AFM/POH for • Providing a seal between the cylinder walls and pistons manufacturer limitations. • Carrying away contaminants Oil filler cap and dipstick Engine Sump oil and return and oil from relief valve Accessory Bearings Pressure oil from oil pump Oil sump Low pressure oil screen Oil pressure relief valve Oil pump High pressure oil screen 245 II5 T 200 I00 P Oil cooler and filter M E P °F I0 I5 0 0 60 20 P S I R E S S 75 0 OIL Figure 7-17. Wet-sump oil system. 7-16