CHAPTER 4. Powerplants Mixing Two-Stroke Oil and Fuel Two-stroke engines require special two-stroke oil to be mixed into the fuel before entering the engine to provide lubrication. In some engines, an oil injection pump is used to deliver the exact amount of oil into the intake of the engine depending on the throttle setting. An advantage of an oil injection system is that pilots do not need to premix any oil into the fuel. However, an important prefl ight check is to ensure the two-stroke oil reservoir is properly fi lled. If a two-stroke engine does not have an oil injection system, it is critical to mix the oil with the fuel before it is put into the tank. Just pouring oil into the fuel tank does not allow the oil to mix with the gas, and makes it diffi cult to measure the proper amount of oil for mixing. To mix two-stroke oil: Find a clean, approved container. Pour some gas into it to help pre-dilute the two-stroke oil. Pour in a known amount of two-stroke oil into the container. Oil should be approved for air-cooled engines at 50:1 mixing ratio (check the engine manufacturer for proper fuel to oil ratio for the WSC aircraft). Use a measuring cup if necessary. Shake the oil-gas mixture to dilute the oil with gasoline. Add gasoline until the 50:1 ratio is reached. If using a water separating funnel, ensure the funnel is grounded or at least in contact with the fuel container. Put the cap on the fuel can and shake the gasoline and oil mixture thoroughly. Starting System Most small aircraft use a direct-cranking electric starter system. This system consists of a source of electricity, wiring, switches, and solenoids to operate the starter and a starter motor. The starter engages the aircraft fl ywheel or gearbox, rotating the engine at a speed that allows the engine to start and maintain operation. Electrical power for starting is usually supplied by an on-board battery. When the battery switch is turned ON, electricity is supplied to the main power bus through the battery solenoid. Both the starter and the starter switch draw current from the main bus, but the starter will not operate until the starting solenoid is energized by the starter switch being turned to the “start” position. When the starter switch is released from the “start” position, the solenoid removes power from the starter motor. The starter motor is protected from being driven by the engine through a clutch in the starter drive that allows the engine to run faster than the starter motor.

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