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be grounded to the aircraft before refueling is begun and
should remain grounded throughout the refueling process.
The passage of fuel through a chamois increases the charge
of static electricity and the danger of sparks.
The aircraft must be properly grounded and the nozzle,
chamois fi lter, and funnel bonded to the aircraft. If a can is
used, it should be connected to either the grounding post or
the funnel. Cell phones should not be used while refueling
due to possible fi re risks.
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
4-17
Figure 4-20. Cylinder head temperature probe (yellow wire) is
under spark plug.
Water Cooler
Oil Cooler
Figure 4-21. Cooling radiators—oil cooler is on top and water
cooler is on bottom.
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.
Oil Systems
In a four-stroke engine, the engine oil system performs
several important functions, including:
• Lubricating the engine’s moving parts.
• Cooling the engine by reducing friction.
• Removing heat from the cylinders.
• Providing a seal between the cylinder walls and
pistons.
• Carrying away contaminants.
Four-stroke engines use either a wet sump or dry sump
oil system. Refer to the Pilot’s Handbook of Aeronautical
Knowledge for more information on four-stroke oil
systems.
Engine Cooling Systems
The burning fuel within the cylinders produces intense heat,
most of which is expelled through the exhaust system. Much
of the remaining heat, however, must be removed, or at least
dissipated, to prevent the engine from overheating.
While the oil system in a four-stroke engine and the fuel-oil
mix in a two-stroke engine is vital to the internal cooling of
the engine, an additional method of cooling is necessary for
the engine’s external surface. WSC engines operate with
either air-cooled or liquid-cooled systems.
Many WSC aircraft are equipped with a cylinder head
temperature (CHT) gauge. This instrument indicates a direct
and immediate cylinder temperature change. This instrument
is calibrated in degrees Celsius or Fahrenheit. Proper CHT
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Weight-Shift Control Aircraft Flying Handbook(49)
