person to the funnel or nozzle. To guard against the possibility of static electricity igniting fuel fumes, a ground wire should be attached to the aircraft before the fuel cap is removed from the tank. The refueling nozzle should then be grounded to the aircraft be- fore 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 noz- zle, chamois filter, 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 as they could pose a fire risk. 

## Mixing Two-Stroke Oil and Fuel 

Two-stroke engines require special two-stroke oil to be mixed into the fuel before reaching the cylinder of the engine. 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 ad- vantage of an oil injection system is pilots don’t have to premix any oil into the fuel. However, an important preflight check is to make sure the two-stroke oil res - ervoir is properly filled. 

If a two-stroke engine doesn’t have an oil injection system, it is critical to mix oil into fuel before it is put into the tank. Just pouring oil into the fuel tank doesn’t give it the proper chance to mix with the gas and makes it difficult to measure the proper amount of oil for mixing. To mix two-stroke oil you should: 

• Find a clean, approved container. Pour a little 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 your PPC). Use a measuring cup if necessary. Shake the oil-gas mixture around a little to dilute the oil with gasoline. 

• Add gasoline until the 50:1 ratio is reached. If you choose to use a water separating funnel, make sure 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 flywheel or the 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. 

## Oil Systems 

In a four-stroke engine, the engine oil system per- forms several important functions, including: 

• Lubrication of the engine’s moving parts. 

Cooling of 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 Chapter 5 of the Pilot’s Handbook of Aeronautical Knowledge for more in- formation on four-stroke oil systems. 

## Engine Cooling Systems 

The burning fuel within the cylinders produces in- tense heat, most of which is expelled through the ex- haust 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 in- ternal cooling of the engine, an additional method of cooling is necessary for the engine’s external surface. Powered parachute engines operate with either air- cooled or liquid-cooled systems. 

Many powered parachutes are equipped with a cylin- der head temperature (CHT) gauge. This instrument indicates a direct and immediate cylinder temperature 

