Powered Parachute Flying Handbook

Chapter 4 — Powerplants

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 advantage 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 reservoir 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 performs 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 drysump oil system. Refer to Chapter 5 of 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. Powered parachute engines operate with either aircooled or liquid-cooled systems.

Many powered parachutes 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 ranges can be found in the pilot’s operating handbook for that machine.

Air cooling is accomplished by air being pulled into the engine shroud by a cooling fan. Baffles route this air over fins attached to the engine cylinders where the air absorbs the engine heat. Expulsion of the hot air takes place through one or more openings in the shroud. If cylinder head temperatures rise too much in an air cooled engine, it is because of lubrication problems: cooling fan drive belt damage or wear, or air blockage in the cooling fins by a bird or insect nest.

Liquid cooling systems pump coolant through jackets in the cylinders and head. The heated liquid is then routed to a radiator where the heat is radiated to the atmosphere. The cooled liquid is then returned to the engine. If the radiator is mounted low and close to the propeller, the propeller can constantly move air across the radiator and keep the engine cool even when the powered parachute is not moving. Radiators mounted high and away from the propeller raise the center of gravity and make it more difficult for the radiator to cool the engine unless the powered parachute is moving. Breaking in an engine through ground runs on a hot day is when radiator placement is most critical.

Liquid-cooled engines can overheat for a number of reasons, such as coolant not at proper levels, a leak, a failed water pump, or a blockage of the radiator. Operating an engine above its maximum design temperature can cause a loss of power and detonation. It will also lead to serious permanent damage, such as scoring the cylinder walls and damaging the pistons and rings. Monitor the engine temperature instruments to avoid high operating temperature.

Operating the engine lower than its designed temperature range can cause piston seizure and scarring on the cylinder walls. This happens most often in liquidcooled powered parachutes in cold weather where large radiators designed for summer flying may need to be partially blocked off.

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