Powered Parachute Flying Handbook

Chapter 4 — Powerplants

Four-Stroke Engine Warming

A four-stroke engine must also be warmed up. The four-stroke engine has a pressurized oil system that provides more uniform engine temperatures to all its components. You can apply takeoff power as soon as the water, cylinder head temperature (CHT), oil temperatures and oil pressure are within the manufacturer’s recommended tolerances for takeoff power applications.


Gearboxes are used on all powered parachute reciprocating engines to take the rotational output of an internal combustion engine which is turning at a very high RPM and convert it to a slower (and more useful) RPM to turn the propeller. Gearboxes come in different gear ratios depending on the output speed of the engine and the needed propeller turning speeds.

A typical two-stroke RPM reduction is from 6,500 engine RPM with a 3.47 to 1 reduction, resulting in 1,873 propeller RPM. A typical four-stroke RPM reduction is from 5,500 engine RPM with a 2.43 to 1 reduction, resulting in 2,263 propeller RPM.

A gearbox is a simple device that bolts directly to the engine and in turn has the propeller bolted directly to it.

A two-cycle engine gearbox is kept lubricated with its own built-in reservoir of heavy gearbox oil. The reservoir is actually part of the gearbox case itself. The gearbox oil has to be changed periodically since the meshing of the gears will cause them to wear and will deposit steel filings into the oil. If the oil is not changed, the filings themselves are abrasive and will cause even more wear.

Some gearboxes have the electric starter motor built into it. When activated, the motor turns the gearing, which in turn cranks the engine itself.

Four-stroke propeller reduction gearboxes use oil from the engine oil system for lubrication.

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