Capt. Ken's comments

Maximizing engine life and efficiency

By Pierre Landry and Ken Armstrong

Winter’s frozen grip is upon us sprinkling additional challenges on our flying fun. Freezing temperatures are synonymous with engine pre-heating, or at least they should be. While most conventional aircraft engines use an oil sump incorporated in the engine itself, Rotax employs a remote oil sump, in the form of a stainless steel tank, which is usually located in the engine compartment and separate from the engine. On most conventional aircraft engines heating the engine also preheats the oil in the sump. Raising the oil’s temperature thins it significantly so it can reach all the nooks and crannies in the powerplant very quickly on start up. Cold oil the consistency of molasses is difficult for the pump to circulate and an engine started cold will suffer more wear and tear in the first minute than hours of flight at normal operating temperatures.
Rotax’s remote oil sump requires special precautions to be taken prior to cold starting the engine. The Rotax 912 and 914 engines have a very specific and sensitive oil lubrication system. It is for this reason that pre-heating of the engine oil and the engine itself is critical before an actual cold start is carried out. Lubrication in these Rotax engines is accomplished by the use of a rotary gear-type oil pump equipped with a spring control relief valve. This pump is activated by a small drive shaft installed in a notched fitting in the gearbox end of the camshaft. Therefore, as the engine is rotated or turned over during start up, the camshaft actually drives the oil pump which in turn supplies oil to the engines rotating parts. The problem with winter operation comes from the fact that the oil supplied to the oil pump is drawn by the pump through the oil cooler and from the remote oil tank through the oil lines before it reaches the engine. If the oil is not preheated throughout the remote oil tank, oil cooler and associated lines prior to starting the engine, the oil pump “works against” the viscosity of the cold oil. This combined with the fact that the passages in the oil cooler are very small and offer a greater resistance to the cold oil flow could result in significant wear during the starting and warm up phase.
Cold engine starts can cause temporary cavitation in oil lines and possible oil starvation to portions of the engine. Considering the cost of Rotax parts we Rotax engine operators should be well motivated to minimize wear and potential damage. Damage to the engine is not limited to cold starts but these starts can also severely shorten the life of the engine by inducing excessive wear caused by the lack of proper lubrication to the engine parts.
For these reasons it is obviously very important to heat the remote oil tank, the oil cooler and the oil lines prior to starting the engine.
Electric heaters are the most popular and efficient method of pre-heating the engine in cold climate conditions. They are also recommended as a safe, even method of pre-heating. Propane torches provide faster heating but there are complications. One must be very careful with the flame as it is quite easy to inflict considerable damage to the aircraft by over heating and area, the risk of fire and the introduction of additional moisture into the engine compartment as a byproduct in the propane. In short, the recommended pre-heat method utilizes an electric heater with a blanket wrapped cowling to maximize even warming of the cowling’s components. For those remote locations where electrical power is not available, a small gas generator can provide all the juice necessary for an inexpensive in-car heater of 750-1,500 watts.
Once your engine is warmed up, it is wise to fly for a lengthy enough period to get engine oil temperature up to 180 F or higher for at least 20 minutes to rid the engine of water and other possible contaminants in the oil. On the other hand, it is unwise to warm up the engine on the ground and shut it down without flying as this technique typically adds moisture and contamination to the oil.

The previous information is presented by Ken Armstrong and Pierre Landry who runs the Aircraft Maintenance Organization of Victoria Flight Training in Victoria B.C. Tel.: 250-656-0301.

Ken Armstrong has enjoyed 14,500 flight hours on more than 350 fixed and rotary wing aircraft. He provides aviation consulting/training services and flies his Diamond Extreme motor glider out of a grass strip near Victoria, B.C.