*** Good Operating Habits ***

Good Operating Habits

There are several good habits that we, as pilots, can develop during pre-flight and engine operation to enhance our safety as well as elongate our engine's life. The following items are not cumbersome to do and really take very little time or effort to perform.

The Pull Through
Before starting the engine and during our pre-flight inspection, we should develop the habit of checking that the ignition switch is in the off position and then pulling the engine through backwards several revolutions. (Even though the engine should not be able to start when rotated backwards we should always perform this procedure with caution.) Pulling the engine through several revolutions, enough to feel the compression strokes of each cylinder, allows us in effect to perform a compression test before every start of the engine. After we have performed this procedure several times we will develop a feel for the resistance to turning that each compression stroke provides. When these compression strokes feel even and the resistance feels like it did the last several times we checked, then we know that the compression on each cylinder is even and at least as good as the last flight that we made. When we feel a change or irregularity in the resistance, we know that there is a cylinder on that engine that may need mechanical attention. By discovering the "Bad Cylinder" during a pre-flight inspection rather than during routine maintenance, we may be able to repair it more easily on a more convenient schedule with a greater margin of safety.
Logging Fuel And Oil Consumption
By making a notation every time oil is added to the engine or engines we will develop a database that can be useful to maintenance personnel, as well as ourselves, to determine general engine health. By being able to average our oil consumption over many hours of operation, and knowing what that average is, makes it easy for us to see changes that might be important. If you know that over last 100 hours of operation you used an average of one quart of oil every seven hours and you find that over the last ten hours of operation you used three quarts of oil it is easy to see a problem developing and when it started. Without logging the oil consumption you most likely wouldn't know you had a problem until the engines usage became extreme and there was a possible safety issue. Likewise, logging and averaging fuel usage may alert us to changes that could cause potential engine problems. Changes in our average fuel consumption, at the same power settings, can alert us to discrepancies in our fuel flow indicating equipment, exhaust gas/ turbine inlet indicating equipment or our fuel metering systems. Catching these problems early can save thousands in cylinder repairs.
Keep RPM To A Minimum At Start Up
After engine start up we should run the engine at the slowest RPM that the engine will continue to run at. If it will stay running at 700 RPM then that is the RPM we should be running at not 1400 RPM. Allowing the engine to run at a high RPM right after start with out letting it warm up can cause premature wear to many internal engine surfaces that are splash lubricated. Some of these splash lubricated components, most notably the camshaft and tappets, are especially susceptible to damage right after start with cold oil and high RPM operation. Keeping the RPM to a minimum will limit the amount of interaction of these components before enough oil has splashed around inside the engine to provide sufficient splash lubrication.
Keep Propeller Cycling To A Minimum
It is absolutely necessary to cycle a constant speed propeller before flight. Not only does this operation exchange cold thick oil in the propeller with warm thinned oil from the engine, it also ensures that the propeller and propeller governor are functioning properly. The amount and frequency of this operation is what is at issue. When we purposely deep cycle our propellers, that is cycle them down more than 400 RPM, we cause more vibration and chatter on the engines counterweight system than we do if we only cycle the prop down only 300 RPM. This increased amount of vibration and chatter can cause increased wear on the engine's counterweight bushings and pins. The fit of these pins and bushings is what allows the counterweight system to absorb a very specific frequency of harmonic vibrations within the engine. If the fit between these components is compromised we are said to have "detuned" the counterweight system and thus we have severely limited the counterweight system's ability to absorb it's intended frequency of vibrations. These vibrations, when not absorbed, can cause many vibration related maintenance problems. Anything from catastrophic engine or propeller failure to minor cracking of engine baffles and cowlings is a possible result of detuned counterweights. By keeping the frequency and RPM that we cycle the propeller to a minimum, we can maintain the counterweight systems ability to absorb it's intended frequency of vibrations and limit any problems related to detrimental harmonic engine vibrations while still testing the propeller and propeller governor properly.
Proper Engine Warm Up
Before initializing a full power application, we should insure that the engine is properly warmed up. We should have at least 220 degrees fahrenheit CHT and an oil temp of 110 degrees fahrenheit on a normally aspirated engine and 130 degrees fahrenheit on turbocharged engines. When an engine is running, it relies on the temperature of certain components to maintain proper clearances between them. The hotter a particular component becomes, the more it expands and thus the larger it gets. If we operate an engine without attaining proper even temperatures, we have some components that aren't big enough and some that are too big. When this happens we can experience excessive wear on the internal components involved. Assuring proper minimum temperatures, will assure proper tolerances, keeping wear to a minimum. In addition to the wear factors, turbocharged engines rely on warm engine oil to properly control the turbo system. Applying full power to a automatic control turbocharger system with improperly warmed up oil can cause the system to react sluggishly to control impulses being supplied by the turbo controllers. This can easily allow an over-boost condition to exist. Over-boosting of an engine not only can cause excessive premature wear but if severe enough it could cause complete engine failure. Properly warmed up oil will also help ensure that all splash lubricated internal components are receiving the proper amount of lubrication.
Proper Engine Cool Down Before Shut Down
Proper shut down procedures are important to all engines but are especially important to turbocharged engines. We should allow a cool down run at 1000 RPM for at least 5 minutes on a normally aspirated engine and 10 minutes on a turbocharged engine. These cool down runs allow internal components to cool and shrink evenly at a acceptable rate eliminating any hot spot within the engine that may have developed during let down and landing. On turbocharged engines these runs allow the turbo itself to cool dramatically from operating temperatures. Shutting the engine down with cylinder heads and turbocharger at too high an operating temperature will cause the oil that is left on internal parts of these components to be cooked and turned into carbon. Carbon build up in cylinder components can cause stuck valves and rings causing high oil consumption. Carbon build up inside of a turbocharger lubrication section will cause seal failure, high oil consumption and eventual turbocharger failure.

These six simple procedures can provide a multitude of benefits to us and our engines, if they are followed regularly. Of course to gain the benefits we must modify our procedures where necessary and use them. In doing so we will be operating our aircraft in a safer, more economical and knowledgeable way.

by Mahlon Russell

Send your questions, to Mahlon at mahlon@mattituck.com

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