Pilot’s primer
by Donald Talleur
As pilots, we are usually careful about pre-flighting our aircraft before a flight. We’ve heard of the dangers of inadequate pre-flight inspections, and many of us know at least one pilot who subsequently dealt with the consequences of a poor pre-flight. But how many of us take the time to carefully examine the propeller? Is it satisfactory to walk by the prop, simply noticing it is attached and has no large chunks missing from it? Of course that doesn’t sound satisfactory at all, but is your examination of the prop any better? Let’s discuss some of the issues surrounding adequate propeller pre-flight.
First, and most important, is a thorough review of the pilot’s operating handbook (POH). Make sure you are aware of any required inspections and servicing recommendations for the prop.
Next comes the visual inspection. An important point here is to avoid moving the propeller before ensuring the ignition is off. Assuming you do not have a "hot mag", this procedure will eliminate inadvertent firing of the engine and may save you an arm, if not your life. As you approach the prop, look for obvious defects such as a bent tip. Such damage is indicative of a prop strike, and will require an inspection or replacement. Gently run a couple of fingers along the leading edge of the prop, from the hub out to the prop tip. Repeat this on the trailing edge as well. If you find any nicks or dents, they should be carefully inspected. Be advised that there is no universal rule for determining when a nick needs to be dressed. Generally speaking, it is always best to have a mechanic inspect any nick that concerns you.
The backside of many propellers is painted with a non-reflective black paint to eliminate glare. An unpainted or faded prop will appear as a hypnotic disk at certain RPMs, and may be somewhat distracting during flight. If, during visual inspection, you note the condition of this paint is poor, it is a good idea to have a mechanic refinish the prop.
Now what about those nasty little bugs smeared on the prop? They certainly reduce the prop’s performance (although not by much), so shouldn’t we wash them off? The answer is yes, but be careful how you go about washing the prop. Spraying it with water, while OK for removing bug debris, can be bad for other things. Water can work its way into the spinner and the prop hub. At minimum, this is a good way to help corrosion take hold. On certain prop installations, spraying water into the hub area can also lead to lubricant breakdown. To avoid these problems, clean the prop with a lightly oiled rag. The bugs will come off and the oil will prevent corrosion.
Two other important tips on propeller care deal with taxiing and tugging. When taxiing or performing run-ups, it is advisable to stay clear of loose dirt or gravel. The airflow created by the prop can pick up rocks and small grit that can create damage. This is the primary cause of small nicks on the prop’s leading edge. When tugging, or moving the aircraft on the ground, be careful not to pull or push on the prop. Remember that the prop is designed to distribute the forces it experiences when running. It is not designed to take the localized force (equal to the weight of the aircraft) that is incurred when you try to pull or push on it to get the aircraft to roll. Instead, always use a tow bar or consult your POH for proper ground handling procedures.
While it’s important to know how to visually inspect and maintain your aircraft’s propeller, it is also important to point out the dangers of a propeller failure in flight. A large enough nick in the prop could set up an internal stress fracture that, under the proper conditions, could lead to propeller failure. We’re not talking about a failure to produce lift, but rather a failure to maintain structural integrity. If a large enough chunk of prop were to come off in flight, the imbalance could tear the engine off the mounts. With your engine gone, the centre of gravity would now be substantially rearward of the centre of lift, and the aircraft would be virtually impossible to control.
While engine separation occurrences are rare, propeller failures are well documented for most types of reciprocating and turboprop aircraft. The pilot’s best prevention for such a disaster is proper pre-flighting, proper ground handling and proper maintenance. Be safe – take care of your prop!
Donald Anders Talleur is an Assistant Chief Flight Instructor at the University of Illinois Institute of Aviation. He holds a joint appointment with the Pilot Training and Aviation Research Laboratory Departments. Talleur has been flying since 1984, and in addition to flight instructing since 1990, he has worked on numerous research contracts for the FAA, Air Force, Navy, NASA, and U.S. Army. He has authored or co-authored over 40 aviation-related papers and articles, and is also working on an M.S. degree in Engineering Psychology at the University of Illinois.
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