Aircraft maintenance: Propeller care

June 26, 2013

Here’s a quiz: What travels at speeds in excess of 500 miles per hour, endures 10 tons to 20 tons of force trying to rip it apart and gets so little respect that the average pilot equates it to a tow-bar? It’s your old pal the propeller.

We often like to think of our aircraft as having personalities, sometimes going so far as to name them. I’ve ended more than one long cross-country flight with a gentle pat on the cowl as if to say: “Thanks old pal. Nice job.” Sometimes, even the parts of an airplane can be deserving of different personalities; like that mischievous autopilot that occasionally acts out, but never in front of an avionics technician.

Jeff SimonEnter the propeller. It’s always got your back. It bears more stress than anything else on the aircraft, all while being slowly eroded by sand, rain, and the occasional small rock. Sadly, it also gets taken for granted by most pilots. After all that work, the cowl gets the pat and the propeller gets used as a tow bar.

It deserves better. After all, you can practice engine-out landings to your heart’s content, but it won’t do you much good if you and your propeller part ways in flight. The vibration resulting from a propeller blade failure can easily tear the engine from its mounts, rendering the aircraft uncontrollable.

In this series, we’ll discuss caring for your propeller, including proper operations, preventive maintenance, performance, and overhauls.

Proper care of your propeller starts with the preflight. Your bare hands are one of the best tools around for detecting anomalies with your propeller. Gently run your fingers over the leading edges of every blade, feeling for nicks, dents, and the overall smoothness of the surface. Dings exceeding one-thirty-second of an inch, dents big enough to deform the metal around them, raw scratches, or cracks are all dangerous and should be attended to before further flight.

General pitting and erosion of the leading edge and back or “face” of the propeller blades are also something to watch for. These pits become focal points for corrosion, which lead to stress concentrations, weakening the aluminum alloy. It’s especially important to keep unprotected aluminum clean and dry whenever possible. Bird droppings, for example, are highly corrosive to unprotected aluminum, not a good thing considering how much they love to perch on top of a vertical prop blade.

When it’s time to move the airplane, never push or pull on the prop blades. Forget what anyone has told you about pulling near the hub or the strength of the propeller. Aluminum blades can bend, and it doesn’t take much to put the blades out of track with one another. This is doubly true for constant-speed propellers, where the blades’ attachments and hub are also subject to damage. The same goes for pushing on spinners. The bottom line is that propellers cost thousands of dollars and a good tow bar can probably be purchased with the cash in your wallet. So, you might as well use the right tool for the job.

While we’re on the subject of tow bars, make a habit of never leaving a tow bar attached to an airplane when it’s not being used. Tow bars and propellers seem to battle it out routinely, and I have yet to see a propeller leave the fight as the victor. This leads us to another note: If a propeller hits a tow bar and nobody except the pilot sees it, it still gets damaged. Don’t assume you can give it a quick once-over and continue your planned flight. The propeller needs to be carefully inspected by a mechanic and have a dye penetrant inspection of any suspect areas. Depending on the situation, it may even be cause for opening up and inspecting the engine itself.

Prior to starting up, be sure to clear away any debris and rocks below and in front of the propeller. At idle and slow taxi speeds, the propeller does a pretty good job vacuuming up just about anything within four feet to six feet in front of it.

Next time, we’ll talk more about preventive propeller maintenance, minor repairs, and how to protect that trusty fan out front to keep it healthy for years to come.

Social FlightJeff Simon is an A&P mechanic, pilot, and aircraft owner. He has spent the last 14 years promoting owner-assisted aircraft maintenance as a columnist for several major aviation publications and through his how-to DVD series: The Educated Owner. Jeff is also the creator of SocialFlight, the FREE mobile app and website that maps over 5,000 aviation events. Free apps available for iPhone, iPad and Android, and on the Web at www.SocialFlight.com.