August 2020 – Stockton Propeller

How To Care For & Maintain A Wooden Propeller

Airplane propeller blades are crafted out of several different materials, including wood, metal, and various composites. Wooden propellers seem to be romanticized by the pilots who prefer them. As a 2003 article from Air & Space magazine bemuses, “Wooden propellers are like Louisville Sluggers.”

While we don’t work on wooden propellers at our shop, we can certainly admire the craftsmanship. So today, we’re sharing a few tips on the care and maintenance of your aircraft’s “Louisville Sluggers”: wooden propellers. This care and maintenance plan includes, of course, knowing when you should have a propeller inspection.

If you know that your composite propeller is ready for a propeller inspection or repair, give us a call. Stockton Propeller is a full-service propeller overhaul and maintenance facility with the needed equipment and expertise to perform static and dynamic balancing. Get inspection and maintenance before failure!

Wood Choice

The wood choice itself doesn’t make much difference when it comes to caring for your wood propellers. Wood propellers could be crafted from almost any type of hardwood.

Historically, the most popular wood choices were mahogany, oak, walnut or black walnut, black cherry, yellow birch, or sugar maple. Almost all wooden propellers are also strengthened in some fashion (like lamination) to add strength. Fabric or metal coverings can also add to the propeller design and reinforce stability.

The Case For Wooden Propellers

Wood propellers are not certified for many planes these days. But for those for which they are certified, there are some definite advantages:

Wood propellers are lighter and increase payload.
Wood propellers can get up to speed much more quickly than most metal propellers.
Wood propellers cause less vibration. Metal propellers accumulate invisible flaws from vibrations and flexing.
Wood propellers are generally the less expensive choice.

What You Can Do To Care For A Wood Propeller Yourself

All propellers are subject to wear, fatigue, corrosion, and erosion. Wooden propellers are especially at risk for erosion and distortion.

A damaged propeller cuts your speed, diminishes your airplane’s performance, and increases your take-off distance. At worst, severely damaged propellers can cause engine failure and catastrophic airplane crashes.

Read Your Owner’s Manuals

Hey, your plane is a considerable investment. Of course, you’ve already done this! But, just on the off chance that you haven’t read them, make sure you read your owner’s manuals on each piece of equipment and the plane itself.

Take inspection and overhaul recommendations to heart. Keep a calendar or record of everything.

Park It Horizontal

When your plane is parked – or if you have to remove your wooden propeller from the aircraft – make sure the propeller is horizontal. If you store it vertically, any moisture in the air around it or on the propeller could migrate to the lower half and cause a disproportionate weight balance or warping of the wood.

If you’ve removed the propeller from the plane entirely, make sure it is horizontal, flat, and out of direct sunlight to keep the wood at its best. Do not ever store a propeller vertically!

Pre-Flight Propeller Inspections

Make sure you conduct your own pre-flight propeller inspections before every flight. It’s essential to routinely check for bruises, scars, or other damage to wood propellers and leading-edge protection. And, remember, more frequent inspections may be necessary when climate changes are extreme.

Clean The Propellers

During flights, propellers can pick up several different problems – including bugs, dirt, debris, and pollutants. All of these can not only cause problems on their own but can also mask issues that you’re trying to spot.

Washing the propellers with a good, old-fashioned soap and water solution and soft brushes or cloths can easily take care of this after every flight. Just be sure you don’t get any liquid dripping down into the propeller’s hub.

If you’ve subjected your plane to saltwater, the propellers may need a little extra TLC. A freshwater flush or two should get rid of all traces of salt. While this may seem like a pain, it’s imperative to take the time to do this to avoid warping and erosion.

Wax The Propellers

Wax your wooden propellers as often as is suggested and with whatever type of wax your owner’s manual recommends. If you don’t have a recommendation, ask your “propeller guy” (like ours here at Stockton Propeller).

Don’t Push Or Pull

Do not ever grab the propellers to push or pull the aircraft. Use the tow bars to move the plane by hand. Exerting any force (pushing or pulling) on the propellers can affect the positioning of the blades. This incorrect positioning can harm flight performance.

When It’s Time For A Professional Propeller Inspection Or Repair

If you notice anything amiss in your pre-flight checks or you’ve hit the mandatory number of hours for an inspection or overhaul, make sure you get your appointment scheduled.

Do not attempt to fly anywhere if your wooden propeller shows any of these damage signs:

Any cracks in the hub bore (small or large)
A long, deep, wide crack parallel to the grain in any spot on the wooden propeller
An oversized or elongated hub bore or bolt holes
An appreciable warp (discovered by inspection or through rough operation)
An appreciable portion of wood missing from the propeller blade
A deep cut across the wood grain
A separated lamination along the length of the wooden propeller

Finally, sometimes, the damage is beyond repair – whether the propeller is too damaged or the repair costs more than a new propeller blade.

If you’re doing pre-flight inspections and paying close attention, it’s much easier to schedule an inspection and maintenance before that happens, though!

Propeller Inspection Checklist

Why Is Aircraft Propeller Inspection Important?

According to the Aircraft Owners and Pilots Association (AOPA), “the root cause of mechanically induced accidents is almost always neglect.” The AOPA continues:

“On takeoff, propeller tip speeds approach the speed of sound. The blades must absorb not only the punishing vibration of the engine’s power pulses but also vibration caused by the oncoming airstream. Centrifugal loads – those forces that try to pull the blade out of the hub – amount to 10 to 20 tons per blade.

The blades twist and flex. The stresses imposed on the prop are more concentrated in the small areas that are nicked or cut. These nicks and scratches act as stress risers, which can weaken the blade enough to eventually cause it to fail.

When an engine quits, the airplane can glide to a safe landing. When a propeller blade is lost, the resulting imbalance can tear the entire engine from the aircraft, putting the center of gravity far beyond limits and rendering the aircraft uncontrollable.”

That scenario, of course, can be avoided with frequent inspections using this propeller inspection checklist. Performing these routine preflight inspections can clue you into any needed propeller maintenance or repairs.

Stockton Propeller’s Propeller Inspection Checklist

A “walkaround” or preflight visual inspection of your aircraft’s propellers is vital for your plane’s safety and health. Even more important is the safety of you and your passengers or cargo.

An important note: While the term “walkaround” may make it sound like this could be just a superficial glance. However, this should instead be a studied review to gauge your craft’s airworthiness.

To perform a preflight visual propeller inspection, follow these steps:

Get a clear view of the propeller area. In other words, make sure your propellers are clean. In the course of any flight, propellers can pick up dead bugs, dirt, and other pollutants. If your propellers are dirty, it will be challenging to get a good view of any defects. If the propellers are dirty, you can easily wash them off with a simple solution of dish soap and water. If you have to wash off the propeller area, make sure that your propellers are in the down position. This will prevent any liquid from getting into the seals and causing issues there.

Check for surface damage. Carefully and thoroughly examine the aircraft’s propeller blades and other parts for any cracks, nicks, chips, corrosion, or other blemishes. Surface damage can be felt by running a fingernail along the propeller’s edge. For propellers made of wood or composite materials, check for delaminations or microcracks on the propeller surfaces, edges, and glue lines. If your propellers have any drain holes, check that they aren’t clogged. Clogged drain holes can lead to moisture retention and more significant problems down the road.

Check for erosion. Examine the propeller for any and all signs of decay. Look over the paint job on the propeller blades and spinners for any imperfections. This paint on the propeller protects the surface from erosion. If erosion starts to occur, it can be a much more costly fix than having a professional touch up your paint job.

Check for any loose or missing hardware or broken safety wire.

Check for any broken or compromised seals.

Check the straightness of the propeller blades. Perform a simple sight check for any deformations down the edges of the propeller blades. You can determine the straightness of the propeller blades with this simple sight check.

Check for looseness. Flex the propeller blades forward and backward to inspect the intersection for any movement. There should be no movement at all.

Check the hub. Gently shake each propeller blade to feel for blade movement in the hub of the propeller. A small degree – up to ⅛ inch – is allowable. If there is more movement than that, maintenance is needed immediately.

Check for oil or grease leakage. Look for any grease or oil. There should be no oil or grease detected on the propeller blades or spinners. A couple of exceptions are if your propellers are brand new or you are in a hot climate with high RPM conditions.

Update maintenance records. If you notice a small imperfection, make sure to note it in your aircraft’s maintenance records. Your repair person will know when you first saw the issue during a walkaround or preflight inspection. They will also know if the issue gets worse over time.

If, when following this checklist, you don’t see any areas of concern, your propellers are airworthy, and you are good to fly away!

How Often Should You Inspect Your Aircraft’s Propellers?

Before any flight, you should perform the above visual propeller inspection checklist of your aircraft’s propellers.

Then, of course, you should follow the manufacturer’s recommendations for your scheduled overhauls and maintenance. Generally, these schedules are based on years and flight hours.
The recommended Time Between Overhaul (TBO) guidelines are mandatory for Part 135 commercial operators but are only recommended for Part 91 pilots not flying for hire. That being said, Part 91 operators should follow the calendar recommendation for overhaul as a recommendation for inspection/reseal at the 5 or 6 year interval if the prop is less than halfway through the hour recommendation. This gives the prop a good inspection, replaces the aging grease and seals, and gives the blades a clean up and repaint. This will allow the prop to operate safely for another calendar period.

Stockton Propeller is a full-service propeller overhaul and maintenance facility in Northern California with the needed equipment and expertise to perform the needed inspection and service on your propeller. Get inspection and maintenance before a failure happens on your aircraft. Contact us today.

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