Wooden Propeller Question

[Steve]

Do Wooden propellers require any additional maintenance or attention than metal propellors? I'm considering buying an aircraft with a wooden prop with 50 hours TT on it. Thanks for any help.

 

[tarp]

I am not a "wood" expert, but these are the rules as I know them:

1.) Wood props are more susceptible to shrinking and expanding with temp and humidity changes, therefore it is a good idea to have them re-torqued every 100 hours or year whichever you are more comfortable with.

2.) The protection of the wood prop comes from the epoxy, varnish or polyurethane coating that is on it. I hear words like five coats vs. 8 coats which describes how many layers of the coating are on the prop. If this starts to disintegrate or is damaged by a stone/FOD/whatever, then you need to dress and re-apply the coating as is necessary. This may take many steps and many days.

3.) There are all manner of leading edge protectors available on the market from good old fashioned brass edges to urethane add-ons (like thick clear tape that folds over the edges). A lot of the modern prop guys swear by these new edge protectors.

4.) Paint your tips white instead of red. Safety over pretty. The white tips create a noticable band (circle) when the prop is turning and keeps more unsuspecting folks away. Red tips, while pretty, kind of dull out to the same shade as the prop wood material.

5.) If a puller type, go ahead and paint the back of the prop in flat black - the glare off a wood prop with a nice clear coat on it is uncomfortable at best when heading either into the sun or away from it.

6.) If a pusher type, use the leading edge material as described above. The gear/wheels tend to kick up stones that hit the prop. Do a very good nick inspection for each flight on pushers.

Wood worked very well for a great many years as the standard for props. The new laminates and urethanes make them more durable than ever.

If purchasing a new prop, try to get the "cruise" version of the prop. A cruise prop can be turned down slowly to a climb prop by shaping and removing wood. A climb prop cannot be changed back into a cruise prop.

That's all I know.

 

[aggiepilot87]

You may have to periodically retorque the bolts. Sensenich recommends rechecking every 50 hrs. There are also special torquing procedures for new installations (install, torque, loosen, retorque, run for 10 days or 10 cycles and retorque... something like that).

Generally, try and keep it dry. Unless it has a leading edge protector, don't fly through rain. I wouldn't fly through rain in either instance if you can help it.

Keep the prop waxed/sealed. Check with your mfgr for their recommendation, but paste auto wax would probably work fine. If it has one, keep the holes in the tip protector clean so water will drain. Repair any dings in the wood finish quickly to keep moisture out of the wood.

 

[avbug]

The number of hours on the wooden prop aren 't too important, as wooden props don't have fatigue limits, and aren't susceptable to fatigue the same way metal props are. The condition in which it was stored, and of course it's present condition, are very important.

Check the bolt holes for corrosion from bolts, and look for any possible evidence of wood rot. Usually this isn't visible even if present, but always check. The same for brass tip or leading edge protectors. Look for loose rivets or any damage to the metal or wood.

Tap-check the length of the propeller using a small metalic object such as a quarter. Don't do it hard enough to mar the finish. You're looking for a distinct change in the sound as you tap. This doesn't work on wood nearly as well as composites, but sometimes it can detect a subsurface flaw. Be especially attentive doing this on wooden surfaces that have been painted.

Do NOT paint the propeller on your own, without guidance from the prop manufacturer. Get specific recommendations on any paint types, thicknesses, etc. Get assistance in painting the prop.

Previous posters mentioned the need for retorque; this is critical on a wooden prop. Whenever the prop isn't turning, Place the blades horizontally. Don't have them vertically, lest you get an accumulation of moisture in the lower blade and an imbalance.

Check the outer coating integrity; if it's checked or flaking away, it can allow too much transfer of moisture. It may need to be resurfaced. You cannot do this on your own if it's going on a certified installation.

Check the laminates closely for signs of separation or other weaknesses and damage. Check the boltholes for elongation, or wear. Check the tips for damage or cracking. Check the hub faces for flaws or imperfections. The opposite faces must be exactly flat, and parallel, and the bolt holes must be perpendicular. This is seldom a problem with established manufacturers, but there are a lot of propellers out there which are made by small shops or unknown makers. If you happen to have an STC's prop from such a maker, use caution.

Be absolutely sure the diameter and pitch, and serial number is appropriate and approved for your installation. Unlike a metal prop, you can't take this one back to be repitched. Propeller-engine combinations are very critical for purposes of balance and vibration.

On the subject of vibration, you'll likely notice a big improvement right away. Wooden propellers tend to dampen vibrations noticably, and aren't subject to much of the harmonic issues that limit metal props.

Consider getting some propeller cuffs or covers to protect your prop when not in use. Also consider some quality leading edge protection tape for your prop; it's more easily damaged than a metal prop. Many propellers already come with nylon or epoxy leading edges, and synthetic or brass tips. If your prop doesn't have these protections, consider having something done for the leading edge. It's worth it in the long run.

As always, don't reuse your propeller bolts. Install new bolts and hardware when putting on a new prop. Enjoy.