PT-13/17 prop preservation

[Tim]

Yesterday I was very excited that I finally picked up a 1944 prop that came off a PT-13 or PT-17 ...including the hub. I need to make a bracket to mount it on the wall, but before I do that, I'd like to do a little restoration/preservation work. The wood is a bit dry and has a few cracks and some splits between ply's. I was thinking about injecting some wood glue into the cracks and wrapping a nylon tiedown around any splits to try to close the gap. I also thought it might help to oil the wood (avoiding the maker decals), but I'm not sure if that would do more harm than good. Do you have any recommendations? ...things to avoid? I don't want to make it bright and shinny, just preserve what I have.

Thanks a bunch,
Tim

[MWP_Lamar]

The "splits between plys" is called delamination. I don't know that I would attempt to repair these, perhaps someone else will have a good suggestion. The general care and feeding of your prop is described in this thread to this forum: http://woodenpropeller.com/forumvB/showthread.php?t=674

Lamar

[Tim]

Thank you, I definitely agree that little to nothing should be done in most cases. The prop looks great the way it is. My biggest concern is preserving it. I've been wondering wondering if applying a couple coats of some kind of furniture oil would help or harm. I believe most of the varnish has worn off.

The delamination isn't too bad but there is one ply that sticks out just a little bit, and it seems like it would be pretty easy to glue and "clamp" it down with a nylon strap until it's dry.

By the way, what is the function of the fabric covering the distal ends of each blade?

-T

[Bob Gardner]

Tim,

There is always a compromise between the size of a fixed taildragging undercarriage (which had to be as short as possible to reduce drag) and the length of a prop (which generally had to be long). This resulted in the tip of the prop being close to the ground, which, incidentally made three-point landings mandatory. The consequence of the blade tip very close to the ground was that the airflow threw up dust, sand, grass, water and FOD in general which was much akin to sandblasting and eroded the protective varnish quickly; hence fabric, which on British aircraft was Irish linen, and which was used as an ablative shield.

A by-product was that the doped linen gave strength to the prop which allowed you to get home in WW1 with a few enemy rounds through a blade, without it disintegrating. Therefore the British use of linen quickly grew from six inches or so at the tip to covering half the blade and very soon almost all the blade.

With kind regards,

Bob

[Bob Gardner]

Tim,

An afterthought; increasing the humidity might close up the laminations. And then polish it with beeswax once a month for a year or two.

With kind regards,

Bob

[Tim]

Ah! That hadn't occured to me but it makes obvious sense to use fabric as a wear gard. ...just like the plastic film we use on modern helicopter rotors and ipods!

Apparently this propeller came from storage in Arizona City, explaining the delamination and cracks. It is now on the west coast, so hopefully the higher humidity will help.

Are there any particular brands of beeswax that you like to use?

thanks a bunch,
Tim

[Bob Gardner]

Tim,

You might consider spraying the prop with water or even immersing it in a bath of water. It will enable the wood to absorb moisture and it will swell. When the delamination has been reduced, use pure beeswax, which you should be able to buy on the internet. Bees only make one type but it must come out of a tin. Some is sold in aerosols to which modern silicones have been added. These are too powerful for old finishes.

With kind regards,

Bob