What about rotten wood?

[Bill Poynter]

The guys who are rebuilding or who have rebuilt their Cadets have probably found some rotten wood during the process.  What do you think are the most likely locations for wood rot on the Cadet airframe? 

Have you ever considered treating the wood with some sort of fungicide or algaecide product?

[Woody]

If you type in wood rot on planes there is a wonderful article on that.  I've read it but don't remember where it is.  This is a deadly culprit with wood.  It is a fungus and it can weaken wood if not stopped or replaced.  There is products that say it will kill the spores in the wood but I would rather replace it with new wood and feel safe.  There is several articles on crashes from wood rot causing severe wood failure in airplanes.  One that comes to mind was a Bellanca that broke up in flight.

[Bill Poynter]

Hi Woody,

Here's a link to the article I think you may be referring to: http://www.culvercadet.com/woodrot.pdf

[Bill Poynter]

What I have in mind is pre-treating the wood so that the rot spores won't ever get started. There used to be a product for preventing wood rot, that contained pentachlorophenol. It was a clear thin liquid that left no visible trace.  I think the EPA made them take it off of the market though.  Perhaps there is a replacement that's not so hazardous.

[Woody]

Thanks Bill ~~ Yes that was the article I read and it really got my attention.  I also looked into treatment of the wood but the A&P that worked on the plane was so through that I did not investigate any more.  At least by replacing dark wood you know you are safe in such.

[Paul Rule]

Keep in mind that there is no such thing as "dry rot".  If you find "rot" then it is the result of 2 things...

1) The wood was not protected ( not varnished or not "re-varnished" as needed).  A good jarnish coat can get wet with no harm.
2) It subsquently got wet AND STAYED WET for a long time....  then it rotted and you are seeing to dried-out results.
2a)  Rot sproes exist in EVERY PIECE OF WOOD you pick up.  They don't do any harm at all unless they get wet.

If the varnish protection is kept in good condition the (now very old and presumably un reliable) 70 year+ casin glue is as good as it ever was.  Check it out all you want with a good coin tap test which will find rot as well as serarated glue joints.  The important things are to inspect very carefully and throughly (probe with an ice pick if you need to...that's FAA approved!) and don't let your Culver get or stay wet for very long.  If in a humid environment,  you might open up and ventilate with a fan regularly or leave a lightbulb lit and hanging in the cockpit.

Almost always the Cadet fuselage suffers from miosture, not the wings.  Why? Because the wings upper surfaces are an unbroken sheet of fabric and funnel rain into the rear spar attach point and into the flat tail cone belly skin.  It is hard to get all the corners and edges varnished inside there and the seat structure, belly plywood and lower longerons seem to suffer about 90% of the damage.

The Helton Larks and several modified Cadets have a large belly inspection doors just aft of the rear spar... large enough to get your head and arms in.  Gives you a real chance to inspect and protect in there.

[Bill Poynter]

I believe that wood rot is a major reason that there aren’t a lot more Culvers around today.  In the 1940’s and 50’s, most planes sat out in the weather.  Since getting rained on wasn’t compatible with their all-wood airframes, a lot of Culvers developed rotten wood.  The first thing to go was the floor of the fuselage, followed by a number of other places where moisture could linger.  A lot of airframes were simply scrapped because of wood rot.  I’m sure their engines went on to other airframes. 

Having owned 12 either all-wood or wood-winged airplanes over the years, I’ve given a lot of thought to wood deterioration.    I concluded a long time ago that there are three things that must be present for wood to rot.  They are moisture, rot spores and warm temperatures.  If you take away any one of those things, you don’t get much rotting.  An example of temperature affecting rotting is found in wooden boats.  You see very few of them in the south.  In cold northern waters you’ll find lots of beautiful mahogany runabouts on the lakes.

The easiest of these factors to control is moisture.  If you simply store the Culver inside and avoid the temptation to wash it like you would your car, rot shouldn’t be much of a problem.  Keeping it dry will also help avoid problems associated with plywood delaminating, wood splitting and glue-joint failure from swell-shrink cycles.

My reason for starting this discussion is that I think it would be useful for us to develop a pre-buy type of inspection checklist, tailored for Culver Cadets.  Among other things, it could point out the most common/critical areas to inspect for damaged or rotten wood and failed glue joints.  This checklist would be useful for both those looking to buy a Culver and those operating an aircraft that hasn’t been restored for many years.     

[Woody]

I think that is an excellent point Bill!   As in my case, I think I was just lucky and the guy selling the plane was honest which resulted in a good exchange.  Had I known what to look for I might not have been in such a hurry and would have been much more prepared to start a project.

[Paul Rule]

Bill, I did not intend to divert your thread...    In looking at my ANC-19 (Wood Aircraft Inspection & Fabrication 1951) :

"Lumber with a moisture content of less then 20% will not stain or decay." 

"Fungi will grow in wood only if both air and water are present, and at temperatures between 35 and 100F.  This varies widely with different fungi."

"The temperatures used in kiln drying are usually sufficiently high to kill any organisms that might be present in the wood.  It is difficult to air dry lumber quickly enough to prevent infection."

There are several paragraphs talking of the importance of good drain holes, marine grommets in critical areas, drain holes at the extreme trailing edge (not 1" away), gasket seals on control cables, and boot.  There is also a paragraph that cautions about fungicide treatments because they might later weaken the glue joint by limiting the glue penitration.

Some indications of infestation do not weaken the wood to any degree and others do.  Example:  brown spots on planed sitka spruce are not usually a problem but longer streaks are (other then sap streaks which are different).

The discussion then becomes very technical (14 pages) listing many different infestations and their scientific names.