'Wow, great information from all of you. Thanks Andrew ,David and Hans.
Sent from my iPad
I used to teach timber design in structural engineering, and yes, it
all depends on storage conditions. Wood is very dynamic in its
response to moisture and will adjust to ambient conditions. If there's
no apparent damage, one other criterion I'd ue is to feel the 'face'
surface. If it's 'ribby', that is, the grain lines are prominent,
don't use them.
Also, check the ends in good light, using a magnifying glass. That's
where cracks will start.
Also pay attention to any plates glued to the spars, and to bolt holes.
I once built a new centersection for a KR-34 when I lived near Austin,
and then moved to Lubbock, which is significantly drier. Over a few
months the wood shrank under the end fittings and cracked from two
bolt holes to the spar ends. The cracks were small, but clearly
visible in good light. (I was able to fix them with plates, without
replacing the spars, but it was a pain.)
If you have any doubts, you can sell them to a local homebuilder for
use as rib or fairing stock. If they look good, even though you may
not be comfortable with them a spars, they will yield a decent amount
of 1/4 sq. rib pieces.
On 7/3/15, Ranchaero Wing Shop
david@ranchaerowingshop.com
[fairchildclub] wrote:
> Mike,
>
> One thing I would keep in mind about old wood is that it sometimes gets
> too dry and becomes brittle. I have no scientific data to back this up
> or to determine any quantitative values but intuitively feel that wood
> can become excessively dry and brittle with age, losing strength and
> resilience to bending. I don't know how you would determine this other
> than through destructive testing. For my own purposes, I observe that
> wood has a certain resonant sound when handled that I associate with
> dryness and brittleness. There's nothing scientific about this - just my
> intuition and experience. Also, this old wood seems very light in
> weight. I would guess because it has such a low moisture content.
> Personally, I wouldn't trust old spars that had these qualities I
> intuitively associate with brittleness from age drying even though there
> was no visible problem. The local climate where the wood lived is likely
> a factor. Aside from dry rot, I believe that seasonal extremes of very
> dry to very damp humidity take a toll on the cellular structure of wood.
> Even though there may be no visible damage, the damage is perhaps on a
> cellular level. If never stressed, this wood might last a long time and
> look fine, but under stress might fail through brittleness.
>
> Personally, I'm quick to replace spars where there's any doubt since
> they are so critical. Spar failures are usually in old wood. A few
> hundred dollars is a worthwhile investment where spars are concerned. I
> could be wrong so do your research. This is all very intuitive for me
> having worked with spruce for many years with spruce piano soundboards
> and spruce wooden aircraft. It's very difficult to scientifically
> explore these questions, though there is probably data somewhere if you
> can take the time to look for it.
>
> David
>
>
>
> On 7/3/2015 8:53 AM, Michael Thomas
michael_thomas8@yahoo.com
> [fairchildclub] wrote:
>> Hans,
>>
>> Thank you for your help. The spars that i have are the original spars
>> from one wing of my airplane and salvaged spars from both wings of
>> another so unfortunately they are not new old stock. The A&P IA that
>> i am working with has not had an opportunity to look at them yet but
>> he told me that he has not had a lot of experience with wood wings and
>> recommended that i see if there is a subject matter expert that could
>> give me a better answer. It is my understanding that the airplane
>> that i have was disassembled in 1961 after it was ground looped and
>> the parts have been stored since then.
>>
>> I live in Marshall so i am only about 50 minutes from Warrensburg.
>> Creve Coeur is about 2 1/2 hours east.
>>
>> Thanks
>> Mike
>> Sent from my iPad
>>
>> On Jul 3, 2015, at 07:38, Hans Friedebach
hans@tsoproducts.com
>> [fairchildclub]
>>
>> wrote:
>>
>>> Michael,
>>>
>>> Age alone does no harm to wood unless the storage conditions were
>>> hostile.
>>>
>>> Sounds like you are near Warrensburg, MO – not that far from that
>>> vintage airplane hotbed called Creve Coeur. Plenty of expertise there.
>>>
>>> Also The AAA Chapter Northwest Missouri, Excelsior Springs airport
>>> 3EX - their Pancake breakfast is July 11^th
http://www.thenew3ex.com/
>>>
>>> Also
http://www.thenew3ex.com/northwest-mo-aaa-chapter/
>>>
>>> How about the A&P / IA you will be working with on your restoration?
>>> You should be working with someone who has the qualifications and
>>> willingness to sign off the 337 for the wood wings they will be used on.
>>>
>>> Curious: were these spars were salvaged from original wings or if
>>> they are NOS spare parts made by the factory or if they are raw,
>>> un-machined and undrilled spar stock?
>>>
>>> Good luck
>>>
>>> Hans
>>>
>>> *From:*
fairchildclub@yahoogroups.com
>>>
>>> [
fairchildclub@yahoogroups.com]
>>> *Sent:* Thursday, July 02, 2015 11:48 PM
>>> *To:*
fairchildclub@yahoogroups.com
>>>
>>> *Subject:* [fairchildclub] Wing Spars Fairchild 24W40
>>>
>>> I have three sets of original wing spars (front and back x 3) for my
>>> 1940 fairchild 24w. All are original but are 75 years old. They
>>> appear to be in good shape but i dont know enough about wood wings to
>>> determine if i should use them or replace them with new. Does anyone
>>> know an expert in wood wings that could tell me if they are useable
>>> or if they should go to the burn pile. They have darkened
>>> considerably with age, dont aprear to have any major cracks and are
>>> straight. How do i know if there is dry rot or anything else that
>>> would render them unserviceable?
>>>
>>> Thanks,
>>>
>>> Mike
>>>
>>> 660-631-3270
>>>
>>
>
>
>
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