I went to the local specialty wood shop to find some Sitka Spruce for my wing ribs. The "expert" there said that Sitka Spruce is Sitka Spruce and there is no distinction for "Aircraft Grade" Sitka Spruce.

This doesn't seem to jibe with something I recall reading somewhere.

Can someone set me straight on this before I go and build a bunch of junk ribs out of crappy wood?

Thanks

Nick

Alright, I answered my own question by finding this article

http://www.sirius-aviation.com/grade.html

In case anyone else is interested.

Anybody know of an aircraft grade sitka spruce supplier in Western Canada, preferably West Coast?

Thanks

Nick

There is one other wood that I would consider, Western Hemlock is a slight bit stronger and weighs but a bit more. I have picked up a few boards from Lowes and the grain is just great. I have talked with a few of the old builders and they used this a lot. I am using this for my ribs and if I can get the correct dimensions will use it for spars also. Jim

I wish the old mil-spec for aircraft Spruce was still available,
but it is now out of print.

Assuming the dealer has some Sitka Spruce, you can grade it yourself to A/C Grade----

No less than 10 growth rings(the lines across the end grain) per inch, measured perpindicular to the rings.

A slope of not more than 1 in 15 for the grain parallel to the
edge of the board.--(you can correct this yourself by sawing an
edge on a wide board parallel to the grain).

Ideally, the grain should be parallel to a face or an edge of the board.You probably won't find any with the rings parallel to the edge, as this is "edge grain" and is required for spars.Flat grain would generate more rib sticks, but you'll probably have to settle for something 30 to 45 deg angled, but this is OK, it just generates a little more waste.

You can correct this by angling the saw blade so that it is either parallel or perpindicular to the growth rings when you rip them into thin boards. At this time you should have a thin piece of plywood, masonite, or even aluminum, with a slit in it just big enough to allow the hollow ground fine tooth blade to penetrate.(this is to prevent the blade from dragging the thin strips down under the table & making you angry.
Your fence will have to fit over it, so it can.t be too thick .
Clamp it firmly to saw table. Ignore what knots you have, until the final sizing then cut the pieces you need from between the knots. If you're lucky you may get two sticks from each little board.
Your biggest difficulty will be getting some pieces long enough for the top & bottom strips.You may have to order some expensive stuff just for this purpose. when you are through, you will have a big pile of sawdust & angled scraps and a few good sticks.

Save the good angled pcs, they may make good glue blocks.

Some wiser heads will have to tell you which way to orient
the grain of the top & bottom strips.--( hope you don't get two
different answers.)

Jerry

Hi Jerry.

That's an interesting answer. Thanks.

Am I to understand that I should probably get "Certified aircraft grade" for the spars but can grade by eye myself if it is for the wing rib cap strips?

Thanks

Nick

Nick--

Why dont'cha order a pc or two from wicks or someone, (I ordered mine 10 years ago from Airspace Goose , and they raised the price 3 times and then two of the boards were NOT acceptable-(had an
up & down grain which was dodging a knot one or two planks away
from the one I got}--lay it flat & you could plainly see the
whiskers on each side of the imaginary knot . Then this outfit told me "we bought it from a certified mill" and therefore it's certified!!!

Read some of these publications before you do your own grading--

http://www.fpl.fs.fed.us/documnts/FPLGTR/fplgtr113/fplgtr113.htm ( the forest products lab handbook)

and http://naca.larc.nasa.gov/--(there's a search index there
somewhere---

lotsa good stuff here, written by the boys that built wood airplanes way back when--

Jerry

Thanks for those references, Jerry. Some great material in there. I never knew there was so much to a hunk of wood!

;D

Nick

Thanks to all for the advice and wisdom. I managed to find a very fine piece of Sitka Spruce locally that will likely make up all the cap strips for all four wings. Using various specs and visual inspection methods, I was able to determine that the wood will do nicely.

Still seeking a local supplier for certified Aircraft Grade Sitka Spruce for the spars. My Dad has offered me a very large Sitka Spruce that is growing on his farm, but it would be a great shame to cut it down, mill and dry it and find out it's not good enough.

Who knew it would be this difficult to find AC grade on the West Coast where it's grown!

The search continues.

Nick

Nick,

When I was ordering rib materials I enjoyed a visit to the Wick's factory just outside of St. Louis. They began as a pipe organ building shop, and used a lot of Sitka spruce for the organ pipes they built. Gradually airplane builders found out about their supply of good wood and began asking to buy some from them. That, they told me, is how Wicks Aircraft Supply came into being.

They have a wonderful planing-dimensioning shop for their spruce. I ordered my rib materials from them and my rib stock arrived perfectly sawn and accurately dimensioned. That was several years ago, but I was extremely pleased. I recommend them highly.

For spars, I was fortunate to live near a real old-time wood and fabric guy, Gus Wiebe, at Halstead Airport in Halstead, Kansas. A visit to his shop is a real trip back in time. Gus and his sons take a trailer to your part of the world once every year or so and bring back beautiful spruce that they saw and plane into spectacular spar stock. Gus is getting up in years now, but could probably tell you where he buys his spruce if you called him. I am sure the number for the Halstead airport is available; also, his son, Dave Wiebe runs the El Dorado, Kansas, airport.

There is an old FAA publication that talks about wood grading...I don't recall the number but I am sure the EAA could help you find a copy. As an historical interest I also read some old engineering texts from the 20s-40s that talked about use of wood in aircraft construction. They have extensive descriptions of grain, etc as well as tables of mechanical properties for many different woods. The department of special collections at Wichita State University (Wichita, Kansas) is very helpful if you have an interest...they have many old texts because of the extensive history of aircraft manufacturing in Wichita (Travel Air, Cessna, Beech, etc). Most of the books I looked through were from the collection of Herb Rawdon, who was the chief engineer at Travel Air. If you would like to find out more, call the library at WSU, ask for Mary in special collections.

Enjoy!!

Paul Uhlig

Thanks for the words of wisdom, Paul. I've been looking seriously at Wicks as a supplier, if I can't find any reliable local shops or mills. The thing is, since some of the best Sitka Spruce is grown in this part of the world, there ought to be SOMEBODY I can buy from around here. But I have heard lots of good things about Wicks so that may be the route I end up going.

Thanks also to everybody else who offered advice both in the forum and through private email. I've learned more about wood properties and grading in the last few days than I ever thought I wanted to know!

Nick

With the demise of our forests and the low quality of the wood being sold in the marketplace, have any of you HATZ builders, conducted and engineering analysis (FEA), on the use of carbon fibre composites for the wing sections and compared the results to that of sitka spruce components???

Yeaaaaah , but sometimes those little carbon fibers break and
stick in your body parts .

Besides, wood feels good, smells good, & looks good.----and it's
just fun to play-(work)- with.

Jerry

For everyone's information, I have located a local (BC) supplier of aircraft grade Sitka Spruce that comes in at about a third the price of ordering it from Wicks or Aircraft Spruce & Specialty. I guess this is because I'm buying direct from the people who cut it down instead of paying for it to go across the border to the US to be milled, then sent back across the border again.

This is beautiful old-growth timber, kiln dried, cut to spec, guaranteed free of defects. Here's the website:

http://www.timberwright.ca/index.html

for those who are interested.

Nick