Tuesday, November 28, 2006

AV - Douglas Fir Isn't


A fir, that is.

Doesn't really matter of course. Unless you're into botany.

But it's not hemlock, either. Although that's what it most closely resembles. Which is why its Latin name means 'False Hemlock.' (Pseudotsugo... pseudo = false, tsugo = hemlock). The complete name is Pseudotsugo menzieii and gives you a hint there's more than one variety of 'Douglas Fir'. In fact, there's about half a dozen 'pseudotsugos' including coastal, mountain, Mexican, Manchurian and a couple others.

Don't worry about it. Go to a lumber yard, ask for Doug Fir, you'll probably get the pacific coastal variety. Other than being a bit brash, Douglas Fir, also known as 'Oregon Pine,' is fine for all aspects of airplane construction, assuming you can afford the weight.

But don't mention airplanes. Tell them you're looking for sucker rods or stair treads or ladder rails. (A sucker rod is that thing going up & down on a windmill. Up to 28 feet long, perfectly clear- grained Doug Fir, up to 4x4 in the middle, thinned down to 2x2 on the ends.) Stair tread stock tends to be heavy, with ring-counts of 16 and up. Ladder rails were long the standard for airplane spars, in both spruce & fir.

Lumber yards that cater to this particular trade usually buy clear-grained balks of Doug Fir in 4x6 or 4x10 rough cuts, up to 32' long. They'll slice off what you need and finish it, too... if they've got the tools. Real lumberyard can start with a tree, give you rungs for a chair.

Here in Sandy Eggo county I think we've got three real lumber yards left. One caters to boaters, one to farmers, the third to yuppies. It's a sixty mile drive to the farmer place but always worth the trip. Little place. Been there forever. They buy about two truck- loads of Select Grade-A DF a year from a little lumber mill in British Columbia, turn it into sucker rods, wagon tongues, ladder rails, pruning poles and the like.

Sitka Spruce is lovely stuff to work with but there are more than a dozen alternatives listed in AC43-13. Lotsa Piper Cubs flew on spars of 'Oregon Pine' and the first Pietenpol used edge-glued Hemlock for spars (according to Mr. Pietenpol).

PS - Some Douglas Firs are bigger than others :-)

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