wood species question

I'm looking to start a home built aircraft. Does anyone have any suggestions on which type of lumber to use that's a good alternative for sitka spruce?

Thanks

Stewart Glenn" wrote in message
om...
I'm looking to start a home built aircraft. Does anyone have any suggestions
on which type of lumber to use that's a good alternative for sitka spruce?

Thanks

Stewart............

While there are several alternatives to Spruce, each has specific
differences, usually on the downside. I must ask, what is the point? While
you may save 50% over the cost of Sitka Spruce, you have to figure that the
cost of the wood is perhaps 20% of the cost of the total aircraft. A little
math reveals that using an alternative wood may save you 10 % of the total
cost.

Even in these days where Spruce is not nearly as plentiful, there are
wholesalers with piles of Spruce 200' long and 100' high and 100' wide. Not
all of it is aircraft quality, but there is plenty for a few more airplanes.
The fun of working with the real stuff is worth the extra few bucks!

Rich S.

I just wish I could find some decent stuff locally, even when you find a
good price that freight shipping just kills ya!

Patrick
student SPL
aircraft structural mech


"Rich S." wrote in message
...
Stewart Glenn" wrote in message
om...
I'm looking to start a home built aircraft. Does anyone have any
suggestions on which type of lumber to use that's a good alternative for
sitka spruce?

Thanks

Stewart............

While there are several alternatives to Spruce, each has specific
differences, usually on the downside. I must ask, what is the point? While
you may save 50% over the cost of Sitka Spruce, you have to figure that
the cost of the wood is perhaps 20% of the cost of the total aircraft. A
little math reveals that using an alternative wood may save you 10 % of
the total cost.

Even in these days where Spruce is not nearly as plentiful, there are
wholesalers with piles of Spruce 200' long and 100' high and 100' wide.
Not all of it is aircraft quality, but there is plenty for a few more
airplanes. The fun of working with the real stuff is worth the extra few
bucks!

Rich S.

On Wed, 13 Jul 2005 23:30:13 GMT, "Stewart Glenn"
wrote:

I'm looking to start a home built aircraft. Does anyone have any suggestions on which type of lumber to use that's a good alternative for sitka spruce?

Thanks

I fly an all-wood airplane, so I've become educated on it somewhat.
The most often mention replacement for aircraft quality spruce is
Douglas Fir. But I've not found any of the aircraft wood suppliers
that sell it. They all have spruce. The Hughes HK-1 was made from
Douglas Fir, not spruce, even though it has always been called the
Spruce Goose. Even if the aircraft suppliers carried Douglas Fir, it
would probably be priced close to spruce. It's 23% heavier, but is
stronger. So after you reduce it's size the weight penalty is only
around 6%. When I grew up in Miami, several of the local builders
used to go to a local lumber yard and select aircraft quality pieces
of Spruce, and used it in their Pitts Special projects. So if you
trust your ability to choose wood of aircraft quality, you should be
able to obtain it locally. The builders I knew were in Homestead, and
built their projects with an occasional visit from Curtiss Pitts. Whom
I'm sure would have pointed out sub-aircraft quality wood if he saw it
in their projects. You might find someone at the local lumber yard
that could select aircraft quality pieces of wood for you.

There are many types of wood that can be used in constructing a proper airframe, as per AC-43.13b.

I happen to like northern white pine, which has nearly the same strength-to-weight ratio as spruce -- and better than that of Douglas fir. NWP is about 15 percent lighter and about 15 percent less strong than spruce, so if your plans specify spruce you will want to increase the dimensions by about 15 percent.

Buying aircraft-certified spruce is certainly the easy route, but it is expensive. I think the savings of selecting good lumber from a lumber yard are well worth the effort. In my area, the Great Lakes region, there is lots of good clear white pine. I can go to any number of lumber yards in the area and select excellent boards that will make lovely longerons, ribs, etc.

For a single-seat Minimax-type airplane, I could probably buy all the wood I need (excluding plywood) for about $100. If you buy certified wood you will pay ten times as much, plus shipping. I don't think that's insignificant. For a two-seat airplane the total cost of lumber and plywood can easily exceed a couple of thousand dollars. Using alternative wood sources you can get started on building the airframe with a minimum layout up front -- if you find that building an airplane is not for you, you will not have paid a lot of money to learn that lesson.

Plywood is a similar story. I can buy excellent Lloyd's approved okoume ply at a marine supplier for a fraction of what I would pay for certified aricraft birch ply. In fact I have more faith in marine ply becasue there is a robust market for it worldwide. Aircrft ply is a nearly extinct market -- it is the lowest priority for the plywood manufacturers, so not much attention is paid to how good the product actually is.



What is really important is to learn as much as you can about wood and how to grade it, in order to properly select lumber from a pile (or plywood for that matter). There are a number of good sources of info, including chapter one of AC-43.13b. Ther are many more source of info, including a good littel book from the EAA.

Once you have selected your lumber it is important to know how to work it and glue it. You have to develop an understanding of grain and how best to orient it. End grain will soak up a lot of glue, for example; yet most of the joints on wood airframes are end-grain butted against face grain.



Also, since most of the lumber you will find at the lumberyard is flat-sawn, you will not be able to use such boards where the plans call for quarter-sawn, such as in solid-plank wing spars. However, you can laminate your spars from several pieces of 1x1 with the grain oriented the correct way. (If you cut a flat sawn 1x6 board into six pieces of 1x1s, you will have the same thing as quarter sawn wood and can use it for longerons, stringers, rib stock, etc.)

Scarfing is another issue that has its subleties.

So you see just buying aircraft-certified wood is no guarantee of a properly constructed wood airframe. It is simply assurance that the wood has been graded properly, which is something you can do yourself at a lumberyard if you learn how.

There is much skill in building with wood, as can be seen in wooden boat building. A good boatbuilder will build a lovely craft from a pile of floorboards salvaged from a an old farmhouse, while others will not do nearly as well even with the best materials money can buy.

When it comes to working with wood, there is no sbustitute for knowledge.

Regards,

Gordon Arnaut.





"Stewart Glenn" wrote in message om...
I'm looking to start a home built aircraft. Does anyone have any suggestions on which type of lumber to use that's a good alternative for sitka spruce?

Thanks

I have been building my plane out of Doug Fir. Although there are times
that the wood splits, after a while you learn how to keep that at a
minimum. Good Doug fir is not hard to find but you do have to go
through some stock to find what your looking for. I milled my pieces
out of 4x4's from Home Depot. When it came time to get longer good
pieces, I contacted a company in Oregon to ship me rough sawn stock. I
got lucky that the saleman was interested in what I was doing and hand
picked the grain for me. Also I found that the rough sawn was a better
way to go when milling your own. I wish I would have started there
instead of ending there.

As for Sitka Spruce, stay away from the advertised companies and look
in the phone book for specialty lumber companies. I found a place in
norhtern Illinois that has good quality straight grain sitka at half
the price. They just don't advertise it as aircraft, no liability.
Also, don't tell them that your building a plane.
Lou

"Lou" wrote in message
ups.com...

As for Sitka Spruce, stay away from the advertised companies and look
in the phone book for specialty lumber companies.

One thing I would add to this. If you buy wood from a Canadian outfit, there
was (and still may be) a prohibitive tariff. If they label it "Aircraft
Parts", no tariff. I know this goes against the advice of not telling them
what your going to use it for. Mebbe you could tell them your going to use
it for a boat, but want it labeled "Aircraft"????

Oh what a tangled web we weave. . .

Rich S.

Gordon Arnaut wrote:

There are many types of wood that can be used in constructing a proper
airframe, as per AC-43.13b.

I happen to like northern white pine, which has nearly the same
strength-to-weight ratio as spruce -- and better than that of Douglas
fir. NWP is about 15 percent lighter and about 15 percent less strong
than spruce, so if your plans specify spruce you will want to increase
the dimensions by about 15 percent.

Trouble is it isn't that simple. Strength of many load bearing members
(those loaded in bending or torsion, for example), is a linear function
of size. It would take virtually a re-engineering of the structure to
change species in most cases.


Matt

Matt Whiting wrote:
Gordon Arnaut wrote:

There are many types of wood that can be used in constructing a proper
airframe, as per AC-43.13b.

I happen to like northern white pine, which has nearly the same
strength-to-weight ratio as spruce -- and better than that of Douglas
fir. NWP is about 15 percent lighter and about 15 percent less strong
than spruce, so if your plans specify spruce you will want to increase
the dimensions by about 15 percent.


Trouble is it isn't that simple. Strength of many load bearing members
(those loaded in bending or torsion, for example), is a linear function
of size. It would take virtually a re-engineering of the structure to
change species in most cases.


Matt

Matt, did you mean to say that it is NOT a linear function of size.

Take a cantilevered beam. Regardless of the thickness, it's bending
strength is the square of the thickness times the tensile strength. Say
the beam as designed is 1" thick and can hold 1000lbs. You substitute a
material twice as strong. Make it 1" thick and it can hold 2000lbs.
Cut it in half (because it's twice as strong) and it can only hold

(.5")^2 * 2000lbs = 500lbs.

I'm not a mechanical engineer, and I've learned just enough to know that
I don't know enough, so I may be wrong on the particulars; but I know
for a fact that twice as strong but half as thick doesn't get you to
where you started.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Ernest Christley wrote:
Matt Whiting wrote:

Gordon Arnaut wrote:

There are many types of wood that can be used in constructing a
proper airframe, as per AC-43.13b.

I happen to like northern white pine, which has nearly the same
strength-to-weight ratio as spruce -- and better than that of Douglas
fir. NWP is about 15 percent lighter and about 15 percent less strong
than spruce, so if your plans specify spruce you will want to
increase the dimensions by about 15 percent.



Trouble is it isn't that simple. Strength of many load bearing
members (those loaded in bending or torsion, for example), is a linear
function of size. It would take virtually a re-engineering of the
structure to change species in most cases.


Matt


Matt, did you mean to say that it is NOT a linear function of size.

Take a cantilevered beam. Regardless of the thickness, it's bending
strength is the square of the thickness times the tensile strength. Say
the beam as designed is 1" thick and can hold 1000lbs. You substitute a
material twice as strong. Make it 1" thick and it can hold 2000lbs. Cut
it in half (because it's twice as strong) and it can only hold

(.5")^2 * 2000lbs = 500lbs.

I'm not a mechanical engineer, and I've learned just enough to know that
I don't know enough, so I may be wrong on the particulars; but I know
for a fact that twice as strong but half as thick doesn't get you to
where you started.


Yes, that is what I meant to say. Too bad my fingers aren't always
connected to my brain. Hopefully, the context of the rest of what I
wrote made the typo obvious.


Matt