Strength by species

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mcrae0104

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From time to time, the relative strength of wood species is discussed here at HBA. I recently ran across the following video from Fisher Flying Products.


Below I have transcribed their results, which I find questionable. Although the weight of the test samples is mentioned, interestingly, there was no mention of the relative strength-to-weight ratios. There are some obvious problems (consistency in placement of the load and small sample size) although I cannot account for all of the tests exceeding Sitka Spruce's strength-to-weight ratio (pine in particular). If Northern White Pine truly performs 30% better than Sitka Spruce, I expect the aircraft industry never would have used Sitka.

SpeciesSpecific gravityLoad carriedUltimate stress (Fb)Strength-to-weightComments
Sitka Spruceas-tested:
ANC-18:
0.415
0.40 avg., 0.36 min.
41.55 lb
37.30 lb (calculated)
10,471 psi
9,400 psi
107%
100% (control value)
result closely matches book value when corrected for higher specific gravity
Northern White Pine
Eastern White Pine
as-tested:
ANC-18:
0.395
0.38 avg., 0.34 min.
47.85 lb
34.52 lb (calculated)
12,059 psi
8,700 psi
130%
97%
ANC-18 values listed are for EWP; both NWP & EWP are Pinus strobus
Yellow Poplaras-tested:
other source:
0.519
0.37 - 0.59
50.90 lb
40.47 lb (calculated)
12,828 psi
10,200 psi
105%
83%
not listed in ANC-18
Douglas Firas-tested:
ANC-18:
0.447
0.51 avg., 0.45 min
46.45 lb
45.63 lb (calculated)
11,706 psi
11,500 psi
111%
96%
performed 15% better than expected despite low specific gravity
 
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TFF

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I think everyone should build with their local ironwood equivalent.

It is not a good test, but I understand why they did it that way. They need consumers to be on their side.

With the Sitka Spruce, the only way to be legitimately test is buy some from Aircraft Spruce. Not that they don’t have returns for quality, but the junk is almost certainly some of the best wood. You have to use the standard to talk about standards. Too scared to test to the real standard.

I have two 4x4Doug Fir posts from Home Depot. When I go I look at that little pile among the fast growth pine. They can be really close to airplane wood. Not main spar good, but good. It took two years to find these. There are always pieces that have good sections, but not good for 8 ft. Do they end up in a plane, RC plane, or dining room table?

There is also a build blog of British wood plane in the US. Trying to use local wood; budget build. Lots of complaints of wood not being to spec. The builder buys some from ACS, and there is a grasp of what airplane wood is over wood. The price becomes understandable.

Im not saying, don’t use something else, but a substitute has to fit the task. Because it’s all you can get is a not an excuse for OK.
 

dog

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I find the idea of white pine,northern,of which I have piles,and have used piles,bieng stronger than spruce,ummm what?
I just got a pile of eastern white spruce,very fresh from the mill,1x5 for boarding in and 2x12x12 for staging plank,the plank was sawed
while I waited,the one is clear for 10'.
Some of the white spruce I would put up against anything,local black spruce can be much stronger ,but the trees are always knotty,
wicked tough though.But white pine,great stuff,
but a lot of it now is from trees that grow on ridges that were never cut in the past as they are "wind shook" and split unpredictably,perhaps old growth stuff ,but nothing second growth as it has anual rings half an inch wide.
Must be austrailian pine or something else,not from north america or old growth from bottom
land,not going to be much of that.
The pine is stiff but it breaks off clean and suddenly,the spruce is tougher and will bend
and the spruce is more tolerant of fasteners
where the pine will break at nail hole or other
defect.
Pine will cut very thin and hold together.
Actualy have to phone a guy about some 2" pine for trim,not old growth ,but natural regrowth.
 

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TFF

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Who is cutting the thin material for you. There is some laminate furniture I would like to make and that’s perfect.
 

Aviacs

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Who is cutting the thin material for you. There is some laminate furniture I would like to make and that’s perfect
How serious are you?
How long do you need?
What species?

I do this professionally.



e h m co fab at g male dot com.

smt
 

ToddK

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I think the challenges with northern white pine are being greatly exaggerated, and that it would work fine in most cases. If you have some concerns, simply substitute a bit of spruce/ash/fur in places where the pine might not be ideal and move ahead.
 

Kiwi303

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Well Radiata pine is better all round than White pine, so I should be fine if I find anything nice in the bins here. Just got to watch the rings per inch as well as grain slope and direction. Tasman forests are known for high-strength pine compared to the likes of Kinleith grown pine.
 

Lendo

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From Memory I remember researching for a Spruce substitutive and finding Radiata Pine was acceptable. It has good strong grain but it is heavier.
George
 

Mad MAC

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It should be pointed out that the standard deviation of wood properties (strength, fatigue, stiffiness etc) is very large (compared to metals), which means premium selection really, really matters, as does ensuring any testing uses large sample sizes.

There is the possibility that modern inspection techniques (100% of material machine testing etc) could make great improvements on the allowable design strength of less suitable species.
 

Kiwi303

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This is the best I had on Radiata, a PhD thesis from 2000 from Canterbury University in Christchurch here in NZ (Not to be confused with the University OF Canterbury in the UK, or the Canterbury Christ Church University again in the UK)

On;y problem being is it's based on the structural timber industry requirements and done using unpruned trees, knots and all.
 

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Goflybefree

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White pine has been used for years by TEAM and others. These aircraft were designed to use it from the start (the stress reports show that to be the case).

My understanding is that Fisher are using old growth Northern White Pine, not plantation stock.

The Europeans have used Baltic Pine (Pinus Sylvestris) for decades in gliders and light aircraft. This is not unlike White Pine and Radiata Pine.

The Australians have used Hoop Pine fairly widely in aircraft and some other timbers such as Klinki Pine and Huon pine to a lesser extent.

Robin built thousands of certified light aircraft using Douglas Fir. Also Delemontez designed his last Jodels (D.18/19/20) to use Douglas Fir from the start.

We built a fuselage for one of the TEAM aircraft out of Radiata Pine as an experiment and load tested it. No issues. The problem with Radiata Pine (Monterey Pine in the US) is that it is a very knotty timber and it is very difficult to find defect free timber that has acceptable grain slope. Also, it is not common for the commercially available Radiata Pine to be quarter saw, which whilst desirable for aircraft timber for stability, is not essential. Radiata pine does not glue as well as other timbers and discolors. Could you build a safe aircraft from it ? Yes, if you know what you are doing.

The only thing that makes a material aircraft grade is that there is a specification that defines what constitutes aircraft grade material. There is a specification for Spruce (MIL-S-6073). Some of the spruce used in homebuilt aircraft have been shown to meet this, but a lot of it has not been and is just commercial timber. Does that make it unsafe. Not if the builder knows what he is doing and selects the wood carefully following the specification as a guide.

I am aware of aeronautical specifications for Douglas Fir, Baltic Pine and many other timbers. None of these are US standards because Sitka Spruce was so plentiful that substitutes were not required. However, Sitka Spruce is now all but unobtanium and the price reflects that (someone told me recently that Aircraft Spruce has no spruce .... can anyone confirm ?).

I have never seen an aeronautical specification for any species of White Pine. I imagine that the kit manufacturers using it have at least a basic specification controlling density, grain slope, defects and ring spacing.

If people are to continue to build wooden aircraft substitutes will be required. This is more of a psychological problem than anything, as for so long, spruce has been synonymous with wooden aircraft. Workability, glue-ability, stability and other attributes are just as important as strength and need to be considered. It is true some of the alternative timbers are more brittle than Spruce. However, it has never been clear to me why brittleness (measured with an Izod like test) is all that important in a well design wooden structure.

ANC-18 contains design allowables for many timbers. Obviously if you are substituting timber then you need to make sure that the new timber is as strong as the old in all attributes. If it is not, it would be prudent to seek some engineering advice. Strength is strongly correlated with density and when selecting alterative timbers the minimum density specified in ANC-18 should be used to select the timber, otherwise there will be no guarantee that the alternative timber will develop the minimum strengths in ANC-18 that have been used to compare its suitability as a substitute for spruce.

Spruce is nominally 28 lb/cu ft. If you start to replace that with 35 lb/cu ft Douglas Fir you are going to end up with an overweight aircraft. It may be possible use smaller sections (as Delemontez did when designing the D.18) if using Douglas Fir or any denser stronger timber. It might also be possible to pick timber with a lower density than that specified in ANC-18 and use the original member sizes. Either way, engineering advice should be sought as this is not always as simple as it might seem.
 
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TFF

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Douglas Fir has been spec in multiple US plane. PT-17s for one, and to build a Pitts M-12 the spars on the plans have to be. It’s not that you can’t put non airplane spec wood in a plane. The question is if it is loaded to break, will it react like the good stuff? Some places like stringers don’t need to be spar stock, but a spar does. Longerons need to be good. A corner block, not so much.

Spruce glues well; kind of important. Especially for amateur wood workers. DF is recommended to clean right before glue, although that was before epoxies. The weights of species is important with the quality of the ring count. Too light or too heavy and it will not have the anticipated strength. It would be a nightmare to resize a known plane design for a different species, for someone who just wants the plans to arrive and start building. Some want to get all geeky on that; that’s 1%. Everyone else wants to get their plane done. It’s already taxing them to build.

I’m all for alternate woods. In my neck of the woods, from what I have seen, buying good spruce is no more expensive than any other species unless it’s sitting in your back yard. At airplane quality. I don’t care about any other quality because that won’t get a project on its way, or it shouldn’t. Pitts M-12 spars in airplane quality DF will make you sweat $$$.
 

Mad MAC

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This is the best I had on Radiata, a PhD thesis from 2000 from Canterbury University in Christchurch here in NZ.
I can add a little bit, Windflow who were Christchurch based, were building 100 ft wind turbines using clear pine laminate in the blades (about the time that report came out), considered the near infinite fatigue life stress to be 50% of the design allowable for pine. The former Windflow staff probably have the most experience with pine under a demanding load environment.
 

Fiberglassworker

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In the UK Scots pine as it is called is also Pinus Sylvestris) . Some years ago I had a glider with a broken wing that was made with Baltic spruce also Pinus Sylvestris) So I first tried in the UK , I almost got laughed out of the first timber merchant I approached. They did not have any and were not able to get any. Eventually I was able to get the manufacturer of the aircraft ( Which they had stopped making years ago.) to send me repair baulks of pine to splice the spar.
A very useful book if you are working on wooden aircraft of European extraction and some wooden home builds is "Workshop practice" this is an English translation of a book by written in the 1930s on building and repairing wooden aircraft mostly gliders and sailplanes by Hans Jacobs. Translated from German to English by Neil Pheiffer and Simone Short. this book is available through the Vintage Sailplane association. This book also has very useful tables of relative strengths of spruce pine and other timbers.
 
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