Page last updated 13/6/2006
The following table was collated with particular interest in propeller manufacture but does include some species (particularly Douglas Fir) which can also be used in aircraft construction.
From the table it can be clearly seen that spruce has a huge advantage in stiffness and strength to weight ratio and is perfect for airframe structures, while beech and maple are best for propeller construction. There are a large number of other species not mentioned which may be viable alternatives but if you are repairing an existing structure it is vital you use exactly the same as what came out, this is to prevent the transfer of loads to the wrong parts of the structure. This is the same reason why a structure should not be stiffened or strengthened unless a clear weakness has been identified, strengthening one area will only transfer the stress to some other part.
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Density | Modulus of Rupture |
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| Hickory | 692 | 138.77 | 12,886 | n/a | 20.76 | 7,553 | |
| Beech Hard | 687 | 126.43 | 14,581 | 59.94 | 17.50 | 6,745 | |
| Saligna | 660 | 90.88 | 11,090 | 56.13 | 11.55 | 5,250 | |
| Tawa | 645 | 114.42 | 13,168 | 39.20 | 12.09 | 4,759 | |
| Elm Rock USA | 630 | 102.00 | 10,600 | 48.60 | 13.20 | n/a | |
| Maple | 630 | 109.00 | 12,600 | 54.00 | 16.10 | 6,400 | |
| Beech Mountain | 607 | 115.50 | 12,512 | 59.30 | 14.78 | 6,082 | |
| Beech Silver | 592 | 99.90 | 11,991 | 47.03 | 12.46 | 4,525 | |
| Pinus Radiata Hi Den | 572 | 114.27 | 11,678 | 48.94 | 14.96 | 6,525 | |
| Eucalyptus Fastigata | 560 | 110.64 | 11,679 | 47.91 | 12.31 | 4,466 | |
| Matai | 534 | 76.35 | 8,119 | 47.00 | 13.30 | 3,353 | |
| Rimu | 504 | 88.39 | 9,555 | 39.29 | 13.69 | 3,466 | |
| Cherry Black USA | 500 | 85.00 | 10,300 | 49.00 | 11.70 | 4,200 | |
| Elm American USA | 500 | 81.00 | 9,200 | 38.10 | 10.40 | 3,700 | |
| Kauri | 495 | 81.76 | 8,704 | 39.21 | 12.38 | 3,202 | |
| Macrocarpa | 436 | 75.96 | 7,418 | 39.74 | 11.37 | 3,217 | |
| Douglas Fir | 427 | 81.12 | 9,159 | 43.09 | 9.82 | 3,613 | |
| Sitka Spruce NZ | 405 | 84.80 | 10,311 | 41.28 | 9.27 | 1,694 | |
| Sitka Spruce USA | 400 | 70.00 | 10,800 | 38.70 | 7.90 | 2,300 | |
| Pinus Radiata Lo Den | 362 | 62.95 | 5,365 | 27.98 | 8.79 | 2,454 | |
| Western Red Cedar | 316 | 53.78 | 4,906 | 30.95 | 7.58 | 1,739 | |
| Units | (kg/m³) | (MPa) | (MPa) | (MPa) | (MPa) | (N) |
The density is that at 12% moister content.
Modulus of Rupture
This is the maximum bending stress before failure tested on a 20x20x300 beam covering a 280mm span and having a point load at mid span.
Modulus of Elasticity or “E” value.
This is a measure of stiffness and is derived from the rupture tests. They are linear results; therefore a piece of timber with twice the E value will be twice as stiff.
Compression strength.
Results are test pieces 20x20x60 mm long.
Shear Parallel to Grain.
Test results are for pieces 20x20x20 mm.
Hardness
This is the force required to embed a rounded tool (11.3mm diameter) to halve its diameter.
It is clear from the table that as a rule the denser a piece of timber the stronger it will be. Spruce which is the favoured timber for aircraft construction follows these same trends except in stiffness where it is equivalent to much denser timbers.
The engineering calculations required to make more sense of the results are rather involved. One would be well advised to contract the services of a qualified engineer before using the results in any design along with adequate safety margins. It is also important to remember that these tests were preformed on small clear pieces and that timber can vary wildly from country to country and from province to province.