Chilton DW-1: Testing of Douglas Fir for Tailplane Spar and Wicks Aircraft Sitka Spruce Spar Stock

I have chosen to redo my tailplane spar in Douglas Fir. I have acquired some very nice Douglas Fir from a local building center and have tested it with the result being very good. While the Douglas Fir is heavier it is not uncommon for the Chilton DW-1 to have some weight added to the back to account for a degree of nose heaviness. How much weight is added? The flanges of the tailplane spar in Sitka Spruce were 8.05 ounces and 8.8 ounces. In Douglas Fir they were 9.75 ounces and 9.55 ounces. A total of 2.45 ounces and in this location on the Chilton will not be an issue. The total weight of the Sitka Spruce spar was 1 lb. 5 oz. and the Douglas Fir spar 1 lb. 7.9 oz. a difference of only 2.9 oz. Not too bad for a $3.09 USD piece of Douglas Fir. The weight per ounce was .25 ounce per cubic inch or 27 lbs. a cubic foot. Referencing ANC-19 Table 2-5 the specific gravity value is .433. According to my ANC-18 Table 2-6 shows an average specific gravity for light Douglas Fir of .43 and a minimum of .38. So the weight is within range.

I also had Sitka Spruce spar stock arrive from Wicks Aircraft this week. The wood was a revelation compared to the Sitka Spruce from Public Lumber. If you need Sitka Spruce and need capstrips and small lengths of Sitka Spruce the wood from Public Lumber works alright. The service and quality from Wicks Aircraft was exceptional. For aircraft I must say that the quality from Wicks is there if you pay the price and well worth it.

On the other end of the spectrum there is sometimes a find to be had at the local home center as the Douglas Fir I found in the past week demonstrates. If you are really new to working with wood for aircraft, I don't think I would suggest beginning to build with home center wood though. I am only considering home center wood after cutting wood now for about 4 years and have seen a few things. If in doubt cut the defect out! It is better doing it before a component is built and thinking better of it and choosing to redo it, as I am doing this week.