Manish Chandrayan Posted October 11, 2022 Share Posted October 11, 2022 (edited) As the title says, started to build a Carl Goldberg Super Chipmunk from an old partially damaged kit. Some of the wood in the kit had the ends soaked in oil at some point and hence was able to buy it at a very good price. The main spars (3/8 sq) supplied in the kit are Bass wood. And have the ends oil soaked. Since I do not have any spare Bass wood stock, I can substitute the damaged spars with either Balsa or Spruce stock from my spares. The wing design is typical D Box structure, sheeted from LE up to main spar and cap strips on the ribs, shear webs from inboard to tips towards the front of the main spar. If I use Balsa spars, can I use shear webs back and front and expect the strength to be similar to bass with shear web only on front? What if I proceed as above, but lay carbon tow over the spars (under the top and bottom sheeting)? The other option is to just substitute the damaged spar with Spruce spar and follow the original design. However that will almost double the weight of the spars. Thoughts welcome please The Edited October 11, 2022 by Manish Chandrayan Quote Link to comment Share on other sites More sharing options...
Edgeflyer Posted October 11, 2022 Share Posted October 11, 2022 I'd use spruce spares every time. They resist wing warping and are much stronger. A few extra grams? Not bothered. Quote Link to comment Share on other sites More sharing options...
kc Posted October 11, 2022 Share Posted October 11, 2022 Spruce would be fine and will likely be intact in a crash and so make the wing repairable. Weight will be OK - try to save some weight at the tail end if you want to compensate. Be aware that the oil soaked wood might have contaminated other parts just enough to make glue joints not as good as normal. Don't take chances on critical joints. Quote Link to comment Share on other sites More sharing options...
Edgeflyer Posted October 11, 2022 Share Posted October 11, 2022 If it helps , when renovating oil soaked models I have found that cyano bonds with castor oil and so may be useful as a last resort, but obviously best to replace oily wood when possible. Quote Link to comment Share on other sites More sharing options...
jrman Posted October 11, 2022 Share Posted October 11, 2022 Rub the oil affected wood with baking soda (bicarbonate of soda) before using cyano. This is also advisable when using cyano on spruce. Quote Link to comment Share on other sites More sharing options...
Manish Chandrayan Posted October 11, 2022 Author Share Posted October 11, 2022 Thank you all. Weighed the four Bass spars that turned out at 120 grams while the Spruce ones weigh 175. Guess, not a really prohibitive weight penalty at 55g overall. Will go with Spruce👍 Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted October 11, 2022 Share Posted October 11, 2022 At least any extra weight around the spars will be on or about the C of G, and will be diluted weight wise, along the wing. Quote Link to comment Share on other sites More sharing options...
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