charlie_alpha
Member
- Joined
- Apr 6, 2022
- Messages
- 14
Aircraft Wood Fir for Spruce
On the West Coast of Canada, my rocky promontory has mostly Douglas Fir and Western Red Cedar. I cut down one small Fir for firewood and noticed there was in excess of 20 rings per inch. The tree was 80 to 100 feet tall and clear (no branches) for at least 60 feet.
I took a look at AC 43.13; Aircraft Woods: Their Properties, Selection, and Characteristics (USDA Forest Service, Forest Products Laboratory, 1941; and something like MIL-S-6073. I think I read that D. Fir was 25% heavier, but up to 26% stronger, depending on how you define strength.
Questions:
1) Does anyone have experience substituting Douglas Fir for Sitka Spruce? Was it a straight swap or did you mill out some material? Perhaps we could limit this to Wing structures for now.
2) Not knowing what wood wings weigh, how much will I add to the structure using Fir? (Sure, about 25%) I’m thinking for a spar there might be a minor weight penalty but allow for increased gross.
3) Is there anywhere in the structure that Fir is undesirable for?
4) Suggestions on wood wing aircraft designs that best match Canadian Ultralight Regs (1200 lbs MTOW and under 45 mph stall)?
Thanks,
CA
On the West Coast of Canada, my rocky promontory has mostly Douglas Fir and Western Red Cedar. I cut down one small Fir for firewood and noticed there was in excess of 20 rings per inch. The tree was 80 to 100 feet tall and clear (no branches) for at least 60 feet.
I took a look at AC 43.13; Aircraft Woods: Their Properties, Selection, and Characteristics (USDA Forest Service, Forest Products Laboratory, 1941; and something like MIL-S-6073. I think I read that D. Fir was 25% heavier, but up to 26% stronger, depending on how you define strength.
Questions:
1) Does anyone have experience substituting Douglas Fir for Sitka Spruce? Was it a straight swap or did you mill out some material? Perhaps we could limit this to Wing structures for now.
2) Not knowing what wood wings weigh, how much will I add to the structure using Fir? (Sure, about 25%) I’m thinking for a spar there might be a minor weight penalty but allow for increased gross.
3) Is there anywhere in the structure that Fir is undesirable for?
4) Suggestions on wood wing aircraft designs that best match Canadian Ultralight Regs (1200 lbs MTOW and under 45 mph stall)?
Thanks,
CA
