When I was building the wings for the SSSC, ( Single Seat Super Cub) Koala. I leveled the building table with a transit and a digital level. Built the first wing and no twist. Checked with the digital level to 1/10 of a degree. After I built the other wing it had a slight twist in the outer 4 feet. Checked the table and it had the exact same twist. Somehow the table must have got bumped and I don't know how or when. I should have checked it before building the second wing and glued to the floor. The wings are geodetic and will not twist, you get what you build like a full plywood or aluminum wing.
In the test flying the airplane it had a heavy wing. I got to thinking of the rear spar attach adjustment on the Cessna 15--172's. The rear wing attach bolt is inside a bushing with the bolt holed drilled off center, you can loosen the attach bolt and turn the bushing with a wrench and raise or lower the rear spar about 1/4" up or down the needed amount to correct for a heavy wing.
So I decided to lower the rear spar on the heavy wing at the attach fitting. How much ? My airplane is all wood with 4130 steel straps that bolt to the fuselage rear spar attach fitting. I welded the wing spar attach fitting and drill the spar attach bolt the amount needed. How I found the needed amount.
Each wing panel is 12" long less the wing tips. So I measured the wing every 4' from the root rib to the tip rib. Root is (0) - 4' -8'-12'. One wing was all +4.0 degrees, The other twisted wing was 4.0-4.0 - 4.2, 4.3 at the tip rib. Straight wing 4.0 x 0 = 4.0 at root Twisted wing 4.0 x 0 = 4.0 at root
4.0 x 4' = 16 at the 4' rib. 4.0 x 4' = 16 at the 4' rib
4.0 x 8' = 32 at the 8' rib. 4.2 x 8' = 33.6 at the 8' rib
4.0 x 12'= 48 at the 12' rib 4.3 x 12'= 51.6 at the 12' rib
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Total --- 100 Ft Angle. Total ----- 105 Ft Angle.
So to change the 100 FA to 105 FA I need to lower the rear spar of the straight wing to a 4.2 angle for a total of 105, the same as the twisted wing.
4.2 x 0'= 4.2 at the root
4.2 x 4' = 16.8 at the 4' rib
4.2 x 8' = 33.6 at the 8' rib
4.2 x 12= 50.4 at the 12'rib.
Total ----- 105 Foot Angle , same as the twisted wing.
Since the distance from the center of the main spar and rear spar is 22" , one degree is .383" divided by .2 = .078"
I unbolted the rear spar straps and tig welded the bolt hole up after C-clamping a piece of brass to back up the hole and dress down flat on both sides and move the hole the .078".
Now tested in dead smooth air there is no heavy wing, I can fly hands off and start a slight turn in neither direction by leaning my body. No wing drop on the stall.
Never heard of anyone doing it this way, but it works.
Dan
In the test flying the airplane it had a heavy wing. I got to thinking of the rear spar attach adjustment on the Cessna 15--172's. The rear wing attach bolt is inside a bushing with the bolt holed drilled off center, you can loosen the attach bolt and turn the bushing with a wrench and raise or lower the rear spar about 1/4" up or down the needed amount to correct for a heavy wing.
So I decided to lower the rear spar on the heavy wing at the attach fitting. How much ? My airplane is all wood with 4130 steel straps that bolt to the fuselage rear spar attach fitting. I welded the wing spar attach fitting and drill the spar attach bolt the amount needed. How I found the needed amount.
Each wing panel is 12" long less the wing tips. So I measured the wing every 4' from the root rib to the tip rib. Root is (0) - 4' -8'-12'. One wing was all +4.0 degrees, The other twisted wing was 4.0-4.0 - 4.2, 4.3 at the tip rib. Straight wing 4.0 x 0 = 4.0 at root Twisted wing 4.0 x 0 = 4.0 at root
4.0 x 4' = 16 at the 4' rib. 4.0 x 4' = 16 at the 4' rib
4.0 x 8' = 32 at the 8' rib. 4.2 x 8' = 33.6 at the 8' rib
4.0 x 12'= 48 at the 12' rib 4.3 x 12'= 51.6 at the 12' rib
______
Total --- 100 Ft Angle. Total ----- 105 Ft Angle.
So to change the 100 FA to 105 FA I need to lower the rear spar of the straight wing to a 4.2 angle for a total of 105, the same as the twisted wing.
4.2 x 0'= 4.2 at the root
4.2 x 4' = 16.8 at the 4' rib
4.2 x 8' = 33.6 at the 8' rib
4.2 x 12= 50.4 at the 12'rib.
Total ----- 105 Foot Angle , same as the twisted wing.
Since the distance from the center of the main spar and rear spar is 22" , one degree is .383" divided by .2 = .078"
I unbolted the rear spar straps and tig welded the bolt hole up after C-clamping a piece of brass to back up the hole and dress down flat on both sides and move the hole the .078".
Now tested in dead smooth air there is no heavy wing, I can fly hands off and start a slight turn in neither direction by leaning my body. No wing drop on the stall.
Never heard of anyone doing it this way, but it works.
Dan
