Longerons
The past days I have been working on the main fuselage longerons. They are made of three 30x10 oregon pine strips, glued together. The longest beam I had was only 3690mm long, but the required length is ~4500mm. The fuselage length from C0 (firewall) to C10 (last bulkhead) is 4250mm but some additional length is required due to the curvature.
Additionally, I discovered a few strips with defects due to knots. In the image, the strips are already cut, the defects were right in the middle of the strips.
×
Planning scarf joints
Because of the defects and the resulting loss of material, I had to plan well to get the required strips made from the material I have.
| Length | L_usable | Count |
|---|---|---|
| 3690 mm | 3650 mm | 1 |
| 2900 mm | 2860 mm | 4 |
| 2320 mm | 2280 mm | 3 |
| 1220 mm | 1180 mm | 7 |
Taper
The longerons are tapered depending on the landing gear configuration. Since I am building the tailwheel variant, the taper starts behind bulkhead C6 and linearly decreases the thickness to 18mm at bulkhead C10.
Taking the taper into consideration, it means that the outmost of the three strips can be ~430mm shorter which literally saved me from purchasing more wood. I managed to find a combination of my available strips that allowed me to assemble the six strips without excessive amouns of scarf joints.
Scarf Jointing
I used a ratio of 1:8 for the taper on the scarf joints. The first step is to plane the strips at the desired angle making sure it is straight in both dimensions. Then, after test fitting and ensuring that the two pieces fit nicely together, glueing them with epoxy is straight forward. It takes less than 20 minutes to make a joint.
×
×
×
Next Steps
The next plans are to continue with the preparation of the longerons. I will also have to prepare the secondary longerons consisting of 9x18 mm strips. These will also require scarf jointing to get to the required lenght.