Last change: 19.08.2017
The Sunbird comes with an all-flying tail. This is a great thing in terms of aerodynamic flexibility, but it needs some careful thoughts at the beginning. You will want to design your elevator linkage with sufficient adjustment range for future optimization. And even more important, the neutral position of the elevator must keep the longitudinal dihedral on the safe side for the maiden flight. We go for an initial +2 degrees.
Longitudinal Dihedral (LD): Difference between the angles of incidence of the wing and the tailplane. The value of LD is positive if the wing incidence is greater. LD is a construction key figure and does not depend on current air flow or flight condition.
We tape a one metre carbon rod onto the chord of the wing root of the fuselage. This indicates the incidence of the wing. The angle of incidence would be the angle between the longitudinal axis of the fuselage and the rod. We do not bother to measure the angle as is not needed to figure out and set the longitudinal dihedral.
Then we flip over the fuselage. The carbon rod lies now flat on the table surface and is aligned with the centimetre-grid. Using the grid and the Sunbird’s wing connector and the ballast weights, we draw a line in parallel to the carbon rod through the elevator’s rotation axis. The rectangular aluminium profile is used for properly reading the grid.
This line (represented here by the long green tape) is the position of the elevator’s chord for a longitudinal dihedral of zero degrees. We measure 86.5 mm from the rotation axis to a selected point close to the trailing edge. The rest is trigonometry: 86.5mm * tan(2°) = 3.02mm. We mark these 3 millimetres with the „+2°“ tape.
We cut a template for the position of the elevator from a sheet of 1 mm cardboard. It is attached to the fin with the two carbon connectors of the elevator.
With the two elevator halves in place for correct position of the connectors and for enhanced rigidity, we clamp the template to the planned 2 degrees of longitudinal dihedral.