The first prototype of the rudder was made out of cardboard – a readily available material that was easy to cut – and rectangular (15x10cm).
The prototype was thick at the bottom and thin at the top, in an attempt to replicate an airfoil. This design feature is included as the majority of fast airflow over the rudder will be rushing upwards as the payload is descending. This creates laminar airflow over the rudder that is easy to control, rather than turbulent air which is difficult to steer in. The shape of this prototype is based on an airfoil, similar to that of the rudder on an airplane but facing downward, ensuring aerodynamic properties in the design.
After brief testing with the first prototype attached to the case, it became apparent that the rudder was far too small to have any noticeable effect on the direction of the payload over a short period of time. The second prototype remained rectangular and made out of cardboard, however increased in size (22.5x15cm). The edge of the rudder now reaches over the edges of the case significantly more than the last prototype, exposing it to more laminar air than the previous model – the case is now also being designed in a way to increase laminar airflow over the rudder.
Another change made was to add thickness to the rudder on the side closest to the case – giving it the same airfoil effect, but on the axis that it will be exposed to air as it travels forward as well as down.
The next prototype material will be balsa wood, as it has a high strength to weight ratio and can easily be carved to feature the airfoil shape. Hopefully this will adequately fit the needs of the rudder, and hence be the final material too.
The servo will be connected to a pushrod, which will stick through a hole in the case and attach (either screwed or soldered) to a clevis and holder that will be screwed to the rudder (as below).
This allows the servo’s movement on only one axis to effect the direction of the rudder, and the servo will be placed inside the case to have best control over this axis.
The rudder will be attached to the case by a pin held into place by the case. It will slide into a hole either cut or drilled into the edge of the rudder, or else external clips will attach it to the pin (if drilling or cutting is likely to break the rudder). This allows the rudder to freely change directions with little friction, while still being fastened securely to the case.