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Rudder sizing
The rudder controls the Yaw motion and is located on the vertical stabilizer. To determine the size of the Rudder we requires all the parameters below.
Rudder Area (SR) Vertical Tail Area(SV) SR/SV Rudder Chord(CR) Vertical Tail Chord (CV) CR/CV Rudder span (bR) Tail Span(bV) bR/bV
We have already determined that the area of the vertical tail is 0.0425 m^2 ( for more information please refer to the empennage design page). From this source:http://aero.us.es/adesign/Slides/Extra/Stability/Design_Control_Surface/Chapter 12. Desig of Control Surfaces (Rudder).pdf we can say that the SR/SV is equal to 0.38.
Using simple math we determine that SR=SV*0.38 = 0.01615m^2
Using the same method, we can compute the mean rudder chord length: CR=CV*0.42= 0.16832*0.42= 0.0707m
Now we need one more dimension, which is the rudder span. bR= SR/CR= 0.01615/0.0707= 0.22844m.
As you noticed the value used is for Light GA type which is the closest to the RC Type. Even though this might not the most optimal rudder, it gives us very good starting to see how flight characteristics behave which changes in these parameters, for more information, please refer to the source and the Fixed wing calculation Excel file.
We also have to determine the maximum deflection of the rudder was straightforward thanks to this source: https://www.fzt.haw-hamburg.de/pers/Scholz/HOOU/AircraftDesign_9_EmpennageGeneralDesign.pdf. So our maximum deflection will be 35 degrees because designing for the extreme case will ensure that all the elements will be intact during high manueavouring speed. In the case of control over sensitivity, we can reduce the max deflection angle of the rudder by manually limiting the angle rotation of the servo.
