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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.

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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.

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Elevator

The elevator controls the pitch motion of the aircraft and is located on the horizontal tail. Similar to the Rudder, the elevator requires the following parameter to determine the elevator size:-

Elevator Area (SE)

Horizontal Tail Area(SH)

SE/SH

Elevator Chord(CE)

Horizontal Tail Chord (CH)

Horizontal Tail Span (bH)

Elevator span (bE)

Based on the tail volume coefficient method, we determined the area of the horizontal tail is 0.0667 m^2. From this source:- http://aero.us.es/adesign/Slides/Extra/Stability/Design_Control_Surface/Chapter 12. Desig of Control Surfaces (Elevator).pdf we can say that the SE/SH equals 0.38.

Using simple calculation we can determine the SE; SE=SH*0.38=0.0667*0.38=0.0253 m^2

The span of the elevator(bE) will equal to span of the horizontal tail(bH). Using this information we can compute the chord length of the elevator. Area of the elevator (SE) = Elevator span (bE)* Elevator Chord(CE). We have one unknown and one equation which is enough to determine the chord length of the elevator. CE= SE/bE= SE/bH= 0.0253/ 0.4662= 0.0543m

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This source also mentioned that having deflection above or below 25 degrees will reduce the effectiveness of the elevator and may result in a stall of the horizontal tail, even a small downward elevator deflection can produce flow separation and loss of pitch control effectiveness. If we require more pitch control authority, then we can increase the elevator area and recompute the chord length of the elevator.