Use this calculator at your own risk.
Whilst every effort for accuracy has been made we accept no liability for the results
obtained.
The maximum torque requirement does not always occur at full deflection. This calculator
determines the torque at every control position, from 1 degree to the max. deflection
specified.
The result is the max torque found, and the position of the control surface when
the max torque was reached.
The formula used to calculate the torque is as follows :
Torque = 8.5E-6
* ( C2 V2 L sin(S1) tan(S1) / tan(S2)] * SAL / CHL
Where:
C = Control surface chord in cm
L
= Control surface length in cm
V = Speed in MPH
S1 = Max control surface deflection
in degrees
S2 = Max servo deflection in degrees
SAL=Servo Arm Length in cm
CHL=Control Horn Length
The original servo torque formula was taken from Craig Tenney. His website features excel
spreadsheets to do detailed analysis of servo torque, and control linkage calculations.
You can also find a very detailed page there that shows the derivation of this model.
Reducing the servo deflection from the default 60 degrees is similar to using ATV
/ Dual Rates to reduce the control throws. If you vary the servo deflection from
the normal 60 degrees, you will see that using "Dual rates / ATV" to set the proper
control surface deflection greatly increases the load on the servo.
Note that the numbers do not always match those generated by another servo calculator
on the web, at www.multiplex-rc.com/calcservo.htm. That calculator uses different
methods, and the formulas and derivations were not available to me at the time this
was created.
The Multiplex calculator factors in wing area, but does not include servo deflection.
Note the following assumptions: The angle of incidence of the wing, stab, or fuse
is zero (relative to the airflow).
Angular velocity and acceleration of the aircraft is zero. Air flow may be modelled
using Bernoulli's equation for dynamic pressure.
Conditions are: sea level, zero humidity, moderate (~55 F) temperature. Control
linkages have zero offset at hingeline and are perpendicular to horns at neutral.
Control mechanisms are frictionless and surfaces are mass-balanced.
The wing, stab, fuse, and control surfaces are thin, flat slabs.
No aerodynamic counterbalances are used. (Account for these manually, if desired.)
The pushrods are significantly longer than the servo and control horns. Please note:
The calculations are completely theoretical. No empirical "tweaking" has been done.
The assumptions (except #6) should generally yield conservative (high) predicted
torques.
Extreme control throws are probably not practical at high speeds.
This model is best used for comparisons.
No guarantees are made of its validity.
Maximum required servo torque may occur at LESS than maximum throw.
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