- Formula Used;
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 maximum
The result is the max torque found
and the position of the control
surface when the max torque was
The formula used to calculate the
torque is as follows:
Torque (oz.-in) =
8.5E-6 * (C2 V2 L sin(S1) tan(S1) /
C = Control surface chord in cm
L = Control surface length in cm
V = Speed in MPH
S1 = Max control surface deflection
S2 = Max servo deflection in degrees
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 the following assumptions:
The angle of incidence of the wing,
stab, or fuse is zero (relative to
Angular velocity and acceleration of
the aircraft is zero.
Air flow may be modeled using
Bernoulli's equation for dynamic
Conditions are: sea level, zero
humidity, moderate (~55 F)
Control linkages have zero offset at
hinge line and are perpendicular to
horns at neutral.
Control mechanisms are frictionless
and surfaces are mass-balanced.
The wing, stab, fuse, and control
surfaces are basic scale shape.
No aerodynamic counterbalances are
used. (Account for these manually,
The pushrods are longer than the
servo and control horns.
The calculations are
completely theoretical. No empirical
"tweaking" has been done.
The assumptions (except
#6) should generally yield
conservative (high) predicted
Extreme control throws
are probably not practical at high
This model is best used
for comparisons. No guarantees are
made of its validity.
Maximum required servo
torque may occur at LESS than