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Chapter 12
Force
The force component is an object that can generate a force acting on the aircraft, possibly used for
lift, propulsion, or control. The amplitude of the force can be a fixed value, or it can be connected to an
aircraft control for trim. The direction of the force can be fixed or connected to aircraft control.
12–1 Control and Loads
The control variables are the force amplitude A and the force incidence and yaw angles. The force
orientation is specified by selecting a nominal direction ef0 in body axes (positive or negative x, y, or
z-axis), then applying a yaw angle ψ, and then an incidence or tilt angle i (table 12-1). The control
variables can be connected to the aircraft controls cAC:
A = A0 + TAcAC
ψ = ψ0 + TψcAC
i = i0 + TicAC
with A0, ψ0 and i0 zero, constant, or a function of flight speed (piecewise linear input). The force axes
are CBF = UiVψ, where U and V depend on the nominal direction, as described in table 12-1. The force
direction is ef = CFBef0. The force acts at position zF . The force and moment acting on the aircraft in
body axes are thus:
F F = ef A
M F = ΔzF F F
where Δz F = z F − z F cg.
Table 12-1. Force orientation.
nominal (F axes) ef0 incidence, + for force yaw, + for force CBF = UiVψ
x forward i up right YiZψ
−x aft −i up right Y−iZ−ψ
y right j aft up ZiX−ψ
−y left −j aft up Z−iXψ
z down k aft right Y−iX−ψ
−z up −k aft right YiXψ