+ - Calculate the angular accelerations
+ - Calculate the translational accelerations
+ - Calculate the angular rate
+ - Calculate the translational velocity
+
+ This class is collecting all the forces and the moments acting on the body
+ to calculate the corresponding accelerations according to Newton's second
+ law. This is also where the friction forces related to the ground reactions
+ are evaluated.
+
+ JSBSim provides several ways to calculate the influence of the gravity on
+ the vehicle. The different options can be selected via the following
+ properties :
+ @property simulation/gravity-model (read/write) Selects the gravity model.
+ Two options are available : 0 (Standard gravity assuming the Earth
+ is spherical) or 1 (WGS84 gravity taking the Earth oblateness into
+ account). WGS84 gravity is the default.
+ @property simulation/gravitational-torque (read/write) Enables/disables the
+ calculations of the gravitational torque on the vehicle. This is
+ mainly relevant for spacecrafts that are orbiting at low altitudes.
+ Gravitational torque calculations are disabled by default.
+
+ Special care is taken in the calculations to obtain maximum fidelity in
+ JSBSim results. In FGAccelerations, this is obtained by avoiding as much as
+ possible the transformations from one frame to another. As a consequence,
+ the frames in which the accelerations are primarily evaluated are dictated
+ by the frames in which FGPropagate resolves the equations of movement (the
+ ECI frame for the translations and the body frame for the rotations).
+
+ @see Mark Harris and Robert Lyle, "Spacecraft Gravitational Torques",
+ NASA SP-8024, May 1969