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These accelerations are measured in units of g which explains why the terms have been
divided by g0. W = m g is the total weight of the aircraft, measured in [N]. Note: the
kinematic accelerations differ from the body-axes velocity rates u˙, v˙, and w˙ , which are
computed in the block uvwdot, because the latter do not contain the angular and translational
velocity cross-product terms.
• Outputs of body-axis accelerometers (specific forces) Ax, Ay, and Az, measured at the
vehicle’s c.g.:
Ax = ax,k + sin q = (Fx − Xgr) /W
Ay = ay,k − cos q sin j = (Fy −Ygr) /W
Az = az,k + cos q cos j = (Fz − Zgr) /W
These specific forces are also measured in units of g.
Inputs
Ftot = [ Fx Fy Fz ]T total external forces, Ftot
Fgrav = [ Xgr Ygr Zgr ]T gravity forces, Fgrav
Outputs
yacc = [ Ax Ay Az ax,k ay,k az,k ]T specific forces and accelerations, yacc
Parameters
Accel needs the parameter vector GM1 to be present in the MATLAB workspace, in order
to extract the mass m of the aircraft (the mass has been implemented as a parameter, i.e.
it is assumed to remain constant during the relative short time intervals considered in
simulations). The definition of GM1 can be found in appendix C. GM1 can be loaded
from the file AIRCRAFT.DAT, using the utility DATLOAD (see section 12.4.2). If this datafile
124 Chapter 8. Aircraft model block reference
has somehow inadvertently been deleted, it can be re-created by running the program
MODBUILD (see section 12.6.1).
Connections
in: Ftot comes from the block FMsort; Fgrav comes from Gravity.
out: yacc is not used by any other block from the aircraft model.
Type browse accel at the command-line for on-line help.
8.2. The aircraft model block libraries 125
Additional Outputs Beaver level 1 / Beaver level 2 / Additional Outputs
Main FDC library / Other (output-) equations
Type
Aircraft-independent subsystem, essential for solving the equations of motion. The subsystem
is not masked.
Description
The subsystem Additional Outputs contains some useful output equations which are not
required to solve the state equations, and which do not logically fit in other subsystems
from the nonlinear aircraft model. The user is free to add other ‘additional output blocks’
to this subsystem, or delete available blocks from this subsystem.
However, it should be noted that the output signals from this subsystem are not meant to
be used as inputs to the forces andmoments blocks or the equations of motion themselves.
The ‘additional outputs’ may be functions of the state variables, their time-derivatives,
external inputs and/or disturbances, or outputs from other subsystems from the aircraft
model.1
Subsystems and/or blocks
The subsystem Additional Outputs contains three blocks:
Accel computes specific forces (outputs of accelerometers) and kinematic accelerations,
Flpath computes some flight-path related variables,
uvwdot computes the time-derivatives of the body-axes velocity components.
Inputs
x = [ V a b p q r y q j xe ye H ]T state vector, x
˙x = [ ˙V
˙a
˙b
˙ p ˙ q ˙ r ˙y
˙q
˙j
˙ xe ˙ ye ˙H ]T time-derivative of state vector, xdot
yhlp = [ cos a sin a cos b sin b tan b sin y cos y sin q cos q sin j cos j ]T
frequently used sines and cosines, yhlp
Ftot = [ Fx Fy Fz ]T total external forces, Ftot
Fgrav = [ Xgr Ygr Zgr ]T gravity forces, Fgrav
Outputs
yfp = [ g fpa c F ]T flight-path variables, yfp
yuvw = [ u˙ v˙ w˙ ]T time-derivatives of body-axes velocities, yuvw
yacc = [ Ax Ay Az ax,k ay,k az,k ]T specific forces and accelerations, yacc
Parameters
The block Accel reads the parameter vector GM1 from the MATLAB workspace; the block
Flpath requires the initial value of the state vector, xinco. GM1 can be loaded from the
file AIRCRAFT.DAT, using the utility DATLOAD (see section 12.4.2); its definition can be
found in appendix C. If this datafile has somehow inadvertently been deleted, it can be
re-created by running the program MODBUILD (see section 12.6.1). The initial value of the
state vector can be computed using the aircraft trim program ACTRIM (see section 11.1),
or loaded from file using the utility TRILOAD (see section 12.4.2).
1Since the outputs from Additional Outputs are not involved in the solution of the state equations
themselves, the use of time-derivatives of state variables within this subsystem does not yield algebraic
loops (see section section 6.4.1). However, if outputs from this subsystem are fed back to the inputside
of the aircraft model, e.g. via an autopilot control loop, an algebraic loop may inadvertently be
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FDC 1.4 – A SIMULINK Toolbox for Flight Dynamics and Contro(62)
