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steady-state error block VORerr. The other outputs are normally primarily used for
evaluations of simulation results. VOR example sends the combined outputvector
yvor to the MATLAB workspace by means of a To Workspace block.
Type browse vor at the command-line for on-line help.
10.1. The radio-navigation blocklibrary 191
VORerr Main FDC library / ILS/VOR radio-nav / VOR signals / VORerr
Radio-navigation library / VOR signals / VORerr
Type
Masked subsystem block.
Description
The block VORerr incorporates a steady-state error in the nominal VOR signal.
Note: contrary to the ILS steady-state errors, the result is expressed in terms of the VOR
deviation angle, not an electrical current. Also, the FDC toolbox does not include VOR
noise models.
Equations
The steady-state error is implemented by multiplying the nominal VOR signal with a gain
value that is slighty offset from the nominal value 1. Some experimental measurements
of overall VOR accuracy have been given in section 5.2.3.
• VOR signal with steady-state error, [rad]:
GVOR,actual = KVORerr · GVOR,nominal
The multiplication factor KVORerr takes into account the offset in the measured VOR bearing.
It is equal to 1 + e
100 with e the overall percentile VOR system error, specified by the
user.
Inputs
GVOR,nominal nomimal VOR bearing, Gamma_VOR (nominal)
Outputs
GVOR,actual indicated VOR bearing, includes system offset, Gamma_VOR (actual)
Parameters
The user must specify the overall VOR system error, expressed in a percentage of the
nominal value. This figure can be entered after double-clicking the block VORerr.
Connections
in: GVOR,nominal is retrieved from the block VOR, which determines the nominal VOR
signals.
out: GVOR,actual can e.g. be used as an input signal for an automatic VOR-tracking controller.
Type browse vorerr at the command-line for on-line help.
192 Chapter 10. Radio-navigation block reference
VOR example Main FDC library / ILS/VOR radio-nav / VOR signals / VOR example
Radio-navigation library / VOR signals / VOR example
Type
Masked subsystem block (contents accessible without unmasking).
Description
The subsystem VOR example demonstrates how the blocks VOR and VORerr can be combined
to build a complete VOR simulation model. The subsystem has been masked to
generate an appropriate block-icon, but its contents are accessible without unmasking
(hence, its light-blue background colour). A slightly modified version of this block has
been included in the autopilot blocklibrary APlib; see chapter 15 for more information.
Subsystems and/or blocks
The subsystem VOR example contains two masked subsystem blocks:
VOR computes the nominal VOR signal,
VORerr incorporates a steady-state error in the VOR signal.
Inputs
x = [ V a b p q r y q j xe ye H ]T state vector from the aircraft model, x
Outputs
GVOR VOR bearing, including system offset, Gamma_VOR
During simulations, the time-trajectories of the VOR signals and some interim results
from the block VOR are collected in the MATLAB workspace variable yvor. Each row from
this matrix corresponds to the vector yvor at a certain data-point, which is defined as:
yvor = [ yvor1 yvor2 yvor3
T yvor4 ]T
with:
yvor1 = GVOR nominal VOR bearing, excluding system offset, yvor1
yvor2 = RVOR ground distance from aircraft to VOR station, yvor2
yvor3 = [ C.O.S.-flag Range-flag ]T flags specifying validity of VOR signals, yvor3
yvor4 = ToFrom To/From flag, yvor4
C.O.S. is an abbreviation for Cone of Silence, which has been discussed in section 5.2.2. Information
about the range of the VOR signals (i.e. the VOR coverage) can also be found
there. For information about the To/From flag, see section 5.2.1.
Note: to plot the resulting time-trajectories of the VOR signals, it is necessary to create
a compatible time-basis in the MATLAB workspace as well. This can be achieved by including
a Clock block, which is connected to a To Workspace block, but in the special case
where the subsystem VOR example is connected to the nonlinear aircraft model Beaver
(see the description of Beaver Level 1 in chapter 8) this is already taken care of within the
aircraft model itself.
Parameters
The user must manually specify the parameters of VOR and VORerr by double-clicking
these blocks individually. For the VOR block, this includes setting the Earth-axes X and Ycoordinates
of the VOR transmitter relative to the aircraft at the start of the simulation (t =
0), the altitude of the VOR transmitter above sea level, and the ‘Course Datum’, which is
the reference radial set on the VOR deviation indicator in the cockpit. See section 5.2.1
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FDC 1.4 – A SIMULINK Toolbox for Flight Dynamics and Contro(92)
