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Connections
in: x comes from the block Integrator; yatm comes from Atmosph; yad1 comes from Airdata1.
out: yad3 is not connected to any other block in the aircraft model.
Type browse airdata3 at the command-line for on-line help.
8.2. The aircraft model block libraries 135
Airdata Group Beaver level 1 / Beaver level 2 / Airdata Group
Main FDC library / Airdata, atmosphere
Type
Aircraft-independent subsystem, part of which is essential for solving the equations of
motion. The subsystem is not masked.
Description
The subsystem Airdata Group is used to compute airdata (-related) variables. Some of
these data are required to solve the equations of motion, while other data is provided as
additional ‘nice to know’ information.
Subsystems and/or blocks
The subsystem Airdata Group contains four blocks:
Atmosph computes basic atmospheric properties (air-temperature, pressure, density) using
the ICAO Standard Atmosphere model, as well as the dynamic viscosity
of the air and the gravitational acceleration,
Airdata1 computes the most important airdata variables which in general are required
to solve the equations of motion of an aircraft,
Airdata2 computes additional airdata (-related) variables which may be useful for such
purposes as comparing simulations with real flight experiments, windtunnel
measurements, etc.,
Airdata3 computes some more additional airdata (-related) variables.
The blocks Airdata2 and Airdata3 do not affect the solution of the aircraft equations of
motion, and can therefore be safely deleted from the model (except that this would require
readjustment of several connecting lines as well). While this might have been useful to
speed up simulations and free memory on slow computer systems in the past, there are
no convincing reasons to do so today. In any case, the blocks Atmosph and Airdata1 are
always required to solve the state equations.
Inputs
x = [ V a b p q r y q j xe ye H ]T state vector, x
Outputs
yatm = [ r ps T μ g ]T basic atmospheric properties, yatm
yad1 = [ a M qdyn ]T basic airdata variables, yad1
yad2 = [ qc Ve Vc ]T additional airdata (-related) variables, yad2
yad3 = [ Tt Re Rc ]T additional airdata (-related) variables, yad3
Parameters
The parameters for the blocks Airdata1, Airdata2, and Atmosph are all defined internally.
Airdata3 reads the parameter vector GM1 from the MATLAB workspace; its definition 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 has somehow inadvertently been deleted, it
can be re-created by running the program MODBUILD (see section 12.6.1).
Connections
in: x comes from the block Integrator (subsystem Aircraft Equations of Motion).
out: yatm, which leaves the block Atmosph is connected to the blocks Airdata1, Airdata2,
and Airdata3, Power, Gravity, and xdotcorr (Beaver); yad1 from Airdata1 is connected
to Airdata2, Airdata3, and FMdims; yad2 from Airdata2 and yad3 from Airdata3 are not
connected to any other block in the aircraft model.
Type browse adgrp at the command-line for on-line help.
136 Chapter 8. Aircraft model block reference
Atmosph Beaver level 1 / Beaver level 2 / Airdata Group / Atmosph
Main FDC library / Airdata, atmosphere
Type
Aircraft-independent masked subsystem block, essential for solving the equations of motion.
Description
The block Atmosph is used to compute some basic atmospheric properties, using the ICAO
Standard Atmosphere model (see for instance ref.[30] for a description of that model). It
also computes the local value of the gravitational acceleration g and the dynamic viscosity
μ. The outputs from Atmosph are used (amongst others) by the block Airdata1 for the
calculation of airdata variables that must be known to solve the equations of motion, and
by the blocks Airdata2 and Airdata3, for the computation of additional airdata (-related)
variables.
Equations
The equations used by the block Atmosph have been discussed in more detail in section
3.5.
• Air temperature T in the troposphere, according to the ICAO Standard Atmosphere
model, [K]:
T = T0 + lH
where T0 = 288.15 K is the air temperature at sea level and l = −0.0065 Km−1 is the temperature
lapse-rate in the troposphere. In this equation the small difference between
the geometrical altitude h and the geopotential altitude H has been neglected in view
of the relatively low altitudes considered; see section 3.5 for more details.
• Static air pressure in Standard Atmosphere ps, [Nm−2]:
ps = p0

T0
T
 g
lR
　
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