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in: x comes from the block Integrator; yatm comes from Atmosph.
out: yad1 is connected to the blocks Airdata2 and Airdata3.
Type browse airdata1 at the command-line for on-line help.
8.2. The aircraft model block libraries 133
Airdata2 Beaver level 1 / Beaver level 2 / Airdata Group / Airdata2
Main FDC library / Airdata, atmosphere
Type
Aircraft-independent masked subsystem block, in general not required for solving the
equations of motion.
Description
The block Airdata2 is used to compute the impact pressure qc, calibrated airspeed Vc, and
equivalent airspeed Ve. While these airdata parameters are important for certain applications
(e.g. for analysing windtunnel measurements or flight tests), they are generally not
required to solve the equations of motion. Therefore, in principle, Airdata2 can safely be
deleted from the SIMULINK model without affecting the solutions of the ODEs (although
this would introduce practical problems, due to broken connections). The equations from
this block are independent of the aircraft under consideration. Other airdata (-related)
equations have been implemented in the blocks Atmosph, Airdata1, and Airdata3.
Equations
The equations used by the block Airdata2 have been discussed in more detail in section
3.5.
• Impact pressure qc, [Nm−2]:
qc = ps
(
1 + g − 1
2
M2
 g
g−1
− 1
)
where g = 1.4 is the ratio of specific heats of air with constant pressure and constant
volume respectively.
• Calibrated airspeed Vc, [ms−1]:
Vc =
vuuut
2g
g − 1
p0
r0
8<
:

1 + qc
p0
g−1
g
− 1
9=
;
where p0 = 101325 Nm−2 is the air pressure at sea level, and r0 = 1.225 kgm−3 is the air
density at sea level.
• Equivalent airspeed Ve, [ms−1]:
Ve = V
r
r
r0
=
s
2qdyn
r0
Inputs
yatm = [ r ps T μ g ]T basic atmospheric properties, yatm
yad1 = [ a M qdyn ]T basic airdata variables, yad1
Outputs
yad2 = [ qc Ve Vc ]T additional airdata (-related) variables, yad2
Parameters
All parameters for Airdata2 are defined within the block itself; Airdata2 does not use any
parameters from the MATLAB workspace.
Connections
in: yatm comes from the block Atmosph; yad1 comes from Airdata1.
out: yad2 is not connected to any other block in the aircraft model.
Type browse airdata2 at the command-line for on-line help.
134 Chapter 8. Aircraft model block reference
Airdata3 Beaver level 1 / Beaver level 2 / Airdata Group / Airdata3
Main FDC library / Airdata, atmosphere
Type
Aircraft-independent masked subsystem block, in general not required for solving the
equations of motion.
Description
The block Airdata3 is used to compute the Reynolds number Rc, which refers to the mean
aerodynamic chord of the aircraft, the Reynolds number per unit length Re, and the total
temperature Tt. While these airdata parameters are important for certain applications (e.g.
for analysing windtunnel measurements or flight tests), they are generally not required to
solve the equations of motion. Therefore, in principle, Airdata3 can safely be deleted from
the SIMULINK model without affecting the solutions of the ODEs (although this would
introduce practical problems, due to broken connections). The equations from this block
are independent of the aircraft under consideration. Other airdata (-related) equations
have been implemented in the blocks Atmosph, Airdata1, and Airdata2.
Equations
The equations used by the block Airdata3 have been discussed in more detail in section
3.5.
• Total temperature Tt, [K]:
Tt = T

1 + g − 1
2
M2

• Reynolds number Rc, [ – ]:
Rc = rVc
μ
• Reynolds number per unit length Re, [m−1]:
Re = rV
μ
Inputs
x = [ V a b p q r y q j xe ye H ]T state vector, x
yatm = [ r ps T μ g ]T basic atmospheric properties, yatm
yad1 = [ a M qdyn ]T basic airdata variables, yad1
Outputs
yad3 = [ Tt Re Rc ]T additional airdata (-related) variables, yad3
Parameters
The block Airdata3 reads the parameter vector GM1 from the MATLAB workspace in order
to extract the mean aerodynamic chord c. The definition of GM1 can be found in appendix
C. The variable 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).
　
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