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the command-line for more information about the outputs from the aircraft model).
out: the wind velocity components can be used to create the input vector uwind for the
aircraft model (since the body-axes wind-components are in general not constant
across the flight-path of the airplane, it will be necessary to compute the timederivatives
of the wind velocity components too, using an additional Derivative
block — the vector uwind can be constructed by muxing the output vector from
BLwind with the time-derivative from this Derivative block).
Type browse blwind at the command-line for on-line help.
9.1. The wind and turbulence blocklibrary 169
Cwind Main FDC library / Wind and turbulence / Wind models / Cwind
Wind and turbulence library / Wind models / Cwind
Type
Masked subsystem block.
Description
The block Cwind calculates components of the wind velocity along the aircraft’s body-axes
for a constant wind (‘C’ stands for ‘Constant’). The user can specify the wind velocity and
direction (both in the horizontal plane and the vertical plane).
Equations
For a detailed discussion of the equations from the block Cwind, refer to section 4.1.
• Horizontal and vertical components of the wind velocity, [ms−1]:
Vwhor = Vw · cos gw
Vwvert  ww = −Vw · sin gw
where gw is the ‘vertical wind direction angle’, i.e. the angle between the wind vector
and the horizontal plane.
• Horizontal components of the wind velocity, aligned along the Earth-fixed reference
frame, [ms−1]:
uw = Vwhor · cos(yw − p)
vw = Vwhor · sin(yw − p)
where yw is the ‘horizontal wind direction angle’, i.e. the direction from where the horizontal
component of the wind (Vwhor ) emanates, measured relatively to the magnetic
north (yw is measured in [rad]; it equals zero when the wind is blowing from the north,
and p when the wind is blowing to the north).
• Wind components, measured along the body-axes of the aircraft, [ms−1]:
VBw
= (TF · TQ · TY) · VEw
where TF, TQ, and TY represent the transformation matrices corresponding to Euler
rotations, and the superscripts denote the applicable reference frame. This transformation
has been written out in more detail in appendix A, equation (A.4).
Inputs
x = [ V a b p q r y q j xe ye H ]T state vector from the aircraft model, x
Outputs
[ uw vw ww ]T wind velocities along aircraft’s body-axes, [uw,vw,ww]’
Parameters
Cwind does not require any workspace parameters to be specified. The user must specify
the wind velocity, horizontal wind direction, and vertical wind direction in the mask
dialog, which is opened after double-clicking the block Cwind.
Connections
in: x is usually extracted from the nonlinear aircraft model (type browse outputs at
the command-line for more information about the outputs from the aircraft model).
out: the wind velocity components can be used to create the input vector uwind for the
aircraft model (since the body-axes wind-components are in general not constant
across the flight-path of the airplane, it will be necessary to compute the timederivatives
of the wind velocity components too, using an additional Derivative
block—the vector uwind can be constructed by muxing the output vector from Cwind
with the time-derivative from this Derivative block).
Type browse cwind at the command-line for on-line help.
170 Chapter 9. Wind and turbulence block reference
Turbulence Group 1 Main library / Wind & turbulence / Atmosph. turb. models / Turbulence Group 1
Wind and turbulence library / Atmospheric turbulence models / Turbulence Group 1
Type
Non-masked subsystem.
Description
The subsystem Turbulence Group 1 determines longitudinal, lateral, and vertical turbulence
velocity components along the body-axes of the aircraft, plus their time-derivatives,
using Dryden filters with constant coefficients. The user must specify the mean airspeed,
scale length, and standard deviation in each of the Dryden filters from this subsystem
(longitudinal, lateral, and vertical). Variations of the filter coefficients with the airspeed
are neglected, as the influence of such variations is usually rather small. If this limitation
is not acceptable, use Turbulence Group 2 instead.
Subsystems and/or blocks
The subsystem Turbulence Group 1 contains three blocks:
UDRYD1 generates the turbulence velocity component along the XB-axis of the aircraft
(‘longitudinal turbulence’), and its time-derivative,
VDRYD1 generates the turbulence velocity component along the YB-axis of the aircraft
　
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