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Calculate wind shear conditions
The Wind Shear Model block adds wind shear to the aerospace model. This implementation is based on the mathematical representation in the Military Specification MIL-F-8785C [1]. The magnitude of the wind shear is given by the following equation for the mean wind profile as a function of altitude and the measured wind speed at 20 feet (6 m) above the ground.
$${u}_{w}={W}_{20}\frac{\mathrm{ln}\left(\frac{h}{{z}_{0}}\right)}{\mathrm{ln}\left(\frac{20}{{z}_{0}}\right)},\text{}3fth1000ft$$
where u_{w} is the mean wind speed, W_{20} is the measured wind speed at an altitude of 20 feet, h is the altitude, and z_{0} is a constant equal to 0.15 feet for Category C flight phases and 2.0 feet for all other flight phases. Category C flight phases are defined in reference [1] to be terminal flight phases, which include takeoff, approach, and landing.
The resultant mean wind speed in the flat Earth axis frame is changed to body-fixed axis coordinates by multiplying by the direction cosine matrix (DCM) input to the block. The block output is the mean wind speed in the body-fixed axis.
Define the units of wind shear.
Units | Wind | Altitude |
---|---|---|
Metric (MKS) | Meters/second | Meters |
English (Velocity in ft/s) | Feet/second | Feet |
English (Velocity in kts) | Knots | Feet |
Select flight phase:
Category C — Terminal Flight Phases
Other
The measured wind speed at an altitude of 20 feet (6 m) above the ground.
The direction of the wind at an altitude of 20 feet (6 m), measured in degrees clockwise from the direction of the Earth x-axis (north). The wind direction is defined as the direction from which the wind is coming.
Input | Dimension Type | Description |
---|---|---|
First | Contains the altitude in units selected. | |
Second | 3-by-3 direction cosine matrix |
Output | Dimension Type | Description |
---|---|---|
First | 3-by-1 vector | Contains the mean wind speed in the body axes frame, in the selected units. |
See Wind Shear ModelWind Shear Model in aeroblk_HL20aeroblk_HL20 for an example of this block.