# Wind Shear Model

Calculate wind shear conditions

• Library:
• Aerospace Blockset / Environment / Wind

## Description

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].

## Ports

### Input

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Altitude, specified as a scalar in specified units.

Data Types: `double`

Direction cosine matrix, specified as a 3-by-3 matrix.

Data Types: `double`

### Output

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Mean wind speed in the body axes frame, returned as a 3-by-1 vector in the selected units.

Data Types: `double`

## Parameters

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Wind shear units, specified as:

UnitsWindAltitude
`Metric (MKS)` Meters/secondMeters
`English (Velocity in ft/s)` Feet/secondFeet

```English (Velocity in kts)```

KnotsFeet

#### Programmatic Use

 Block Parameter: `units` Type: character vector Values: ```'Metric (MKS)'``` | ```'English (Velocity in ft/s)'``` | ```'English (Velocity in kts)'``` Default: ```'Metric (MKS)'```

Flight phase, specified as:

• `Category C - Terminal Flight Phase`, as specified by Military Specification MIL-F-8785C.

• `Other`

#### Programmatic Use

 Block Parameter: `phase` Type: character vector Values: ```'Category C - Terminal Flight Phase'``` | `'Other'` Default: ```'Category C - Terminal Flight Phase'```

Measured wind speed at a height of 6 m (20 ft) above the ground, specified as a scalar.

#### Programmatic Use

 Block Parameter: `W_20` Type: character vector Values: `scalar` Default: `'15'`

Wind direction at a height of 6 m (20 ft) above the ground, specified as a scalar, 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.

#### Programmatic Use

 Block Parameter: `Wdeg` Type: character vector Values: `scalar` Default: `'0'`

## Algorithms

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.

where uw is the mean wind speed, W20 is the measured wind speed at an altitude of 20 feet, h is the altitude, and z0 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.

## References

[1] U.S. Military Specification MIL-F-8785C, November 5, 1980.