Wind Shear Model

Calculate wind shear conditions

Library

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]. 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.

uw=W20ln(hz0)ln(20z0), 3ft<h<1000ft

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.

Dialog Box

Units

Define the units of wind shear.

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

English (Velocity in kts)

KnotsFeet

Flight phase

Select flight phase:

  • Category C Terminal Flight Phases

  • Other

Wind speed at 6 m (20 feet) altitude (m/s, f/s, or knots)

The measured wind speed at an altitude of 20 feet (6 m) above the ground.

Wind direction at 6 m (20 feet) altitude (degrees clockwise from north)

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.

Inputs and Outputs

InputDimension TypeDescription

First

 Contains the altitude in units selected.

Second

3-by-3 direction cosine matrix 

OutputDimension TypeDescription

First

3-by-1 vector Contains the mean wind speed in the body axes frame, in the selected units.

Examples

See Wind Shear ModelWind Shear Model in aeroblk_HL20aeroblk_HL20 for an example of this block.

Reference

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

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