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Ideal Airspeed Correction

Calculate equivalent airspeed (EAS), calibrated airspeed (CAS), or true airspeed (TAS) from each other

  • Library:
  • Aerospace Blockset / Flight Parameters

  • Ideal Airspeed Correction block

Description

The Ideal Airspeed Correction block calculates one of these airspeeds from one of the other two airspeeds:

  • Equivalent airspeed (EAS)

  • Calibrated airspeed (CAS)

  • True airspeed (TAS)

Limitations

This block assumes that the air flow is compressible dry air with constant specific heat ratio, γ

Ports

Input

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True input airspeed, specified as a scalar, in the units specified by the Units parameter.

Dependencies

To enable this port, set Airspeed input to TAS.

Data Types: double

Equivalent input airspeed, specified as a scalar, in the units specified by the Units parameter.

Dependencies

To enable this port, set Airspeed input to EAS.

Data Types: double

Calibrated input airspeed, specified as a scalar, in the units specified by the Units parameter.

Dependencies

To enable this port, set Airspeed input to EAS.

Data Types: double

Speed of sound, specified as a scalar, in the units specified by the Units parameter.

Data Types: double

Static pressure, specified as a scalar, in the units specified by the Units parameter.

Data Types: double

Output

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Equivalent output airspeed, returned as a scalar, in the units specified by the Units parameter.

Dependencies

To enable this port, set Airspeed input to TAS or CAS and Airspeed output to EAS.

Data Types: double

Calibrated output airspeed, returned as a scalar, in the units specified by the Units parameter.

Dependencies

To enable this port, set Airspeed input to TAS or EAS and Airspeed output to CAS.

Data Types: double

True output airspeed, returned as a scalar, in the units specified by the Units parameter.

Dependencies

To enable this port, set Airspeed input to CAS or EAS and Airspeed output to TAS.

Data Types: double

Parameters

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Input and output units, specified as:

Units

Airspeed Input

Speed of Sound

Air Pressure

Airspeed Output

Metric (MKS)

Meters per second

Meters per second

Pascal

Meters per second

English (Velocity in ft/s)

Feet per second

Feet per second

Pound force per square inch

Feet per second

English (Velocity in kts)

Knots

Knots

Pound force per square inch

Knots

Programmatic Use

Block Parameter: units
Type: character vector
Values: 'Metric (MKS)' | 'English'
Default: 'Metric (MKS)'

Airspeed input type, specified as:

TAS

True airspeed

EAS

Equivalent airspeed

CAS

Calibrated airspeed

Programmatic Use

Block Parameter: vel_in
Type: character vector
Values: 'TAS' | 'EAS' | 'CAS'
Default: 'TAS'

Airspeed output type, specified as:

Airspeed Input

Airspeed Output

TAS

EAS (equivalent airspeed)

CAS (calibrated airspeed)

EAS

TAS (true airspeed)

CAS (calibrated airspeed)

CAS

TAS (true airspeed)

EAS (equivalent airspeed)

Programmatic Use

Block Parameter: vel_out_tas, vel_out_cas, vel_out_eas, depending on the input velocity type, vel_in. For more information, see the airspeed output type table.
Type: character vector
Values: 'EAS' | 'CAS''TAS'
Default: 'EAS'

Method for computing the conversion factor, specified as:

Table Lookup

(Default) Generate output airspeed by looking up or estimating table values based on block inputs.

If the Subsonic airspeeds only check box is selected, the Ideal Airspeed Correction block generates code that includes subsonic (Mach < 1) lookup table data.

If the Subsonic airspeeds only check box is cleared, the Ideal Airspeed Correction block generates code that includes all (Mach < 5) lookup table data. Beyond Mach 5, the block uses the equation method.

The Table Lookup method is not recommended for either of these instances:

  • Speed of sound less than 200 m/s or greater than 350 m/s.

  • Static pressure less than 1000 Pa or greater than 106,500 Pa.

Using the Table Lookup method in these instances causes inaccuracies.

Equation

Compute output airspeed directly using block input values.

Calculations involving supersonic airspeeds (greater than Mach 1) require an iterative computation. If the function does not find a solution within 30 iterations, it displays an error message.

The block does not include lookup table data in generated code.

The Ideal Airspeed Correction block automatically uses the Equation method for any of these instances:

  • Conversion with Airspeed input set to TAS and Airspeed output set to EAS.

  • Conversion with Airspeed input set to EAS and Airspeed output set to TAS.

  • Conversion when block input airspeed is greater than five times the speed of sound at sea level (approximately 1700 m/s).

Programmatic Use

Block Parameter: method
Type: character vector
Values: 'Table Lookup' | 'Equation'
Default: 'Table Lookup'

Select this check box to use this block only with subsonic airspeed (airspeeds less than Mach 1) applications. Selecting this check box may improve performance.

The block generates code as follows:

  • If this check box is selected, the Ideal Airspeed Correction block generates code that includes subsonic (Mach < 1) lookup table data if Method is set to Table Lookup.

    Selecting this check box displays the Action for out-of-range input parameter.

  • If this check box is cleared, the Ideal Airspeed Correction block generates code that includes all (Mach < 5) lookup table data if Method is set to Table Lookup.

Programmatic Use

Block Parameter: SubOnly
Type: character vector
Values: 'off' | 'on'
Default: 'off'

Out-of-range block behavior, where airspeed is greater than Mach 1, specified as follows.

ValueDescription

None

Does not display warning or error.

Warning

Displays warning and indicates that the airspeed is greater than Mach 1.

Error

Displays error and indicates that the airspeed is greater than Mach 1.

Dependencies

This parameter is enabled only if the Subsonic airspeeds only check box is selected.

Programmatic Use

Block Parameter: action
Type: character vector
Values: 'None' | 'Warning' | 'Error'
Default: 'None'

References

[1] Lowry, J. T., Performance of Light Aircraft, AIAA Education Series, Washington, DC, 1999.

[2] Aeronautical Vestpocket Handbook, United Technologies Pratt & Whitney, August, 1986.

[3] Gracey, William, Measurement of Aircraft Speed and Altitude, NASA Reference Publication 1046, 1980.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Introduced before R2006a