Ideal Airspeed Correction

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

• Library:

• Aerospace Blockset / Flight Parameters

• 

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

TAS — True input airspeed

scalar

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

EAS — Equivalent input airspeed

scalar

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

CAS — Calibrated input airspeed

scalar

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

a — Speed of sound

scalar

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

Data Types: double

P0 — Static pressure

scalar

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

Data Types: double

Output

EAS — Equivalent output airspeed

scalar

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

CAS — Calibrated output airspeed

scalar

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

TAS — True output airspeed

scalar

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

Units — Units

Metric (MKS) (default) | English (Velocity in ft/s) | English (Velocity in kts)

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 — Airspeed input type

TAS (default) | EAS | CAS

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 — Airspeed output type

EAS (default) | CAS | 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 — Method for computing conversion factor

Table Lookup (default) | Equation

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'

Subsonic airspeeds only — Use with subsonic airspeed

off (default) | on

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'

Action for out-of-range input — Out-of-range block behavior

None (default) | Warning | Error

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

Value	Description
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'

Model Examples

Lightweight Airplane Design

How to use MathWorks® products to address the technical and process challenges of aircraft design using the design of a lightweight aircraft.

Open Model

True Airspeed from Indicated Airspeed Calculation

How to compute true airspeed from indicated airspeed using the Ideal Airspeed Correction block. The Aerospace Blockset™ blocks are indicated in red.

Open Model

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™.