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

Flight Parameters

The Ideal Airspeed Correction block calculates one of the following airspeeds: equivalent airspeed (EAS), calibrated airspeed (CAS), or true airspeed (TAS), from one of the other two airspeeds.

Three equations are used to implement the Ideal Airspeed Correction block. The first equation shows TAS as a function of EAS, relative pressure ratio at altitude (δ), and speed of sound at altitude (a).

$$TAS=\frac{EAS\times a}{{a}_{0}\sqrt{\delta}}$$

Using the compressible form of Bernoulli's equation and assuming isentropic conditions, the last two equations for EAS and CAS are derived.

$$EAS=\sqrt{\frac{2\gamma P}{\left(\gamma -1\right){\rho}_{0}}\left({\left(\frac{q}{P}+1\right)}^{(\gamma -1)/\gamma}-1\right)}$$

$$CAS=\sqrt{\frac{2\gamma {P}_{0}}{\left(\gamma -1\right){\rho}_{0}}\left({\left(\frac{q}{{P}_{0}}+1\right)}^{(\gamma -1)/\gamma}-1\right)}$$

In order to generate a correction table and its approximate
inverse, these two equations were solved for dynamic pressure (*q*).
Having values of *q* by a function of *EAS* and
ambient pressure at altitude (*P*) or by a function
of *CAS*, allows the two equations to be solved using
the other's solution for *q*, thus creating a solution
for *EAS* that depends on *P* and *CAS* and
a solution for *CAS* that depends on *P* and *EAS*.

**Units**Specifies the input and output units:

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

**Airspeed input**Specify the airspeed input type:

`TAS`

True airspeed

`EAS`

Equivalent airspeed

`CAS`

Calibrated airspeed

**Airspeed output**Specify the airspeed output type:

Velocity Input

Velocity Output

`TAS`

EAS (equivalent airspeed)

CAS (calibrated airspeed)

`EAS`

TAS (true airspeed)

CAS (calibrated airspeed)

`CAS`

TAS (true airspeed)

EAS (equivalent airspeed)

**Action for out-of-range input**Specify if an out-of-range input (supersonic airspeeds) invokes a warning, an error, or no action.

Input | Dimension Type | Description |
---|---|---|

First | Contains the selected airspeed in the selected units. | |

Second | Contains the speed of sound in the selected units. | |

Third | Contains the static pressure in the selected units. |

Output | Dimension Type | Description |
---|---|---|

First | Contains the selected airspeed in the selected units. |

This block assumes that the air flow is compressible, isentropic (subsonic flow), dry air with constant specific heat ratio, γ.

See the `aeroblk_indicated`

model
and the `aeroblk_calibrated`

model
for examples of this block.

Lowry, J. T., *Performance of Light Aircraft*,
AIAA Education Series, Washington, DC, 1999.

*Aeronautical Vestpocket Handbook*, United
Technologies Pratt & Whitney, August, 1986.

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