Calculate relative atmospheric ratios

Flight Parameters

The
Relative Ratio block computes the relative atmospheric ratios, including
relative temperature ratio (*θ*), $$\sqrt{\theta}$$, relative pressure ratio (*δ*),
and relative density ratio (*σ*).

*θ* represents the ratio of the air stream
temperature at a chosen reference station relative to sea level standard
atmospheric conditions.

$$\theta =\frac{T}{{T}_{0}}$$

*δ* represents the ratio of the air stream
pressure at a chosen reference station relative to sea level standard
atmospheric conditions.

$$\delta =\frac{P}{{P}_{0}}$$

*σ* represents the ratio of the air stream
density at a chosen reference station relative to sea level standard
atmospheric conditions.

$$\sigma =\frac{\rho}{{\rho}_{0}}$$

The Relative Ratio block icon displays the input units selected
from the **Units** list.

**Units**Specifies the input units:

Units Tstatic Pstatic rho_static `Metric (MKS)`

Kelvin Pascal Kilograms per cubic meter `English`

Degrees Rankine Pound force per square inch Slug per cubic foot **Theta**When selected, the

*θ*is calculated and static temperature is a required input.**Square root of theta**When selected, the $$\sqrt{\theta}$$ is calculated and static temperature is a required input.

**Delta**When selected, the

*δ*is calculated and static pressure is a required input.**Sigma**When selected, the

*σ*is calculated and static density is a required input.

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

First | Contains the Mach number. | |

Second | Contains the ratio between the specific heat at constant pressure
(C) and the specific heat
at constant volume (_{p}C).
For example, (_{v}γ = C/_{p}C)._{v} | |

Third | Contains the static temperature. | |

Fourth | Contains the static pressure. | |

Fifth | Contains the static density. |

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

First | Contains the θ. | |

Second | Contains the $$\sqrt{\theta}$$. | |

Third | Contains the δ. | |

Fourth | Contains the σ. |

For cases in which total temperature, total pressure, or total density ratio is desired (Mach number is nonzero), the total temperature, total pressure, and total densities are calculated assuming perfect gas (with constant molecular weight, constant pressure specific heat, and constant specific heat ratio) and dry air.

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

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