airspeed

Bidirectional CAS / Mach / TAS conversions with ISA atmosphere and temperature sensors.

• Rust core (PyO3 / maturin) — validated inputs, no silent numeric failures
• Errors as values — nothing is raised; success and failure are distinct types
• Three temperature sources — ISA model, direct SAT, or TAT probe with Newton-Raphson solver

See AERO.md for the implemented equations and references.

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Prerequisites

• Python ≥ 3.12
• Rust toolchain — install via rustup
• uv for Python dependency management

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Build

# Create virtual environment and install dev dependencies
uv sync --group dev

# Compile the Rust extension and install in editable mode
uv run maturin develop --release

# Run tests with coverage
uv run pytest tests/ --cov=src --cov-report=term-missing

# Lint and type-check
uv run ruff check src/ tests/
uv run pyright src/

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Examples

CAS + altitude → Mach, TAS

from airspeed import cas_to_mach_tas, Isa
from airspeed import CasResult, AirspeedError

match cas_to_mach_tas(250.0, 35_000.0, Isa()):
    case CasResult() as r:
        print(f"Mach {r.mach:.3f}  TAS {r.tas_kt:.1f} kt  ΔT {r.dt_isa:+.1f} °C")
    case AirspeedError() as e:
        print(f"Error: {e}")

Mach + altitude → TAS, CAS

from airspeed import mach_to_tas_cas, Sat
from airspeed import MachResult, AirspeedError

match mach_to_tas_cas(0.80, 35_000.0, Sat(-44.34)):
    case MachResult() as r:
        print(f"TAS {r.tas_kt:.1f} kt  CAS {r.cas_kt:.1f} kt  SAT {r.sat_c:.2f} °C")
    case AirspeedError() as e:
        print(f"Error: {e}")

TAS + altitude → Mach, CAS (TAT probe, iterative)

from airspeed import tas_to_mach_cas, Tat
from airspeed import TasResult, AirspeedError

match tas_to_mach_cas(398.7, 35_000.0, Tat(-23.36, eta=1.0)):
    case TasResult() as r:
        print(f"Mach {r.mach:.3f}  CAS {r.cas_kt:.1f} kt  SAT {r.sat_c:.2f} °C")
    case AirspeedError() as e:
        print(f"Error: {e}")

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API

Temperature source

Isa()                                      # ISA standard atmosphere at altitude (default)
Sat(temperature_c: float)                  # direct static air temperature in °C
Tat(temperature_c: float, eta: float=1.0)  # TAT probe reading in °C + recovery factor η

tas_to_mach_cas has no default temperature — TAS→Mach always requires a temperature source.

Result types

All fields are plain float. The three types share AirConditions as a base:

Field	Description
sat_c	static air temperature, °C
speed_of_sound_kt	kt
pressure_mbar	mbar (= hPa)
t_isa_c	ISA temperature at altitude, °C
dt_isa	SAT − T_ISA, positive = ISA+
temperature_source	the Isa, Sat, or Tat passed in

Type	Computed fields
CasResult	mach, tas_kt
MachResult	cas_kt, tas_kt
TasResult	mach, cas_kt

type AirspeedResult = CasResult | MachResult | TasResult is exported as a convenience alias.

Errors

Class	Fields
OutOfRangeError	field: str, unit: str, value: float
SupersonicError	mach: float
TatBelowSatError	tat_c: float, sat_c: float
SolverNoConvergenceError	iterations: int

All inherit from AirspeedError.

Valid input ranges

Input	Range
CAS, TAS	(0, 661) kt
Mach	[0, 1)
Altitude	[0, 65 617] ft
Recovery factor η	(0, 1]

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License

MIT — see LICENSE.