Flight Condition

About

Airspeed conversions (true/calibrated/equivalent/Mach), atmospheric data, and more with built-in unit checking. Specific sub-modules include:

• flightcondition: input altitude to compute common flight condition data. Easily swap between true airspeed, calibrated airspeed, equivalent airspeed, and Mach number. Includes atmospheric data.
• atmosphere: input altitude to compute atmospheric data. Many relevant, derived quantities are included. The upper limit is 86 km for the 1993 International Standard Atmosphere model and 10,000 kilometers for the NRL MSIS model.
• units: built-in unit-checking and conversion using the pint package.

See the web application here: https://flightcondition.streamlit.app

Author

Matthew C. Jones matt.c.jones.aoe@gmail.com

Installation

Install Commands

Install using the pip package-management system. The easiest method is to open the terminal and run:

pip install flightcondition

Alternatively, manually download the source code, unpack, and run:

pip install <path/to/flightcondition>

Dependencies

• numpy: package for scientific computing.
• pint: package for dealing with units.
• pymsis: package for NRL MSIS atmospheric model.

Usage

Import all utilities with,

from flightcondition import *

or more explicitly as shown in the following examples.

Flight Condition

The FlightCondition class is used to compute and interact with common flight condition data. Inputs include altitude, velocity in some format, and an optional length scale.

Input Arguments

Input arguments include:

1. Altitude: h (aliases include: alt, altitude)
2. Velocity (pick one):
   • True airspeed: TAS (aliases include: tas, true_airspeed, U_inf, V_inf)
   • Calibrated airspeed: CAS (aliases include: cas, calibrated_airspeed)
   • Equivalent airspeed: EAS (aliases include: eas, equivalent_airspeed)
   • Mach number: M (aliases include: mach, Mach, M_inf, mach_number)
3. Length-scale (optional): L (aliases include: ell, bylen, length, length_scale, l)

Input quantities must be dimensionalized - see the usage below. Alternatively use KTAS, KCAS, or KEAS for convenience. For example, KCAS=233 is equivalent to CAS=233*unit('knots').

Output Quantities

The following tables list the quantities and the variables used to access them. Quantities may be accessed by either (a) their abbreviated variable, e.g. .TAS, or (b) by their full names, e.g. byname.true_airspeed. They may also be accessed through their particular sub-category: byalt, byvel, or bylen, e.g. .byvel.TAS or .byvel.byname.true_airspeed.

| Altitude Quantity | Variable | Full Name (via .byname.) | |-----------------------|----------|----------------------------| | Geometric altitude | h | geometric_altitude | | Geopotential altitude | H | geopotential_altitude | | Pressure | p | pressure | | Temperature | T | temperature | | Density | rho | density | | Sound speed | a | sounds_speed | | Dynamic viscosity | mu | dynamic_viscosity | | Kinematic viscosity | nu | kinematic_viscosity | | Thermal conductivity | k | thermal_conductivity | | Gravity | g | gravity | | Mean free path | MFP | mean_free_path |

| Velocity Quantity | Name | Full Name (via .byname.) | |----------------------------------|-----------|----------------------------------| | True airspeed (TAS) | TAS | true_airspeed | | Calibrated airspeed (CAS) | CAS | calibrated_airspeed | | Equivalent airspeed (EAS) | EAS | equivalent_airspeed | | Mach number | M | mach_number | | Mach angle | mu_M | mach_angle | | Dynamic pressure | q_inf | dynamic_pressure | | Impact pressure | q_c | impact_pressure | | Stagnation pressure | p0 | stagnation_pressure | | Stagnation temperature | T0 | stagnation_temperature | | Recovery temperature (laminar) | Tr_lamr | recovery_temperature_laminar | | Recovery temperature (turbulent) | Tr_turb | recovery_temperature_turbulent | | Reynolds number per unit length | Re_by_L | recovery_temperature_turbulent |

| Length-Scale Quantity | Name | Full Name (via .byname.) | |--------------------------------------------------|-------------|----------------------------------| | Length scale | L | length_scale | | Reynolds number | Re | reynolds_number | | Boundary layer thickness (laminar) | h_BL_lamr | boundary_thickness_laminar | | Boundary layer thickness (turbulent) | h_BL_turb | boundary_thickness_turbulent | | Flat plate skin friction coefficient (laminar) | Cf_lamr | friction_coefficient_laminar | | Flat plate skin friction coefficient (turbulent) | Cf_turb | friction_coefficient_turbulent |

Example Usage

from flightcondition import FlightCondition, unit

# Compute flight condition at 3 km, Mach 0.5
fc = FlightCondition(h=3*unit('km'), M=0.5)

# Uncomment to print summary of flight condition quantities:
#print(f"{fc}")

# Uncomment to print abbreviated output in US units:
#print(f"\n{fc.tostring(full_output=False, units="US")}")

# Convert true, calibrated, equivalent airspeeds
KTAS = fc.TAS.to('knots')
KCAS = fc.CAS.to('knots')
KEAS = fc.EAS.to('knots')
print(f"Flying at {KTAS.magnitude:.4g} KTAS,"
      f" which is {KCAS.magnitude:.4g} KCAS,"
      f" or {KEAS.magnitude:.4g} KEAS")
# >>> Flying at 319.4 KTAS, which is 277.7 KCAS, or 275.1 KEAS

# Access atmospheric data (see Atmosphere class for more)
h, p, T, rho, nu, a = fc.h, fc.p, fc.T, fc.rho, fc.nu, fc.a
print(f"The ambient temperature at {h.to('km'):.4g} is {T:.4g}")
# >>> The ambient temperature at 3 km is 268.7 K

# Change airspeed to 300 KEAS and altitude to 12 kft
fc.EAS = 300 * unit('knots')
fc.h = 12 * unit('kft')
#print(f"{fc}")  # uncomment to print output

# Recompute for a range of altitudes at 275.14 knots-equivalent
# airspeed with a characteristic length scale of 10 meters
fc = FlightCondition(h=[0, 9.8425, 20]*unit('kft'),
                    EAS=275.14*unit('kt'),
                    L=10*unit('m'))

# Compute additional derived quantities - explore the class for more!
print(f"\nThe dynamic pressure in psi is {fc.q_inf.to('psi'):.3g}")
# >>> The dynamic pressure in psi is [1.78 1.78 1.78] psi
print(f"The Reynolds number is {fc.Re:.3g}")
# >>> The Reynolds number is [9.69e+07 8.82e+07 7.95e+07]
h_yplus100 = fc.wall_distance_from_yplus(100)
print(f"The wall distance where y+=100 is {h_yplus100.to('in'):.3g}")
# >>> The wall distance where y+=100 is [0.0126 0.0138 0.0153] in

# Alternatively access quantities by their full name
print(fc.TAS == fc.byname.true_airspeed)
# >>> [ True  True  True]

# Or by their sub-categories: `byalt`, `byvel`, or `bylen`
print(fc.byvel.TAS == fc.byvel.byname.true_airspeed)
# >>> [ True  True  True]

Atmosphere

The Atmosphere class can be used to compute and interact with common standard atmosphere data and derived quantities. See the list of output quantities in the FlightCondition documentation above. See also layer for layer properties such as layer.name for the layer name.

Note that all Atmosphere properties can be accessed through the FlightCondition class, however, this class stands on its own if the additional velocity and length-scale quantities are not desired.

Input Arguments

The input argument is geometric altitude h. Aliases include alt and altitude. Note that these geometric altitude must be input as dimensional length quantities - see the usage below. Alternatively input un-dimensionalized numbers using h_kft or h_km for kilofeet and kilometers respectively.

Example Usage

from flightcondition import Atmosphere, unit

# Compute atmospheric data for a scalar or array of altitudes
h = [0.0, 44.2, 81.0] * unit('km')
atm = Atmosphere(h)

# Uncomment to print all atmospheric quantities:
#print(f"\n{atm}")

# Uncomment to print while specifying abbreviated output in US units:
#print(f"\n{atm.tostring(full_output=False, units="US")}")

# See also the linspace() function from numpy, e.g.
# h = linspace(0, 81.0, 82) * unit('km')

# Access individual properties and convert to desired units: "
p, T, rho, nu, a, k = atm.p, atm.T, atm.rho, atm.nu, atm.a, atm.k
print(f"\nThe pressure in psi is {p.to('psi'):.3g}")
# >>> The pressure in psi is [14.7 0.024 0.000129] psi

# Compute additional properties such as mean free path
# Explore the class data structure for all options
print( f"\nThe mean free path = {atm.MFP:.3g}")
# >>> The mean free path = [7.