flightcondition 22.7.17

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.

Flight Condition

The Flightcondition class can be used to compute and interact with common flight condition data. Access flight condition quantities through altitude, speed, and length objects.

Outputs include:

1. atm atmospheric quantities - see Atmosphere class below.

2. vel airspeed quantities: Mach number M, true airspeed TAS, calibrated airspeed CAS, equivalent airspeed EAS, dynamic pressure q_inf, and Reynolds number per unit length Re_by_L .

3. len length-scale quantities: Reynolds number Re.

Quantities may also be accessed using their full name with the byname object. For example, Mach number can be accessed using vel.M or by its full name using byname.mach_number

Usage:

from flightcondition import FlightCondition, unit, dimless

# Compute flight condition at 3 km, Mach 0.5
fc = FlightCondition(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, US_units=True)}")

# Access true, calibrated, equivalent airspeeds
KTAS = fc.vel.TAS.to('knots')
KCAS = fc.vel.CAS.to('knots')
KEAS = fc.vel.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)
atm = fc.atm  # access Atmosphere object
h, p, T, rho, nu, a = atm.h, atm.p, atm.T, atm.rho, atm.nu, atm.a
print(f"The ambient temperature at {h.to('km'):.4g} is {T:.4g}")
# >>> The ambient temperature at 3 km is 268.7 K

# Compute again instead using true airspeed and altitude in km
fc = FlightCondition(3.048*unit('km'), TAS=401.7*unit('mph'))
#print(f"{fc}")  # uncomment to print output

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

# Compute additional derived quantities
# Explore the class data structure for all options
print(f"\nThe dynamic pressure in psi is "
    f"{fc.vel.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.len.Re:.3g}")
# >>> The Reynolds number is [9.69e+07 8.82e+07 7.95e+07]

# Alternatively access quantities by their full name
print(fc.vel.TAS == fc.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.

Outputs include:

• Pressure p

• Temperature T

• Density rho

• Sound speed a

• Dynamic viscosity mu

• Kinematic viscosity nu

• Thermal conductivity k

• Layer name layer.name

• Geometric altitude h

• Geopotential altitude H

• Acceleration due to gravity g

• Mean free path MFP

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, US_units=True)}")

# 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 = [7.25e-08 4.04e-05 0.00564] yd

Units

Conveniently input, output, and convert units using pint units.

from flightcondition import unit, printv

h = 33 * unit('km')
print(h.to('kft'))
# >>> 108.26771653543307 kft
printv(h, to='kft')
# >>> h = 108.27 kft

U_inf = 20 * unit('knots')
rho_inf = 1.225 * unit('kg/m^3')
q_inf = 0.5*rho_inf*U_inf**2
printv(q_inf, to='psi')
# >>> q_inf = 0.0094042 psi

Note that pint does not support conflicting unit registries so avoid interactions between flightcondition.unit and a separate pint.UnitRegistry.

Command Line Interface

It is also possible to compute flight conditions from the command line for convenience but with limited functionality. Run flightcondition -h for help.

An example call is provided for the flight condition of 233 knots-equivalent-airspeed at 23 kilo-feet with a length scale of 4 feet:

flightcondition --alt 23 kft --EAS 233 kt --len 4 ft