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Jerommaas edited this page Sep 26, 2019 · 21 revisions

Aerodynamic functions

This module contains a set of standard aerodynamic functions, constants and conversions used in aeronautics. On this webpage, the functions and conversions are discussed and a few examples on their usage are given. On the bottom of this page, the constants used in Bluesky are listed.

Functions

The aerodynamic functions in this module include:

  • Speed of sound [m/s] computation for a given altitude [m]. This is done by calling the function vvsound()
  • Air density computation for a given altitude. This is done by calling the function vdensity()
  • Pressure, air density and temperature computation for a given altitude. This is done by calling the function vatmos()

Conversions

In addition, the module contains some useful speed conversion tools.

  • True airspeed [m/s] to Mach number [-] conversion (mach2tas)
  • Equivalent airspeed [m/s] to true airspeed [m/s] (eas2tas)
  • True airspeed [m/s] to equivalent airspeed [m/s] (tas2eas)
  • Calibrated airspeed [m/s] to true airspeed [m/s] (cas2tas)
  • True airspeed [m/s] to calibrated airspeed [m/s] (tas2cas)
  • Mach number [-] to calibrated airspeed [m/s] (mach2cas)
  • Calibrated airspeed [m/s] to mach number [-] (cas2mach)
  • Meters [m] to feet [ft] (meters_to_feet_rounded)
  • Metric speed [m/s] to knots [kts] (metric_spd_knots_rounded)

Examples

# Create arrays of altitude h and tas:
h = np.array([0, 1000, 2000])
tas = np.array([100,450,300])

# Compute aero results and print:
a = vvsound(h)
m = vtas2mach(tas,h)
p, rho, T  = vatmos(h)
print('vvsound:',a)
print('mach:',m)
print('p',p)
print('rho',rho)
print('T',T)

OUT:

vvsound: [340.29398803 336.43397149 332.52915068]
mach: [0.29386355 1.33755815 0.90217654]
p [101324.99850086  89872.57620224  79491.64759792]
rho [1.225      1.11161793 1.0064451 ]
T [288.15 281.65 275.15]

Constants

The constants used in BlueSky consist of:

  • kts = 0.514444 (m/s of 1 knot)
  • ft = 0.3048 (m of 1 foot)
  • fpm = ft/60 (feet per minute)
  • inch = 0.0254 (m of 1 inch)
  • sqft = 0.09290304 (m of 1 square feet)
  • nm = 1852. (m of 1 nautical mile)
  • lbs = 0.453592 (kg of 1 pound mass)
  • g0 = 9.80665 (m/s^2 Sea level gravity constant)
  • R = 287.05287 (Used in wikipedia table: checked with 11000 m)
  • p0 = 101325. (Pa Sea level pressure ISA)
  • rho0 = 1.225 (kg/m^3 Sea level density ISA)
  • T0 = 288.15 (K Sea level temperature ISA)
  • Tstrat = 216.65 (K Stratosphere temperature (until alt= 22km))
  • gamma = 1.40 (cp/cv: adiabatic index for air)
  • gamma1 = 0.2 ((gamma-1)/2 for air)
  • gamma2 = 3.5 (gamma/(gamma-1) for air)
  • beta = -0.0065 ([K/m] ISA temp gradient below tropopause)
  • Rearth = 6371000. (m average earth radius)
  • a0 = np x sqrt(gamma x R x T0) (sea level speed of sound ISA)
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