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Appendix 1
2 Poisson’s ratio (ν preferred).
3 Prandtl interference factor (biplane).
4 Stefan-Boltzmann constant.
5 Electrical conductivity.
6 Velocity error, eg in INS readout.
7 Standard deviation.
8 Normal stress (also f) ; at least 15 variations, with
suffixes; also surface tension (γ more common).
9 Radar cross-section.
10 Subscript zero, incremental backscatter coefficient.
11 Generalized symbol for solidity.
12 Ratio of chordwise position of leading edge at tip to
length of root chord.
13 Subscript y, aircraft response to gust or turbulence.
14 Subscript H, Hertz pressure.
Σ (capital sigma)
Generalized symbol for a summation.
τ (tau) 1 Temperature (also θ ).
2 Transmission factor or coefficient.
3 Shear stress in fluid (also q).
4 Period (growth or decay), or time delay; also translational
time response, distance constant divided by TAS.
5 Radar pulse width [subscript comp, compressed pulse
width].
υ (upsilon) No aerospace meanings, loosely used interchangeably
with v.
φ (phi) 1 Generalized function symbol.
2 Angle of bank or roll.
3 Angle between flight path and local horizontal; also
induced angle of attack.
4 Slope of runway.
5 Rotor inflow angle.
6 Effective helix angle.
7 Latitude, terrestrial, celestial etc.
8 Shear strain (also γ, also called fluidity).
9 Polar co-ordinate angle.
10 Radiant [luminous] or magnetic flux (also capital).
11 Entropy.
12 Velocity potential.
13 Phase displacement (also θ); subscript m, phase
margin.
14 Cos φ, electrical power factor.
15 Flight-control input frequency.
16 Wagner function.
Φ (capital phi) 1 Flux, magnetic or luminous.
2 Thrust or lift augmentation ratio in ejector.
3 Phase angle between input signal and polar coordinates
of digital filter.
4 Φ . Frequency difference between input signal and
digital filter.
5 Φ . ω Power spectral density.
χ (chi) 1 Mass.
2 Magnetic susceptibility.
3 Symbol for probability.
4 Helicopter-rotor wake skew angle.
ψ (psi) 1 Stream function.
2 Angle of yaw.
3 Azimuth angle.
4 Electrostatic, dielectric or luminous flux.
5 Helmholtz free energy.
6 Sweep angle of fin (vertical stabilizer), often with
suffix number giving % chord of point of measurement.
7 Helicopter rotor-blade azimuth position, or Küssner
function.
8 Rate of turn [ o / s ].
Ψ (capital psi)
Ψ w
Electric flux.
Age of a wake, especially from a rotating blade.
ω (omega) 1 Frequency (suffix c, carrier; n, natural or
damped; r, resonant).
2 Angular velocity in rad/s.
3 Vorticity.
4 ω¯ , Specific weight, esp. piston engines.
5 ω g, Gust frequency.
Ω (capital omega) 1 Ohms resistance.
2 Resultant velocity.
3 Solid angle (also ω).
4 Angular velocity, or rotational frequency, e.g. of helicopter
rotor, or vorticity.
5 Turn rate, essentially same as 4.
6 Spatial frequency, ω divided by TAS.
Ωs Ohm-second, = henry.
Ω s
Ω
Spin rate, rad/s.
Conductance.
Greek Symbols
795