Basic equation

$ω$Airparticle collision frequency

$n$Air number density

$σ_{allA}$Allowable axial stress

$P_{allB}$Allowable bearing stress

$σ_{allB}$Allowable bending stress

$σ_{allC}$Allowable combined stress

$τ_{allS}$Allowable shear stress

$p_{air}$Atmospheric pressure air

$d_1$Basic minor diameter of external thread

$D_1$Basic minor diameter of internal thread

$d_2$Basic pitch diameter of external thread

$D_2$Basic pitch diameter of internal thread

$d_3$Basic smaller diameter of external thread

$A_b$Cross‐sectional area of the bolts

$ρ_{air}$Density air

$t_1$Depth in the hub

$t$Depth in the shaft

$μ$Dynamic viscosity

$H$Geopotential altitude

$g$Gravitational acceleration

$r_2$Groove rounding

$h$Height key

$H$Height of fundamental triangle

$ν$Kinematic viscosity

$H_b$Lower limit geopotential altitude

$p_b$Lower limit pressure

$T_b$Lower limit temperature

$r_1$Max. rounding the key

$σ_{max}$Maximum normal stress

$v̄$Mean airparticle speed

$l$Mean free path of air particles

$σ_{nom}$Nominal or reference normal stress

$H_p$Pressure scale height

$γ_{air}$Specific weight air

$a$Speed of Sound

$K_t$Stress concentration factor

$K_{ts}$Stress concentration factor for shear stress

$K_{tg}$Stress concentration factor with the nominal stress based on gross area

$K_{tn}$Stress concentration factor with the nominal stress based on net area

$T$Temperature $ T $

$β$Temperature gradient $ β $

$λ$Thermal conductivity

$l_t$Tolerance of key length

$t_{1t}$Tolerance of the groove height in the hub

$t_t$Tolerance of the groove height in the shaft

$b$Width key