The aerodynamic coefficients and parameters frequently used in OpenVSP and VSPAero plots and output files are defined here for reference. These are in accordance to conventions in their respective fields of use.
A = π*R^2Area of rotor or prop disk
dF =Local sectional force
CN = dot(dF,nvec) / (density * A *(Omega*R)^2)Normal force coeff.
CS = dot(dF,svec) / (density * A *(Omega*R)^2)Chordwise force coeff.
CP = 2*π*CQProp convention power coeff.
CP_H = CQ_HHelicopter convention power coeff.
CT = Prop Thrust / (density * n^2 * D^4)Prop convention thrust coeff.
CT_H = Rotor Thrust / (density * A *(Omega*R)^2)Helicopter convention thrust coeff.
CQ = Shaft moment / (density * n^2 * D^5)Prop convention torque coeff.
CQ_H = Shaft moment / (density * A * (Omega*R)^2 * R)Helicopter convention torque coeff.
D =diameter of rotor or prop
EtaP = J * CT / (2 * π * CQ)Prop efficiency
FOM = CT_H^1.5 / (sqrt(2) * CP_H)Figure of merit
J = Vinf/ (n * D)Prop advance ratio
n =angular velocity in revolutions per second
nvec =chord normal vector
svec =chordwise vector from LE to TE
Omega =angular velocity in radians per second
R = D/2radius of rotor or prop
RPM = Omega*60/(2*π)angular velocity in revolutions per minute