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^2
Area of rotor or prop diskdF =
Local sectional forceCN = 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*CQ
Prop convention power coeff.CP_H = CQ_H
Helicopter 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 propEtaP = J * CT / (2 * π * CQ)
Prop efficiencyFOM = CT_H^1.5 / (sqrt(2) * CP_H)
Figure of meritJ = Vinf/ (n * D)
Prop advance ration =
angular velocity in revolutions per secondnvec =
chord normal vectorsvec =
chordwise vector from LE to TEOmega =
angular velocity in radians per secondR = D/2
radius of rotor or propRPM = Omega*60/(2*π)
angular velocity in revolutions per minute