FMdims computes forces in [N] and moments in [Nm] from dimensionless force and moment coefficients, using the dynamic pressure and some geometric properties of the aircraft, see the equations below. In the 'Beaver' model, FMdims is used by the subsystem blocks Aerodynamics Group (Beaver) and Engine Group (Beaver) of the Beaver model, where it is being applied to aerodynamic forces and moments and propulsive forces and moments, respectively. (In those subsystems, the non-dimensional coefficients are computed within the blocks Aeromod and Engmod.)
yad1 = [a M qdyn]' (airdata variables which are computed in the block Airdata1) Caero= [CXa CYa CZa Clt Cma Cna]' (dimensionless aerodynamic force and moment coefficients, computed in Aeromod (Beaver)) Cprop= [CXp CYp CZp Clp Cmp Cnp]' (dimensionless propulsive force and moment coefficients, computed in Engmod (Beaver)) {a : speed of sound [m/s] } {M : Mach number [-] } qdyn : dynamic pressure [N/m^2] CXa, CYa, CZa: aerodynamic force coefficients along the aircraft's body-axes Cla, Cma, Cna: aerodynamic moment coefficients along the aircraft's body-axes CXp, CYp, CZp: engine force coefficients along the aircraft's body-axes Clp, Cmp, Cnp: engine moment coefficients along the air- craft's body-axes
The inputvariables which are not actually used by FMdims have been displayed between brackets.
FMaero= [Xa Ya Za La Ma Na]' (vector with aerodynamic forces & moments) FMprop= [Xp Yp Zp Lp Mp Np]' (vector with engine forces & moments) Xa, Ya, Za: aerodynamic forces along aircraft's body-axes [N] La, Ma, Na: aerodynamic moments along aircraft's body-axes [Nm] Xp, Yp, Zp: propulsive forces along aircraft's body-axes [N] Lp, Mp, Np: propulsive moments along aircraft's body-axes [Nm]
X = CX*qdyn*S, Y = CY*qdyn*S, Z = CZ*qdyn*S L = Cl*qdyn*S*b, M = Cm*qdyn*S*c, N = Cn*qdyn*S*bwhere:
S = wing area [m^2] c = cbar = mean aerodynamic chord [m] b = wing span [m]
CX, CY, ... , Cn may equal CXa, ... Cna, CXp, ... Cnp, or any other sequence of force and moment coefficients which have been made dimensionless in the same way as the aerodynamic and propulsive forces and moments.