diff --git a/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSource.C b/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSource.C
index 3b300e08ae..80e12aae66 100644
--- a/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSource.C
+++ b/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSource.C
@@ -354,25 +354,33 @@ void Foam::rotorDiskSource::constructGeometry()
     {
         const label cellI = cells_[i];
 
-        // position in rotor co-ordinate system
+        // position in (planar) rotor co-ordinate system
         x_[i] = coordSys_.localPosition(C[cellI]);
 
         // cache max radius
         rMax_ = max(rMax_, x_[i].x());
 
-        // determine swept angle relative to rDir axis
-        scalar psi = x_[i].y() - rDir.y();
+        // swept angle relative to rDir axis [radians] in range 0 -> 2*pi
+        scalar psi = x_[i].y();
+        if (psi < 0)
+        {
+            psi += mathematical::twoPi;
+        }
 
-        // blade flap angle
+        // blade flap angle [radians]
         scalar beta = flap_.beta0 - flap_.beta1*cos(psi) - flap_.beta2*sin(psi);
 
-        // determine rotation tensor to convert into the rotor cone plane
-        scalar c = cos(-beta);
-        scalar s = sin(-beta);
-        R_[i] = tensor(1, 0, 0, 0, c, s, 0, -s, c);
+        // determine rotation tensor to convert from planar system into the
+        // rotor cone system
+        scalar cNeg = cos(-beta);
+        scalar sNeg = sin(-beta);
+        R_[i] = tensor(cNeg, 0.0, -sNeg, 0.0, 1.0, 0.0, sNeg, 0.0, cNeg);
+        scalar cPos = cos(beta);
+        scalar sPos = sin(beta);
+        invR_[i] = tensor(cPos, 0.0, -sPos, 0.0, 1.0, 0.0, sPos, 0.0, cPos);
 
-        // geometric angle of attack - not including twist
-        alphag_[i] = trim_.alphaC - trim_.A*cos(psi) - trim_.B*sin(psi);
+        // geometric angle of attack - not including twist [radians]
+        alphag_[i] = trim_.alphaC + trim_.A*cos(psi) + trim_.B*sin(psi);
     }
 }
 
@@ -439,6 +447,7 @@ Foam::rotorDiskSource::rotorDiskSource
     profiles_(coeffs_.subDict("profiles")),
     x_(cells_.size(), vector::zero),
     R_(cells_.size(), I),
+    invR_(cells_.size(), I),
     alphag_(cells_.size(), 0.0),
     area_(cells_.size(), 0.0),
     coordSys_(false),
diff --git a/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSource.H b/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSource.H
index 7565fa17ce..ae2d8a2a47 100644
--- a/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSource.H
+++ b/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSource.H
@@ -131,17 +131,18 @@ public:
 protected:
 
     // Helper structures to encapsulate flap and trim data
+    // Note: all input in degrees (converted to radians internally)
 
         struct flapData
         {
-            scalar beta0;   // coning angle [deg]
+            scalar beta0;   // coning angle
             scalar beta1;   // lateral flapping coeff
             scalar beta2;   // longitudinal flapping coeff
         };
 
         struct trimData
         {
-            scalar alphaC;  // collective pitch angle [deg]
+            scalar alphaC;  // collective pitch angle
             scalar A;       // lateral cyclic coeff
             scalar B;       // longitudinal cyclic coeff
         };
@@ -186,6 +187,9 @@ protected:
         //- Rotation tensor for flap angle
         List<tensor> R_;
 
+        //- Inverse rotation tensor for flap angle
+        List<tensor> invR_;
+
         //- Geometric angle of attack [deg]
         List<scalar> alphag_;
 
diff --git a/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSourceTemplates.C b/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSourceTemplates.C
index acadb0ec9d..f4d02efd54 100644
--- a/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSourceTemplates.C
+++ b/src/finiteVolume/cfdTools/general/fieldSources/basicSource/rotorDiskSource/rotorDiskSourceTemplates.C
@@ -29,7 +29,7 @@ License
 #include "unitConversion.H"
 #include "volFields.H"
 
-using namespace Foam::constant;
+using namespace Foam::constant::mathematical;
 
 // * * * * * * * * * * * * Protected Member Functions  * * * * * * * * * * * //
 
@@ -124,11 +124,11 @@ Foam::tmp<Foam::volVectorField> Foam::rotorDiskSource::calculateForces
 
             const scalar radius = x_[i].x();
 
-            // apply correction due to flap in cartesian frame
-            vector Uc = R_[i] & U[cellI];
+            // velocity in local cylindrical reference frame
+            vector Uc = coordSys_.localVector(U[cellI]);
 
-            // velocity in local reference frame
-            Uc = coordSys_.localVector(Uc);
+            // apply correction in local system due to coning
+            Uc = R_[i] & Uc;
 
             // set radial component of velocity to zero
             Uc.x() = 0.0;
@@ -149,7 +149,16 @@ Foam::tmp<Foam::volVectorField> Foam::rotorDiskSource::calculateForces
             blade_.interpolate(radius, twist, chord, i1, i2, invDr);
 
             // effective angle of attack
-            scalar alphaEff = alphag_[i] + twist - atan(Uc.z()/Uc.y());
+            scalar alphaEff = pi + atan2(Uc.z(), Uc.y()) - (alphag_[i] + twist);
+            if (alphaEff > pi)
+            {
+	        alphaEff -= twoPi;
+            }
+            if (alphaEff < -pi)
+            {
+                alphaEff += twoPi;
+            }
+
             AOAmin = min(AOAmin, alphaEff);
             AOAmax = max(AOAmax, alphaEff);
 
@@ -175,10 +184,13 @@ Foam::tmp<Foam::volVectorField> Foam::rotorDiskSource::calculateForces
                 tipFactor = 0.0;
             }
 
-            // calculate forces
-            const scalar pDyn = 0.5*rho[cellI]*sqr(magUc);
-            const scalar f = pDyn*chord*nBlades_*area_[i]/(mathematical::twoPi);
-            const vector localForce(0.0, f*Cd, tipFactor*f*Cl);
+            // calculate forces perpendicular to blade
+            scalar pDyn = 0.5*rho[cellI]*sqr(magUc);
+            scalar f = pDyn*chord*nBlades_*area_[i]/twoPi;
+            vector localForce = vector(0.0, f*Cd, tipFactor*f*Cl);
+
+            // convert force from local coning system into rotor cylindrical
+            localForce = invR_[i] & localForce;
 
             // accumulate forces
             dragEff += localForce.y();