From ea8bfba98adbdfea204b5b109077cb38a5b079a6 Mon Sep 17 00:00:00 2001
From: Henning Stahlke <github@henningstahlke.de>
Date: Fri, 5 May 2017 16:25:16 +0200
Subject: [PATCH] YASim: add method to Wing and clarify member name.

---
 src/FDM/YASim/Wing.cpp | 18 +++++++++++++++---
 src/FDM/YASim/Wing.hpp |  7 +++++--
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/src/FDM/YASim/Wing.cpp b/src/FDM/YASim/Wing.cpp
index 81aa4e3e9..e8c77be07 100644
--- a/src/FDM/YASim/Wing.cpp
+++ b/src/FDM/YASim/Wing.cpp
@@ -11,7 +11,7 @@ Wing::Wing(Version *ver, bool mirror, float* base, float chord,
     _chord(chord),
     _length(length),
     _taper(taper),
-    _sweep(sweep),
+    _sweepAngleCenterLine(sweep),
     _dihedral(dihedral),
     _twist(twist)
 {
@@ -129,7 +129,7 @@ void Wing::calculateWingCoordinateSystem() {
   // (tail incidence is varied by the solver)
   // Generating a unit vector pointing out the left wing.
   float left[3];
-  left[0] = -Math::tan(_sweep);
+  left[0] = -Math::tan(_sweepAngleCenterLine);
   left[1] = Math::cos(_dihedral);
   left[2] = Math::sin(_dihedral);
   Math::unit3(left, left);
@@ -175,9 +175,21 @@ void Wing::calculateMAC()
     const float commonFactor = _chord*(0.5+_taper)/(3*_chord*(1+_taper));
     _mac = _chord-(2*_chord*(1-_taper)*commonFactor);
     _macRootDistance = _netSpan*commonFactor;
-    _macX = _base[0]-Math::tan(_sweep) * _macRootDistance + _mac/2;
+    _macX = _base[0]-Math::tan(_sweepAngleCenterLine) * _macRootDistance + _mac/2;
 }
 
+float Wing::calculateSweepAngleLeadingEdge()
+{
+    if (_length == 0) {
+      return 0;
+    }
+    return Math::atan(
+      (sin(_sweepAngleCenterLine)+(1-_taper)*_chord/(2*_length)) /
+      cos(_sweepAngleCenterLine)
+    );  
+}
+
+
 void Wing::compile()
 {
     // Have we already been compiled?
diff --git a/src/FDM/YASim/Wing.hpp b/src/FDM/YASim/Wing.hpp
index e7496c61d..ac206bd4e 100644
--- a/src/FDM/YASim/Wing.hpp
+++ b/src/FDM/YASim/Wing.hpp
@@ -31,7 +31,7 @@ public:
     // fraction of chord at wing tip, 0..1
     float getTaper() const { return _taper; };
     // radians
-    float getSweep() const { return _sweep; };
+    float getSweep() const { return _sweepAngleCenterLine; };
     // radians, positive is "up"
     void setDihedral(float dihedral) { _dihedral = dihedral; }
     float getDihedral() const { return _dihedral; };
@@ -96,6 +96,7 @@ private:
     void calculateTip();
     void calculateSpan();
     void calculateMAC();
+    float calculateSweepAngleLeadingEdge();
     void addSurface(Surface* s, float weight, float twist);
     
     struct SurfRec { Surface * surface; float weight; };
@@ -110,9 +111,11 @@ private:
     bool _mirror {false};
     float _base[3] {0,0,0};
     float _chord {0};
+    // length is distance from base to tip, not wing span
     float _length {0};
     float _taper {1};
-    float _sweep {0};
+    // sweep of center line, not leading edge!
+    float _sweepAngleCenterLine {0}; 
     float _dihedral {0};
     
     // calculated from above