More work to get the starter behavior right, without breaking David's

work on the pa28 idle and without creating ridiculous side effects
(like being able to fly the aircraft with the starter motor, heh).
This one looks pretty good for now, pending work on the propeller to
get its low speed drag in line with reality.

diff --git a/src/FDM/YASim/PistonEngine.cpp b/src/FDM/YASim/PistonEngine.cpp
index 9635f2ea4d691d1677eb5831c575daf86047e3a1..e88178fb20c0568ade2e4a18c60a6cb880ae16ff 100644 (file)
--- a/src/FDM/YASim/PistonEngine.cpp
+++ b/src/FDM/YASim/PistonEngine.cpp
@@ -130,7 +130,7 @@ float PistonEngine::getEGT()
 
 void PistonEngine::calc(float pressure, float temp, float speed)
 {
-    if(_magnetos == 0 || speed < 200*RPM2RADPS)
+    if(_magnetos == 0 || speed < 60*RPM2RADPS)
        _running = false;
     else if(_fuel == false)
         _running = false;
@@ -191,20 +191,25 @@ void PistonEngine::calc(float pressure, float temp, float speed)
     float power = _power0 * burned/_f0;
     _torque = power/speed;
 
-    // Figure that the starter motor produces 60% of the engine's
-    // cruise torque.  That sounds like a lot to me, but it's
-    // necessary to produce the right acceleration.  Someone should
-    // find a good reference for this...
+    // Figure that the starter motor produces 15% of the engine's
+    // cruise torque.  Assuming 60RPM starter speed vs. 1800RPM cruise
+    // speed on a 160HP engine, that comes out to about 160*.15/30 ==
+    // 0.8 HP starter motor.  Which sounds about right to me.  I think
+    // I've finally got this tuned. :)
     if(_cranking && !_running)
-       _torque += 0.60f * _power0/_omega0;
+       _torque += 0.15f * _power0/_omega0;
 
-    // Also, add a negative torque of 10% of cruise, to represent
+    // Also, add a negative torque of 8% of cruise, to represent
     // internal friction.  Propeller aerodynamic friction is too low
     // at low RPMs to provide a good deceleration.  Interpolate it
-    // away as we approach cruise RPMs, though, to prevent interaction
-    // with the power computations.  Ugly.
-    if(speed > 0 && speed < _omega0)
-       _torque -= 0.16f * (_power0/_omega0) * (1 - speed/_omega0);
+    // away as we approach cruise RPMs (full at 50%, zero at 100%),
+    // though, to prevent interaction with the power computations.
+    // Ugly.
+    if(speed > 0 && speed < _omega0) {
+        float interp = 2 - 2*speed/_omega0;
+        interp = (interp > 1) ? 1 : interp;
+       _torque -= 0.08f * (_power0/_omega0) * interp;
+    }
 
     // Now EGT.  This one gets a little goofy.  We can calculate the
     // work done by an isentropically expanding exhaust gas as the