diff --git a/src/Autopilot/xmlauto.cxx b/src/Autopilot/xmlauto.cxx
index 8a91a091c..8d07a66bd 100644
--- a/src/Autopilot/xmlauto.cxx
+++ b/src/Autopilot/xmlauto.cxx
@@ -40,14 +40,42 @@
 using std::cout;
 using std::endl;
 
+FGPeriodicalValue::FGPeriodicalValue( SGPropertyNode_ptr root )
+{
+  SGPropertyNode_ptr minNode = root->getChild( "min" );
+  SGPropertyNode_ptr maxNode = root->getChild( "max" );
+  if( minNode == NULL || maxNode == NULL ) {
+    SG_LOG(SG_AUTOPILOT, SG_ALERT, "periodical defined, but no <min> and/or <max> tag. Period ignored." );
+  } else {
+    minPeriod = new FGXMLAutoInput( minNode );
+    maxPeriod = new FGXMLAutoInput( maxNode );
+  }
+}
+
+double FGPeriodicalValue::normalize( double value )
+{
+  if( !(minPeriod && maxPeriod )) return value;
+
+  double p1 = minPeriod->get_value();
+  double p2 = maxPeriod->get_value();
+
+  double min = std::min<double>(p1,p2);
+  double max = std::max<double>(p1,p2);
+  double phase = fabs(max - min);
+
+  if( phase > SGLimitsd::min() ) {
+    while( value < min ) value += phase;
+    while( value > max ) value -= phase;
+  } else {
+    value = min; // phase is zero
+  }
+
+  return value;
+}
+
 FGXMLAutoInput::FGXMLAutoInput( SGPropertyNode_ptr node, double value, double offset, double scale) :
   value(0.0),
   abs(false),
-  property(NULL),
-  offset(NULL),
-  scale(NULL),
-  min(NULL),
-  max(NULL),
   _condition(NULL) 
 {
   parse( node, value, offset, scale );
@@ -62,6 +90,7 @@ void FGXMLAutoInput::parse( SGPropertyNode_ptr node, double aValue, double aOffs
     scale = NULL;
     min = NULL;
     max = NULL;
+    periodical = NULL;
 
     if( node == NULL )
         return;
@@ -92,6 +121,10 @@ void FGXMLAutoInput::parse( SGPropertyNode_ptr node, double aValue, double aOffs
       abs = n->getBoolValue();
     }
 
+    if( (n = node->getChild( "period" )) != NULL ) {
+      periodical = new FGPeriodicalValue( n );
+    }
+
     SGPropertyNode *valueNode = node->getChild( "value" );
     if ( valueNode != NULL ) {
         value = valueNode->getDoubleValue();
@@ -161,6 +194,10 @@ double FGXMLAutoInput::get_value()
         if( value > m )
             value = m;
     }
+
+    if( periodical ) {
+      value = periodical->normalize( value );
+    }
     
     return abs ? fabs(value) : value;
 }
@@ -246,6 +283,8 @@ void FGXMLAutoComponent::parseNode(SGPropertyNode* aNode)
         umaxInput.push_back( new FGXMLAutoInput( child ) );
     } else if ( cname == "u_max" ) {
         umaxInput.push_back( new FGXMLAutoInput( child ) );
+    } else if ( cname == "period" ) {
+      periodical = new FGPeriodicalValue( child );
     } else {
       SG_LOG(SG_AUTOPILOT, SG_ALERT, "malformed autopilot definition - unrecognized node:" 
         << cname << " in section " << name);
@@ -314,6 +353,11 @@ void FGXMLAutoComponent::do_feedback_if_disabled()
 
 double FGXMLAutoComponent::clamp( double value )
 {
+    //If this is a periodical value, normalize it into our domain 
+    // before clamping
+    if( periodical )
+      value = periodical->normalize( value );
+
     // clamp, if either min or max is defined
     if( uminInput.size() + umaxInput.size() > 0 ) {
         double d = umaxInput.get_value( 0.0 );
diff --git a/src/Autopilot/xmlauto.hxx b/src/Autopilot/xmlauto.hxx
index 549244c32..efdf2f3ce 100644
--- a/src/Autopilot/xmlauto.hxx
+++ b/src/Autopilot/xmlauto.hxx
@@ -34,16 +34,28 @@
 #include <simgear/structure/subsystem_mgr.hxx>
 #include <simgear/props/condition.hxx>
 
+typedef SGSharedPtr<class FGXMLAutoInput> FGXMLAutoInput_ptr;
+typedef SGSharedPtr<class FGPeriodicalValue> FGPeriodicalValue_ptr;
+
+class FGPeriodicalValue : public SGReferenced {
+private:
+     FGXMLAutoInput_ptr minPeriod; // The minimum value of the period
+     FGXMLAutoInput_ptr maxPeriod; // The maximum value of the period
+public:
+     FGPeriodicalValue( SGPropertyNode_ptr node );
+     double normalize( double value );
+};
 
 class FGXMLAutoInput : public SGReferenced {
 private:
      double             value;    // The value as a constant or initializer for the property
      bool               abs;      // return absolute value
      SGPropertyNode_ptr property; // The name of the property containing the value
-     SGSharedPtr<FGXMLAutoInput> offset;   // A fixed offset, defaults to zero
-     SGSharedPtr<FGXMLAutoInput> scale;    // A constant scaling factor defaults to one
-     SGSharedPtr<FGXMLAutoInput> min;      // A minimum clip defaults to no clipping
-     SGSharedPtr<FGXMLAutoInput> max;      // A maximum clip defaults to no clipping
+     FGXMLAutoInput_ptr offset;   // A fixed offset, defaults to zero
+     FGXMLAutoInput_ptr scale;    // A constant scaling factor defaults to one
+     FGXMLAutoInput_ptr min;      // A minimum clip defaults to no clipping
+     FGXMLAutoInput_ptr max;      // A maximum clip defaults to no clipping
+     FGPeriodicalValue_ptr  periodical; //
      SGSharedPtr<const SGCondition> _condition;
 
 public:
@@ -71,9 +83,9 @@ public:
 
 };
 
-class FGXMLAutoInputList : public std::vector<SGSharedPtr<FGXMLAutoInput> > {
+class FGXMLAutoInputList : public std::vector<FGXMLAutoInput_ptr> {
   public:
-    FGXMLAutoInput * get_active() {
+    FGXMLAutoInput_ptr get_active() {
       for (iterator it = begin(); it != end(); ++it) {
         if( (*it)->is_enabled() )
           return *it;
@@ -82,7 +94,7 @@ class FGXMLAutoInputList : public std::vector<SGSharedPtr<FGXMLAutoInput> > {
     }
 
     double get_value( double def = 0.0 ) {
-      FGXMLAutoInput * input = get_active();
+      FGXMLAutoInput_ptr input = get_active();
       return input == NULL ? def : input->get_value();
     }
 
@@ -147,6 +159,7 @@ protected:
     FGXMLAutoInputList referenceInput;
     FGXMLAutoInputList uminInput;
     FGXMLAutoInputList umaxInput;
+    FGPeriodicalValue_ptr periodical;
     // debug flag
     bool debug;
     bool enabled;
@@ -221,6 +234,8 @@ public:
     bool isPropertyEnabled();
 };
 
+typedef SGSharedPtr<FGXMLAutoComponent> FGXMLAutoComponent_ptr;
+
 
 /**
  * Roy Ovesen's PID controller
@@ -384,7 +399,7 @@ public:
 
     bool build( SGPropertyNode_ptr );
 protected:
-    typedef std::vector<SGSharedPtr<FGXMLAutoComponent> > comp_list;
+    typedef std::vector<FGXMLAutoComponent_ptr> comp_list;
 
 private: