diff --git a/Engine/propC10v.xml b/Engine/propC10v.xml
index 8e22c673a..6eccdbb5b 100644
--- a/Engine/propC10v.xml
+++ b/Engine/propC10v.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <FG_PROPELLER  NAME="Clark Y 0.08 thickness/chord ratio variable pitch">
-  IXX       5
+  IXX       1.8
   DIAMETER  84
   NUMBLADES  2
   MINPITCH 11
diff --git a/Engine/propC6v.xml b/Engine/propC6v.xml
index 921231d56..15704a02c 100644
--- a/Engine/propC6v.xml
+++ b/Engine/propC6v.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <FG_PROPELLER  NAME="Clark Y 0.06 thickness/chord ratio variable pitch">
-  IXX       5
+  IXX       1.8
   DIAMETER  84
   NUMBLADES  2
   MINPITCH 11
diff --git a/Engine/propC8v.xml b/Engine/propC8v.xml
index f61fd0390..4145aa08a 100644
--- a/Engine/propC8v.xml
+++ b/Engine/propC8v.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <FG_PROPELLER  NAME="Clark Y 0.08 thickness/chord ratio variable pitch">
-  IXX       5
+  IXX       1.8
   DIAMETER  84
   NUMBLADES  2
   MINPITCH 11
diff --git a/Engine/prop_generic2f.xml b/Engine/prop_generic2f.xml
index 87afe3e2a..cd56b8064 100644
--- a/Engine/prop_generic2f.xml
+++ b/Engine/prop_generic2f.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <FG_PROPELLER  NAME="generic2f">
-  IXX       5
+  IXX       1.8
   DIAMETER  76
   NUMBLADES  2
   C_THRUST 12 1