The attached patch modifies the JSBSim config file for the f15. The patch does two things:

1) It increases the fuel load to nearly full internal fuel -- the current default load-up only has 100 lbs of fuel onboard and thus runs out of gas after less than a minute of flight time. Max internal fuel capacity was updated based on data obtained from the globalsecurity.org web site.

2) The outputs from the pitch damper, roll damper, and yaw damper FCS components defined in the XML config file are summed with the pilot commands on each axis, so the dampers actually contribute to the final control surface positioning (they didn't do anything previously). This greatly improves the f15 model's "flyability", if that's a word.

I have dreams of someday trying to implement a reasonably accurate model of the F-15's FCS, using information available on Gene Buckle's web site, http://www.f15sim.com (look in the "Operation" section), and from some NASA reports. If somebody is already working on this, I'd be interested in helping.

Thanks,
-Eric

*** f15.xml_ORIG        Mon Jun 21 21:19:51 2004
--- f15.xml     Mon Sep 20 22:17:37 2004
***************
*** 112,119 ****
        YLOC       0.0
        ZLOC       4.5
        RADIUS    29.0
!       CAPACITY 185.0
!       CONTENTS 100.0
      </AC_TANK>
  
      <AC_TANK TYPE="FUEL" NUMBER="1">
--- 112,119 ----
        YLOC       0.0
        ZLOC       4.5
        RADIUS    29.0
!       CAPACITY 6561.5
!       CONTENTS 6500.0
      </AC_TANK>
  
      <AC_TANK TYPE="FUEL" NUMBER="1">
***************
*** 121,128 ****
        YLOC       0.0
        ZLOC       4.5
        RADIUS    29.0
!       CAPACITY 185.0
!       CONTENTS 100.0
      </AC_TANK>
  
    </PROPULSION>
--- 121,128 ----
        YLOC       0.0
        ZLOC       4.5
        RADIUS    29.0
!       CAPACITY 6561.5
!       CONTENTS 6500.0
      </AC_TANK>
  
    </PROPULSION>
***************
*** 130,144 ****
  
    <FLIGHT_CONTROL NAME="f15">
  
      <COMPONENT NAME="Pitch Trim Sum" TYPE="SUMMER">
         INPUT        fcs/elevator-cmd-norm
         INPUT        fcs/pitch-trim-cmd-norm
         CLIPTO       -1 1
      </COMPONENT>
-     <COMPONENT NAME="Pitch Damper Gain" TYPE="PURE_GAIN">
-        INPUT        velocities/q-rad_sec
-        GAIN         0.000698
-      </COMPONENT>
      <COMPONENT NAME="Elevator Control" TYPE="AEROSURFACE_SCALE">
         INPUT         fcs/pitch-trim-sum
         MIN          -26
--- 130,145 ----
  
    <FLIGHT_CONTROL NAME="f15">
  
+     <COMPONENT NAME="Pitch Damper Gain" TYPE="PURE_GAIN">
+        INPUT        velocities/q-rad_sec
+        GAIN         0.000698
+      </COMPONENT>
      <COMPONENT NAME="Pitch Trim Sum" TYPE="SUMMER">
         INPUT        fcs/elevator-cmd-norm
         INPUT        fcs/pitch-trim-cmd-norm
+        INPUT        fcs/pitch-damper-gain
         CLIPTO       -1 1
      </COMPONENT>
      <COMPONENT NAME="Elevator Control" TYPE="AEROSURFACE_SCALE">
         INPUT         fcs/pitch-trim-sum
         MIN          -26
***************
*** 146,154 ****
--- 147,160 ----
         OUTPUT        fcs/elevator-pos-rad
         GAIN          0.01745
       </COMPONENT>
+      <COMPONENT NAME="Roll Damper Gain" TYPE="PURE_GAIN">
+       INPUT          velocities/p-rad_sec
+       GAIN          -0.013963
+      </COMPONENT>
       <COMPONENT NAME="Roll Trim Sum" TYPE="SUMMER">
         INPUT         fcs/aileron-cmd-norm
         INPUT         fcs/roll-trim-cmd-norm
+        INPUT         fcs/roll-damper-gain
         CLIPTO        -1 1
       </COMPONENT>
       <COMPONENT NAME="Left Aileron Control" TYPE="AEROSURFACE_SCALE">
***************
*** 165,183 ****
         GAIN          0.01745
         OUTPUT        fcs/right-aileron-pos-rad
       </COMPONENT>
!      <COMPONENT NAME="Roll Damper Gain" TYPE="PURE_GAIN">
!       INPUT          velocities/p-rad_sec
!       GAIN           0.013963
!     </COMPONENT>
       <COMPONENT NAME="Yaw Trim Sum" TYPE="SUMMER">
         INPUT        fcs/rudder-cmd-norm
         INPUT        fcs/yaw-trim-cmd-norm
         CLIPTO       -1 1
       </COMPONENT>
-      <COMPONENT NAME="Yaw Damper Gain" TYPE="PURE_GAIN">
-        INPUT        velocities/r-rad_sec
-        GAIN         0.001745
-      </COMPONENT>
       <COMPONENT NAME="Rudder Control" TYPE="AEROSURFACE_SCALE">
         INPUT        fcs/yaw-trim-sum
         MIN         -30
--- 171,186 ----
         GAIN          0.01745
         OUTPUT        fcs/right-aileron-pos-rad
       </COMPONENT>
!      <COMPONENT NAME="Yaw Damper Gain" TYPE="PURE_GAIN">
!        INPUT        velocities/r-rad_sec
!        GAIN        -0.001745
!      </COMPONENT>
       <COMPONENT NAME="Yaw Trim Sum" TYPE="SUMMER">
         INPUT        fcs/rudder-cmd-norm
         INPUT        fcs/yaw-trim-cmd-norm
+        INPUT        fcs/yaw-damper-gain
         CLIPTO       -1 1
       </COMPONENT>
       <COMPONENT NAME="Rudder Control" TYPE="AEROSURFACE_SCALE">
         INPUT        fcs/yaw-trim-sum
         MIN         -30
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