fgdata/Aircraft/ufo/ufo-set.xml

<?xml version="1.0"?>

<PropertyList>

 <sim>

  <description>UFO from the 'White Project' of the UNESCO</description>
  <author>ET</author>

  <flight-model>ufo</flight-model>

  <sound>
   <path>Aircraft/ufo/ufo-sound.xml</path>
  </sound>

  <panel>
   <visibility>false</visibility>
  </panel>

  <model>
   <path>Aircraft/ufo/Models/ufo.xml</path>
  </model>

  <help>
   <title>UFO</title>
   <key>
    <name>joystick fire button</name>
    <desc>fly backwards</desc>
   </key>
   <key>
    <name>[ ]</name>
    <desc>increase/decrease maximum speed</desc>
   </key>
  </help>

 </sim>

 <nasal>
  <ufo>
   <script>
       var maxspeed = props.globals.getNode("engines/engine/speed-max-mps");
       var speed = [5, 10, 20, 50, 100, 200, 500, 1000, 2000, 5000, 10000, 20000, 50000];
       var current = 8;

       controls.flapsDown = func(x) {
           if (!x) { return }
           if (x > 0 and current > 0) {
               current -= 1;
           } elsif (x &lt; 0 and current &lt; size(speed) - 1) {
               current += 1;
           }
           var s = speed[current];
           maxspeed.setDoubleValue(s);
           gui.popupTip(sprintf("MaxSpeed " ~ s ~ " m/s"));
       }
   </script>
  </ufo>
 </nasal>
</PropertyList>