Recently I've noticed that the direction to lightning strikes as displayed
on the Chelton have not aligned to the visible thunderstorms.  I decided to
check it out at the Lancair Flyin where a representative of the stormscope
manufacturer was attending to help with skin mapping and other problems.

We discovered that the bearing to the lightning strike will always display
relative to magnetic north rather than relative to the heading of the
airplane.  In other words, if a lightning strike occurs directly ahead while
on a heading of 210°, the display will show the strike at 360°.  If on a
heading of 360° when a strike occurs directly ahead the display will show
the strike at the correct location.  This display problem is consistent at
all points around the compass rose.  For example, when on the 210° heading
(or any heading for that matter), a lightning strike off your right wing
will display as at 90°.

This condition was duplicated on another identical installation with the
same results.  Interestingly, the other airplane tested had a Garmin 530/430
that correctly displayed the lightning strikes.

Kirk Hammersmith is now aware of this problem and is spearheading the
solution.  He'll be in contact with the Chelton software people to work on
the problem.  I'm guessing that we'll see a new version of the Chelton 5.0
software soon.

In the mean time I'd suggest that you don't utilize the stormscope for
weather detection if you have the Chelton 5.0 software.  Its unknown if the
previous software versions had this problem.  Somewhere in the past (before
5.0) I remember that the display was consistent with the observed
thunderstorm locations, but I can't be sure.

Believe me when I say that I'm not picking on either Chelton or the
Stormscope.  I love my Chelton and I'm fond of the stormscope.  I'm sure
that a fix will be quickly forthcoming.  My interest is solely to warn of
the situation so that nobody mistakenly flies into a thunderstorm while
thinking that they've deftly dodged the beast.  You shouldn't be using the
system to pick your way through thunderboomers anyway.

Hal Woodruff
LNC4/P