Q. ... Incidentally, are you aware of any specific results of
GRP gliders being struck by lightning? Everyone mentions the English event
where the beast became briefly biplanar as the water in the ballast bags
superheated and expanded, but I gather that is rare. Presumably it wouldn't
be good for the instruments, but I note that Alice [an LS4] has metal straps
to form an electrical continuum in the event of Huey hitting the 'smite'
key. I gather the average instructor feels that being struck by lightning
is an unfortunate event for a glider, but do you know of definite structural
problems that have resulted?
Yours seeking enlightenment,
Al.
A. I flew through a thunderstorm once, when I was younger and
more heroic - it was quite frightening, I assure you, with bolts of lightning
zapping down to left and right. Having achieved my goal (2nd turnpoint,
after a 300' save rounding the first) I then showed incredible stoicism
and flew back through it, penetrating through off-the-clock sink to get
back in front of the stormgust which I then flew to the third turnpoint
near Bogan Gate and most of the way home, landing just in time for the
squall line to hit the Forbes strip.
Subsequently I read a little of the effects of lightning on aeroplanes,
and remained convinced for many years that a strike, although frightening
and detrimental to avionics, would have no effect on the structure or the
occupant/s.
Not so, I later discovered. Firstly, GRP sailplanes (and most others)
do not have the little metal strips on the trailing edges of their wings
which you will find on GA aircraft. These strips do the same job as the
earthstraps you used to see on cars years ago - they dispel static charges.
Without them, the bolt will exit through the path of least resistance,
often via the aileron and rudder hinges - welding them solid in the process
(hence the doodads Gary attached to Alice).*
So you're belting along near Vne, trying to stay out of the cloud a
handspan above the canopy which same is now largely opaque due to the copious
quantity of water bucketing down on it, bolts from the blue crackling about
your wingtips like The Mariner's worst nightmare of St Elmo's Fire, and
suddenly the controls freeze. You think about this for a moment. Perhaps
three milliseconds.
Kaboom! Struth, that was close. BANG. Glancing to your left,
you are presented with an unimpeded if somewhat murky view of the world
some 10,000 feet below. This is something of a worry considering that there
was a nice shiny white wing there last time you looked.
Fibreglass gelcoat, as it becomes older, will often become porous and
admit minute quantities of water into the structure. Lightning superheats
this water instantaneously, causing anything from minor delamination to
structural failure.
And you're quite right, it's very rare. When was the last time you saw
some idiot flying in a thunderstorm?
R.
P.S. But there is NOTHING like the buzz of riding a storm front!
*Gary Speight's LS4, now famous for it's short-fielder on Lake
Keepit.
ASK21 disintegrates after lightning strike, UK, April 1999
"hearing a 'very loud bang' and then 'feeling very draughty' ... slowly
becoming aware that 'something was seriously amiss'"
http://www.dft.gov.uk/stellent/groups/dft_foi/documents/page/dft_foi_038203.pdf
Ian Bennning of Sunraysia Gliding Club, who sent the ASK21 reference
above, also mentioned that "lightning struck our IS28 a few years ago while
it was on wire launch, no damage or injuries."
LIGHTNING STALLED AIRCRAFT
http://www.science-frontiers.com/sf091/sf091g15.htm
Further reading: A Stranger
to the Ground - Richard Bach.
