Originally Posted by a64pilot
Anytime a certified aircraft is built from composites, there are steps taken to deal with lightning and to a lesser degree EMI/EMC.
Most often itís Imbedding a metal mesh and if panels
there will be exposed metal on the edges to connect with metal in the airframe.
Iíve seen a carbon fiber antenna
get hit, after the hit it looked like a womanís pony tail. Nothing left but long hair.
On inspecting aircraft composite components, they are either ultrasound, But that requires a pre existing good ultrasound to compare the inspection with, or they are X-rayed, the coin tap test is actually better than many think, most want an electronic gadget, but a coin or tap hammer in the hands of an experienced inspector finds more faults than you might think.
I would expect on a boat about all that could be done is a visual and a coin tap test looking for voids as if there was lightning damage, surely there would be voids?
IR as an inspection method is way overblown, reason is anyone can buy an IR camera
for not much money
and claim that it works miracles.
Iíve not seen IR as an aircraft inspection method, but Iíve been out of the aircraft world for awhile.
I was for a short time a level III aircraft NDI inspector. The requirements to maintain a level III are quite vigorous so I didnít maintain it.
I think this information is very relevant. Particularly the metal screening and edge terminating practices.
I am aware of the consequences when a nearby large catamaran
was hit by lightening ... carbon fiber mast. It appears that the very large current
flow went down through metal wiring
(instruments etc) causing immense damage to the boat. Various cables
turned into a mess of metal strands and woolen like plastic. Many $$$.s worth. However, the carbon fiber mast itself suffered damage as well. The damage seemed to be at places where metal fittings were attached to the mast e.g. SS rigging
etc. Adjacent to these places it seems that the current
discharge from the carbon fiber to the metal "bits" caused sever damage to the carbon fiber and as the owners could not fully ascertain the degree and coverage of the damage, then the mast was a write off.
So if you are checking for lightening damage to a carbon fiber structure,it may pay to look at areas where current flowing through the carbon fiber matrix may find a better (easier) pathway to where ever it was headed. Metal skin fittings? Earth plate fittings etc. If there are many dispersed such fittings the localized damage may be less (per site) . However, the variables are just too extensive.
There are a few web sites that deal with electrical
conductivity of carbon fiber layups but it is tricky stuff as lightening currents are at the extreme end of any considerations.
Maybe using a sound tapping tool may reveal something. Assume that large areas without any metal fittings escaped damage and then try testing around suspect areas where metal fittings are in place. If it sounds different then it probably is different.
I suppose that the real problem is that carbon fiber does provide an electrical
pathway with relatively high resistance compared to steel
or aluminium hulls. That impedance is the source of the problems. Gawd, just too difficult.