effects of lighting strike ?

[cpt]

Hello rotorheads,
As I have been currently flying in areas where rainy seasons are sometimes fairly active I very often ask to myself what could be immediate effects of a lighting strike on the helicopter flight.
I assume this will be directly linked to:
1/ Intensity of the lighting
2/ Size of helicopter
3/ Airframe materials (metalic / composite)
But I am curious to know what could be the immediate results on blades, flight controls, avionics....(albeit longer term effects, as with this last summer S76-blades sad story)
I have never heard about an helicopter having been immediatly fully destroyed in flight because of a lighting strike and I don't think it is only because we carrefully avoid Cbs.
I am sure some of you know much more about this !

[KENNYR]

The only incident of lightening striking a helicopter that I know of was in W.Germany near Dortmund when a German Police BO105 was hit on the mast. It immediately delaminated the blades with the resultant loss of the helicopter and its crew.

[jonnyg]

A Bristows helicopter returning from a rig in the North Sea had a lightning strike which overloaded the tail rotor blades (which promptly failed). The pilots managed to sucessfully put it down on the water with floats without doing too much harm....

[S76Heavy]

BHL also suffered a strike on a 76.
One of the blades ended up, after extensive checks, on VX and caused it to crash 3 years later.
Avionics were pretty cooked after the strike, I believe. Must be a report on it somewhere.

[Barannfin]

How about the effects on Magnets? like the compass, if your avionics get fried I would assume thats your last resort for nav.

[zhishengji751]

http://www.aaib.dft.gov.uk/bulletin/mar01/gbhbf.htm

Sikorsky S76A (Modified), G-BHBF
The aircraft was in the cruise, en-route from Norwich to the offshore Clipper gas field. Whilst cruising at 2,000 feet in IMC (just above the cloud base) the aircraft was struck by lightning. Approximately 30 seconds later, the crew became aware of a smell of burning. They rapidly descended below cloud and returned visually to Norwich. The landing was uneventful.

http://www.aaib.dft.gov.uk/special/gbjvx/gbjvx.htm
11 souls lost.
This rotor blade was manufactured in March 1981. In 1999 when fitted to Sikorsky S76A G-BHBF it was damaged by a lightning strike (see AAIB Bulletin 3/2001). At that time the blade had accumulated 8,261 hours usage. The blade was returned to the manufacturer for assessment where, following inspection, it was repaired and returned to service. Neither the thermal damage to the spar nor the manufacturing anomaly were detected during this inspection. At the time of the accident, the blade had accumulated 9,661 hours usage. The airworthiness limitation life of the blade is 28,000 hours.

The AAIB and the helicopter's manufacturer are of the opinion that the electrical energy imparted by the lightning strike in 1999 exploited the anomaly that was built into the blade at manufacture and damaged the spar.


There are also some interesting threads on strikes, found via the search function.

[cpt]

Rather frightening stories actually.
Apparently, a lightning strike seems to be much more damaging on metallic/composite structures (ie. blades with a metallic spar)
Usually, composite parts of airframes I know, include a metalization sheet, but I don't think such a device is found on blades...could it be a reason of such damaging effects on them ?Despite their possible dramatic results,I wonder why lightning strike doesn't seems to be of a primary hazard concern amongst helicopter people. Maybe is it because experience shows they have limited effects on fixed wings ( usually bigger and with less composite components)...maybe is it only just because we consider them as part of our fate ?:p

[Lu Zuckerman]

As previously stated some composites have aluminum mesh embedded in the composite structure in order to deflect the charge to either metallic airframe or to some common ground connector. This works in theory or when the lightning attachment is over a very short period. If the charge is attached for a longer time the mesh can be destroyed and the composite which can conduct low level of charge (static electricity) then becomes a resistor and can explode.

When I worked on the A-129 program I attended an engineering meeting where they were discussing composite blade design. I asked if they were considering some means of dissipating a lightning attachment and they said the composites (carbon based) would act as a conductor and carry the charge to the blade root and then to the rotorhead. I stated that with the high voltage and amperage of a lightning attachment the composites would act as a resistor and the blades would self-destruct. I would assume this is what happened on the delaminated blades described above.

Another problem is streamers. When you have a metallic airframe that has composite panels and those panels do not have the mesh incorporated you can have a problem with a lightning strike. When the lightning strikes the fuselage the ground plane of the airframe is the same as the lightning charge. With the metal fuselage at lightning potential the composite panel appears to be a hole relative to the surrounding charge. Streamers can develop from large metallic parts inside the fuselage and try to equalize the charge on the composite panel. These streamers can develop an explosive force and blow the panel off the airframe or at the least blow a hole in the panel.

Lightning can also develop charge differentials and the equalization of the charges can develop extremely high pressure differentials (shock waves) that are so strong they can deform metal tubes to the point of destruction.

:eek:

[S76Heavy]

The reason why lightning strikes don't seem a primary concern for us helicopter people is because most of them are associated with CBs and TS, and we tend to stay well clear of those, therefore avoiding the highest risk areas.

We do worry about it, but unless there is a proper system to warn us, we won't know we're in danger until we get that bolt out of the blue..:(

[212man]

One interesting aspect of lightning strikes is that they tend to occur in liquid precipitation in temperatures within about 5 degrees of freezing. This explains why they are more common in the UK and Northern Europe, than in the States and the Tropics.

I hardly recall seeing lightning in the North Sea yet know of several cases of strikes on all types, and have seen the results. In Nigeria I have seen the most spectacular lightning imagineable both in daytime and at night (and heard it in the cockpit; not pleasant!) yet have not heard of any lightning strikes to helicopters to us or any operator in all the time rotary operations have existed here.

[SASless]

212man.....there have been some interesting fireworks displays in the skies of Nigeria.....and too true the sound of thunder booming around you while flogging the skies in the world's oldest 212's.....but you have never seen what it can be like in the USA when the big boomers start rolling east from the Rockies. When the tops start peaking out at 60,000 +........you just cannot imagine the power of those storms. But then....everyone with any sense at all avoids them like the plague thus the incidence of strikes is greatly diminished. The storms I am talking about fetch up the concept of being a "no brainer" kind of thing......setting through one on the ground in a car will give you religion much less getting bold enough to enter one in the air. Get the "Trellis Climber" to tell you about some of the storms that abound in our part of the world.

When the winds generated are strong enough to cause three articulated lorrys to disappear from the truck yard in Oklahoma City......things that were low drag and weighed almost 40,000 pounds.....and they just vanished into the air not to be found again.....now that is a storm!

Any truth to the rumor the vaunted EC-155 is now going to be dedicated to the offshore sites and the customer is going to bring in Bell 412's to replace the 76's and the World's oldest 212's?

[212man]

SASless,
I don't doubt what you say, and wasn't try to say anything about the ferocity of the storms I've seen; I agree they aren't that bad. It was simply the comparison between strike rates and perceived lightning density I was quoting, and this is borne out in various studies (such as one done by the NBAA).

I can't comment on your other remarks; even if I knew I wouldn't discuss contractual stuff here.

[cpt]

By the way, talking about thunderstorms and weather, does anybody knows a good book about tropical meteorology...in this part of the world (the heart of the darkness, to dramatize a little....) it's looks to be sometimes more mystical than rational. I am particulary interested in winds at low altitudes, and others jokes of that intertropical front.:confused:
To come back to come back to ligthnings; thanks to the very comprehensive and very technical posts until now.