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Dick Kreidel. (Mr. Plumer's response follows)
Subject: Long-EZ Lightning Strike 22 July, 1987
References: Your Letter of 3 June, 1986, Same Subject, with Dick Kriedel's Letter Attached.
Scaled Composites, Inc.
Mojave, CA 93501
I have studied the interesting account of a lightning strike to a Long-EZ by pilot Dick
Kreidel, accompanying your letter of 3 June, and have the following comments:
1. After beginning the deviation North, the aircraft entered an electrically charged region, as indicated by the static in the communications system, "small electrical shocks" and "blue glow" (Corona) on aircraft extremities. The electric shocks were due to electric field penetration of the non-conductive fiberglass air frame. The erratic behavior of the instruments was also due to electric field interaction with the inter-connecting wiring. It is very likely that the Corona was indeed occurring inside the cockpit as Mr. Kreidel suspected.
2. The synoptic weather conditions reported by the pilot are very characteristic of those reported by other operators when lightning strikes have occurred (~14,000 feet; icing, precipitation, within a cloud, outside air temperature plus or minus five degrees of freezing). Apparently the aircraft was near embedded thunderstorms cells, though lightning strikes have been known to originate in "layered" clouds as well as CB clouds.
3. The "flash of light" and "loud crack" indicate the lightning strike, although evidently one of mild intensity, is indicated by the comparatively minor effects on the aircraft. At 14,000 feet it is likely that the aircraft encountered a branch of a flash, rather than the main channel of a cloud to earth flash; as illustrated in the following sketch.
Click to enlarge
4. The electric currents in a branch (of which there are a lot in a typical flash structure) are usually much less than that in the main channel. Even so, the flash and noise can be frightening if experienced close at hand.
5. Apparently the lightning current entered one wing tip (take your pick) and exited from the other, being conducted by internal metal conductors between. The amount of damage to the fiberglass and foam structures indicates a very mild strike, perhaps 5 kiloamperes or less (part 23 rules require an air frame to tolerate 200 kiloamperes).
1. Pilot Kreidel was lucky. A more severe strike may well have
caused major structural damage and lethal voltage differences among metal objects in the
cockpit (column, petals, headphones, etc.) as well as severe damage to internal electrical
conductors such as control cables, hinges, bearings, rods, electrical wiring. These
voltages and currents can be far in excess of fatal levels. Electric fields and lightning
strikes themselves will directly penetrate unprotected fiberglass structures, attracted by
metal objects within - no matter how small.
2. This is another example of the fact that ATC cannot be relied upon to vector an aircraft safely around - and clear of - hazardous thunderstorms. Controllers are not provided with sufficient (and timely) information for this purpose. Even though avoiding areas of heavy precipitation the aircraft ran into an electrically active region.
3. This incident is not a good example of what would occur to a Long-EZ in a lightning strike. A "full threat" stroke would likely have ripped a hole a foot or more in diameter through the composite and vaporized small diameter control cables and inter-connecting wiring. The accompanying shock waves would have caused extensive internal damage, delamination, etc.. I doubt very much whether the aircraft or pilot could have survived such a strike.
1. Continue to warn pilots of this class of aircraft to stay VFR and
avoid weather clouds, precipitation, and icing within five degrees of the freezing level
should be especially avoided.2. This Long-EZ should be thoroughly inspected to be sure
that there has not been damage to any internal metal parts. All internal part should be
inspected. It is quite probable, for example that the strike burned some strands of control cables, electrical wires, etc..
Thank you for sharing this interesting account with me. Please give me a call if you have any further questions.
J.A. Plumer, President
Lightning Technologies, Inc.