Posted By Wai Ming WU
Do aeroplanes need lightning protection? If yes, how?

WM WU

Posted By lawrence baldwin
Its fair to say everything needs protection from lightning which on the ground is provided by a rod which gives passage of least resistance to earth. Aircraft are not earth tied so do not have this capability, so lightning will pass through the aircraft on its route to earth.
Prevention is by avoidance, air traffic rerouting away from weather and pilots avoiding weather systems that is likely to give rise to this phenomena if possible by flying above the potentially dangerous clouds or by giving such cloud formations wide berths.

However lightning strikes do occurr, they can either pass along the outside of the aircraft or produce a track through the fuselage similar to that of a bullet. Continuity bonding is very important in aircraft maintenance, not only for providing a passage of least resistance but also to enable the dissipation of static electricity which is built up through normal flying.

My experience is with helicopters, to receive a lighting strike is not uncommon. The best control is not to fly into potentially dangerous weather conditions in the first place.

Posted By Alec Wood
Lightning, as with all electric current, will always follow the path of least resistance. Thus a lightning strike on a metal skinned aircraft will normally flow through the aircraft skin and, as long as the panel to panel bond is good, it will be contained inside the fabric of the skin of the aircraft. The paint will be scorched because it forms a small point of high resistance and is thus subject to electrical heating.

Therefore, lightning strikes are not normaly dangerous to aircraft, however, the large current flows, general increases in static charge and electromagnetic pulses associated with lightning can risk an aircraft if all conductive objects are not at the same potential, i.e. bonded together, a practice called equipotential bonding, or more colloquially, "earthing". Obviously, all wiring cannot be "earthed", so power and signal wiring is generally contained within screened or metal enclosures which are electrically bonded to the aircraft frame.

It is this bonding, or rather its breakdown, which risks the aircraft rather than the lightning strike itself. The extremely careful maintenance schedule in place for the space shuttle makes me highly skeptical of the lightning theory since a good skin panel bond means no sparking, no heating and thus no fire or explosion. To the lay person though, it sounds pretty good - which in modern journalism seems much more important than facts.

It is worth reminding ourselves that any object travelling through the air at speed will generate a huge static charge of hundreds of thousands of volts, which will be discharged when the aircraft lands, or the first time its metal parts touch anything conductive. Such a discharge will be accompanied by a massive spark if not properly controlled. The big risk here would be discharge through the fuel rig, sparks at the dispensing nozzle are not a good thing! This is why aircraft use conductive tyres, trailing earth straps and are connected to grounding rods while on the deck. This risk far exceeds any from lightning.

Alec Wood
Viewtek Display Services Ltd