HIGH-VOLTAGE LABORATORY TEST simulates lightning, allowing engineers to assess aircraft safety.
Image: COURTESY OF EDWARD J. RUPKE
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Edward J. Rupke, senior engineer at Lightning Technologies, Inc., (LTI) in Pittsfield, Mass., provides the following explanation:
It is estimated that on average, each airplane in the U.S. commercial fleet is struck lightly by lightning more than once each year. In fact, aircraft often trigger lightning when flying through a heavily charged region of a cloud. In these instances, the lightning flash originates at the airplane and extends away in opposite directions. Although record keeping is poor, smaller business and private airplanes are thought to be struck less frequently because of their small size and because they often can avoid weather that is conducive to lightning strikes.
The last confirmed commercial plane crash in the U.S. directly attributed to lightning occurred in 1967, when lightning caused a catastrophic fuel tank explosion. Since then, much has been learned about how lightning can affect airplanes. As a result, protection techniques have improved. Today, airplanes receive a rigorous set of lightning certification tests to verify the safety of their designs.
Although passengers and crew may see a flash and hear a loud noise if lightning strikes their plane, nothing serious should happen because of the careful lightning protection engineered into the aircraft and its sensitive components. Initially, the lightning will attach to an extremity such as the nose or wing tip. The airplane then flies through the lightning flash, which reattaches itself to the fuselage at other locations while the airplane is in the electric "circuit" between the cloud regions of opposite polarity. The current will travel through the conductive exterior skin and structures of the aircraft and exit off some other extremity, such as the tail. Pilots occasionally report temporary flickering of lights or short-lived interference with instruments.
Most aircraft skins consist primarily of aluminum, which conducts electricity very well. By making sure that no gaps exist in this conductive path, the engineer can assure that most of the lightning current will remain on the exterior of the aircraft. Some modern aircraft are made of advanced composite materials, which by themselves are significantly less conductive than aluminum. In this case, the composites contain an embedded layer of conductive fibers or screens designed to carry lightning currents.
Modern passenger jets have miles of wires and dozens of computers and other instruments that control everything from the engines to the passengers' headsets. These computers, like all computers, are sometimes susceptible to upset from power surges. So, in addition to safeguarding the aircraft's exterior, the lightning protection engineer must make sure that no damaging surges or transients can reach the sensitive equipment inside the aircraft. Lightning traveling on the exterior skin of an aircraft has the potential to induce transients into wires or equipment beneath the skin. These transients are called lightning indirect effects. Careful shielding, grounding and the application of surge suppression devices avert problems caused by indirect effects in cables and equipment when necessary. Every circuit and piece of equipment that is critical or essential to the safe flight and landing of an aircraft must be verified by the manufacturers to be protected against lightning in accordance with regulations set by the Federal Aviation Administration (FAA) or a similar authority in the country of the aircraft's origin.
The other main area of concern is the fuel system, where even a tiny spark could be disastrous. Engineers thus take extreme precautions to ensure that lightning currents cannot cause sparks in any portion of an aircraft's fuel system. The aircraft skin around the fuel tanks must be thick enough to withstand a burn through. All of the structural joints and fasteners must be tightly designed to prevent sparks, because lightning current passes from one section to another. Access doors, fuel filler caps and any vents must be designed and tested to withstand lightning. All the pipes and fuel lines that carry fuel to the engines, and the engines themselves, must be protected against lightning. In addition, new fuels that produce less explosive vapors are now widely used.
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8 Comments
Add Commentone of the image in concepts of physics by halliday resnick walker shows a man changing the spacer on high voltage power line with the help of an helicopter why is he not affected by that high voltage
Reply | Report Abuse | Link to thisIn terms of triggering lightning, how often would a civil aircraft trigger short burst bolts on say a normal transatlantic cruise without stormy weather actually being present?
Reply | Report Abuse | Link to thisCould an aircraft be designed to actually increase the number of strikes it receives per mission? If so how could this be done?
This event reminds me of the tragic explosion and crash of an airliner durring Dec. 1963 outside Elkton, Md but brings to mind the lightning strike on a glider in England. It is known that there are super bolts of lightning, the exact voltage unknown and effects unknown. I think there has been speculation that Sprights and other above cloud discharges sighnify these super bolts. Could one of the satilites or space station or high altitude recons. have recorded an event in the general area this aircraft was last heard from?
Reply | Report Abuse | Link to thisThis event reminds me of the tragic explosion and crash of an airliner durring Dec. 1963 outside Elkton, Md but brings to mind the lightning strike on a glider in England. It is known that there are super bolts of lightning, the exact voltage unknown and effects unknown. I think there has been speculation that Sprights and other above cloud discharges sighnify these super bolts. Could one of the satilites or space station or high altitude recons. have recorded an event in the general area this aircraft was last heard from?
Reply | Report Abuse | Link to thisWow, that is quite fascinating. I think the turbulence they experienced may have been to blame here. It would appear that the aircraft came apart in the air and tumbled into the Atlantic.
Reply | Report Abuse | Link to thisRT
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pummy:
Reply | Report Abuse | Link to thisThe man is at the same electric potential as the power line, and is not in contact with any conducting body at a different electrical potential. Therefore, the man simply assumes the electric potential of the power line, and no current flows once that state is reached.
If the man were touching the power line and a metal ladder on the ground at the same time, he would complete the circuit and be electrocuted.
There are lightning flashes and there are lightning strikes. Flashes between clouds are of a lesser magnitude than lightning strikes to ground. While flying at low altitude below a thunderstorm in a DC-3, the airplane was hit by a bolt of lightning and it was like we had beemn slammed by a huge sledge hammer, the lights went out and the rain started pouring into the pasenger compartment. We were a short distance from the landing strip so the pilot managed to land in spite of the sputtering left engine. The DC 3 is an all metal aircarft and the force of the lightning still opened the top of the fulselage. Modern carbon fiber aircraft have lightning protection that was tested in a lab, with maybe a million volts of manmade lightning, in nature lightning has a potential of tens of millions of volts. Expert are saying that the AirBus A330 have protetion from lightning for the fly by wire computer because it's wiring is grounded. Grounded to what? The carbon fiber fuselage?
Reply | Report Abuse | Link to thisI saw the event in real time (premonition - i have had this ability since a serious accident as a child.) I usually see events exactly 12 hours or 24 hours in advance. But this one was in real time, so I found out the following day. I saw a hole in the front left wall near the left wing but it was the barrier wall, between two passenger areas, where the kitchen or toilet is. The hole I saw was 40cm round and in the upper middle of that wall. It had dirty water coming through it into the cabin and i believe it was petrol. Could anyone explain what could cause this hole. Not what the water was? I would feel less confused about this if I knew what could cause a hole like that.? Was it a pipe?
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