Lightning Diversion Systems - Aircraft Lightning Diversion Strips

Lightning Diverter Strips

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	LDS Diverter Strips featured on the History Channel's Most Shocking Episode
	Significant Advantages of LDS Segmented Diverter Strips Over Solid Diverters
	Improved Lightning Diverter Strip Data
	Comparative Breakdown Tests Between Original and Recent Diverter Strip Designs

LIGHTNING PROTECTION SYSTEM

Lightning Diversion Systems has developed a new and improved lightning protection device that diverts lightning strokes from aircraft nose radomes and other sensitive areas. The protection system consists of a segmented diverter strip which provides maximum multiple-strike protection with negligible effect on RF pattern characteristics. Attached to an aircraft's radome, the system allows a lightning stoke to travel safely and directly to ground in an ionized channel created in the air above the diverter strip. It combines permanent protection with a low drag aerodynamics and has insignificant effect on radar antenna radiation patterns. The electrostatic shield created by the system provides a new source of streamers outside the radome wall to the fuselage. The resistance material in the strips help initiate the ionized channels and provides a bleed-off path for P-static. The small diameter of the disc segments (1/10 wavelength or less at X band) makes the strip compatible with radar system operation up to and including Ku band. If necessary, disc size can be reduced for optimum antenna patterns at higher frequencies.

The nose and tail of an aircraft, the ideal location for radar an communication antennas, are also the most common targets for lightning strikes. Radar and communication antennas aboard aircraft and ground based installations are contained within non-metallic radomes or other nonmetallic fairings to protect them from damaging airflow and precipitation. Many of these installations are located at the nose or tail of an aircraft where lightning is prone to strike. The metal radar antenna housed within the non-conductive reinforced plastic radome is the main source of ionized streamers created at the nose of the aircraft by high stress fields. These streamers pass through an unprotected radome providing a path for the lightning stroke. When lightning strikes an unprotected nose radome, it can penetrate the radome wall and attach to enclosed metal structures such as a radar antenna. The resulting explosion can cause extensive damage to the radome installation. Pilots' lives are in danger.

PROBLEMS WITH OTHER AVAILABLE SYSTEMS

Foil strip system protects for one strike only as the foil evaporates when struck. Over time, the foil cracks, causing sparks during P-static conditions, leading to severe P-static interference on VHF Comm and NAV frequencies.

Solid metal diverter bar system protects for more than one strike but at the cost of increased drag and weight. Bars deform during heavy strikes causing radome to buckle. Holes drilled for mechanical inserts often cause cracks and allow moisture in the radome laminate.

Internal rod system connects to buttons flush with radome exterior and reduces drag problem, but introduces complex fastener design and testing problems because of the magnetic forces developed at rod/button junctures. Rods will bend during heavy strike and damage the radome structure.

All of the above system seriously influence the radiation patterns of enclosed radar antennas.

ADVANTAGES OF LDS MULTI-STRIKE LIGHTNING PROTECTION SYSTEM

Permanent, multi-strike protection.

Negligible effect on RF pattern characteristics.

Low drag aerodynamics.

Low maintenance, eliminates possibility of catastrophic damage.

Conductive segments are grounded through resistance material - no arcing between segments during P-static charging conditions.

The p-static channel created by the resistance material in the LDS diverter strip eliminates the problems inherent in the design of the foil strip, solid metal diverter bar and internal rod systems.

Sophisticated technology requires congruent safety devices. Pitot boom installations on a nose radome increase the possibility of lightning damage. Damage from lightning striking this type of installation can cause malfunctions of adjacent instrumentation systems. Diverter strips placed on the radome and canopy allow lightning to travel in an ionized channel above the strip without harm to vital instruments and cockpit personnel.

The forces of lightning strokes that sometimes damage conventional protective systems by bowing the permanent strips between attach screws, breaking ground bolts, and breaking diverter strips where right-angle turn occur, are not present when the LDS strip is used. Under Air Force Materials Laboratory Contract F33615-71-C-1380 Project 392-0 (Brunswick Corporation, prime contractor and McDonnell-Douglas (now The Boeing Company), subcontractor), tests also compared the performance of a conventional solid metal strip diverter with the segmented LDS strip in conjunction with a low-sidelobe antenna housed in a ogive nose cone. The conventional diverter raised the sidelobes typically by 10dB, while the LDS diverter limited sidelobe increase to 1dB - a 35:1 improvement. Radar pattern distortion from signal degradation obstructions may jeopardize the accuracy of early developing airborne pulse doppler radar systems. These systems rely on extremely low sidelobes to permit detection of targets and to prevent "clutter: in the direction of the ground.

Extensive testing indicates that the LDS strips will withstand current transfer greater than 200,000 amperes with little or no damage. (More than 99.5% of natural lightning strokes measured display peak current of less than 150,000 amperes.)

Helicopters being considered all weather flight condition vehicles and employing composite techniques now need to seriously address protection from lightning effects.

INSTALLATION

The LDS Multi-Strike Lightning Protection System consists of a thin, flexible, segmented diverter strip that combines 0.10" nominal diameter metal disc segments with appropriate resistance material on a thin (0.005-0.010") laminate. Strips are easily bonded with a compatible adhesive to the outer surface of the radome, and are just as easily repaired or replaces. The strip is attached to the grounding bolt to allow smooth transfer of current.

STORM HAZARDS PROGRAM

f106.jpg (12075 bytes) The LDS Multi-Strike Lightning Protection System is currently used to protect the nose radome on the CV580 which is being flown in a multi-agency program of the FAA and Air Force for atmospheric and weather hazards research. The LDS diverter strip also protects the nose radome on the F106B being flown by NASA at Langley Research Center for similar research.