Research on Lightning Protection of Heavy Helicopter

In order to reduce the weight of heavy helicopters,
composite materials are widely used. The structural weight
mainly includes rotor weight, fuselage weight and landing
gear weight. The structural weight coefficient is the
percentage of the structural weight to the total weight of the
helicopter. On the premise of meeting the structural strength
of the body, its structural weight coefficient can be reduced to
less than 30%. However, the introduction of composite
materials into the helicopter body structure brings the special
problem of lightning hazard.

Lightning strike has direct and indirect impact on
helicopter. The direct impact of lightning stroke mainly
includes the following two aspects. One is that the
communication antenna exposed outside the fuselage is often
damaged by lightning, resulting in communication system
failure. On the other hand, the electrical conductivity of
composites is poor, so it is difficult to conduct the current in a
short time when lightning strikes. When the temperature rises
sharply, the composites are deeply stratified or severely
ablated, resulting in structural damage.
In terms of indirect impact, the high voltage and strong
current generated by lightning strike will cause damage to
helicopter systems, magnetization of individual helicopter
components and interference to electronic equipment. Under
low protection or no protection device, it may cause
permanent damage to the helicopter and affect the normal
operation of the system. Even worse, it may cause disastrous
consequences.
The lightning strike accident of Mi-26,the biggest heavy
helicopter in the world, was studied in the article. The direct
effect of the attack was that the trailing edge of tail rotor and
glass reinforced plastic pipe girder were detached by the
sheering force and centrifugal force, which made the hammer
brace unbalanced with a physical tearing of about 1m as the
secondary damage. In order to investigate the cause of
lightning stroke accident of Mi-26 helicopter, the 3D model of
Mi-26 helicopter is established. The TLM (transmission line
matrix method) of MS studio of CST is used to simulate and
analyze the surface current distribution and internal electric
field distribution when a specific lightning stroke path hits the
tail rotor of Mi-26 helicopter. The analysis shows that when
lightning strikes the composite structure, it leads to structural
failure or large-area damage. Based on the guidance and
standards of DOT / FAA / CT-89 / 22 and the interim defense
standard 59-113 of the British MoD, several improvement
measures are given. Typical lightning protection included
adding wire and wire netting to the structure’s surface which
has possibility of direct lightning adherence.