MIL-HDBK-274A
TABLE I. Lightning characteristics.
Characteristic |
Specification |
Types |
Intra/Inter Cloud Cloud-to-Ground |
Potential |
Positive or Negative 30 - 100 MV |
Current |
Up to 650 kA (peak) |
Power |
1012 W nominal (peak) |
Energy |
5 X 108 J nominal (200 lb TNT equivalent per strike |
Extent |
3-30 km per strike (path is predominantly horizontal) |
Spectrum |
Peak energy near 10 kHz, some above 10 MHz |
Duration |
Strike - 100 µs Flash 0.2 second (1- 20 strikes) |
4.4.2.4.1 Typical discharge. A typical discharge between cloud and ground starts in the cloud and eventually neutralizes tens of coulombs (C) of negative cloud charges. The total discharge is called a flash and lasts less than ½ second. A flash is made up of various discharge components, among which an average of three or four high-current pulses occur, called strokes, and a possible continuing current stage. In the idealized models, electrical storms cause the clouds to acquire a negative charge. The Earth, or in this case the aircraft, has an opposite charge and lightning occurs when the electric field in the vicinity of the charge center of the cloud builds up to the point where the air starts to ionize.
4.4.2.4.2 Cloud breakdown. The breakdown within the cloud produces what is called a stepped leader. The leader starts from the cloud and heads toward the ground. The leader advances in a series of rapid discontinuous steps each about 50 meters (m) long and separated by pauses of about 50 µs. The luminous diameter of the stepped leader is between 1 and 10 meters (m), although it is thought that the leader current of about 100 amperes flows in a small diameter core at its center. The average propagation velocity is about 1 meter per second. It
looks like a column of light with branches emanating from the sides. The electric potential of the leader channel with respect to the ground is about -l x l08 V. As the leader tip nears ground or aircraft, the electric field beneath it becomes very large and causes one or more upward-moving discharges, which start the attachment process. When one of the upward-moving discharges
from the ground contacts the downward-moving leader, the leader tip is connected to ground or aircraft potential. The leader channel is then discharged into the aircraft. The height of the aircraft affects the probability of this happening. The taller the aircraft the more likely it is to
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