The net charge acquired by the aircraft can be attributed to triboelectricity processes and first corona inception (positive or negative) from the aircraft. The latter depends only on the ambient field and aircraft geometry. When an aircraft flies in a thunderstorm in a region of intense ambient field, the corona charging process may become dominant. The negative net charge is an increasing function of the ambient field (Figure 4). It can be attributed to the asymmetric inception threshold between positive and negative coronas. The correlation coefficient for the CV580 is about 0.58 and 0.18 for the C-160.
Figure 4. The negative net charge is an increasing function of ambient field because of the asymmetric inception threshold between positive and negative coronas. |
Analysis revealed that the higher the ambient field, the lower the leader phase duration. Further investigation is required to explain this result.
As the ambient field increases, the time between the positive and the negative leaders inception decreases (Figure 5). When the ambient field is intense, the positive leader velocity may be higher, which leads to a higher injecting charge into the plane. The field enhancement due to both the net charge and the ambient field strongly increases and reaches the electrical condition for negative leader inception more quickly.
Figure 5. The time between the positive and the negative leader inception decreases with an increasing ambient field. |
According to the most recent hypothesis, the recoil streamers onset is related to conductivity instabilities within the positive leader channels. This conductivity depends on the channel temperature, which depends on the current flowing through leader channels. If the continuous current is too low, the channel temperature drops and a recoil streamer occurs. The energy produced by the peak current pulse heats the leader channel. From this it is believed that the recoil streamer is the result of a low continuous current. However, during further analysis, researchers found no direct correlation between the recoil streamer parameters and the continuous current.
A mean current waveform was deduced from the in-flight database
(Figure 6). The development of the positive leader is associated with a continuous current (a few amperes deduced from E-field variation). From tb, the negative leader develops from the aircraft. During 3 ms, 10 pulse currents of 850 A, separated by a mean period of 250 �s, superimpose on the continuous current, which progressively increases to 330 A. The continuous current phase continues during 200 ms. The recoil streamer phase starts 50 ms after the positive leader inception. This phase is composed of 15 pulse currents separated by 20 ms. The peak current of these pulses cannot be deduced from the available data.
Figure 6. Mean current waveform created form the in-flight database. |
This waveform is not a maximum threat, but an average. It is different from the one typically used in regulation.
