Thesis Colloquium of Sayantan Das

Thesis Title:  Modeling of lightning attachment to aircraft and  quantification of the influencing parameters

Guide: Prof. Udaya Kumar

Degree registered:          Ph.D.

Date and Time:              11^th November 2022, 9:30 AM
Meeting link:                  https://teams.microsoft.com/l/meetup-join/19%3ameeting_MDg5YzdhYWUtMTc3Zi00Yjg0LWE1ZTktYjgyY2I5Y2MyNDI4%40thread.v2/0?context=%7b%22Tid%22%3a%226f15cd97-f6a7-41e3-b2c5-ad4193976476%22%2c%22Oid%22%3a%227ef4df52-6005-46aa-bff3-d96db1a85b71%22%7d

Abstract: According to Air Transport Action Group (ATAG), 45 million aircraft took off worldwide in 2020, which translates to 1.5 lakh per day. Statistically, the aviation industry is found to double its fleet size every fifteen years. Lightning is considered one of the dreadful environmental threats to aircraft. Past incidents show that lightning strikes can lead to structural damage, operational interruption, and loss of lives. Field data suggest that, on average, an aircraft gets struck by lightning once or twice a year. Therefore, the threat due to lightning is considered a crucial safety aspect of an aircraft.

Design of suitable lightning protection for aircraft involves Zoning of its skin. It is intended to differentiate lightning attachment points, channel slipping regions, and regions that carry just the stroke current. The first step of Aircraft Zoning is to identify the initial attachment points. For the same, different methods like Laboratory experiments, similarity principle, Rolling Sphere Method (RSM), and Field-based approach are suggested in the standard ARP5414. In reality, the lightning strikes to aircraft can be of two modes, Aircraft-initiated and Aircraft-intercepted. In the former one, under the influence of a thundercloud or descending lightning leader, the aircraft initiates stable bipolar connecting leaders, upward and downward leader toward the ground. These leaders are deemed to propagate hundreds of meters to complete the lightning strike. In Aircraft-intercepted strikes, the aircraft intercepts a descending lightning leader and hence gets struck. The laboratory experiments on scaled aircraft models or isolated aircraft parts are inadequate to assess the initial attachment points. The similarity principle suggested in the standard is qualitative and can’t be extended to aircraft of any size and shape. The 25m Rolling Sphere Method (RSM) is routinely employed to determine the attachment points. This method doesn’t consider the connecting leader discharges from aircraft and therefore overestimates the possible attachment points. Most (90%) of the lightning strikes to aircraft are attributed to aircraft-initiated mode, which involves significant connecting leader activities. Therefore, it has to be traced accurately to assess attachment points.

In literature, it is difficult to find a model for bipolar leader discharges from aircraft. However, work on either negative or positive leader inception and propagation from laboratory gaps and their extension can be relatively found. Based on them, the present work aims to develop a suitable model for simulating bipolar leader discharges from aircraft. Additionally, the aircraft-intercepted mode of lightning strikes is also included. In summary, a novel model adapting the pertinent physical aspects of the leader discharges has been developed to accurately assess initial lightning attachment points to aircraft. 

Using the model developed, the following practically important questions are addressed: 

1. Dependency of the frequency of lightning strikes to aircraft on its shape and size.
2. Rate of lightning strikes to aircraft at different altitudes
3. For a given aircraft and its route, the number of times it gets struck by lightning
4. The average number of strikes to an aircraft per year

To present a quantitative assessment, two different aircraft models, McDonnell Douglas DC-10 and Standard Dynamic Model are considered.

In summary, a novel model based on physical grounds has been developed to assess the initial lightning attachment points on aircraft. Using the same, further methodologies are constructed to quantify the dependency of the strike rate on aircraft size, altitude, and possible average strike rate.

ALL ARE WELCOME