Grounding and Bonding in Aircraft


ESD and Lightning Strike in eVTOL Aircraft

Electric Vertical Takeoff and Landing (eVTOL) aircraft, which are designed for urban air mobility and powered by HV electric propulsion systems, have unique requirements for Electrostatic Discharge (ESD), grounding, and lightning strike protection and dissipation. These requirements arise due to the unique characteristics and vulnerabilities of electrically powered aircraft. Effective bonding and grounding is crucial for eVTOL aircraft to mitigate the risk of electrostatic discharge, which can impact sensitive electronic components and systems. Electric propulsion systems generate static electricity during their operation, and without proper grounding, accumulated current can discharge unexpectedly, leading to electronic equipment malfunctions. Adequate grounding measures are implemented to ensure a controlled dissipation of static electricity or fault current events and prevent interference in the aircraft’s avionic and control systems. There are four principal areas of focus in eVTOL bonding and grounding: 1. Equipment Grounding: eVTOL aircraft are constructed from composite materials, such as carbon fiber- reinforced polymers, for their lightweight and high-strength properties. These materials are electrically conductive thanks to the addition of subsurface layers of conductive foil, but must also incorporate additional conductive elements within the composite structure to ensure proper ground points and paths for effective grounding and bonding of aircraft equipment. 2. Lightning Diversion and Dissipation: Lightning poses a significant risk to all aircraft, including eVTOL designs. As lightning strikes occur most often during the climb

and descent phases of flight at an altitude of 5,000 to 15,000 feet (1,524 to 4,572 meters), the probability of a lightning strike in eVTOL aircraft operating exclusively at these altitudes is relatively higher. Lightning protection systems in eVTOL aircraft mimic those employed in conventional aluminum airframe platforms, and involve a combination of conductive paths, bonding, and lightning diverters. Defined pathways safely conduct lightning energy across the composite skin of the aircraft, minimizing the likelihood of localized damage. Additional lightning dissipation devices, such as static wicks, are installed to facilitate the safe dissipation of the electrical energy. 3. Electrical System Shielding: HV Power transmission cabling in eVTOL aircraft should be adequately shielded to prevent electromagnetic interference (EMI) from radiating and grounding to low-power signal lines and cabling. Shielding measures include the use of overbraided cable shielding, auxiliary flexible ground straps, and faying surface preparation between metallic elements of the power transmission and motor propulsion system. 4. High-Voltage Fault Grounding: Creating an “Equipotential Zone” (EPZ) is a precautionary measure followed to de-energize and ground equipment in eVTOL for personnel safety. It is a “lock out, tag out” procedure required before any high-voltage equipment (batteries, controllers, motors) are accessed for maintenance. The procedure could extend to any personnel, including first responders, who might come in contact with high-voltage power equipment on the aircraft—even in a powered-down state— that could still carry a charge and constitute a shock hazard.

QwikConnect • July 2023


Powered by