GLENAIR
effective shielding of critical-path EWIS cabling from lightning strike and HIRF is a routine requirement in commercial aircraft. Addressing eVTOL lightning strike requirements with cable shielding solutions that do not add significantly to aircraft all-in weight will require ultra- lightweight designs and material selection including microfilament and metal-clad composite plastic material types. • Ground straps and bonding jumpers are essential parts in establishing a common ground reference across multiple structural elements. Movable surfaces, hinges, panels, and electronics typically require ground strap technology. A single lightning strike can hit an aircraft with as much as 1,000,000 volts. Static electricity can charge an aircraft, particularly in cold and wet air, with enough electrical potential to result in a discharge that can fry EWIS wiring and avionics gear. Power storage systems (lithium battery- based) can also produce transient electrical current that can potentially damage electronic systems. Damage from these events is minimized and managed in aircraft through the use of electrical bonding. Flexible bonding straps are attached between equipment and airframes as well as between structural elements and flight control surfaces to conduct destructive electrical surges to ground or to bus bar components capable of absorbing significant amounts of transient voltage. • Sensor wiring that routes along retractable landing gear in certain air taxi designs will be exposed to excessive currents that travel through the vehicle structure and through the landing gear struts before leaving the vehicle. Values as high as 20,000 amps can be experienced with a 80,000-amp strike. Shielded conduit and shielded cable assemblies can be used not only for physical protection but lightning protection as well in applications of this type. • Low-resistance cable shield termination is a critical element in the overall EMC / Lightning assurance plan. The use of cable shield termination and strain relief backshells, as well as conductive feed-thru fittings and other EMC and wire management connector accessories have become absolute standards in commercial airframe applications and will necessarily find considerable use in the UAM market space.
Physical Separation of Individual Power Lines and Cable Bundles EWIS designs, incorporating wire protection conduit and/or
molded cable assemblies are routinely used to meet the FAR 25.1707 requirements. FAR 25.1707 System Separation states:
(a) Each EWIS must be designed and installed with adequate physical separation from other EWIS and airplane systems so that an EWIS component failure will not create a hazardous condition. Unless otherwise stated, for the purposes of this section, adequate physical separation must be achieved by separation distance or by a barrier that provides protection equivalent to that separation distance. (i) EWIS must be designed and installed with adequate physical separation between the EWIS and flight or other mechanical control systems cables and associated system components. (j) EWIS must be designed and installed with adequate physical separation between the EWIS components and heated equipment, hot air ducts, and lines. (k) For systems for which redundancy is required, by certification rules, by operating rules, or as a result of the assessment required by §25.1709, EWIS components associated with those systems must be designed and installed with adequate physical separation. (l) Each EWIS must be designed and installed so there is adequate physical separation between it and other aircraft components and aircraft structure, and so that the EWIS is protected from sharp edges and corners, to minimize
potential for abrasion/chafing, vibration damage, and other types of mechanical damage.
The use of suitable wire insulation, cable bundle overmolding, encapsulation in insulation-protected conduit, and other EWIS design methodologies are essential in meeting the FAR 25.1707 System Separation standard.
QwikConnect • July 2021
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