In the thin atmosphere thousands of meters above the earth, commercial and military aircraft cruise near the speed of sound. Inside these aircraft, thousands of kilometers of cables act like a nervous system, carrying critical signals for navigation, communication, flight control, life support systems, and more. The sheathing material that wraps around these "nerves" must reliably operate in extreme cold, intense ultraviolet (UV) radiation, drastic temperature changes, and low pressure. In this demanding environment, silicone rubber stands out as one of the preferred materials for aerospace cable insulation due to its unique combination of properties.

Extreme Temperature Resistance

One of the primary challenges comes from extreme temperature variations. At cruising altitudes in the stratosphere, external temperatures can drop to –70°C, while areas near engines or electronic compartments may exceed 150°C. Cables must remain flexible and insulated across such a wide range. Silicone rubber has a glass transition temperature (Tg) as low as –120°C, remaining soft and pliable down to –65°C without becoming brittle like PVC or polyethylene. It also maintains structural integrity at high temperatures, ensuring it does not soften or deform. This characteristic of being "non-brittle when cold, non-soft when hot" is fundamental for ensuring cable reliability throughout its lifespan.

Superior Electrical Insulation

Excellent electrical insulation is particularly important at high altitudes where air density decreases, making insulating materials more prone to corona discharge or partial discharges, which can lead to material carbonization and breakdown over time. Silicone rubber features a low dielectric constant (≈3.0), high volume resistivity, and excellent arc resistance, effectively suppressing discharge phenomena. Its surface also possesses some degree of "self-healing"—even if locally damaged, it resists forming continuous conductive paths in dry environments.

Radiation and Weather Resistance

Resistance to radiation and weathering is crucial. UV intensity at high altitudes is several times greater than on the ground, compounded by cosmic rays and ozone exposure. Most organic polymers degrade under these conditions through chain scission, cross-linking, or discoloration. However, silicone rubber's inorganic backbone provides natural resistance to UV and ionizing radiation, with minimal degradation in mechanical and electrical properties over decades of service, ensuring stable operation for ten years or more.

Flexibility and Lightweight Design

Low-temperature flexibility and lightweight design are essential for aircraft. With a density of about 1.1–1.3 g/cm³, silicone rubber is lighter than many engineering plastics, contributing to reduced overall aircraft weight. Its flexibility facilitates easy installation in confined spaces, reducing installation stress and preventing conductor breakage due to bending fatigue.

Manufacturing Techniques

Aerospace cables often use liquid silicone rubber (LSR) extrusion coating technology. This method produces thin-walled (less than 0.3mm), uniform, pinhole-free insulation layers with good adhesion to conductors. Some advanced cables employ a dual-layer structure: an inner layer of high-purity insulating silicone rubber and an outer layer containing flame-retardant fillers (such as platinum-based synergistic systems) to balance electrical performance with fire safety.

Stringent Certification Requirements

Aviation-grade silicone rubber must pass extremely rigorous certifications, including U.S. military standards like MIL-DTL-27502, FAA airworthiness regulations, and Airbus/Boeing material specifications. These cover burn characteristics (vertical burning self-extinguishing), smoke density, toxic gas emissions, fluid resistance (hydraulic oils, aviation fuels), and mold resistance. Only products meeting all criteria can be used in critical flight systems.

Emerging Applications

In emerging electric vertical takeoff and landing (eVTOL) vehicles and satellite systems, silicone rubber cables are employed for high-voltage battery connections and solar array wiring. Versions modified for atomic oxygen resistance (for low Earth orbit) and anti-static properties continue to expand their application boundaries.

In summary, the application of silicone rubber in cable sheathing exemplifies material science’s commitment to the "safety first" philosophy of aviation. By silently enveloping each cable, it ensures the accurate transmission of every bit of signal at high altitudes—the foundational logic for flight safety.




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