aricraft structures Archives - Leeham News and Analysis

Leeham News and Analysis contributor Bjorn Fehrm continues his multi-part series on aircraft structures with Part 7, turning attention to fiberglass as a structural and semi-structural composite material in commercial and transport-category airframes. The series has been tracing the evolution of materials used in modern airliners, with the composites segment examining how multi-material construction has progressively displaced traditional aluminum alloy in primary and secondary structure. Fiberglass — the earliest widely adopted composite in aviation — represents a foundational chapter in that story, predating the carbon fiber-reinforced polymer (CFRP) revolution that now defines programs like the Boeing 787 and Airbus A350.

Fiberglass, or glass fiber-reinforced polymer (GFRP), entered aviation structures decades before CFRP became viable at scale. Its combination of low cost, corrosion resistance, radio-frequency transparency, and reasonable specific strength made it attractive for fairings, radomes, control surface skins, and interior panels long before engineers trusted composites in primary structure. Understanding its mechanical properties — particularly its lower stiffness-to-weight ratio compared to carbon fiber and its sensitivity to moisture absorption over time — remains directly relevant to maintenance personnel and operators managing aging fleets, where fiberglass components may exhibit delamination, impact damage, or water ingress that is not visible on the surface. Pilots operating under Part 91, 91K, or 135 certificates benefit from understanding how composite damage manifests differently than metal fatigue, since airworthiness determinations for composite structure require different inspection methodologies than those applied to aluminum.

The structural series from Fehrm carries operational significance beyond the academic. As aircraft like the ATR 72, regional jets from Embraer and Bombardier, and even legacy Boeing and Airbus narrowbodies incorporate fiberglass in flight control surfaces and empennage skins, the material's behavior under load, thermal cycling, and UV exposure becomes a factor in dispatch decisions and deferred maintenance analysis. For corporate flight departments operating under Part 91K or business aviation operators under Part 135, maintenance tracking on composite components often surfaces during pre-buy inspections and involves nuanced structural repair manual (SRM) interpretation. A working understanding of why fiberglass behaves as it does — its anisotropic nature, its failure modes, and its bond-line vulnerabilities — gives technically informed pilots and chief pilots better context for evaluating maintenance write-ups and vendor repair documentation.

The broader trend Fehrm's series illuminates is the industry's decades-long material migration, from steel to aluminum to hybrid metallic-composite to near-all-composite airframes. Fiberglass sits at the beginning of that arc, but it has not been retired from new designs. It remains cost-effective in non-primary structure and continues to appear in next-generation programs for radomes, interior panels, and aerodynamic fairings. JetZero's blended-wing-body program — which broke ground on a factory this week — and other advanced air mobility and next-generation transport concepts will likely continue leveraging fiberglass in secondary applications even as CFRP dominates their load-bearing structure. For the aviation professional community, Fehrm's technical series provides a structured framework for understanding why the aircraft being flown today are built the way they are and what that means for long-term airworthiness, performance degradation, and structural integrity decisions throughout the fleet's operational life.