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Abstract
Classical efficiency metrics are widely used to evaluate the performance of aviation systems, yet they often fail to explain the persistent saturation observed in aircraft range, helicopter hover endurance, and unmanned aerial vehicle (UAV) flight time. Modern propulsion systems already operate near high thermal or electrical efficiency, but improvements in engine performance do not translate proportionally into mission-level gains. This study introduces a Unified Energy Survival–Conversion Law that explains these limitations by recognizing that useful output is governed by the fraction of energy that survives irreversible degradation across multiple stages before being converted into useful work. The framework defines an energy survival factor (Ψ) representing the persistence of absorbed energy against aerodynamic losses, induced flow, turbulence, and entropy generation, and an internal conversion competency (Cint) describing the finite ability of a system to transform surviving energy into lift, thrust, or mission output. Together, these variables yield a universal relation: Euseful = Ein × Ψ × Cint. Application of the model to fixed-wing aircraft, helicopters, and UAVs demonstrates that aviation performance is fundamentally survival-limited rather than efficiency-limited. The framework provides a thermodynamically consistent basis for diagnosing performance saturation and guiding survival-centric aerospace system design.