直升机因其独特的飞行能力在军事与民用领域得到广泛应用，但其复杂的飞行包线和固有的非线性、强耦合动力学特性，使得飞行安全面临严格的边界限制。飞行边界保护技术旨在通过预测潜在的越限风险并采取有效的避免措施，以降低飞行员工作负荷、提升飞行安全和最大化可用机动性能，是现代直升机飞行控制领域的核心研究方向。本文系统综述了直升机飞行边界保护的关键技术与研究进展。首先概述了直升机飞行边界的构成、分类及其典型限制参数。随后，按照“边界预测”与“边界规避”两大核心环节，详细阐述了多种边界保护方法。在边界预测方面，重点分析了动态配平法、峰值响应估计法和数据驱动方法的原理与适用性；在边界规避方面，评述了基于座舱告警的边界保护策略，以及基于指令限制和控制限制的自动干预架构、基于保护量反馈的边界保护技术，以及边界约束与控制律的融合设计等方法。通过对不同边界保护方法的仿真对比，展现了各种方法在机动性、边界保护效果及鲁棒性等方面的特点。最后，总结了当前研究面临的主要挑战，如先进构型直升机的特殊需求、边界保护与飞行品质的权衡以及不确定性与故障下的鲁棒保护等，并对未来向智能化、自适应化和一体化发展的趋势进行了展望。本文旨在为直升机边界保护技术的研究与工程应用提供有价值的参考。

Helicopters are extensively utilized in both military and civilian sectors due to their unique flight capabilities. However, their operational safety is constrained by complex flight envelopes and inherent nonlinear, strongly-coupled dynamics. Flight Envelope Protection (FEP) technology, which aims to mitigate these limitations by predicting potential limit exceedances and implementing effective avoidance measures, has emerged as a critical research area in modern helicopter flight control to reduce pilot workload, enhance flight safety, and maximize available maneuverability. This paper presents a comprehensive review of the key technologies and research progress in helicopter FEP. It begins by outlining the composition, classification, and typical limit parameters of the helicopter flight envelope. Subsequently, following the two fundamental stages of "envelope prediction" and "envelope avoidance," a variety of protection methods are elaborated. For envelope prediction, the principles and applicability of prominent algorithms such as the dynamic trim method, the peak response estimation method, and the data-driven method are analyzed. For envelope avoidance, cockpit-cueing-based protection strategies, automatic intervention architectures based on command limiting and control limiting, protected-variable-feedback methods, and approaches that integrate envelope constraints into controller design are reviewed. A comparative analysis based on simulation results highlights the distinct characteristics of these methods in terms of maneuverability, protection effectiveness, and robustness. Finally, the paper summarizes the primary challenges in the field, such as the special demands of advanced rotorcraft configurations; the trade-off between FEP and handling qualities and the robust protection under uncertainties and fault conditions. Future trends toward more intelligent, adaptive, and integrated FEP systems are also prospected. This review is intended to provide a valuable reference for both research and engineering applications in helicopter FEP technology.