运输类飞机结构设计安全系数的探讨

中国民用航空规章运输类飞机适航标准25.303要求采用1.5的安全系数,该要求同其他相关适航条款,例如25.307"结构符合性的证明"、25.603"材料"、25.605"制造方法"、25.613"材料的强度性能和材料的设计值"等,共同保证了飞机结构的高可靠性。理论上,当材料、载荷、分析等方面的不确定性降低,采用低于1.5的安全系数可以保证结构具有同等的高可靠性;另一方面,当材料、载荷、分析等方面的不确定性大于目前适航规章所允许的水平,通过采用大于1.5的安全系数也可以保证结构具有等同的高可靠性。为了在民用运输类飞机的适航取证/审定过程中,在保证结构可靠性的前提下,能够根据具体情况适当调整结构安全系数,在综合研究中国民用航空规章第25部《运输类飞机适航标准》相关条款内在联系的基础上,探讨了载荷、材料性能、分析方法等不确定性对飞机结构安全系数的贡献。研究结果表明,目前1.5的飞机结构安全系数,用于考虑载荷、材料性能、分析方法等不确定性的系数分量分别为1.2、1.12、1.116.

Discussion on the Safety Factor of the Structure Design for Transport Aircraft

Safety factor of 1.5 was specified in paragraph 25.303 in China Civil Aviation Regulations(CCAR)Part 25.This requirement and other relevant paragraphs in CCAR25, such as CCAR25.307"Proof of Structure",25.603"Materials",25.605"Fabrication methods",25.613"Material strength properties and material design values", ensure the reliability of airplane structure collectively.Theoretically, when the uncertainty for material properties, load and analysis reduces, the application of safety factor less than 1.5 can ensure equivalent reliability for airplane structure. In other hand, if the uncertainty for material properties, load and analysis exceed the allowable level implied in current airworthiness standards, application of safety factor greater than 1.5 may still ensure equivalent reliability for airplane structure. To determine proper safety factor for certain certification circumstance without reduction in the structure reliability, the composition of safety factor 1.5 was researched. Based on the investigation of the relationship among the relevant paragraphs of China Civil Aviation Regulations (CCAR) Part 25, the safety factor of 1.5 specified in CCAR 25.303 is divided into three sub-factors. The sub-factor for load uncertainty is determined to be 1. 2; the sub-factor for material properties uncertainty is determined to be 1.12; the sub-factor for analysis methods uncertainty is determined to be 1.116.