The required files for aircraft structural strength design fall into two categories: military and civil. The function of the force specification is to ensure the flight performance and safety of the aircraft.
The specifications stipulate the loading and environmental conditions that the aircraft structure must meet, as well as the design, manufacturing, testing, maintenance and use requirements. Aircraft types and models are more and more diverse, their functions and requirements are different, which makes uniform regulations impossible, therefore strength specifications have their own requirements for different types of aircraft.
Such as military and civil use, fixed-wing and rotary-wing, manned and unmanned, single-purpose and multi-purpose, aircraft and spacecraft, etc., all have their own applicable strength specifications. The intensity specifications are mainly promulgated by the corresponding agencies of the governments of various countries (such as the Ministry of the Air Force, the Ministry of Aviation and Aviation, the Civil Aviation Administration, etc.).
In formulating strength specifications, it not only addresses the new problems encountered in aircraft development and reflects the latest scientific and technological achievements to solve these problems, but also meets the actual policies and conditions in the country. Therefore, the specifications of each country are not the same, and with intervals of a few days. Reviewed once a year.
The world’s oldest strength specification was published by Germany in 1916. Then the United Kingdom, the United States, and the Soviet Union successively distributed their respective strength specifications.
The US military specification is the MIL series, which includes the aircraft structural integrity program and aircraft damage tolerance requirements, and the civil specification includes the Federal Aviation Regulations (FAR).
The UK has military specs (AP970) and civil specs (BCAR). The Soviet Union has aircraft strength specifications and civil airworthiness standards. Advanced industrialized countries have their own strength specifications.
In addition, there are international airworthiness regulations such as the “Joint Airworthiness Requirements” (JAR) of Western Europe and the “Airworthiness Technical Manual” (ATM) of the International Civil Aviation Organization. China drafted the “Air Force Specification” (trial version) in 1975 and started to formulate the official version in 1983.
The strength specification stipulates the design requirements, environmental and loading conditions, and development procedures for the airframe. In terms of the first proposed static strength, there are mainly several typical design load conditions, including load size and distribution, and sometimes detailed load distribution. The strength specification stipulates three levels of loads for the design of aircraft structures: use loads, verification loads, and design loads.
The operating load, or limit load, is the maximum load that the aircraft can support during its normal operation; the verification load is the product of the operating load and a given coefficient, which is between the operating load and the design load; the design load, or ultimate load, is Use the product of the load and the factor of safety. The usage load can be expressed as:
Use load = load factor × weight of the whole machine
The size of the load can be calculated based on the factor of safety and the load factor (also known as overload factor) in the strength specification. The factor of safety for manned aircraft is usually 1.5, and the load factor used by fighter jets can be around 8.
For rockets and missiles, the United States stipulates a safety factor of 1.25 for flight conditions, 1.5 for ground operations and 2 or more for pressurized manned cabins.
The static strength specification also has requirements on the stiffness characteristics of the structure. In addition to static strength, the updated specifications also cover dynamic, fatigue and fracture strength, and thermal strength, among which loading conditions for fatigue and fracture analysis are specified as load spectra.
The strength specification also presents requirements for measures to ensure the reliability of the control system and the control system, specifies the strength design procedure and the content and layout of the test structure, and finally specifies the types, formats and contents of the data and reports to be provided during acceptance.