Reliability and safety of the helicopter design
Complete reliability and safety of the structure of the helicopter during the entire service life can only be ensured proper surveillance system during its operation. The designer must understand that no calculations and tests on samples, and stands not guarantee the performance of the complications. Their cause may be the limitations of knowledge. Therefore, the task of creating a safe and reliable design is to develop a monitoring system at the time of operation, which in due time would signal the emergence of any unsafe condition. Without exception, all units should be seen as a system that includes the design and everything that relates to the control of her during operation and maintenance.
Based on the analysis of calculations, tests of samples, natural bays and experienced product designer should identify critical places to choose such control methods that guarantee detection of defects on a safe stage of its development, determine a frequency of inspection of critical spots to in between the defect is not time to reach the critical value.
Particular attention should be paid to the selection of an effective method of control: all you need to provide approaches for visual inspection. Where it is impossible to provide approaches that have to be worked out methods of inspection of optical devices; where such inspection is not possible and it is necessary to develop methods of nondestructive testing tool. The design must be operational and flaw detection manufacturability. Without this it is impossible to create a safe design with more resources.
A prerequisite to ensure flight safety consideration is feasible dangerous cases for each structural element and each of the functional system of the helicopter.
Static strength and endurance of the helicopter structure shall be such as to prevent the destruction of dangerous helicopter design elements under the action of loads in the anticipated operating conditions within the specified resources and service life.
Particular attention should be paid to the design process to ensure trouble-free operation of each functional system malfunction in which all possible combinations of external conditions affecting the system can
lead to catastrophic air accidents. The possibility of failures of elements that lead to the failure of a functional system or its dangerous consequences, should be kept to a minimum by design measures.
According to the degree of responsibility for safety and details of all units of the helicopter can be divided into four groups.
1 group - units, the failure of which leads to the immediate and complete breakdown of health and safety in difficult to detect, early occurrence of fatigue cracks. This group may include blade spar frame which is sheathed and allows to inspect it after the flight number of the closed sleeve parts for inspection and control systems IV and PB, HB shaft, etc.
2 group - units, the failure of which could result in the immediate and complete malfunction design and flight safety, but there is a possibility of early detection of occurrence of a fatigue crack. This includes blades with an alarm system to operate reliably cracking and all other units assigned to Group I, if the appearance of the fatigue crack in them can be found in a preflight inspection.
3 group - units, the failure of which leads to a partial loss of working capacity of the structure and threatens flight safety, but allows you to make an emergency landing without breaking the helicopter. This group includes many of the elements of the fuselage, the gear frame even if it is made on the statically indeterminate scheme.
4 group - units, the destruction of which causes partial loss of working capacity of the helicopter, with the possibility of continuing the flight does not entail the rapid destruction of other units and can detect failure during ground inspection. This group includes many elements of the fuselage, the stabilizer, and a number of similar structural elements.
Details and components should be designed not only for the safety criteria of durability and resistance to the process of destruction, ie, so that the cracked parts can be detected and replaced before structural failure. A vital part of the structure must be available for inspection, and in case of unavailability of the inspection - is designed with a large margin or duplicated. In the presence of cracks remaining structural strength must be located within predetermined limits the terms of reliability.
Addressing security helicopter transport is included in the scope of works and measures aimed at:
a) improvement of the organization, technical equipment and staff of all services of air transport; creating potential safety helicopter, corresponding to the level and conditions of operating organizations;
b) increase the survival of passengers and crew in contact with the helicopter in an emergency or disaster.
Development of the construction should be part of an integrated program design, calculation and experimental research work, devoted mostly on reliability and service life.
The calculated and experimental research while creating construction unit are carried out in three stages.
1. In the first phase, in addition to the usual checks on the strength of the load, determines the rate of strength, produced at least the following design works:
- Optimization of supply and economic indicators;
- Calculation of the power of endurance and longitudinal set of basic-loaded nodes;
- Determination of compliance with the scheme and the type of design requirements for safe destruction.
All these calculations are made at a very early design stage to lay in the design of those basic principles that later can not be adjusted. The volume of theoretical studies and defines the methods of their execution. Without the use of computer calculations required volume impractical.
2. Design development should precede or, in extreme cases, to accompany test specimens and structural models of the second phase of the study. At the second stage, the: allowable compressive stress in the longitudinal force set; regular endurance zone upper and lower sets of longitudinal force; Endurance critical construction sites, mainly transverse joints (to select the type of interface and assess its compliance with the required resources); velocity of propagation of cracks in the specimens to verify the choice of material and type of construction.
3. The final, third stage of a comprehensive program should be tested full-sized compartments and stands entirely units on static strength of the test program to a resource (including tests on crack propagation rate, safety in case of partial destruction, acoustic durability, etc.) and functional testing units mechanization checking their health.
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