Reliability and safety of the helicopter design
Reliability and safety of the helicopter design

Reliability and safety of the helicopter design


The complete reliability and safety of the helicopter's design throughout the entire service life can only be ensured by the correct observation system during its operation. The designer should understand that no calculations and tests on samples and stands do not guarantee against operational complications. Their cause may be limited knowledge. Therefore, the task of creating a reliable and safe design includes the development of such a control system for the period of operation, which would promptly signal the appearance of any dangerous defect. All units without exception should be considered as a system, which includes both the design and everything that relates to the control of it 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.


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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.


  • Group 1 - aggregates, the destruction of which leads to an immediate and complete disruption of performance and safety at the beginning of the appearance of a fatigue crack, which is difficult to detect. This group includes blades, the spar of which is sheathed with a frame and does not allow inspecting it after the flight, a number of bushings and the control system IV and RV closed for inspection, the NV shaft, etc.

  • Group 2 - units, the destruction of which could lead to an immediate and complete disruption of the structure and flight safety, but there is a possibility of early detection of the appearance of a fatigue crack. This includes blades with a reliably working crack signaling system and all other units classified in group I, if the appearance of a fatigue crack in them can be detected during pre-flight inspection.

  • Group 3 - units, the destruction of which leads to a partial loss of the structure's operability and threatens the safety of the flight, but allows an emergency landing without breaking the helicopter. Many elements of the fuselage belong to this group, even the gear frame, if it is made on a statically indeterminate scheme.

  • Group 4 - aggregates, the destruction of which causes a partial loss of the helicopter's operability while maintaining the possibility of continuing the flight, does not entail the rapid destruction of other aggregates and allows detecting destruction during a ground inspection. This group includes many elements of the fuselage, 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.

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Addressing security helicopter transport is included in the scope of works and measures aimed at:


  • a) improvement of the organization, technical equipment and advanced training of personnel of all services of the air transport system; creation of a potentially safe helicopter corresponding to the level and conditions of the operating organizations;

  • b) increasing the survival rate of passengers and crew when the helicopter gets into an emergency or catastrophic situation.

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. At the first stage, in addition to the usual verification of strength by loads determined by strength standards, at least the following design work is performed:
- optimization of mass and economic indicators;
- calculation of the endurance of the power longitudinal set and the main loaded units;
- determination of the conformity of the scheme and type of structure to the requirements of 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. The design development should be preceded or, in extreme cases, accompanied by tests of structural samples and models of the second stage of the study. At the second stage, the following are determined: allowable compression stresses in the power longitudinal set; endurance of the regular zone of the lower and upper strength longitudinal sets; endurance of critical points of the structure, mainly of transverse joints (to select the type of joint and assess its compliance with the required resource); the rate of crack propagation on specimens to check material selection and design type.

3. The final, third stage of the comprehensive program should be tests of full-size compartments, stands and entire units for static strength according to the life test program (including tests for crack propagation rate, safety in partial failure, acoustic strength, etc.) and functional tests mechanization units with a check of their performance.

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