Research methods to improve reliability of passive redundant control subsystems of aircraft with due consideration of tolerances

The paper studies the reliability of passively redundant subsystems of aircraft, taking into account tolerances for a decrease in their output parameters in case of sudden component failures. The influence of the reliability values of elements, tolerances of two levels and the redundancy ratio on the reliability of passively redundant subsystems as a whole have been investigated; the examples of such subsystems have been given. There have been presented the results of analysis of the aircraft subsystems features with allowance for tolerances. First of all, these include the availability of technical specifications and realized tolerances determined by the reservation structure; implementing each tolerance with different values of the multiplicities of redundancy; using the main tolerance grid by multiple backup methods; presence of critical probabilities narrowing the reliability range of the elements, where this type of reservation is beneficial from the range $0$–$1$ to the range of the supercritical area $(p_{kr}-1)$. The influence of the element reliability values, tolerances of two levels and the redundancy ratio on the failure-free operation of passively redundant subsystems in general and in supercritical areas has been investigated. It is shown that the minimum redundancy multiplicities in the interests of increasing the reliability of the considered subsystems of aircraft are advantageous to use only with large tolerances and low probabilities of failure-free operation of their elements. Under close tolerances and any reliability values of elements, as well as with large tolerances (more than $25\%$), high reliability values of this class of aircraft subsystems can be achieved only with large redundancy multiplicities. It has been inferred that there are extreme reliability differences of a passively redundant subsystem and its element, which allows to set the task of developing highly reliable passively redundant subsystems of aircraft taking into account tolerances from relatively unreliable elements.