Aerospace Technic and Technology

One of the most significant characteristics of the aircraft is its resource. Airplane elements are subject to fatigue damage in operation. For a theoretical assessment of the accumulated fatigue damage, durability and design life, it is necessary to know the loads acting on the aircraft. The main contribution to fatigue damage is made by loads from gusts which are of a random nature. The magnitude of this damage depends on the flight conditions, namely on the flight speed, altitude, and aircraft weight. With good accuracy, the loading process of the structure in flight can be described using the overloads integral repeatability at the center of gravity of the aircraft. This function is obtained experimentally in flight tests. However, the article proposes a method for calculating the function of the overloads increments integral repeatability at the design stage. This approach allows us to take into account the expected operating conditions of the aircraft being created and to assess its loading. Using the standard flight profiles and the relative flight time over them, the loading conditions for the generalized typical flight were obtained. The reliability of the proposed method was confirmed by comparing the theoretical and experimental data on the overloads integral repeatabilities per flight for various aircraft of IL-76T type. The typical flights' profiles of the Il-76T (TD) aircraft fleet were compiled by the author earlier by statistical processing of the forms data of these airplanes. As a result, good agreement was obtained between the calculated and measured curves of the overloads integral repeatabilities. Accounting for various typical profiles allowed to explain the variation of experimental data. The possibility of a theoretical estimate of the maximum overload of the ground-air-ground cycle is shown. This parameter can contribute more than half of the fatigue damage to the structure per flight and requires precise determination. In general, the developed method for calculating the overloads integral repeatability at the center of gravity later serves to calculate the design, accumulated and residual life of the transport category aircraft, taking into account the intended operating history.

type flight profile; overload; integral repeatability; transfer function; random loading

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