In this paper, we present an approach to fatigue estimation of a Main Landing Gear (MLG) attachment frame due to vertical landing forces based on Operational Loads Monitoring (OLM) system records. In particular, the impact of different phases of landing and on ground operations and fatigue wear of the MLG frame is analyzed. The main functionality of the developed OLM system is the individual assessment of fatigue of the main landing gear node structure for Su-22UM3K aircraft due to standard and Touch-And-Go (T&G) landings. Furthermore, the system allows for assessment of stress cumulation in the main landing gear node structure during touchdown and allows for detection of hard landings. Determination of selected stages of flight, classification of different types of load cycles of the structure recorded by strain gauge sensors during standard full stop landings and taxiing are also implemented in the developed system. Based on those capabilities, it is possible to monitor and compare equivalents of landing fatigue wear between airplanes and landing fatigue wear across all flights of a given airplane, which can be incorporated into fleet management paradigms for the purpose of optimal maintenance of aircraft. In this article, a detailed description of the system and algorithms used for landing gear node fatigue assessment is provided, and the results obtained during the 3-year period of system operation for the fleet of six aircraft are delivered and discussed.
The Su-22 fighter-bomber is a military aircraft used in the Polish Air Force (PLAF) since the mid 1980’s. By decision of the Ministry of National Defence Republic of Poland, the assumed service life for this type of aircraft was prolonged up to 3200 flight hours based on the Full Scale Fatigue Test (FSFT) results. The FSFT was conducted using the real load profile defined during the Operational Load Monitoring Program (OLM) and the 3200 hour service life was also based on this load profile.In order to assure safe operation of all the 18 Su-22 aircraft, the Individual Aircraft Tracking program was introduced. The program was based on the results of the FSFT as well as the analysis of the flight parameters recorded by the THETYS onboard flight recorder.In this paper, the authors present the methodology, assumed fatigue hypothesis and preliminary results of the IAT program for the Polish Su-22.
Article citation info: (*) Tekst artykułu w polskiej wersji językowej dostępny w elektronicznym wydaniu kwartalnika na stronie www.ein.org.pl IntroductionThis contribution presents a reliability prediction as well as sustainability methods for selected areas of the airframe in terms of fatigue processes and the aging process. Supporting structure may be classified as an element with a high correlation between the airworthiness parameter values and adequate fatigue life of the aircraft [27].One of the most important issues associated with aircraft maintenance is analysing durability of their structure components [10,20]. The previous experience in operation confirms that exhaustion of aircraft service life cannot be unambiguously identified with its unserviceability for further, reliable flights. Not always does the service life exhaustion result in the loss of aircraft technical condition and in the reliability parameters exceedance. The inadequacies of the traditional (service life) approach to aircraft maintenance used were the reason for developing new methods for assessing the durability of the aircraft structure, which are presented in the new study [21,22].The presented mathematical model is implemented with the use of specialized software known as PRobability Of Fracture (PROF) [13] and is commonly used by United States Air Force [4,6]. National Research Council Canada [12,24] uses a similar mathematical approach for reliability analysis of aircraft structure in its ProDTA (PRObabilistic Damage Tolerance Anylisis) software.The presented method and the research results make it possible to extend aircraft service life. Discussed procedures are not performed for aircraft owned by Polish Air Force, particularly for PZL-130 TC II ORLIK aircrafts. The exceptions are the F-16, for which such analyses are performed by Lockheed Martin. The reliability prediction method of support structure pointsFailure rate function [5, 9] is defined as the limit, if it exists, of the ratio of the conditional probability that the instant of time, T, of a failure of an item falls within a given time interval t t + ∆ and the length of this interval, t ∆ , when t ∆ leads to zero, given that the item is in an up state at the beginning of the time interval, which can be described as:where T is a continuous positive random variable of device operation time.If T has a density f(t) and the distribution F(t) equation (1) will take the form [1÷3]:whereGiven the failure rate λ(t) the life distribution can be calculated by the equation:Woch M, KurdelsKi M, MATyjeWsKi M. reliability at the checkpoints of an aircraft supporting structure. eksploatacja i NiezawodnoscMaintenance and reliability 2015; 17 (3): 457-462, http://dx
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