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1

Influence of source data on fatigue estimation of a fighter aircraft

Reymer P., Zieliński W., Kurnyta A.

Journal of KONBiN

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2018

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No. 48

301--322

EN

Aircraft structures during operation are exposed to fluctuating loads caused both by aerodynamic and inertial loads. This fluctuation leads to the creation of fatigue cycles, which gradually diminish the residual durability of the structure. During the design process, the flight envelope is defined as well as the design load spectrum, which then defines the durability of the structure (often expressed in means of flight hours). However, during the operation of an individual aircraft the actual load cycles can be significantly lower or higher than the designed; therefore, load monitoring is essential for safe operation of aircraft structures. The following article shows the results of fatigue analysis based on flight data from different flight data recorders for the Su-22 fighter aircraft.

PL

Statki powietrzne w trakcie eksploatacji poddawane są zmiennym obciążeniom wynikającym z oddziaływania sił aerodynamicznych oraz masowych. Zmienność tych obciążeń skutkuje występowaniem cykli zmęczeniowych, stopniowo wyczerpujących trwałość zmęczeniową struktury statku powietrznego. W trakcie projektowania statków powietrznych przyjmuje się obwiednię obciążeń określającą zakres bezpiecznej eksploatacji danego płatowca oraz przyjmuje się wyjściowy profil eksploatacji, dla którego określa się trwałość struktury (najczęściej wyrażoną w godzinach lotu). Jednak w trakcie eksploatacji cykle te mogą być znacząco mniejsze lub większe od założonych, stąd nieodzowne jest monitorowanie eksploatacji dla poszczególnych płatowców. Niniejsze opracowanie przedstawia analizę wpływu źródła danych eksploatacyjnych na oszacowanie zużycia zmęczeniowego na przykładzie samolotów Su-22.

2

Introduction of an Individual Aircraft Tracking Program for the Polish Su-22

Reymer P., Kurdelski M., Leski A., Leśniczak A., Dziendzikowski M.

Fatigue of Aircraft Structures

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2017

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Iss. 9

101--108

EN

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.

3

The Definition of the Load Spectrum for SU-22 Fighter-Bomber Full Scale Fatigue Test

Reymer P., Kurdelski M., Leski A., Jankowski K.

Fatigue of Aircraft Structures

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2015

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Iss. 7

28--33

EN

The Su-22 fighter-bomber is a military aircraft used in the Polish Air Force since the mid 1980’s. By the decision of the Polish Ministry of Defense the predicted service life for this type of aircraft will be extended to 3200 flight hours. Due to the fact that some aircraft were nearing the end of the service life guaranteed by the manufacturer, the actual service life, determined based on the flight profile in the Polish Air Force, had to be validated. Consequently, the Full Scale Fatigue Test (FSFT) had to be carried out in order to verify that the required service life was attainable. This article describes the process of preparation of the load spectra used in the Su-22 FSFT. Due to the fact that the Su-22 has a variable sweep wing the whole test was divided into three Stages (landing, flight and flap loads) carried out at different wing sweep angles (30°/45°/30°). The spectra were developed using the historical data gathered from Flight Data Recorders (FDR), strain signals acquired during the Operational Load Monitoring program (OLM) and aerodynamic calculations.

4

The Concept of a Full Scale Fatigue Test of a Su-22 Fighter Bomber

Reymer P., Leski A., Zieliński W., Jankowski K.

Fatigue of Aircraft Structures

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2014

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Iss. 6

79--87

EN

This article presents a concept of the full scale fatigue test of a Su-22 fighter bomber. The authors define the general concept and goals of the test as well as the tasks to be accomplished in the preparation stage. The current work status is summarized and future tasks are defined.

5

Simulating Crack Propagation of a Selected Structural Component of the PZL-130 Orlik TC-II Aircrafts

Jankowski K., Reymer P.

Fatigue of Aircraft Structures

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2014

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Iss. 6

119--127

EN

This paper presents the process of estimating crack propagation within a selected structural component of the PZL-130 Orlik TC-II using a numerical model. The model is based on technical drawings and measurements of the real structure. The proper definition of the geometry, including the location and size of the gap between elements, is significant for mesh generation. During the simulation process the gap is combined node by node. Each time, the strain energy release rate (G) is calculated. The stress intensity factor and geometry correction factor are defined for consecutive crack lengths, and used further on to estimate crack propagation.

6

Fatigue Properties of Polyurethane Foams, with Special Emphasis on Auxetic Foams, Used for Helicopter Pilot Seat Cushion Inserts

Lisiecki J., Nowakowski D., Reymer P.

Fatigue of Aircraft Structures

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2014

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Iss. 6

72--78

EN

Seat cushion inserts in military helicopters crew seats, as suggested by the helicopters manufacturers, are made of traditional polyurethane foams. Elastic polyurethane auxetic foams are materials that exhibit different utility properties compared to traditionally used polyurethane foams, such as polyether or polystyrene foams. All the differences result from the primary physical property of elastic polyurethane auxetic foams which is a negative Poisson’s ratio. Auxetic materials are characterized by better utility properties than conventional foam materials – they can potentially increase safety in the event of a crash and offer higher comfort during regular use. Application of auxetic materials as seat cushion inserts would also decrease harmful health effects of vibrations. This paper presents the results of the fatigue tests carried out on different foam samples by pressing an indenter into the foams' surface that was much larger than the indenter’s surface. A maximum value of the load used during the test was within a defined range in every fatigue cycle. In order to test 150x150x50 mm foam samples a special indenter was designed and manufactured according to the PN-EN ISO 3385 and PN-EN ISO 2439 standards. The indenter’s dimensions were consistent with the standards in relation to the tested foams' size. The fatigue tests of both conventional and auxetic foams were carried out according to the above given standards by applying 80,000 load cycles at 70 cycle/min frequency. Tests of viscoelastic foam and multilayer foam specimens, for which the upper layer was made of viscoelastic foam, were carried out according to the ASTM D 3574 standard applying 12 ,000 load cycles at 10 cycle/min frequency. All the tests were carried out using the MTS 370.10 strength testing machine. Changes in thickness and density were determined throughout the tests. Moreover, the influence of the volumetric compression ratio on the fatigue properties of auxetic foam samples and the dependence of foam deflection on the number of cycles were examined. Finally, the test results obtained for conventional and auxetic foams were compared and discussed.

7

Recent Progress in Full Scale Fatigue Test of PZL-130 "Orlik" TC-II Structure

Reymer P., Leski A., Dragan K.

Fatigue of Aircraft Structures

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2012

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Iss. 4

76--81

EN

This article presents preparation of the Full Scale Fatigue Test of the PZL-130 "Orlik" TC-II. After completing the flight load acquisition stage [1] a load block representing 200 Simulated Flight Hours in 194 flights was developed. This load block was further modified in order to introduce fatigue markers on the crack surface [2] visible during Quantitative Fractography, planned to take place during the Teardown Inspection of the structure after completion of the test. Meanwhile, the test rig along with the loading system and the test specimen were prepared at Výzkumný a Zkušební Letecký Ústav (VZLU, Prague, Czech Republic). The test specimen, consisting of the overhauled fuselage, modernized wings and the landing gear, was instrumented with the identical strain gauge measuring system as presented in [3], which was calibrated before the commencement of fatigue testing. Finally, some preliminary issues encountered during the fatigue test startup were highlighted and the outline for future work was described.

8

Preliminary Verification of Selected Solutions for Crack Detection

Kurnyta A., Reymer P.

Fatigue of Aircraft Structures

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2012

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Iss. 4

58--63

EN

Throughout its service life an aircraft is subjected to varying loads. Because of those periodically appearing stresses, undesirable and irreversible changes in structure may occur. As a consequence, cracks are formed, which reduce aircraft structural strength, significantly affecting structural integrity. For that reason, intensive research works are carried out around the world to develop innovative and reliable methods for detection of cracks initiation and propagation. This paper presents two methods of crack detection. One of them uses wireless polymer gages for determining deformation in a test region. The other one uses electrical, resistive ladder sensors for detection of cracks and their length determination.

9

Introduction of Fatigue Markers in Full Scale Fatigue Test of an Aircraft Structure

Leski A., Kłysz S., Lisiecki J., Gmurczyk G., Reymer P., Bochenek D., Zasada D.

Fatigue of Aircraft Structures

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2012

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Iss. 4

29--37

EN

Air Force Institute of Technology participates in the service life assessment programme SEWST. The aim of this programme, funded by the Polish Ministry of Defense, is to modify the operation system of PZL-130 "Orlik" TC-II turbo propelled trainer aircraft. The structural part of the programme is focused on the Full Scale Fatigue Test of the whole airframe to be conducted at the VZLU in the Czech Republic. The load spectrum for the test was developed by the AFIT based on the flight test results. The basic load block represents 200 simulated flight hours and consists of 194 flights showing different levels of severity. At the end of the Full Scale Fatigue Test a teardown inspection is planned during which it would be most beneficial to be able to determine crack propagation rate by means of a crack surface inspection. Markers are usually visible on most fatigue crack surfaces, however they occur randomly therefore it is almost impossible to conclude anything about the crack history. Since the preliminary load block consisted of separate flights (flight loads together with landing and taxing loads) showing significantly different levels of severity, the easiest way to modify the load block was to change the order of flights within the block. Hence a pilot programme was started at the AFIT which was focused on the determination of the influence of flight sequence on crack appearance. Several load blocks were determined using various techniques of rearranging the order of flights within the preliminary load spectrum. This approach ensured the preservation of the initial severity of the load block and simultaneously enabled a significant increase in the probability of the markers occurrence introducing neither artificial underloads nor overloads that would most probably affect the crack propagation rate. Fatigue crack surfaces were inspected using Scanning Electron Microscope. As a result of the investigations a series of images were obtained showing the specimen microstructure with visible markers arranged in the desired sequences. Based on the obtained pictures the most promising load block arrangements were chosen for the Full Scale Fatigue Test.

10

Validation of the FEM model of the Mi-24 tail boom and vertical stabilizer

Reymer P.

Journal of KONES

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2011

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Vol. 18, No. 2

369-376

EN

The scope of this work was the validation process of the numerical model of the Mi-24 helicopter tail boom and vertical stabilizer. In order to obtain a detailed geometry of the actual structure the sophisticated reversed engineering techniques were used. The measurement was performed using two separate techniques: one based on digitalphotogrammetry and other based on a three dimensional laser scanning with ATOSIII scanner. The numerical model was created with use of the obtained geometry, available technical documentation and detailed inspection of the structure. The obtained FEM model was validated using strain measurements of the real structure during characteristic flight maneuvers. A system of foil strain gauges was installed on the tail boom in previously selected locations. Calibration process, using known loads, was performed in order to determine response of the measurement system. To enable a quick and reasonable comparison of results from the experiment and calculations a special element was introduced in the FEM model. Their task was to monitor local strains in places corresponding to those where the strain gauges were installed. Detailed analysis of results confirmed, that after some minor modifications, the developed finite element model represents the actual structure reasonably well. Particular attention was paid to the representation of the boundary conditions and how to implement loads, which can significantly affect the obtained results. The analysis carried through confirms, that the presented validation technique, based on strain measurements, allows verifying a complicated numerical model in a relative cheap, fast and reliable way.

11

Global FEM model of combat helicopter

Gmurczyk G., Reymer P., Kurdelski M.

Journal of KONES

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2011

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Vol. 18, No. 2

137-144

EN

Air structures like Mi-24 were designed in last decades of the XX century, when computer aided design was not available. Philosophy of the exploitation so-called "safe life" postulate exploitation is defined by the manufacturer time. Such attitude turned out very uneconomical because of the various profiles of the use of aircrafts. Extending the initial period of exploitation is a quite common way to extend an aircrafts' life. Such solutions are accepted in the majority of countries, even the richest. In order to obtain detailed geometry of the real structure reversed engineering techniques were used. The geometry was obtained using two methods: digital photogrammetry and optical scanning using ATOS scanner from GOM Company. Geometric model, which was used for numerical Finite Element Method model, was developed based on the data from measurements, available technical documentation and detailed inspection of the structure. Global FEM model is being used for finding critical elements of aircraft's structure. Structure elements such as stringers, ribs or frames were modelled using bar and beam elements with specially defined properties and cross sections. Structure elements which didn't take part in transferring the loads, but with significant mass were made in a simplified manner so that their weight in the model correspond to actual or were modelled as concentrated masses.

12

Flight Loads Acquisition for PZL-130 Orlik TCII Full Scale Fatigue Test

Reymer P., Leski A.

Fatigue of Aircraft Structures

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2011

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Iss. 3

78--85

EN

The following article presents the research conducted under a complex structure integrity program for PZL-130 "Orlik" TC-II trainer aircraft. The aim of the research was to obtain the actual flight loads characteristic for the Polish Air Force which further on will be used to determine characteristic load spectrum for the Full Scale Fatigue Test purpose. This paper presents the methodology as well as a brief discussion of the obtained results.

13

Analysis of residual strength of a helicopter tail boom

Reymer P., Leski A.

Journal of KONES

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2010

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Vol. 17, No. 1

343-349

EN

The aim of this work is to determine the residual strength of a Mi-24 helicopter's tail boom with a structural damage. The idea of this work has come from the fact that these helicopters are operated on a battlefleld and often suffer such damages. It may be crucial to make a quick estimation whether any particular damage can cause a critical failure to the whole structure. The scope of this work covers static loading of the structure during landing. The analysis has been based on a numerical model that makes use of the Finite Element Method. The model has been developed using reverse engineering techniques. Structural discontinuities have been modelled in characteristic sections where stress concentrations occur. Boundary conditions and loads applied have been chosen to simulate normal and hard landings. Two failure criteria have been chosen: one based on the Crack Tip Opening Angle (CTOA) method that enables very efficient verification, and the second concerning the tail boom tip dislocation, taken from the helicopter,s alignment manual. The specific load history has been designed to enable detection of tail boom tip dislocation due to plastic strain in the vicinity of damage tips after the hard landing.

14

Fatigue Life Estimation of the Tail Boom and Vertical Stabilizer of MI-24 Helicopter

Reymer P., Leski A.

Fatigue of Aircraft Structures

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2010

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Iss. 2

79--86

EN

The aim of this work was to estimate fatigue life of the Mi-24 helicopter tail boom and vertical stabilizer sheathing. The analysis was based on a numerical model of the helicopter airframe crucial to obtain stress fields under defined loads and to estimate fatigue life. In order to do so, the load spectrum, specific for Polish army helicopters, was obtained by means of strain gauge measurements during a series of experimental flights. Data collected during flights was post-processed to create a characteristic ten hour spectrum that would statistically represent the flight profile for Polish Army Mi-24 helicopters. The third crucial element of the analysis was the safe S-N curve that was created on the basis of 2024-T3 aluminum S-N curve. Two factors were introduced in order to change the curve in a way that would guarantee a higher level of certainty that the outcome is not overrated. As a result of this analysis the total fatigue life was estimated including the list of critical locations in which fatigue damage is prone to occur. These regions are going to be carefully examined during scheduled inspections.