Czech Aeronautical Research and Test Institute

Prague, Czech Republic

Czech Aeronautical Research and Test Institute

Prague, Czech Republic
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Cecrdle J.,Czech Aeronautical Research and Test Institute
Applied and Computational Mechanics | Year: 2017

Whirl flutter is a specific type of flutter instability, relevant for turboprop aircraft, caused by the effect of rotating parts as a propeller or a gas-turbine engine rotor. The proposed optimisation-based analytical procedure is used to determine the critical values of the engine attachment stiffness parameters for the preselected flutter speed. For the half-span model, two design variables are used. The objective function is defined as the minimization of the engine vibration mode frequency sum. Design constraints keep the engine frequency ratio and the flutter stability at the selected velocity. However, application of a full-span model is necessary in some cases. In this case, special models of both symmetric and antisymmetric engine vibrations and four design variables must be used. Design constraints maintain the pitch mode frequency ratio, the yaw mode frequency ratio and the critical mode frequency ratio. Critical modes are dependent on the relation between the rotational direction of both propellers (identical or inverse). A flutter design constraint is applied as well. The described methodology is demonstrated on the application example of a twin-engine commuter aircraft. Demonstrated cases include symmetrical revolutions of propellers for both identical and inverse directions of rotation, cases of single engine failure and single propeller feathering, and finally, cases of unsymmetrical revolutions including the reduced and increased revolutions of a single propeller, for both identical and inverse directions of rotation. © 2017 University of West Bohemia. All rights reserved.


Sedek J.,Czech Aeronautical Research and Test Institute
EAN 2017 - 55th Conference on Experimental Stress Analysis 2017 | Year: 2017

The strain constraint investigation using finite element method is presented. Three-dimensional (3-D) models of standard test specimens (M(T), C(T) and SE(T)) are analysed from the point of view of out-of-plane constraint. The constraint factor α was defined according to Newman Jr. J. C. New relationship of constraint in dependence on the ratio of plastic zone size versus thickness is proposed. The global and local behaviors of constraint factors are presented. The local constraint is adopted via equivalent thickness in dependence on the through-thickness position on the crack front. © 2017 Technical University of Košice - Faculty of Mechanical Engineering.


Fatigue is one of the most common failure modes of structures and components. The prediction of fatigue crack propagation in real structures must take into account realistic boundary conditions. The purpose of this paper is to describe a technique for modelling fasteners through FEM global structure modelling and using the model for stress state analyses and crack growth prediction. The consideration of fastener stiffness during stress analysis is an integral part of the damage tolerance philosophy. The FASTRAN retardation model with a load sequence simulating the real operational service of an aircraft structure was used for crack growth prediction. © 2015 The Authors. Published by Elsevier Ltd.


Cecrdle J.,Czech Aeronautical Research and Test Institute
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering | Year: 2015

This paper deals with updating of the aircraft structure finite element (FE) model according ground vibration test (GVT) results. Paper describes possible approaches of flutter analysis as regards to the incorporation of GVT results including: (1) the direct usage of GVT results and (2) updating of analytical FE model. Then the theoretical background of the model updating methods including Bayesian parameter estimation and more generic optimization using powerful nonlinear gradient-based methods are given. Finally, the methodology of an aircraft structure FE model updating is described. The practical application of the procedure is documented on the EV-55M turboprop utility aircraft example. Selected results are shown, evaluated and the conclusions are formulated. © Institution of Mechanical Engineers 2016.


Sedek J.,Czech Aeronautical Research and Test Institute
EAN 2016 - 54th International Conference on Experimental Stress Analysis | Year: 2016

The contribution deals with work concerning the design and optimization of composite rib intended for use in airliner door construction. New progressive tailoring blank technology of manufacturing thermoplastic composites requires specific demands on rib design. Replacing the metal machined rib by the composite one brings advantages of lower weight and effectively utilized material with minimal waste. The optimization process involved cut-out design and lamina placement. Numerical tools were utilized using finite element software ABAQUS and Hashin and LaRC failure theories were incorporated. Based on the optimization, the real part was manufactured and the static strength was evaluated. The experimental deformation and strain field measured by non-contact optical measuring system (DIC) was in good accordance with numerical analysis. Finally, the test of static strength was performed and strength according to strength theories was evaluated.


Fedosov V.,Czech Aeronautical Research and Test Institute | Peresty R.,Czech Aeronautical Research and Test Institute
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2011

Aeronautical Research and Test Institute (VZLU) is a joint stock company which serves as Czech national center for research, development and testing in aeronautics and space branches. Since 2002 VZLU has been dealing with development and manufacturing of electrostatic high-sensitive microaccelerometer (MAC) to measure microaccelerations (within the range ± 2*10 -4 m/s 2) on board of space platforms intended for space science missions (for example, ESA Earth Observation Program or bio/technological research in microgravity conditions). The paper describes principle measurement of the device, instrument performances and application of the accelerometer in recent space research projects. The emphasis will be placed on aspects of accelerometer orbit operation and its functionality verification in orbit. © 2011 IFAC.


Cecrdle J.,Czech Aeronautical Research and Test Institute
Journal of Aircraft | Year: 2012

This paper deals with aircraft structure whirl-flutter analysis. It gives a summary of the requirements of airworthiness regulations, the theoretical background, and aircraft certification-related issues. The focus is on the whirl-flutter analyses of the new Czech twin turboprop utility aircraft. Ordinary and optimization-based analytical approaches are described. An optimization-based analytical procedure to determine the whirl-flutter stability boundaries for certification speed is employed. Analyses include nominal state calculation and evaluation of the influence of secondary parameters to whirl-flutter stability. Finally, the propeller-nacelle-wing interference effects (downwash) are evaluated, and future work is outlined.


Cecrdle J.,Czech Aeronautical Research and Test Institute
29th Congress of the International Council of the Aeronautical Sciences, ICAS 2014 | Year: 2014

This paper deals with an aircraft structure analytical dynamic model updating to ground vibration tests (GVT) results. Paper describes possible approaches of flutter analysis as regards to the incorporation of GVT results - The direct usage of GVT results and analytical model updating. Then the theoretical background of the model updating methods including Bayesian parameter estimation and more generic optimization using powerful nonlinear gradient-based methods are given. Finally, the methodology of an aircraft structure dynamic model updating is described. The practical application is documented on the EV-55M turboprop utility aircraft model updating. Selected results are shown, evaluated and the conclusions are formulated.


Bohacova M.,Czech Aeronautical Research and Test Institute
Engineering Failure Analysis | Year: 2013

The field of non-destructive inspection (NDI) is an integral part of aircraft maintenance and service. It is optimal to apply the eddy current (EC) method on the complex multi-layered metal aircraft structure to detect cracks and other damage. A range of standard eddy current probes giving satisfactory results with respect to crack detection are available. However, these EC probes are not always suitable for the detection of short fatigue cracks hidden under a rivet head. This article presents a new methodology for eddy current inspection of a critical area on the wing. The development of the new methodology was inspired by a catastrophic glider accident in 2010. Because of this accident, all glider service was prohibited. The critical area is located in the structure of the wing spar, which consists of six layers. The position of the critical area is hidden under the countersunk rivet head in the third layer of the spar flange and under two layers of metal sheets. Thus, the actual location of the area is in the fourth layer, created by the countersunk rivet head. In addition, another rivet of a smaller diameter is inserted into the rivet in the flange. This article presents the work related to the development of a special EC probe that is able to measure in an operating frequency range between 200. Hz and 100. kHz with a single-value interpretation of the individual EC signals. © 2013 Elsevier Ltd.


Behal J.,Czech Aeronautical Research and Test Institute | Novakova L.,Czech Aeronautical Research and Test Institute
Engineering Failure Analysis | Year: 2013

The FASTRAN crack growth retardation model uses stress state descriptors to consider the local stress state ahead of the crack tip. Using the FASTRAN model implemented in the AFGROW computing code, the descriptor is input into the retardation model as a constant tensile (compressive) constraint factor along with the corresponding crack growth rate. The paper presents an evaluation based on a fractographic analysis of fracture surfaces of middle tension M(T) specimens from Al-alloy, which were used for the standard crack growth rate measurement under constant amplitude loading. There are typically three zones on the fracture surface: the flat zone that is perpendicular to the loading force and represents the tension mode of specimen cracking, the slant zone that is approximately 45° deviated from the loading force direction and a transient zone between them. It is shown that a significant correlation between crack length, local crack growth rate and the sizes of the zones exist. Crack lengths relevant to the zones and corresponding crack growth rates were processed by statistical procedures. A continuous uniform distribution is a very good statistical model of the logarithm of the crack growth rates on both sides of the transient zone. In the retardation model, this distribution can be accounted for by using the means of the probability functions.A sub-scale structural model was tested for fatigue crack growth under a random loading process representing real operational conditions. Using the typical values of constraint factors for a "pure" plain stress and plain strain states and the crack growth rates evaluated by the fractographic analysis as input parameters, the crack growth curves calculated by the AFGROW code using the FASTRAN retardation model were compared with the crack growth data measured in the experiment. The AFGROW output crack growth curves fit to the experimental measured ones without any additional tuning of the retardation model parameters. © 2013 Elsevier Ltd.

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