Techniques to generate and optimize the load spectra for an aircraft
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Techniques to generate and optimize the load spectra for an aircraft Krishna Lok Singh • D. V. Venkatasubramanyam
Received: 24 November 2009 / Accepted: 31 March 2010 / Published online: 13 April 2010 Ó Springer Science+Business Media, B.V. 2010
Abstract In this article, described the various techniques to generate the load spectra for an aircraft and optimize the generated loading sequence. The generation of loading sequence is carried out from the Flight Data Recorder (FDR), which records various parameters in flight. In this article main focus is on ‘g’ accelerations as these are used for load spectra generation. This article describes the techniques viz., (i) Peak-trough counting, (ii) Level cross counting algorithms to count the number of exceedances. After implementing and using these techniques, listed the advantages and disadvantages of these techniques. For a successful usage of generated load sequence for a test/analysis, it is necessary to optimize the generated loading sequence or turning points. The optimization of generated load sequence is carried out by filtering small cycle amplitudes of load/‘g’ ranges. At different range levels the filtering has been carried out, to arrive at an optimum range level of filtering. In order to be certain that the optimized spectra has not lost its severity and shape it has been re-plotted with the original spectra on the same graph. This optimization exercise useful in reducing the testing time. Keywords Aircraft Fatigue Load spectra Optimization Rainflow K. L. Singh (&) D. V. Venkatasubramanyam Structural Technologies Division, National Aerospace Laboratories, Bangalore 560017, India e-mail: [email protected]
1 Introduction The service fatigue life of a component depends on both the variable amplitude load conditions and the assumptions during fatigue design. Hence, in order to estimate a proper fatigue damage, it is important to consider real service loads (Johannesson 2006). For simulating the service loads on the airframe, a spectrum (one dimensional set) of variable amplitude load sequence has been generated from Flight Data Recorder (FDR). Earlier the Standard Load Sequence (SLS) like FALSTAFF (Fighter Aircraft Loading STAndard For Fatigue evaluation) is for military/air force aircraft application had been generated (Van Dijk and de Jonge 1975; Schijve 2009). FALSTAFF is a standard load sequence (Molent and Aktepe 2000; Heuler and Klatschke 2005) considered to represent the load time history generated from the location of the lower wing skin near the wing root of a fighter aircraft. In the present article among the various parameters (three accelerations, stabilizer deflection, mach number, altitude, etc.) that are recorded continuously at a rate of one data per second, on the metallic tape. These data were transferred to the computer in the digital format through an interface. Among these various parameters only the transverse and vertical accelerations parameters are discussed in this article. Either for fatigue test/analysis the generation of the lo
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