Computational and experimental modal analysis of the Lasta aircraft

by Jelena Dimitrijevic (Military Technical Institute of Serbian Army, Department for aircraft), Predrag Kovacevic (Military Technical Institute of Serbian Army, Department for aircraft), Vojislav Devic (Military Technical Institute of Serbian Army, Department for aircraft)

Wednesday 8 Dec 2010, 18:00 → 19:00 Europe/Belgrade

301 F (Mathematical Institute)

During designing and development of an aircraft prototype it is required to be confirm that the aircraft is free from flutter in the range of the designed speed. Wing, ailerons, stabilizer, or whole aircraft flutter is a phenomenon of self-induced undamped oscillations begins of coupling aerodynamic, elastic and inertial forces at high flight speeds. Flutter is very dangerous because it can cause aircraft construction crash. This presentation presents Computational and Experimental Modal Analysis procedures that are applied during designing and examination of the LASTA prototype aircraft. Computational Modal Analysis is done by using Finite Element Method. Main assemblies of the aircraft wing, fuselage and stabilizers are modeled and analyzed separate. While modeling main assemblies we took care of the real construction elastic and inertial characteristics representation. This presentation gives the results of Modal Analysis of the LASTA aircraft. Critical flutter speeds calculation is done according to these results. After the prototype manufacturing, Experimental Modal Analysis is required to obtain data that are more precise for further critical flutter speed calculation. Aircraft preparation, testing method, excitation position, data acquisition and processing are presented in the presentation. Obtained results – modal frequencies, damping and mode shapes are presented, too. According to these results final critical flutter speed calculation is done. In addition, the aircraft finite element model will be verified and fit (according to these results) for further use in the analysis of the aeroelastic phenomena and aircraft dynamic response. - - - - - - - - - - U procesu projektovanja i razvoja letelica značajno mesto zauzima zadovoljenje zahteva da letelica bude bezbedna od pojave flatera u okviru upotrebnih brzina. Flater krila, krilaca, repova, ili celog aviona je pojava samopobudnih neprigušenih oscilacija nastalih sprezanjem aerodinamičkih, elastičnih i inercijalnih sila pri velikim brzinama leta. Flater je veoma opasan jer može da izazove lom konstrukcije aviona. Da bi se kritične brzine flatera mogle pouzdano proceniti neophodni su podaci modalne analize letelice. U ovoj prezentacije će biti predstavljeni postupci računske i eksperimentalne modalne analize koji su primenjeni u toku projektovanja i ispitivanja prototipa aviona LASTA. Računska modalna analiza je obavljena primenom metode konačnih elemenata. Posebno su modelirani i analizirani osnovni sklopovi konstrukcije aviona krilo, trup i repovi, a zatim je od njih formiran model kompletnog aviona. Pri modeliranju osnovnih sklopova se vodilo računa da oni i po elastičnim i po inercijalnim karakteristikama predstave realnu konstrukciju. U prezentaciji su prikazani rezultati modalne analize kompletnog modela aviona. Na osnovu njih je dalje obavljen proračun kritičnih brzina flatera. Posle izrade prototipa, da bi se dobili što tačniji podaci za proračun kritičnih brzina flatera, obavezno se obavlja eksperimentalna modalna analiza. U prezentaciji je prikazana priprema aviona za ispitivanje, izbor metode ispitivanja, način pobuđivanje, prikupljanja i obrade podataka. Predstavljeni su dobijeni rezultati - sopstvene frekvencije, prigušenja i sopstveni oblici oscilovanja. Na osnovu ovih rezultata se radi završni proračun kritičnih brzina flatera kao i podešavanje modela konačnih elemenata aviona kako bi on mogao da se koristi za dalje analize aeroelastičnih pojava i dinamičkog odziva aviona. References [1] FELIPPA,C.A.: Introduction to Finite Element Methods, Department of Aerospace Engineering Sciences, September 2006. [2] BATHE,K.J., WILSON,E.L.: Numerical Methods in Finite Element Analysis, Prentice-hall, inc., Englewood Cliffs, New Jersey, 1976. [3] WILSON,E.L.: Numerical Methods in Offshore Engineering, John Wiley & Sons, 1987. [4] WILKINSON,J.H.: The Algebric Eigenvalue Problem, Clarendon press, Oxford, 1965. [5] OJALVO,I.U.: Proper Use of Lanczos Vectors for Large Eigenvalue Problems, Computers & Structures, vol. 20, No. 1-3, 1985. [6] HUGHES,T.J.R.: The Finite Element Method, Static and Dynamic Finite Element Analysis, Prentice Hall, 1987. [7] FEDERAL AVIATION ADMINISTRATION: Advisory Circular, Means of Compliance With Section 23.629-1B, Flutter, 2004 [8] HUTIN,C.: Modal Analysis Using Appropriated Excitation Techniques, Data Physics SA, Voisins le Bretonneux, France, 2000. [9] WELARANTA,S.: Advanced Data Acquisition and Signal Analysis Packages Can Enable Effective Ground Vibration Testing, Aerospace Testing International, May 2003. [10] PEETERS,B., HENDRICX,W., DEBILLE,J., CLIMENT,H.: Modern Solutions for Ground Vibration Testing of Large Aircraft, LMS International, Leuven, Belgium and EADS CASA, Getafe, Spain, January 2009. [11] KOVAČEVIĆ,P., DIMITRIJEVIĆ,J., DEJANOVIĆ, N., BANOVIĆ,N.: Ispitivanje vibracija na zemlji aviona Lasta P1, Vojnotehnički institut VS, maj 2010. [12] KOVAČEVIĆ,P., DIMITRIJEVIĆ,J.: Obrada podataka sa ispitivanja vibracija na zemlji aviona Lasta P1, Vojnotehnički institut VS, maj 2010.