Flutter Calculation Based on GVT-Results and Theoretical Mass Model

Chajec, Wojciech

doi:10.3846/1648-7788.2009.13.122-129

Cited by 13 publications

(12 citation statements)

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“…Based on GVT results (Lorenc et al, 2015) GVT are different, so the procedure Seibert, 2011 andChajec, 2016b) of normal modes computation based on GVT results of aircraft before mass alteration was implemented.…”

Section: Comparison Of Pipistrel Virus Sw 121 Aircraft Flutter Computation Resultsmentioning

confidence: 99%

“…The modes are processed by using the author's own procedure described in Chajec and Seibert (2011) and Chajec (2016b). It uses a low number of degrees of freedom (DoFs) mass model (Nowak and Potka nski, 1976), which gives an opportunity to calculate generalized masses as well as complete the measured modes orthogonalization adopted many years ago by author from Baruch (1980).…”

Section: Work Descriptionmentioning

confidence: 99%

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Comparison of flutter calculation methods based on ground vibration test result

Chajec

2019

AEAT

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PurposeA low-cost but credible method of low-subsonic flutter analysis based on ground vibration test (GVT) results is presented. The purpose of this paper is a comparison of two methods of immediate flutter problem solution: JG2 – low cost software based on the strip theory in aerodynamics (STA) and V-g method of the flutter problem solution and ZAERO I commercial software with doublet lattice method (DLM) aerodynamic model and G method of the flutter problem solution. In both cases, the same sets of measured normal modes are used. Design/methodology/approachBefore flutter computation, resonant modes are supplied by some non-measurable but existing modes and processed using the author’s own procedure. For flutter computation, the modes are normalized using the aircraft mass model. The measured mode orthogonalization is possible. The flutter calculation made by means of both methods are performed for the MP-02 Czajka UL aircraft and the Virus SW 121 aircraft of LSA category. FindingsIn most cases, both compared flutter computation results are similar, especially in the case of high aspect wing flutter. The Czajka T-tail flutter analysis using JG2 software is more conservative than the one made by ZAERO, especially in the case of rudder flutter. The differences can be reduced if the proposed rudder effectiveness coefficients are introduced. Practical implicationsThe low-cost methods are attractive for flutter analysis of UL and light aircraft. The paper presents the scope of the low-cost JG2 method and its limitations. Originality/valueIn comparison with other works, the measured generalized masses are not used. Additionally, the rudder effectiveness reduction was implemented into the STA. However, Niedbal (1997) introduced corrections of control surface hinge moments, but the present work contains results in comparison with the outcome obtained by means of the more credible software.

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Section: Comparison Of Pipistrel Virus Sw 121 Aircraft Flutter Computation Resultsmentioning

confidence: 99%

Section: Work Descriptionmentioning

confidence: 99%

Comparison of flutter calculation methods based on ground vibration test result

Chajec

2019

AEAT

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“…There are many publications from the area of aircraft vibration testing, like the ones recognized by authors and worth of being referenced in this elaborate. 2,6–15 Unfortunately, most of them are focused on testing objects and obtained results, but not necessarily on the core of experiment which in fact is a technological process including specific working techniques. Some of them are at least briefly described in current point.…”

Section: Measuring Equipment and Applied Methodologymentioning

confidence: 99%

Application of ground vibration testing in small manned or unmanned aircraft prototyping

Olejnik

Kachel

Rogólski

et al. 2020

Proceedings of the Institution of Mechanical Engineers, Part G:

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The article describes the vibration measurement technology used in experimental investigation of light aircraft and some series of exemplary results obtained during the prototyping process. The aim of investigations presented herein was to determine the resonant frequencies and natural modes of an aircraft or its selected structural components. Ground vibration testing is an essential dynamic structural test necessary to carry out before the aircraft certification. This test should be performed on the aircraft example which is predicted to be tested in flight. The measuring system used for ground vibration testing in the Institute of Aviation Technology of the Military University of Technology consists of a multi-channel LMS SCADAS analyzer, a set of piezoelectric accelerometers, two vibration exciters equipped with impedance heads and a computer with the Test.Lab Software. The aim of the article was to present the methodology of performing ground vibration testing tests. Having applied the equipment to measure an airplane or its airframe component, key vibration characteristics corresponding to specific resonant points can be determined. Not only completed aircraft can be tested but also its isolated fragments (wings, stabilizers, tail units) or just empty airframe. Testing separately supported components allows examining their aeroelastic properties at early stage of prototyping. Ground vibration testing technology applied in various stages of the prototyping process was demonstrated in four peculiar research cases. The testing examples presented herein were the following: the isolated strut-braced wing of a light reconnaissance airplane, the light drone imitating an aerial target for some on-ground anti-aircraft artillery sets, the empty airframe of a very light jet and the miniature UAV. Some exemplary results obtained from testing these objects were presented. At the end, some observations and conclusions were noted in the context of usefulness of conducted researches.

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“…Flutter calculation was performed directly basing on GVT results, taking into account the simple mass and aerodynamic models (no stiffness data were necessary). The methodology was described by Chajec (2009).…”

Section: Flutter Calculation Of Autonomous Uav – Samonit Projectmentioning

confidence: 99%

“…The simulation of disconnection (as a result of damage) of selected control surfaces is possible even if the GVT were provided on undamaged vehicle. To do it the rotational mode of so‐called “free control surface” was prepared (as an artificial resonant mode) for all deflected control surfaces, next the all resonant modes were orthogonalized (Baruch, 1980; Chajec, 2009) with respect to this artificial control surfaces mode. However, the simulation of disconnection was here of an approximate type, because the full symmetry was assumed (the both left and right segments were disconnected).…”

Section: Flutter Calculation Of Autonomous Uav – Samonit Projectmentioning

confidence: 99%

Aeroelastic analysis of remotely controlled research vehicles with numerous control surfaces

Goraj

Chajec²

2011

International Journal of Structural Integrity

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PurposeThe purpose of this paper is to find an influence of the reduced stiffness of actuators, located on the most outer parts of ailerons, flaperons, rudders, elevators and elevons on the excitation of flutter. This phenomenon is especially important for unmanned aerial vehicles because they continuously use all these control surfaces for trimming and stabilisation and on the other hand, the numerous statistics show that failure of elements of flight control systems are still the most probable reasons of aircraft critical failure.Design/methodology/approachFlutter calculations were performed by use of the classical modal approach. The normal vibrations of the free aircraft were measured in the ground vibration test (GVT). Test results were used either for verification of the FEM model of the structure – in this case for flutter calculation the MSC.Nastran software was used, or directly for flutter calculation. Based on the flutter analysis, the control surfaces critical for flutter were determined.FindingsThese so‐called critical control surfaces –, i.e. surfaces responsible for flutter excitation at first – are localized on outer parts of wing and empennage. It was found that the critical surfaces should have been mass balanced or should be irreversible. In the second case, i.e. when the control surfaces are irreversible, the actuators and drivers should have been of a high reliability, because disconnection of these elements could involve flutter.Research limitations/implicationsThis approach within the computational analysis is limited to linear case, otherwise NASTRAN software cannot be used for flutter analysis. GVTs could be performed successfully independently if the structure has linear or non‐linear properties.Practical implicationsIt was found that before any flight the stiffness in the flight control system of all control surfaces must carefully be checked and kept above the critical stiffness value. Safety level strongly depends on the reliability of actuators used on such unmanned aerial vehicles. The simulation of disconnection (as a result of damage) of selected control surfaces is possible even if the GVT were provided on undamaged vehicle. To do it, the rotational mode of so‐called “free control surface” should be prepared (as an artificial resonant mode) for all deflected control surfaces; next all the resonant modes should be orthogonalized, relative to this artificial control surfaces mode.Originality/valueThis paper was based on two big European and national projects, and all presented results are original and were never published before. Some selected graphs were shown during the EASN Workshop, Paris, September 2010 at the presentation entitled: “Aeroelastic analysis of remotely controlled research vehicles with numerous control surfaces”.

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Flutter Calculation Based on GVT-Results and Theoretical Mass Model

Cited by 13 publications

References 1 publication

Comparison of flutter calculation methods based on ground vibration test result

Comparison of flutter calculation methods based on ground vibration test result

Application of ground vibration testing in small manned or unmanned aircraft prototyping

Aeroelastic analysis of remotely controlled research vehicles with numerous control surfaces

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