Multibody Dynamics Modeling of Flexible Aircraft Flight Dynamics

150 Pages·2014·13.79 MB·English

Multibody Dynamics Modeling of
Flexible Aircraft Flight Dynamics
Load Prediction in the Preliminary Design Phase
R.L.C. Kalthof
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Multibody Dynamics Modeling of
Flexible Aircraft Flight Dynamics
Load Prediction in the Preliminary Design Phase
Master of Science Thesis
For obtaining the degree of Master of Science in Aerospace
Engineering at Delft University of Technology
R.L.C. Kalthof
June 12, 2014
007#14#MT#FPP
Faculty of Aerospace Engineering · Delft University of Technology
Copyright (cid:13)c Flight Performance and Propulsion
All rights reserved.
Delft University of Technology
Department of
Flight Performance and Propulsion
The undersigned hereby certify that they have read and recommend to the Faculty of
Aerospace Engineering for acceptance a thesis entitled
Multibody Dynamics Modeling of Flexible Aircraft Flight Dynamics
by
R.L.C. Kalthof
in partial fulfillment of the requirements for the degree of
Master of Science Aerospace Engineering
Dated: June 12, 2014
Head of department:
Prof.dr.ir. L.L.M. Veldhuis
Supervisor:
Dr.ir. M. Voskuijl
Readers:
Dr.ir. R. De Breuker
Dr.ir. R. Vos

Acknowledgements
This thesis report is written as a part of the Master Program in Flight Performance and
Propulsion at the Faculty of Aerospace Engineering of Delft University of Technology. It
forms the final step in completing this study and thereby also the end of my time as a student
in Delft.
Lookingbackatperformingsevenmonthsofresearch,readingroughly200articlesandwriting
some 10000 lines of code, I would like to thank a number of people for their help. First of
all, I would like to express my gratitude towards my supervisor, dr.ir. Mark Voskuijl, for his
excellent guidance during the project, from beginning to end, and for his invaluable advice,
especiallyonthesubjectofflightmechanics. Furthermore,Iwouldliketothankdr.ir.Roeland
DeBreuker, forsharingwithmehisknowledgeaboutaeroelasticity. Iwouldalsoliketothank
prof.dr.ir. Leo Veldhuis and dr.ir. Roelof Vos, for completing my graduation committee.
Many thanks to all the people that helped make my time as a student absolutely terrific.
Although there are too many to mention here, I would like to extend a special thanks to the
people that helped me during this thesis research: the students of Kamertje 1, for the many
laughs, discussions and other pleasant distractions, and Almira, Bob, Diego, Max and Niels
for reading through part of this report and providing me with valuable comments. I would
also like to thank my parents, who have supported me in everything I did and whose posi-
tive attitude reflected on me. Finally, I would like to address a special person, my girlfriend
Nanda, for her continuing support, involvement and encouragements.
Roelant Kalthof
Delft, June 2014
Master of Science Thesis R.L.C. Kalthof
ii Acknowledgements
R.L.C. Kalthof Master of Science Thesis
Abstract
Because of the focus on weight minimization, aircraft are becoming more and more flexible.
Therefore, thefrequencyseparationbetweenflightmechanicsmotionandstructuralvibration
decreases. This calls for a flight mechanics model that includes aeroelasticity. The develop-
mentofsuchamodelwasthesubjectofthecurrentresearch. Thismodelcanbeusedforgust
andmaneuverloadpredictioninthepreliminarydesignphase. Withaccurateloadprediction,
structural integrity can be ensured and unstable flight conditions can be avoided. Moreover,
themodelmaybeusedtodesignactiveloadalleviationsystemstoincreasepassengercomfort,
reduce fatigue, and decrease loads on the wing structure.
Table 1 shows the approaches that were used for the disciplines involved in the aeroelastic
flight mechanics model. The upper part represents the aeroelastic wing model, which was
extensively verified. The qualitative, steady-state and transient behavior were assessed and a
comparison was made with an existing lumped-parameter model. The lower part represents
the flight mechanics model, which was verified as well. For an A320-like aircraft, the qual-
itative behavior was investigated and the stability characteristics and trim conditions were
compared with information from literature. Validation has not been performed, because of
the absence of complete validation data for aeroelastic flight mechanics models.
Table 1: The approaches taken for the various disciplines.
Discipline Approach
Structures Modal approach in a linear time-invariant state-space system
Aerodynamics Look-up tables using the quasi-steady α
eff
Control surfaces Only aerodynamic contribution considered
Load prediction Summation of forces (with multibody system dynamics)
Fluid-structure interaction Conventional serial staggered partitioned approach
Flight Dynamics Multibody system dynamics
Trimming Combined implicit and explicit Jacobian approach
Linearization Jacobian linearization
The complete multibody system dynamics model can be constructed automatically, based on
Master of Science Thesis R.L.C. Kalthof
iv Acknowledgements
user input. In this manner, it can be included in a design optimization framework and many
different analyses can be easily performed.
AnA320-likeaircraftwasanalyzedinthecurrentresearch. Theeffectofaeroelasticityonflight
mechanics was investigated. Inclusion of flexibility substantially affected the trim control
variables, but had an almost negligible effect on the flight mechanics modes and stability
derivatives. When flexibility increases, these parameters are affected. Aeroelasticity has a
non-negligible effect on the (peak) wing loads after maneuvers or disturbances. Especially
for maneuvers or disturbances that increase lift, and therefore wing deformation, the peak
loads are affected. Moreover, wing loads are particularly affected by disturbances that have
a direct effect on the wing, such as aileron deflection.
Theobjectiveofthecurrentresearchwastoimproveonanexistingaeroelasticflightmechanics
model, based on the lumped-parameter approach. The modal model created in the current
research proved to have a computational effort that is several times lower than the lumped-
parameter model. In addition, the accuracy of the modal model can be increased beyond
that of the lumped-parameter model at only a small additional computational cost. Because
of the reduced computational cost, and the potentially increased accuracy, the modal model
performs better than the lumped-parameter model.
Due to the qualitative nature of these conclusions, it is probable that they can be extended to
other conventional, low aspect-ratio aircraft in the subsonic flight regime. Definitive, quan-
titative conclusions could not be formulated, because of the absence of complete validation
data.
R.L.C. Kalthof Master of Science Thesis