Optimization strategy for conceptual airplane design

128 Pages·2014·5.58 MB·English

Master of Science Thesis
Optimization strategy for conceptual
airplane design
P.T. Vasseur B.Sc.
May 9, 2014
Faculty of Aerospace Engineering · Delft University of Technology

Optimization strategy for conceptual
airplane design
Master of Science Thesis
For obtaining the degree of Master of Science in Aerospace
Engineering at Delft University of Technology
P.T. Vasseur B.Sc.
May 9, 2014
Faculty of Aerospace Engineering · Delft University of Technology
Copyright ' P.T. Vasseur B.Sc.
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 “Optimization strategy for
conceptual airplane design” by P.T. Vasseur B.Sc. in partial fulfillment of the
requirements for the degree of Master of Science.
Dated: May 9, 2014
Head of department:
prof.dr.ir. L.L.M. Veldhuis
Supervisor:
dr.ir. R. Vos
Reader:
dr.ir. H.G. Visser

Abstract
Due to the ever growing demand for more efficient aircraft novel aircraft concepts have
to be explored. By improving design tools the potential of unconventional configurations
can be further studied. This requires improvement of conceptual design tools such that
more knowledge can be gathered on alternative solutions as early in the design process
as possible. Multidisciplinary design optimization (MDO) can support this process by
providing an environment in which the various disciplines can be designed and optimized
concurrently, while a certain level of consistency is maintained.
An optimization design tool has been created to assess the potential performance gains
of novel aircraft configurations. It connects with the Initiator design tool, which is a
conceptual design framework. As such, it can also be used as a means to expose any
analysis or design issues that may exist in the Initiator.
With the optimizer tool the following four case studies were performed: a conventional
AirbusA320,aforward-sweptcanardaircraft,athree-surfaceaircraftandanoval-fuselage
aircraft. For this purpose the genetic algorithm, sequential quadratic programming al-
gorithm and a hybrid genetic algorithm were used. From the case studies followed that
large improvements can be obtained with unconventional aircraft configurations when
compared to the initial aircraft design proposed by the Initiator design tool. Up to 20%
improvement was found with the three-surface and canard aircraft. The oval-fuselage
aircraft could be improved by a solid 10%, while the lowest improvement was attained
with the conventional A320.
Among all cases the most contributing factors were the wing longitudinal position, sweep
angle and wing aspect ratio. There is a tendency towards lower sweep angles due to the
positive effect on the weight of the wing and an underestimation of the drag rise. With
the forward-swept canard relatively high sweep angles were found, which contradicts
the findings of the aft-swept wings. Therefore, the aerodynamics routine needs further
investigation. Fromthehighlyswept, highaspectratiowingsoftheforward-sweptcanard
aircraft followed that the weight penalty of forward swept wings is underestimated.
In three cases the fuselage fineness ratio was involved in the optimization. The results
showed that changing the fineness ratio offered some reduction in fuselage weight due to
a more favourable structural loading.
v
vi Abstract
The sizing routine of the control surfaces is found to be inadequate, since the Initiator
derives most parameters directly from the wing and does not properly take into account
controlandstabilityrequirements. Resultshaveshownthatthismainlyregardsthesweep
and dihedral angle. Especially, the sweep angle is of concern, since it changes the lift-
curveslopeandthereforealsostallcharacteristics. Thesesizingissuesalsoaffectthestatic
margin. It was found that class II design information was not fed back to the control
surface sizing.
Other discrepancies were found with the wing dihedral. Due to a lack of lateral stability
analysis of the Initiator the dihedral was driven by the lift-to-drag ratio rather than its
stabilizing effect. As a result a lower dihedral was observed among the cases.
From the used optimization algorithms can be concluded that the gradient algorithm was
the least effective. It had difficulties with the uncertainties in the computed results of the
Initiator. It sometimes stopped prematurely or started oscillating. This was alleviated
by increasing the step size of the algorithm, but at the expense of accuracy. The genetic
algorithm was found to be the best option since it proved to be very robust. It is far
less sensitivity to noise, because it does not use gradient information. Its computational
cost could be significantly reduced by applying parallel optimization and using a caching
mechanism. The hybrid algorithm was found to be too computational expensive. The
obtained increase in objective value did not outweigh the added cost.
Acknowledgements
This thesis marks the final step in completing the Master Program in System Engineering
and Aircraft Design at the faculty of Aerospace Engineering. I had a great time studying
at Delft University of Technology, with the company of my fellow students and friends.
The research presented in this report would not have been possible without the support
of a number of people whom I hereby would like to thank.
Fist of all, I would like to express my gratitude to my supervisor dr.ir. Roelof Vos for his
feedback, support and valuable insights during the course of my master thesis. I would
alsoliketothankthemembersofmycommittee, prof.dr.ir. LeoVeldhuisandDriesVisser
for their time to assess my work. I want to express my appreciation to Reno Elmendorp
for providing feedback on the optimizer tool and helping me out with integration in the
Initiator.
Last but not least, I would like to thank my parents for their continuous support and
encouragement throughout my study.
Delft, The Netherlands P.T. Vasseur B.Sc.
May 9, 2014
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viii Acknowledgements