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05 AIRCRAFT DESIGN, TESTING AND PERFORMANCE
by a set of normal modes which have been updated by results of
ground resonance survey tests. Flutter calculations in open and
closed loop on different flight conditions as well as incidence
variations are demonstrated as common flutter plots. For the flutter
analysis a set of notch filter is required, which should be determined
in an integrated design step.
Author
Control Systems Design; Flight Mechanics; Flight Control; Flutter
Analysis; Aeroservoelasticity; Mathematical Models; Dynamic
Models
20000053165 Manchester Univ., School of Engineering, UK
CHARACTERISATION OF NONLINEAR AEROSERVOELASTIC
BEHAVIOUR
Dimitriadis, G., Manchester Univ., UK; Cooper, J. E., Manchester
Univ., UK; Structural Aspects of Flexible Aircraft Control; May 2000,
pp. 8-1 - 8-11; In English; See also 20000053157; Copyright
Waived; Avail: CASI; A03, Hardcopy
The characterisation of the behaviour of nonlinear aeroelastic
systems has become a very important research topic. Nevertheless,
most of the work carried out to date concerns the development of
unsteady CFD solutions in the transonic region. Important though
this work is, there is also a need for research which aims at
understanding the behaviour of nonlinear systems, particularly the
occurrence of Limit Cycle Oscillations (LCOs). The purpose of this
paper is to study the stability of a simple aeroservoelastic system
with nonlinearities in the control system. The work considers both
structural and control law nonlinearities and assesses the stability of
the system response by use of bifurcation diagrams. It is shown that
simple feedback systems designed to increase the stability of the
linearized system also stabilise the nonlinear system, although their
effects can be less pronounced. Additionally, a nonlinear control law
designed to limit the control surface pitch response was found to
increase the flutter speed considerably by forcing the system to
undergo limit cycle oscillations instead of fluttering. Finally, friction
was found to affect the damping of the system but not its stability, as
long as the amplitude of the frictional force is low enough not to
cause stoppages in the motion.
Author
Aeroservoelasticity; Flutter; Nonlinear Systems; Control Systems
Design; Systems Stability; Aircraft Control
20000053168 Air Force Research Lab., Wright-Patterson AFB, OH
USA
THE IMPACT OF ACTIVE AEROELASTIC WING TECHNOLOGY
ON CONCEPTUAL AIRCRAFT DESIGN
Flick, Peter M., Air Force Research Lab., USA; Love, Michael H.,
Lockheed Martin Tactical Aircraft Systems, USA; Structural Aspects
of Flexible Aircraft Control; May 2000, pp. 10-1 - 10-10; In English;
See also 20000053157; Copyright Waived; Avail: CASI; A02, Hardcopy
Active Aeroelastic Wing (AAW) Technology represents a new
design approach for aircraft wing structure. The technology uses
static aeroelastic deformations as a net benefit during maneuvering.
AAW is currently being matured through a flight research program;
however, transition of the technology to future systems will require
educating designers in multiple disciplines on this new design
approach. In order to realize the full benefits of AAW, aeroelastic
effects will need to be accounted for from the beginning of the design
process. Conceptual design decisions regarding wing aspect ratio,
wing thickness-to-chord ratio. and wing torque box geometry will be
influenced if designers choose to utilize AAW. This paper will present
current work in developing conceptual aircraft design guidance for
AAW and identify improvements to the design process that could
facilitate future AAW design applications. This process involves
using results from aeroelastic design methods, typically used in
preliminary design, with conventional conceptual design methods.
This approach will allow aeroelastic effects to be accounted for while
making conceptual design decisions.
Author
Aeroelasticity; Aircraft Design; Aircraft Structures; Aeroelastic
Research Wings
20000053169 DaimlerChrysler Aerospace A.G., Military Aircraft,
Munich, Germany
ACTIVE AEROELASTIC AIRCRAFT AND ITS IMPACT ON
38
STRUCTURE AND FLIGHT CONTROL SYTSEMS DESIGN
Schweiger, Johannes, DaimlerChrysler Aerospace A.G., Germany;
Krammer, Johann, DaimlerChrysler Aerospace A.G., Germany;
Structural Aspects of Flexible Aircraft Control; May 2000, pp. 11-1 -
11-8; In English; See also 20000053157; Copyright Waived; Avail:
CASI; A02, Hardcopy
Active aeroelastic concepts have been proposed for several
years now. Their common incentive are improvements of aircraft
performance and stability by the intentional use of aeroelastic
effects. This means that the basic flexibility characteristics of a new
aircraft project must be included in the early conceptual design
process, and the structural and flight control system design must be
coupled very closely. The knowledge about the magnitude of
aeroelastic impacts on aerodynamic forces and aircraft stability is
still very limited within the community of people involved in aeronautical
engineering - even among the specialists in aeroelasticity. For a
successful application of active aeroelastic concepts, their proper
identification is therefore the first step. It will be shown for some
selected examples, which static aeroelastic effects are usually very
important for conventional designs, and how they can be made even
more effective in a positive sense for future designs. The accuracy
and proper use of aeroelastic prediction methods and analysis
models is addressed briefly in the context of interactions with other
disciplines, and ideas are developed for the multi-disciplinary design
process of active aeroelastic aircraft concepts. Whereas static
aeroelastic effects usually only become important with increasing
airspeed, a concept will be demonstrated for aeroelastic improvements,
which also works at low speeds.
Author
Aircraft Design; Control Systems Design; Flight Control; Aircraft
Structures; Aeroelasticity; Active Control
20000053170 Northrop Grumman Corp., Military Aircraft Systems
Div., Pico Rivera, CA USA
AEROSERVOELASTIC CHARACTERISTICS OF THE B-2
BOMBER AND IMPLICATIONS FOR FUTURE LARGE AIR-
CRAFT
Britt, R. T., Northrop Grumman Corp., USA; Volk, J. A., Northrop
Grumman Corp., USA; Dreim, D. R., Northrop Grumman Corp.,
USA; Applewhite, K. A., Northrop Grumman Corp., USA; Structural
Aspects of Flexible Aircraft Control; May 2000, pp. 12-1 - 12-12; In
English; See also 20000053157; Copyright Waived; Avail: CASI;
A03, Hardcopy
Design and development of the B-2 Bomber presented many
challenges in flexible vehicle control, many related to the unique
configuration and design requirements, The technical challenges
posed by the aeroelastic characteristics of the all-wing aircraft were
recognized at the outset of the development program and included
the configuration’s near-neutral pitch stability and light wing loading
which made the aircraft highly responsive to atmospheric turbulence.
This dictated the requirement for an active digital flight control
system to provide both stability augmentation and gust load alleviation.
The gust load alleviation flight control system was designed by
a multidisciplinary team using a combination of optimal and classical
control design techniques and a common analysis model database.
Accurate representation of the vehicle aerodynamics characteristics,
actuators, and sensors were key to successfully developing and
testing the flight control system and verifying performance requirements.
Flight test data analysis included the extraction of the vehicle
open loop response which were utilized to adjust the analytical
models and make final revisions to control law gains. The multidisciplinary
design approach resulted in the successful development of
a control augmentation system that provides the B-2 with superb
handling characteristics, acceptable low altitude ride quality, and
substantial alleviation of gust loads on the airframe. With this back
drop, a technology assessment is performed which discusses potential
technology improvements for application to future bomber and
large transport aircraft.
Author
Active Control; Aeroservoelasticity; Aircraft Design; Control Systems
Design; Control Theory; Flight Control; Technology Assessment;
B-2 Aircraft
20000053172 Deutsche Forschungsanstalt fuer Luft- und
Raumfahrt, Inst. of Structural Mechanics, Brunswick, Germany
DESIGN ASPECTS OF THE ELASTIC TRAILING EDGE FOR AN
ADAPTIVE WING