Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

20000064593 NASA Langley Research Center, Hampton, VA USA
Session on High Speed Civil Transport Design Capability Using MDO and High Performance Computing
Rehder, Joe, NASA Langley Research Center, USA; February 2000; In English; See also 20000064579; No Copyright; Abstract
Only; Available from CASI only as part of the entire parent document
Since the inception of CAS in 1992, NASA Langley has been conducting research into applying multidisciplinary optimization
(MDO) and high performance computing toward reducing aircraft design cycle time. The focus of this research has been the
development of a series of computational frameworks and associated applications that increased in capability, complexity, and
performance over time. The culmination of this effort is an automated high-fidelity analysis capability for a high speed civil transport
(HSCT) vehicle installed on a network of heterogeneous computers with a computational framework built using Common
Object Request Broker Architecture (CORBA) and Java. The main focus of the research in the early years was the development
of the Framework for Interdisciplinary Design Optimization (FIDO) and associated HSCT applications. While the FIDO effort
was eventually halted, work continued on HSCT applications of ever increasing complexity. The current application, HSCT4.0,
employs high fidelity CFD and FEM analysis codes. For each analysis cycle, the vehicle geometry and computational grids are
updated using new values for design variables. Processes for aeroelastic trim, loads convergence, displacement transfer, stress
and buckling, and performance have been developed. In all, a total of 70 processes are integrated in the analysis framework. Many
of the key processes include automatic differentiation capabilities to provide sensitivity information that can be used in optimization.
A software engineering process was developed to manage this large project. Defining the interactions among 70 processes
turned out to be an enormous, but essential, task. A formal requirements document was prepared that defined data flow among
processes and subprocesses. A design document was then developed that translated the requirements into actual software design.
A validation program was defined and implemented to ensure that codes integrated into the framework produced the same results
as their standalone counterparts. Finally, a Commercial Off the Shelf (COTS) configuration management system was used to organize
the software development. A computational environment, CJOPT, based on the Common Object Request Broker Architecture,
CORBA, and the Java programming language has been developed as a framework for multidisciplinary analysis and
Optimization. The environment exploits the parallelisms inherent in the application and distributes the constituent disciplines on
machines best suited to their needs. In CJOpt, a discipline code is ”wrapped” as an object. An interface to the object identifies
the functionality (services) provided by the discipline, defined in Interface Definition Language (IDL) and implemented using
Java. The results of using the HSCT4.0 capability are described. A summary of lessons learned is also presented. The use of some
of the processes, codes, and techniques by industry are highlighted. The application of the methodology developed in this research
to other aircraft are described. Finally, we show how the experience gained is being applied to entirely new vehicles, such as the
Reusable Space Transportation System. Additional information is contained in the original.
Author
Aircraft Design; Computational Fluid Dynamics; Computer Networks; Design Analysis; Finite Element Method; Software Engineering;
Multidisciplinary Design Optimization; Computer Aided Design; Systems Engineering
20000064900 Cranfield Univ., Flight Test and Dynamics Group, Cranfield, UK
An Analysis of the Flight Dynamics of a Second Generation SST Aircraft Interim Report
Steer, A. J., Cranfield Univ., UK; October 1999; 86p; In English
Report No.(s): COA-9914; ISBN 1-86194-046-7; Copyright; Avail: Issuing Activity
The principal aerodynamic properties that distinguish the low speed stability, control and handling characteristics of an SCT
aircraft are: (1) The requirement for relaxed longitudinal stability in order to reduce trim drag, both at higher speeds as the aerodynamic
centre moves aft and to improve performance at lower speeds through reduced control surface sizing. The relaxed stability,
achieved through locating the CG at the NP, results in an unconventional dynamic response on the approach characterized by a
3doscillatory mode with short period damping and phugoid like frequency combined with two real modes, one of which is unstable.
(2) The low static margin when flying at low-speed coupled with the absence of a second control surface results in relatively
low pitch damping, M(sub q), combined with a high pitch inertia, I(sub y). The aircraft’s unaugmented longitudinal response to
a control input is thus characterized by a low pitch acceleration, hence sluggish pitch response combined with a slow time to settle.
Solutions include feeding back either incidence or pitch rate to restore stability and enhance the maneuver response as well as
augmenting control power by providing a second pitch control surface. (3) The delta wing’s low lift curve slope requiring large
angles of attack on the approach in order to generate sufficient low-speed lift at the expense of considerable amounts of induced
drag. Hence the aircraft flies considerably below the minimum drag speed, known as ’backside’ operation, resulting in speed instability
and difficult flightpath control. The effects of speed instability are that at a constant engine thrust on a -3 deg. flightpath,
the short term response to an aft stick movement is an increase in height relative to the flightpath. The long-term effect is an
increase in drag and consequent steepening of the flightpath. Conversely, a forward stick movement initially steepens the flightpath
and in the long term, the increase in speed causes the aircraft to fly above the flightpath. These effects can be overcome by
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