Abstract:
This
study is concerned with a methodology for the aerodynamic analysis and
preliminary design of a novel configuration for high subsonic civil transport, based on
the
flying wing concept, known a Blended Wing Body (BWB).
A
response surface based optimisation method is developed, enabling the designer to
monitor the effect of shape modification on the controllability of the aircraft in both
longitudinal and lateral/directional motion and on the Wing structural weight, while
maximising the aerodynamic efficiency. The design aspects considered included high-
speed aerodynamics, flight static-stability and trim characteristics.
The
response surface Scheme employs a space filling design of experiment technique
to build least
square fitting quadratic polynomials, used in place of the original
computational modules in a gradient based search. A optimisation test indicated that
the
present method is more effective in leading the design near to the global optimum
as
opposed to a conventional gradient method with direct search, despite that the
constructed
approximation may not represent accurately the actual surface. With this
system, multiple constrained optimisation problems are successfully solved in the
favourable case of smooth objective/constraint function. Where these functions may
exhibit
high non-linear trends, an iterative response surface method refining both
approximation and bounds of the design space is proposed. The capabilities of such a
technique are shown for transonic aerofoil optimisation problems, demonstrating that
the
proposed method is more efficient and more effective than some other state-of-
the-art methods.
As a result of these studies, the aerodynamic efficiency of a large capacity BWB
configuration has been considerably improved by re-designing the external shape to
generate a spanwise loading intermediate between triangular and elliptic. The
longitudinal static stability analysis revealed that the aircraft is stable except at low-
weights with zero-payload. The lateral/directional analyses showed that the aircraft is
stable in roll, but unstable in yaw. Despite that the winglets are found to stabilise the
aircraft, it is directionally unstable without additional vertical stabilisers.
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