Aerodynamic Design of Unmanned and Scaled Supersonic ...

K. Yoshida and Y. Makino
airplane. The main part of the improvement was based on how to simulate the operation
condition of engine, that is, how to estimate inflow into the intake and outflow from the
nozzle as precisely as possible. In general, we often analyzed the flowfield around the
airplane using the so-called flow–through-nacelle condition as an approximation. To validate
this approximation was one of the targets of developing advanced design technologies.
1) Concepts related to the aerodynamic design of NEXST-1 airplane
In order to improve subsonic aerodynamics, a higher aspect ratio wing was desired after
designing the NEXST-1 airplane. Keeping the same kink position of both leading and trailing
edges for simplicity, we selected a modified arrow planform with the aspect ratio of 2.4 with
0.2 higher than that of the NEXST-1 airplane. However, the increment of the aspect ratio led
to reducing the swept angle of outer wing. Therefore, the outer wing had a supersonic leading
edge and every section had a pointed leading edge to reduce the profile drag.
A warped wing was designed according to the same design procedure as the NEXST-1
airplane without nacelle condition. The NLF wing design was applied at inner wing only
because the outer wing section had a pointed leading edge. The shpae of the target pressue
distribution was the same as that of the NEXST-1 airplane, but the pressre level was different.
In general, it is difficult to incorporate any influence of shock waves due to the nacelles into
the target pressure distribution. Therefore, the design C L for warp design was specified by
removing the increment due to compression lift generated by two nacelles from the total lift.
JAXA’s CFD calculatons estrimated that the increment of compression lift was about 0.06 at
the total lift of C L =0.1. Therefore, the NLF wing design was conducted at low lift condition,
that is, C L =0.04 without nacelles. In the design process, geometry modification was also
performed for the simple configuration without nacelles, but CFD analysis for estimating flow
characteristics was conducted for a complete configuration with nacelles.
2) New design concepts
An axisymmetrical area-ruled body for the NEXST-2 airplane was also designed by the
same design procedure as the NEXST-1 airplane under the the following constraints:
minimum diameter, minimum volume and maximum length. These constraints made it
difficult to apply the exact area-ruled body concept based on linear theory because of the
existence of two large engine nacelles. In addition, the design concept besed on linear theory
can not treat the influence of shock and expansinon waves due to intake and nacelle. Therfore,
the area-ruled body concept need to be expanded to include any nonlinear effects.
The key point of the non-axisymmetrical area-ruled body concept is to optimize the upper
and lower geometries of fuselage independently, using a certain mathematical fomulation of
two kinds of radial distributions as design variables. And total pressure drag was chosen as an
objective function. In addition, the overset grid method is also very useful in optimizing a
complicated wing-body configuration with such large nacelles. The optimum configuration
designed using our CFD-based optimization method was storngly influenced by the initial
configurtion. We designed the initial configuration using present aerodyanimc design
technique of the NEXST-1 airplane.
In the develpment phase of the method, we designed a non-axisymmetrical optimum area-
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