In 1989 Scaled Composites was approached by
the Northrop Corporation for the structural design and fabrication
of a Radar Cross Section (RCS) model of the B-2 aircraft.
There was considerable concern over making a large enough
RCS model to ensure accurate full scale fidelity while trying
to remain within the weight and gust load limits of the
measuring facility. A 4/10 scale model (with a resulting
wingspan of about 70 ft) was believed to be the optimum
size for accurate measurement. The model would have to be
disassembled into sections for crating and shipment from
the fabrication facility to the test site, and would have
to be easily reassembled on site while maintaining the step
and gap tolerances required for testing. The model would
also require representative engine inlets and outlets and
top and bottom rotator assemblies.
Scaled elected to use its proven sandwich
panel structural arrangement with carbon fiber/epoxy skins
and PVC foam cores, virtually identical to a manned aircraft.
The use of sandwich panels provided extremely stiff outside
skins, which accurately maintain their contours, even when
exposed to personnel walking loads.
Inspections showed the model to be well within
the contour, wave and step and gap tolerances. The complete
model structure weighed 6,700 lb, which was considerably
under the weight goal.
This entire effort was accomplished on schedule and at approximately
2/3 of the original predicted budget on a CPFF contract.
Scaled was given a first-ever Northrop vendor award for
this effort.
Although this was Scaled's first experience in RCS model
fabrication, we found that our standard aircraft fabrication
methods were ideally suited to these special requirements;
this also gave Scaled an excellent opportunity to develop
its capabilities in a technically demanding specialty. We
also learned that LO techniques are not necessarily cost
drivers; our basic structural approach naturally results
in very accurate, smooth surfaces, with excellent step,
gap, and wave performance.
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