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Multifunctional structures will provide attractive benefits for
UAVs, with unprecedented weight/power ratios. One approach studied
by DARPA for multifunction structures is the monopolar proton
exchange membrane fuel cell, which can be shaped into a UAV
airfoil skin.
Monopolar fuel cells differ from bipolar
(conventional) fuel cells by having the anodes of multiple cells
sharing a common hydrogen filled internal volume as a manifold.
The cell's cathodes are the outer surface, open to the air.
Individual cells are interconnected by metal conductive elements,
with a single metal grid serving as the current collector and
electrode support for the anode of one cell and the cathode of the
next cell.
Fabricated multifunctional structures achieved an
active fuel cells area of 85 % of the external surface, with an
output of 1 W/gr. or 100mW/cm2). When applied to the skin,
wings and antenna of the MAV, the generated power levels could be
sufficient to power a MAV. By proper selection of materials, it
can be sufficiently strong that no additional reinforcement is
required.
 Another feature of this multifunctional structure is the
use of an integral metal grid, for effective electromagnetic
insulation. Therefore, the structure can be used as an antenna,
for communications or as part of a detector payload. Different
approaches are used to develop multifunction structure plus power.
A constant mass aerodynamic shape structure-battery is being
developed based on Telcordia's PLiONTM battery cells to be used in
an AeroVironment's Black-Widdow MAV. Another approach is studying
constant shape autophagous (self consuming) structure fuel,
consuming solid fuel elements which provide structural stiffness
until they are transformed or consumed for propulsion. Other
approaches consider Variform - variable mass structure-power,
utilizing inflatable wing structure that collapses in a prescribed
manner to maintain aerodynamic function.
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