IEEE Spectrum May, 2007 - 34

mation is proportional to the electric field's strength, and once
the field is removed, the sheet returns to its original shape.
The solid-state aircraft will have wing-shaped sheets of the
material sandwiched between two metal grids: an anode grid on
the bottom and a cathode grid on top, each containing thousands
or even tens of thousands of electrodes. A computer control system will supply voltage to the electrodes. By applying different
voltage levels to different portions of the sheet, we can make it
change its shape to flap. Our hope is that with a very fine grid
we'll be able to emulate the wings of flying vertebrates.
We're far from that level of control. In our first test, we
started small, with two 5-centimeter-long IPMC strips [see
photo, "Wings on a Stick"]. We then attached control electrodes
to each little wing and applied a variable voltage. It was fascinating to see this primitive contraption beating its wings fairly
well, even at high flapping rates.
We then built a larger model with 46-cm-long wings. This
required producing newspaper-size sheets of the IPMC material-
to our knowledge, the largest ever made. Alas, this prototype
responded erratically to the electric field. We weren't surprised
by the problems, given that IPMC is still a relatively new material; making it in large sheets requires a good deal of trial and
error, with some batches working better than others.
We expect to solve these fabrication problems over the next
several years, and then we'll begin the next step: integrating
the IPMC material with layers of photovoltaic and lithium-ion
or lithium-polymer materials. Our plan is to apply the same
thin-film coating technology that is used to make certain semi-

conductor, optical, and ceramic devices. Thin-film solar cells
have been around for years, although they're still expensive, and
thin-film batteries are beginning to emerge from the lab. For the
solid-state aircraft, we hope to produce sheets of those materials
that can bend and twist extensively without breaking.

iF We build it, Will it Fly? To answer that question, we considered two variables: the power the aircraft requires to fly and
the power available in the environment where it's deployed.
Obviously, if the former is greater than the latter, the plane
won't be able to get off the ground.
Because the solid-state aircraft is powered by the sun, the
amount of power available will depend on where and when it is
flying, as well as on the characteristics of its solar cells. Using
high-performance solar cells, with a high specific power rating of 1 kilowatt per kilogram and a conversion efficiency of
10 percent, our calculations showed that the maximum available
power on Earth at an altitude from 1 to 35 kilometers would be
90 watts per square meter of solar cell. On Venus, it would be
150 W/m2 at an altitude of 53 to 82 km, and on Mars, 55 W/m2 at
1 to 7 km above the surface.
The aircraft's power needs, on the other hand, depend on its
size and weight, the wing's shape and motion, and the power
required by onboard systems. Key parameters in this calculation
are the wings' lift and drag coefficients (which we determined
in our computational-fluid-dynamics analysis) and the plane's
weight (2 kilograms per square meter for the IPMC, for example).
We used a range of values for the length of the wings and the

MorpHing to Fly

other groups working on shape-change aircraft
FlAPPer: In a test flight last
summer, the University of Toronto's
flapping plane flew for 14 seconds
at about 1 meter above the runway.

Flexsys Ann Arbor, Mich.

University oF FloridA Gainesville

Founded by Sridhar Kota, this company is developing a wing capable of curving its trailing edge
downward or upward based on a lightweight
aluminum structure that flexes on command.
More: http://www.flxsys.com/Projects/MACW

KonKUK University seoul, south Korea

One of the projects at the university's Artificial
Muscle Research Center is the development of
a biologically inspired flapping robot powered
by piezoceramic composites or electroactive
polymers. More: http://artm.konkuk.ac.kr

ieee Spectrum | May 2007 | NA

Researchers at the university's Center
for Morphing Control led by Rick Lind are
investigating the time-varying dynamics and
nonlinear control schemes of small and micro air
vehicles. More: http://mav.mae.ufl.edu/morph

University oF Bristol england

A group led by Michael I. Friswell is using
computer simulations and wind-tunnel tests to
study concepts like adaptive winglets that could
replace conventional control surfaces. More:
http://www.aer.bris.ac.uk/research/morphing

University oF toronto Canada

A team led by James DeLaurier has built a
piloted flapping aircraft [see photo]. The wings'
center section moves up and down by means of
pylons connected to a small internal-combustion
engine. More: http://www.ornithopter.ca

www.spectrum.ieee.org

uNiverSity of toroNto

Cornell University ithaca, n.y.

A team led by Ephrahim Garcia is researching
bioinspired aircraft capable of macroscale
structural shape changes, as well as flapping
mechanisms, tail configurations, and novel skins.
More: http://morphing.mae.cornell.edu

http://morphing.mae.cornell.edu http://artm.konkuk.ac.kr http://www.aer.bris.ac.uk/research/morphing http://www.flxsys.com/Projects/MACW http://mav.mae.ufl.edu/morph http://www.ornithopter.ca http://www.spectrum.ieee.org

Table of Contents for the Digital Edition of IEEE Spectrum May, 2007