IEEE Spectrum September, 2016 - 33

did not change the wings' shape throughout flight, but rather
ncouraged by this success, in 2009, the Air Force Research
manipulated FlexFoil on the ground. Over a series of 22 flights
Lab at Wright-Patterson and NASA asked us to retrofit a
above NASA's Armstrong Flight Research Center in Edwards,
Gulfstream III aircraft. This time, the mission would be
Calif., those wings took on shapes that varied their camber
to test FlexFoil on the wings of the airplane rather than danfrom 2 degrees up to 32 degrees down. In other words, the
gling it from below, as we did during the White Knight flights.
wings' trailing edges raised slightly and then rotated down to
For this round, we made a new prototype and replaced each
about the same position used by traditional flaps for takeoff.
of the jet's flaps with a 7-meter span of FlexFoil that ran along the
Afterward, our data showed that FlexFoil produced a maxlength of the wings' trailing edges. This installation is similar to
imum of 5,000 kilograms of lift while it was set into these
what we would do for an installation on a brand new airplane.
positions. It achieved this lift while the aircraft executed a
This prototype was made from common aerospace-grade
range of maneuvers at altitudes of 20,000 to 40,000 feet
materials such as aluminum alloys and composites. We built
under heavy loads. During the tests, the aircraft was subit with design tools and algorithms produced by my team that
jected to a maximum dynamic pressure of 1,875 kilograms
allowed us to arrange curved and straight structural beams
per square meter, which is well above the load that any
into a pattern so that each beam bent like a bow in response to
commercial aircraft would ever experience. In every case,
force. This pattern formed the internal skeleton of a FlexFoil
FlexFoil performed flawlessly.
span. Placing pressure at one or two points on the structure
Based on data from the tests, FlexFoil was able to withstand
changed the entire span's shape depending on how much
temperatures ranging from -53 °C to 82 °C and estimated to
force was applied and where it was placed.
last five times the life cycle of a commercial aircraft. The
The finished control surface weighed approximately
results showed for the first time that practical, lightweight,
110 kilograms (about 240 pounds), which was roughly the
and durable shape-changing surfaces installed on modern
same as the flaps and associated guide tracks that it replaced.
aircraft can deliver top performance under a wide range of
At each end of the span, elastic mechanisms covered in an
flight conditions.
elastomer skin formed an accordion-like bridge to
Our priority now is to make aviation leaders, who
the wing that expanded and contracted as FlexFoil
poSt yoUr
CommeNtS at
are understandably cautious when it comes to radimorphed, with no external joints or hinges to hinder
http://spectrum.
cally new technologies, aware of the advantages and
the flow of air.
ieee.org/
NASA's acoustic experts have estimated that this flexiblewing0916 reliability of our shape-changing wing. Last November,
we entered into a joint venture with Seattle's Aviation
seamless covering would allow FlexFoil to potentially
Partners, which sells efficiency-boosting winglets for airlinreduce a plane's landing noise by 40 percent. The agency
ers. Together, we created a new company called Aviation
was scheduled to conduct flight tests to verify such benefits
Partners FlexSys to commercialize FlexFoil. We plan to test
beginning this month. Airframe noise, which is much louder
it on a commercial aircraft by 2020.
than engine noise during landings, is caused by air flowing
The technology also fits very well with a coming generation
through the gaps between traditional flaps and wings.
of aircraft that, aviation experts predict, will blend wings and
In a conventional airplane wing, the flaps are moved by a
fuselage together in one seamless design. In particular, Boeing
pair of hydraulic cylinders. For simplicity, our prototype was
and NASA have experimented with a futuristic blended-wing
designed to connect to those cylinders as well. As I envision
aircraft, which FlexFoil could transform into a fantastically
the commercial version, a flight control system could change
smooth, quiet, and efficient flier.
the camber of FlexFoil using only one motor per wing, while
In the more distant future, our flexible control surface
twisting its shape would require two (one to pull, and one to
could find applications beyond fixed-wing flight. Any object
push). Because these motors already exist in a typical large
moving through air, or water, could benefit. My colleagues
aircraft wing, the design would not be subject to the addiand I have already developed prototypes of helicopter rotor
tional testing that regulators would require if I were to bring
blades that would morph their leading and trailing edges
a new power source on board.
several times per revolution to improve performance. Early
After the Air Force invited us to outfit the Gulfstream III, it
demonstrations show that these blades can change shape up
took five years to complete the design, installation, ground
to 15 times per second, which could improve a helicopter's
testing, and scheduling required for the first flight. FlexFoil
lift-to-drag ratio and reduce vibration. Other applications
and the aircraft were again fully instrumented by NASA to
might include components for submarines, automobiles,
record flight conditions and measure how well the technoland wind turbines.
ogy endured high wind speeds, low temperatures, and sudIt's not unusual for it to take at least 15 years to develop
den changes in air pressure. FlexFoil alone had 112 strain
and test a new technology for commercial flight, but the
gauges, 60 accelerometers, and enough sensors to gather
turnaround time for these other applications could be much
over 4,300 data points during each flight.
faster if engineers embrace flexible design as a principle that
On 6 November 2014, the Gulfstream III took to the skies of
can deliver more efficient shape-changing forms, as I have
the California high desert, held aloft by the world's first modern
found to be true for flight. n
pair of flexible wings. For safety during these initial tests, we
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SEP 2016

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Table of Contents for the Digital Edition of IEEE Spectrum September, 2016