Specifically, the team had been developing the Wrasse-inspired Agile Near-shore Deformable-fin Automaton, or
WANDA, a portable AUV with robotic fins. However, the
design was not conducive to long distance travel, because
while flapping is a highly maneuverable method of traveling
underwater, it’s not particularly efficient for traveling at fast
speeds. Thus, the team turned to another biological muse,
The resulting vehicle design is capable of flying and
swimming, and is aptly named Flimmer.
“You can look at any number of birds – there are a lot of
biologic flyers that also swim – they all seem to solve the
splash down and the underwater part differently,” explains
Dan Edwards, Aerospace Engineers, Vehicle Research
Section, NRL. In fact, flying fish and even squid get out of
the water using unique traits.
“I don’t know of anyone who has thought through
combining underwater flapping propulsers into a flying
vehicle,” adds Edwards, although he admits that nature has
solved this problem in ways that designers and engineers
have yet to answer.
Today, the design features four servo actuators that
control four fins on the vehicle’s 3D-printed plastic housing,
which can rotate independently. The combination of these
maneuvers is what controls the vehicle under water, but
making it fly is the tricky part, according to Edwards.
Into the Air
Flimmer has several takeoff options, including an air
launch from a larger plane. During testing, the NRL team
launched it off of the ground from a pneumatic launcher,
which Edwards describes as “a giant glorified potato
cannon” set up specifically for launching vehicles.
“Once airborne, Flimmer has a small electric motor in the
back that acts as a pusher,” he adds. The motor is powered
by on-board batteries which provide enough energy to hold
altitude and climb.
In order to be flight capable, the team had to find a
balance between an underwater vessel, in which weight is
not normally a concern, and an airplane, in which weight is
extremely critical. “It’s crazy how much effort aircraft spend
to reduce the smallest mass fractions,” explains Edwards.
As such, the team had to make a lightweight vehicle that
would still be capable of surviving a tough splashdown.
While the trade between weight and function can be
solved with math, according to Edwards. “The tricky part is
how you get it into the water.”
As the vehicle flies over water it’s traveling at a high
speed in a low density medium. To transition underwater,
the vehicle must slow down and enter a much thicker
Nature has long been an inspiration for designers and engineers. So when researchers
at the U.S. Naval Research Laboratory
(NRL) were experimenting with flapping
propulsion mechanisms for autonomous
underwater vehicles, they naturally turned
to fish for inspiration.
By Melissa Fassbender, Editor
FLIMMER IN THE SKY
KEEPS ON SOARING