Stephen J. Mraz
Senior Editor
It’s taken Graham Hawkes more than 20 years to
realize a lifetime goal: to build and “fly” an underwater
vehicle, and possibly make some money doing
it. He and his company, Malibu-based Hawkes
Ocean Technologies, are now selling their fourthgeneration
submersible, the Super Falcon. It’s a far
cry from their first sub, Deep Flight I, but they both
rely on the same principles to maneuver through
and under the water.
Downward lift
Hawkes’ submersibles, like airplanes, have wings,
ailerons, and rudders, but the wings
are upside down compared to a plane’s.
With electric motors and propellers
providing thrust, the wings travel
through the water generating downward
“lift,” keeping the slightly buoyant
craft beneath the surface. To go
deeper, you push the joystick control
forward, the nose angles down, and
the craft descends. The newest craft,
for example, the Super Falcon, can
dive at 320 fpm and climb at 600 fpm.
In the hands of a trained pilot, the craft
can bank through turns, snap rolls,
and loops. And if the craft slows down
too much, the wings stall, lose lift, and
the sub rises to the surface. Hawkes
even coined a new word for this type
of underwater flight: hydrobatics.
“Conventional subs are like underwater balloons, adjusting their buoyancy in the
medium, which is water not air, to ascend and descend,”
says Hawkes. “But we do underwater flight.
We’re more like planes than balloons.”
Heck of a Hull
One of the most startling innovations in the Super
Falcon is its hull. Pressure hulls in conventional
submarines and bathyspheres have round cross sections
because that shape evenly distributes the hoop
stresses generated by outside water pressure. But if
the hull’s circular shape deforms by 1 or 2%, water pressure instantly crushes the hull if it
is deep enough.
The Aviator, the predecessor to the
Super Falcon, has a cast-aluminum
hull that conforms roughly to the pilot’s
shape, but still has circular cross
sections. “It’s a curved and tapered cylinder,”
says Hawkes. “Sort of a banana
with round cross sections.”
Super Falcon’s hull, a prebuckled
pressure hull according to Hawkes, is
made of a proprietary isotropic composite
that is incredibly strong and
relatively light. “We used the strength
of the material to break the rule about
round cross sections,” says Hawkes.
“It let us build a shape that better fits a
recumbent pilot. And compared to the
Aviator, there’s more shoulder room
and a few extra inches everywhere it
matters for pilot comfort. And even
if the hull deforms under pressure or
impact, it won’t collapse.”
The pilot and passenger ride in a
hull pressurized to within about 1% of
normal atmospheric conditions and
breath normal air. Outside metal panels
make up the body or skin and they
are attached to the hull. The body provides
the aerodynamic form and covers
most of the equipment, which is also housed outside the hull. But the outside skin
is not watertight; rather it lets water in, keeping
pressure equalized inside and outside the body.
Of course, this means components have to withstand
enormous pressures. (The Super Falcon is
rated for 1,000 ft, where water pressure is 460 psi,
but has a safety factor of two built in to the rating.
So the hull should not crush until it gets below
2,000 ft, where pressure is 905 psi.)
The electric motors that power the propellers,
for example, are filled with oil, making them immune
to pressure. And in the Aviator, the leadacid
batteries were similarly filled with oil. “The
lead-acid chemistry doesn’t care about pressure,”
says Hawkes. “Our pressure-compensated versions will work all the way down to
the bottom of the ocean. But if you
take the submersible inverted, in
effect flying upside down, the acid
and oil switch places and the battery
doesn’t work anymore.”
The newer Super Falcon uses
lithium batteries that rely on lithium-
iron-phosphate chemistry instead
of the older lithium cobalt.
“The newer batteries are safer because
they are not as much at risk
of thermal runaway,” says Hawkes.
“They also have a better life expectancy
that is rated in thousands of
cycles. The batteries may well outlive
the rest of the submersible.”
The batteries are also solid and in
a sealed housing, so they are also
ideally suited to the pressures of the
deep.
Keeping it safe . . .
Another difference between
Aviator and Super Falcon is the flight system. In
the Aviator, flight controls were mechanical with
direct linkages, Super Falcon uses lighter, morecompact
fly-by-wire technology and a three-axis
joystick. Other instruments include a compass
and depth gage, pitch-and-roll indicators, speedometer,
battery voltage, current draw and electrical
leakage status, and critical life-support parameters
including cabin pressure and air quality. And
life support, mainly air, is also microprocessor
controlled in the newer craft. “It’s relatively easy
and inexpensive to get hardware and software
that monitors air quality 1,000 times per minute
and keeps pressure inside the hull to within 0.5%
of that at sea level,” notes Hawkes.
For communication, Hawkes uses UQC, a
two-way communication system developed by
the Navy for use by scuba divers and submarine
crews. It uses a high-frequency acoustic carrier
modulated by the voice signal. The high-frequency
carrier gives better voice quality but limits
range. “Range depends on power, so for the
Challenger, which was supposed to go 37,000 ft
down, we had a custom UQC built which has the
power to span that distance,” says Hawkes.
Inside, the pilot and crew are in a shirt-sleeve
environment with no heater or air conditioning.
But Hawkes admits that in the Bahamas where
his underwater flight school is located, the tropical
waters, coupled with sunlight hitting the canopy,
can make it uncomfortably warm inside the
sealed submersibles. But there are no heaters or
air conditioners in his designs. There are no fire
extinguishers either, so far.
“Fire in small enclosed spaces is a terrifying
idea,” says Hawkes, “So to minimize the
risk and reduce complexity, we just don’t let
anything in the sub that resembles a fuel or ignition
source. For example, we limit electrical
current to 4 A for inside the hull and put all
high-power circuits outside the hull.”
The craft also lacks an emergency exit.
“Not having emergency-egress procedures
is common on deep submersibles,” explains
Hawkes. “The pressure differences from inside
to outside the hull are just too large.”
Instead Hawkes relies on his ultimate safety
feature: the fact the his craft surfaces if power
is lost, all motors fail, or the propellers fall off.
Of course, this also means the craft cannot be
stopped to observe life and geology outside,
nor can it “rest” on the bottom of the sea.
But Hawkes still takes safety seriously.
When it comes to batteries, for example, he carries a full-sized redundant backup pack outside
the hull with the normal battery pack. “Internal
backup batteries are often as small as possible to
maximize available room and minimize weight,”
notes Hawkes. “But if you are in an emergency
and need power for life support or communications,
it’s best to have a backup with enough
power for everything you might need.”
. . . But exciting
Hawkes realizes he is pioneering a new form
of underwater travel and he has a bit of the daredevil
in him. He seems intent on making sure the
experience of taking one of his creations out for a
cruise is more like riding a performance motorcycle
than a station wagon, more like flying a jet
fighter than an airliner.
“One of my fears with the Aviator when we
were testing it was that it would be so docile as a
flyer that it would be dull to drive,” says Hawkes.
“So I wanted it to stall with a bite, so you actually
had to fly the sub. And the first time I stalled
an Aviator, got going too slow to counter the
buoyancy, the sub rocketed up to surface out of
control. I was quite delighted with that. But I’ve
always knows that this technology, the birth of
underwater aviation, barnstorming beneath the
waves, would have an interesting future. Should
be a heck of a lot of fun.”
Make Contact
Hawkes Ocean Technologies,
deepflight.com