Barrel-rolling to the bottom of the sea

DN Staff

April 22, 1996

7 Min Read
Barrel-rolling to the bottom of the sea

Graham Hawkes may quite possibly be the world's deepest thinker. Aeronautical engineer, submersible designer and pilot, and smitten explorer of the fathomless oceans, he's designed the first hydrobatic submersible, Deep Flight 1 (DF-1). Capable of plunging--or barrel-rolling or looping, if desired--to 1,000m depths, the winged, torpedo-shaped craft represents a fundamentally new type of submersible.

Its design promises to open a porthole into the earth's most uncharted regions. Yet, Deep Flight's strength isn't numerous scientific breakthroughs, but rather, the unique application of proven technologies to a novel, unorthodox design. Quite simply, it flies.

"The real innovation with Deep Flight is throwing away the buoyancy system," says Hawkes. Conventional submersibles move up and down like elevators, dropping ballast to change buoyancy state usually just once per voyage. By contrast, DF-1 maintains a slight, but constant positive buoyancy. To descend, it harnesses the downward lift generated by two stubby, inverted airfoils attached to its flanks. No weights; no water ballast. The method is elegantly simple and infinitely renewable.

"I think this could completely change the way people think of submersibles and the ocean in general," says Hawkes of his creation. "It's like the Bell X-1, the first aircraft to break the sound barrier. Just a few years later came Concorde. With submersibles, people still see the Bell X-1, and not the Concorde."

Depth breaker. Deep Flight's barrier to break isn't sound, of course, but depth. More precisely it's the Challenger Deep, a 36,198-ft chasm southwest of Guam in the Marianas Trench and the deepest point on earth. "It's only seven miles down," rationalizes Hawkes. "Deep Flight would take no more energy to go those seven miles than it would to go seven horizontally. The limit is entirely mental."

Just two men have ever confronted that limit and visited Challenger Deep. Jacques Piccard and Donald Walsh, dangling from a thin wire cable, were lowered there in the bathyscaph Trieste in 1960. "We've been to the moon," observes Project Engineer Bob Whiteaker, "yet, here we live on an ocean planet, and the only time we've been to the very bottom was 35 years ago."

Deep Flight 1 won't change that. It's actually a fully functional prototype created to prove that the winged-flight concept works. Beginning in 1997, engineers will apply what they've learned to the design of Deep Flight 2, a slightly larger submersible built of carbon fiber and exotic ceramics that can withstand the pressures at 11,000m.

Design for the deep. For now, what separates flesh from fish is four inches of fiberglass hull. Whiteaker and a staff of engineers and volunteers wound it in a continuous wrap around a 26-inch-diameter cylindrical mandrel that now lies rusting outside the Scientific Search Project headquarters. The search and salvage operation is one of two Hawkes companies involved in Deep Flight. The other, Deep Ocean Engineering, is a world-renowned submersible manufacturer, co-owned with marine biologist Sylvia Earle. Due to this partnership, there are actually two Deep Flight 1's, both identical.

A hemispherical cap--also wound of fiberglass--forms the rear of the pressure vessel. It contains a hole at its apex sealed with a tapered aluminum plug. Three 20-strand electrical cables carry instrumentation and control signals through sealed bores in the plug. Uniquely, no mechanical linkages penetrate the hull, a first for any submersible.

The pilot lies prone on a molded fiberglass body pan inclined at 13 degrees--an empirically derived value that lends some comfort to the position. A harness provides additional restraint to prevent the pilot from careening about the cabin during particularly athletic maneuvers.

A $20,000 acrylic dome cast by Reynolds Polymer Technologies, Grand Junction, CO, presents a panoramic view of the depths. To maintain an even stress distribution, the dome tapers from 4.0 inch thick at the base--where it's bonded to an aluminum collar--to just 1.7 inches at the apex. Acrylic's index of refraction closely matches that of sea water, minimizing visual distortion and allowing the dome to seemingly disappear while submerged.

A full fiberglass fairing surrounds the pressure hull and shrouds the support structure for the wings, tail fins, propeller inlets, and side-pods. Carbon-fiber cloth reinforcing the tail section was added as part of a redesign intended to stiffen the structure.

Propulsion system. A pair of 7-hp, adjustable-speed dc electric motors, supplied by Baldor, Fort Smith, AZ, power thrusters that drive DF-1 to a top speed of 10 kts. They draw current from two banks of lead-acid, gel-cell batteries housed in rectangular pods on either side of the hull. To guard against pressure and corrosion, the motors are filled with oil. A pressure-compensation system also protects the exposed batteries. It consists of Tygon tubing from Norton Performance Plastics, Akron, OH, joined to hollow "T" connectors plugged into each battery cap. The tubing runs to a bladder filled with hydraulic fluid.

Hawkes' design exceeds the limited storage capability of the current batteries; he's actively looking for advanced versions to replace them. At full throttle, he expects 20 to 30 minutes of power, though cruising at the minimum control speed of about 4 kts should greatly increase that.

Engineers took an unusual approach to environmentally protect the electronics. In a typical submersible, they are potted and sealed in aluminum cylinders, with only wires penetrating the case through sealed openings. This "black box" method makes electrical failures particularly difficult to diagnose.

"Graham said, 'why not make the cylinders out of acrylic instead?'" says Whiteaker. "We added status LEDs to the boards, and now we can troubleshoot visually without having to open the bottles."

Deep-sea flight control. Pitch and roll are handled by a pair of elevators, similar to an aircraft, powered by two screw-drive actuators. Pilots feed commands to the control surfaces and thrusters via switches and buttons on two pistol-grip joysticks. The joysticks are hard-mounted to give the pilot something to hang on to.

A multifunction instrument panel, still under design, lies between the joysticks. It displays all essential heading, speed, depth, and status information. It's tied to an on-board computer system that also governs throttle and steering inputs. "This is the only submersible I know of that has an electronic flight-control system," Hawkes claims.

The two main wings extend 24 inches from each battery pod, giving DF-1 an overall width of 8 ft. Though the wings are fixed, adjustable flaps on the trailing edge can be preset to produce a range of lift and trim conditions. The inverted standard NACA airfoil shape generates sufficient force to pull Deep Flight down at 480 fpm, or ascend, assisted by natural buoyancy, at 650 fpm.

The advantages of this system over a fixed-ballast design are enormous. "You can generate 200 lbs of downforce, even poorly, with an airfoil having a 10-to-1 lift-to-drag ratio," says Hawkes. "So, I increase drag by 20 lbs to have 200 lbs of vertical force, which is completely renewable and controllable." A water-ballast system, such as that used by nuclear submarines, allows repeated, controlled descents, but proves impractical operating against 16,000-psi water pressure at 36,000 ft.

Attached beneath each wing on pylons reside two 6.25-inch-diameter cylindrical pods that house forward obstacle-avoidance sonar, side-scan sonar for search operations, and--surprise--a ballast system.

An adventurer, but not a fool, Hawkes incorporated an emergency weight-drop mechanism into the pods. It consists of lead ballast attached to a collet retained by six small, stainless-steel balls around its periphery. A spring-loaded, stainless-steel collar surrounds the balls. Rotating the collar .25 turn allows the balls to move radially outwards, releasing the collet. With Deep Flight's electrical system running, a solenoid holds the collar in place. Should the power fail, however, the collar turns, the ballast drops away, and the submersible bobs to the surface.

Life support consists of oxygen bottles, a CO2 scrubber system, and medical monitors that measure the partial pressure of oxygen. With the hull's small volume, the system can maintain life support for 24 hours.

Design aids. Though no CAD program has proven flexible and fast enough to keep up with Hawkes' creative, conceptual brainstorms, he and the engineering staff use AutoCAD for detail design. "He's the typical mad scientist," says Whiteaker of Hawkes. "He can't keep track of his wallet, but he can design a submarine in an hour."

A labor of love, the Deep Flight crew has constructed the pair of submersibles over a period of eight years at a cost of about $1 million. Ready to soar, at last, the submersibles are currently being put through trials in San Francisco Bay.

Sign up for the Design News Daily newsletter.

You May Also Like