Fly Like an Eagle, to the Sea

28.03.13

Categorie: Air, Naval, Robots, Steve Weintz |
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by STEVE WEINTZ

One of the many stimulating concepts John Smart (yes, that’s his name) put forth in his keynote at West 2013 was that of naval applications of biomimicry, or the science of technological analogues to biological function. Dr. Smart chose a very topical example to illustrate the kind of change coming down the pike: folding, morphing wings and control surfaces for drones that look and work very like birds’ wings and tails. Certainly this technology would be extraordinarily useful for launching and landing aircraft from small naval vessels and crowded flight decks. How he asked, might the defense R&D and procurement chain structure its search for such a solution?

Before embarking on such a bold initiative, however timely in the face of oncoming developments, it would be well to review previous approaches to the problem.

Aerodynamic forces and systems impose their own strict limits; missions requiring heavy payloads and long endurance have traditionally demanded large, heavy aircraft, which in turn demand tremendous lift. Naval aviation relies on three factors to get a heavy fixed-wing plane off a ship: thrust, assist and windspeed. The aircraft’s engines at full power supply the thrust; the ship’s catapult, strap-on JATO units, or other launch-assist means add thrust; and the ship’s bow is turned into the wind at speed to generate a high wind over the flight deck.

Even using these three factors, it still requires a very large flight deck to safely operate large, heavy, all-weather jet aircraft at sea. This has imposed a giantism upon carriers and other “aviation-capable” ships for many decades. But like the megafauna of past ages, the giant capital ships are in danger of losing the environment that sustained them as the fiscal and political climates change.

All sorts of ideas have been tried to get fixed-wing aircraft to go up and down. The Navy’s decades-long quest for robust VTOL non-rotary-wing solutions, a drive championed by Adm. Elmo Zumwalt and others, may now deliver on the proof of the Harrier and the Osprey and the promise of the F-35C. On ships where deck space is at a premium such as the DDG-51 and LCS, fixed-wing aircraft have been limited to small UAVs launched by catapult and recovered by snares of various sorts.

If you have no room and don’t want to count on the wind, you can try launching your aircraft like missiles. The British bravely tried the idea during the Battle of the Atlantic with rocket-powered “Hurricats” mounted aboard merchant ships for convoy defense. In the 1950′s the USAF fooled around with the “Zero-Length Launch” concept, even test-firing a piloted F-104 off the back of a truck trailer. (Recovery remained the bedeviling glitch; the test pilot was injured when the giant inflatable mattress prepared for his landing failed to sufficiently blunt the impact.) While no one apparently thought of a manned Regulus missile, the Navy looked at tailsitters, nutcrackers and ducted-flap concepts.

Launch at sea is one thing; recovery is quite another. Eugene Ely’s pioneering 1911 shipboard landing and takeoff presaged all the basics of the art: a sturdy purpose-built flight deck on a large vessel (a 100-foot section of thick oak planks atop the quarterdeck of the battleship USS Pennsylvania), a set of arresting wires (metal cables weighted with gunnysacks) and an arresting hook on the aircraft (a butcher’s meathook).

Wire snares have been tried with surprisingly good effect, allowing specially rigged ships to snag small observation planes; more elaborate patents have detailed workups of fantastic-seeming skycranes that could snatch a hovering plane out of the air and deposit it on a deck. How well such complicated gantries would work during wartime, after a few months of seawater and damage, was left to be explored.

It might be worth looking at the other solution to naval aviation, the seaplane. The aerodynamic and hydrodynamic limitations of the type have in some ways been addressed using techniques borrowed from racing yacht design, and the inherent risks to aircrews can be avoided by using UAVs. At one time the U.S. Navy serviced and operated large multiengine seaplane squadrons from tenders, and equipped every capital ship with at least one catapult-launched seaplane for spotting and recon. In protected waters a small ship could service and operate a large number of seaplane drones such as Warrior (Aeromarine)’s Gull UAV.

If you have neither much thrust nor launch assist, you can sometimes make up for them with windspeed. A carrier turns its great bow into the wind, so that the breeze flowing across the airfoils adds needed lift. Arctic bush pilots have long used windspeed to effect remarkable STOL operations. It might be possible to use the Littoral Combat Ship’s great speed to generate lift for drones launched and recovered from its flight deck. Perhaps some form of armored slat arrangement on either beam forward of the flight deck might channel airflow from the ship’s motion across the deck in a controlled manner.

One old technique seldom revisited: more wing surface. Scott Lowther discovered photos of a very odd wind-tunnel model from the late 1940s, which appears to be a design for a turboprop (even turbojet?) biplane. Design a pop-up X-wing biplane drone, and R2D2 won’t need a Jedi!

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