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Sikorsky Test-Flies X-Rotor Helo
Sikorsky rolled out its ^-rotor helicopter prototype in September, and test-flew it in November. The X-wing’s rigid rotor allows it to rise vertically, then it locks in place like a Wtng and uses a separate engine this case, two pod-mounted General Electric TF34s) for forward propulsion. In this way, it achieves a much higher efficiency in orward flight, but can still rise and hover like a helicopter. The ultimate A-wing would use a single convertible engine, which could provide shaft
Wsepower to the rotor and thrust for forward propulsion in varying Proportions. Although the experimental X-wing employs separate rotor engines (two General Electric T58s), the TF34 is being developed as a c°nvertible engine, using a variable-geometry fan module.
The X-wing may be an alternative to tilt-wing (V-22 Osprey) technol- °8y. In each case, the goal may be to achieve higher and more efficient orward speed than a conventional helicopter, without losing the ability 0 hover for protracted periods. Conventional helicopters are limited in °rward speed partly because the greater the speed, the greater the differ- enhal in lift between advancing (effective speed equals bladespeed plus airsPeed) and retreating (effective speed equals bladespeed minus airsPeed) blades. Typically, blade-pitch is varied to compensate, but the range of effective bladespeeds (like the envelope of airspeeds an airplane Can tolerate) is inherently limited.
The most helicopter-like alternative is the advancing blade concept—a c osely-coupled pair of coaxial (opposite-rotating) rotors—in which ■Post of the lift comes from the two advancing blades; the limited lift of e retreating blades can be accepted because the opposite rotation puts an advancing blade on each side of the helicopter at all times. Efficient 'gh-specd flight also may require the addition of stub wings to add to 0verall lift after takeoff.
None of these alternatives is new. Hybrids were once called conver- 'P anes; some flew three decades ago. Eastern Airlines tested a tilt-wing a|rplane in the eastern corridor more than a decade ago. They have be- c°me much more practical as lightweight, high-strength materials (e g., 0r blades) have become more common, and as turbofan and turboshaft Cngines have become substantially lighter.
hybrid aircraft are attractive for several naval missions, partly because ney can operate from relatively restricted spaces on board surface com- atants or more easily from crowded carrier decks. High forward speed wPUld be valuable in, for example, Marine Corps amphibious attacks (to achieve surprise), and in antisubmarine warfare (to reach a datum T"ckly). in the latter case, speed is likely to become more important as Prospective enemy submarines become faster and quieter, i.e., as search around a datum becomes more difficult, so that the premium on quickly Caching the datum increases.
New ASW Missile to Carry Murene
Several new systems were announced at the French Le Bourget Naval ^Position late in October, including a new stand-off antisubmarine war- are (ASW) missile—to enter service about 1990—to carry the new ( Ufene lightweight torpedo out to a range of about 22 nautical miles, i .e.
0 a typica| Mediterranean convergence zone range. Murene is a Mark 46 replacement, reportedly with alternative search and attack speeds of 38 o 50 knots, respectively, a range of six nautical miles (12,000 yards), dntl a maximum operating depth of 1,000 meters (3,280 feet). It weighs
285 kilograms (about 630 pounds).
The current French ASW missile, Malafon, is roughly equivalent to the Australian Ikara. It carries a 21-inch torpedo out to direct-path range— about 10,000 yards. In the past, longer stand-off ranges have generally been avoided because sonar data from the convergence zone was too vague to use as the basis for torpedo homing. The French announcement suggests that Murene will have a sufficient acquisition range to overcome this limitation or that cross-correlation between hull and towed arrays (or between different ships) will increase the precision of sonar location.
MSH Killed; Lericis Funded
Congressional action in October made official a Navy action in August to kill the surface effect minehunter (MSH) program, although $5 million in remaining funds are to be spent on further studies of surface effect technology. It was hoped, as shown in earlier British studies of flexible- skirted hovercraft, that the air cushion could shield a small minehunter from the shock of mine explosions. The U. S. MSH program suffered from excessive weight, and it was by no means clear that a rigid-sidewall craft would enjoy the same advantages as the British flexible-skirt craft.
Instead, the Navy is to buy a U. S.-built version of the Italian Lerici- class minehunter, paying for the design and lead-ship construction with unexpended fiscal year 1986 MSH funds. The new ship has been designated the MHC-51 (MHC is a designator used in the 1950s for converted and specially built minehunters). Ironically, a larger version of the Lerici proposed by Marinette lost out in the original MSH competition; it was considered too large and too expensive. It now appears that the MSH designers underestimated the size required to accomodate sophisticated minehunting gear.
The Lerici was laid down in 1978 and entered service in 1985. She displaces 470 tons and is built of glass-reinforced plastic. Presumably, a U. S. version would be somewhat larger because the U. S. minehunting suite includes a larger minehunting vehicle.
Congress did attempt to revive the other current U. S. Navy surface effect ship program, the medium special warfare craft (SWCM). The SWCM reportedly encountered some weight problems, but its primary problem was the bankruptcy of its builder, Rohr Marine Incorporated (RMI). When RMI filed for liquidation in August, the lead ship was about 65% complete. Congress called for the ship to be completed “expeditiously,” preferably by a firm with surface effect ship experience, with an automatic option on the planned fiscal year 1987 SWCM.
Some of the congressional support for the SWCM can be traced to increased interest in special (in this case, SEAL [sea, air, land forces]) operations. Nineteen SWCMs were planned: the lead ship in fiscal year 1984, three in fiscal year 1986, six in fiscal year 1987, six in fiscal year 1988, and three in fiscal year 1989. However, the fiscal year 1986 authorization was shelved owing to difficulties in building the craft, and only one is to be requested in fiscal year 1987.
The RMI staff consisted largely of survivors of the most ambitious U. S. surface effect program, the “3K SES” a 3,000-ton surface effect ship of the 1970s. RMI sought new but less ambitious projects. The only major current U. S. Navy project in this area is the air cushion landing craft (LCAC) built by Bell-Halter (which also built three 110-foot, rigid- sidewall air cushion craft for the Coast Guard). All of these craft have
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Pr°«edinRs / January 1987
Spanish Navy to
i
encountered problems, and some critics have suggested that the Navy may have to retreat to more conventional high-speed hull technology for the SWCM and perhaps even for part of the LCAC mission. For example, the LCAC was chosen after cancellation of a fast. 130-foot, planing medium landing craft (LCM[9]), which reflected new rough-water, planing-hull technology developed in the early 1970s. The LCM(9) was too expensive and offered too little payload, while the LCAC combined the ability to cross the beach with a greater payload and much greater substained speed.
Spanish Navy to Install Searchwater
Several recent developments in airborne early warning (AEW) deserve notice. Early next year, the Spanish Navy expects to place British Searchwater radars in Sikorsky SFI3D helicopters on board its two vertical/ short takeoff and landing carriers. It will, therefore, be the first export user of a system originally developed (in great haste) for the Royal Navy during the Falklands Conflict. The Thom EMI thorn emi Searchwater is unique; the only other Royal Navy configuration naVal shipboard AEW system—the U. S. Grumman E-2C—can fly only from a large carrier. Other potential customers include the Indian Navy (which recently bought the British carrier Hermes and operates another ex-British carrier, the Vikrant), the Brazilian and Argentine navies (each of which operates one ex-British carrier), the Italian Navy, and even the French Navy, the carriers of which are too small to accommodate the E-2C.
Helicopterbome AEW systems are limited in two ways. First, the endurance of the helicopter is limited because it is inherently inefficient in terms of fuel consumption. Thus, it is relatively difficult to maintain continuous coverage. Second, the helicopter’s altitude range is limited, and thus its radar is limited in range, particularly against low fliers.
These two considerations make airships increasingly interesting, particularly because some modern radars can function for extremely long periods without maintenance. Thus, a manned or unmanned airship might accompany surface ships or small carriers for the length of an extended deployment, descending toward the surface (if at all) only to refuel. The U. S. Navy considered just such a system in the early 1970s in connection with the sea control ship (which was clearly too small to accommodate an E-2C).
Another exotic future AEW vehicle would be a long-endurance, remotely-piloted vehicle, presumably relying on a conformal-array radar (e.g., mounted in the leading edges of its wings). Such a radar might scan electronically, and it would not have to be very heavy. Using existing technology, a carefully built lightweight unmanned airplane can enjoy extraordinarily long endurance, and yet might be launched vertically (since there would be no pilot to shield from untoward acceleration) and recovered by parachute. Recent press reports of exotic RPVs suggest this possibility. Presumably, the RPV could maneuver against the wind or bypass bad weather.
The Marine Corps is seeking its own AEW system. Reportedly, the alternatives are the E-2C (which requires a prepared field ashore and cannot fly from the big amphibious carriers), an airship, and a classified program.
Meanwhile, the intense competition for a British AEW system continues; alternatives have been narrowed to the existing British Nimrod AEW.3 and the Boeing E-3. The British have already rejected the Grumman E-2C, the Lockheed AEW Orion (which is still seeking export customers), and an airship. The British planned to evaluate the two finalists in collaboration with a French team, as France may decide to buy the airplane selected, reducing the total program cost. Thirteen AEW Nim- rods have already been built. From a naval point of view, the impact of any British decision might be twofold. First, the British will probably have to make a major new investment just as Trident submarine spending escalates. The major victim may well be the British surface fleet. Second, continued failure to sell the Lockheed AEW version of the Orion may reduce the chances that many smaller navies will be able to enjoy long-endurance airborne radar coverage. Cheaper alternative AEW aircraft, such as an adaptation of the Britten-Norman Islander commuter transport, have nothing like the range, endurance, or data processing power of the larger E-2C and AEW Orion.
Help Wanted!
Work is already in progress for the next edition of the Naval Institute Press’s Combat Fleets of the World and the International Navies Issue of Proceedings. Photographs for these internationally recognized guides are needed—can you help?
- Surface and aerial views of current warships, auxiliaries, service craft, and naval aircraft from all the world’s navies, coast guards, and paramilitary forces are needed.
- Unencumbered backgrounds, like those in the examples shown, are preferred.
- Overall views are most desirable, although close- up depiction of new equipment is also helpful.
- Black and white photographs, up to 8" x 10", are preferred.
- Please include the day, month, and year the photograph was taken, as well as the appropriate crediting information.
- Also welcomed is information in support of the text; shipbuilders are encouraged to forward information on their new vessels, for example.
Please submit your photographs and/or information as soon as possible to:
Editor, Combat Fleets of the World
Naval Institute Press
U. S. Naval Institute, Annapolis, MD 21402
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Proceedings / January 1987