Graham Warwick/WASHINGTON DC
VALUEFORMONEY is an overused phrase, but it is the central tenet of the US Marine Corps' programme to upgrade its Bell AH-1WSuperCobra and UH-1N Huey helicopters for continued service through to 2020. To gain approval for the programme, the Marines had to prove that the upgrade would be cheaper than buying and operating new McDonnell Douglas AH-64 and Sikorsky CH-60 helicopters. The key to providing that proof was the commonality between the two aircraft which will result from the upgrade.
The AH-1 gunship was derived from the utility UH-1 which made its mark during the Vietnam War, but subsequent development of the two helicopters diverged. Now the two paths are being brought together again, and the upgraded AH-1W and UH-1N (now dubbed the 4BW and 4BN, but likely to be redesignated the AH-68 Viper and UH-69 Venom, respectively) will share the same rotors, transmissions, engines and avionics. Across the Marine Corps' fleet of 180 AH-1s and 100 UH-1s, that commonality translates into savings in life-cycle cost, says Bell programme manager Jim Manning.
Marine requirements
The reason for the upgrade is not to save money, but to improve the helicopters' capabilities in an affordable manner by remanufacturing the existing aircraft, Manning explains. The current helicopters no longer meet the Marine Corps' mission requirements, he says. The AH-1W upgrade will increase weapons carriage ("...not new types, but more of the same," he says), improve performance and agility, and update what Manning describes as "the cockpit from hell. Every time they got money, they added something. Nothing is integrated." The UH-1N upgrade will improve performance and payload, and extend service life.
Under the H-1 upgrade programme, Bell will develop a new four-bladed rotor and uprated drive train and qualify the new dynamic system in both the AH-1W and the UH-1N. The company will also manage development of a new integrated avionics suite (IAS) for the AH-1W, which the Marine Corps plans to adapt for the UH-1N. Selection of an avionics integrator is planned by the end of August, Manning says.
The main rotor, transmission, engines, infra-red suppressors, auxiliary power unit (APU), gearboxes, tailboom and tail rotor will be common to both helicopters. Two General Electric T700 turboshafts will replace the Pratt & Whitney Canada PT6T Twin Pac in the UH-1N, providing commonality with the T700-powered AH-1W. The new transmission's power capability is uprated 30%, to 1,955kW (2,625shp), and is "not a typical Bell design", Manning says, as its casing rises higher up the mast to take rotor loads.
To save weight, the current H-1 drive train uses magnesium gearbox casings. This results in corrosion problems in a maritime environment, and the H-1 upgrade will introduce new aluminium cases. Bell is designing for 5,000h between overhauls on all gearboxes. This compares with 1,100-1,400h for the AH-1W and 1,800h for the UH-1N. The main- and tail-rotor lives will be set at 10,000h, compared with 2,000-2,400h today, Manning says.
The composite, bearingless, main rotor is based on that used on Bell's Model 430 commercial helicopter. The hub consists of two glassfibre re-inforced plastic "flexbeam" yokes to which the blades are attached, with stiff "cuffs" to transmit pitch-change inputs to the blades. The blades are also composite, but a metal leading-edge abrasion strip is added.
Blade folding has been introduced to enable the aircraft to be parked on the decks of Marine Corps helicopter carriers. Manning says that a system had to be designed which does not require a person to climb up on to the aircraft to fold and unfold the rotor, as the "skinny"AH-1W is often parked at the deck edge.
Completing the dynamic system, the new tail rotor is Bell's first four-bladed design. The unit has composite blades and elastomeric bearings. To reduce noise, the blades will not be set at 90í to each other, Manning adds.
Increased tolerance to ballistic damage is being designed into the H-1 upgrade. Survivability testing using 23mm rounds has been completed on the main rotor, and a full live-fire demonstration will be conducted using the first upgraded AH-1W, rotors turning, weapons loaded and crewed by dummies, Manning says. The live-fire test on the upgraded UH-1N will not be as severe, he says, and will focus on items peculiar to that aircraft.
System changes
Several systems changes come as part of the H-1 upgrade, including the installation of an APU to provide engine starting as well as electric power and bleed air while on the ground. Manning says that the AH-1W's electric starter requires high maintenance. The APU - the same unit as used on the Sikorsky UH-60 Black Hawk - will provide pneumatic starting. The unit will be mounted above the main engines.
Other changes include introducing new hydraulic pumps, actuators and tubing, use of the "ribbonised" wiring system which saved money on the Bell-Boeing V-22 tilt-rotor, and commonality of fasteners between the upgraded aircraft. Airframe changes are more extensive on the UH-1N than on the AH-1W.
The old Huey fuselage will essentially be thrown away, with only the nose, roof and doors re-used, Manning says. The airframe will be stretched 530mm, behind the pilots' doors, to correct the centre of gravity. The additional space will be used to house avionics racks as the Marines do not require a larger cabin. "The Huey is underpowered today, and they can't use the cabin space available," he says. The tailboom will be new, with the same part number as that on the AH-1W. Composites will be used "-where they make sense", Manning says.
After the new dynamic system, the major change will be in the avionics. The Marine Corps has wanted to upgrade the AH-1W cockpit for some time, but cancelled its Integrated Weapon Systems update. The requirement was later resurrected, but rather than award the contract to Bell, the Marines directed the manufacturer to conduct a competition to select an avionics integration specialist. Bidders include EFW, a subsidiary of Israel's Elbit, GEC-Marconi, Honeywell and Rockwell Collins. An option to install the same system in the upgraded UH-1N was added later.
The IAS update is intended to reduce crew workload and will result in both cockpits in the AH-1W being identical. The main cockpit features are two 150 x 200mm liquid-crystal multi-function displays and side-mounted cyclic and collective controllers. Cockpit commonality is made possible by an upgrade to the Israeli-supplied night targeting system (NTS), which removes the need for a direct-view optical-relay tube in the forward, gunner's, position. This will enable the pilot to fly the upgraded AH-1W from either cockpit, Manning says.
The upgraded NTS-A has a high-resolution forward-looking-infra-red (FLIR) sensor, a dual-field-of-view television camera and a laser rangefinder/designator. A pilotage FLIR is planned, with the infra-red image presented on a helmet-mounted or head-down display, but the Marines may elect to stay with night-vision goggles, Manning indicates. The upgraded AH-1W has a low-airspeed sensor similar to that installed on US Army Cobras, and the avionics suite includes a global-positioning/ inertial-navigation system, digital map, digital datalink and a digital data-loader which will also record helicopter health information.
If the Marine Corps opts to upgrade the UH-1N with the IAS, the same controls and displays will be used, allowing crews to be cross-trained to fly both helicopters, which are operated by the same units. Three or four liquid-crystal displays would be mounted side-by-side on the instrument panel, Manning says.
Improved mission capability is the reason for the H-1 upgrade, which offers substantial operational enhancements. The upgraded AH-1W has 30% more power and 30% more internal fuel, while the improved UH-1N has 100% more power and almost 90% more internal fuel. Empty weight of the 4BW is increased by 520kg, to 5,500kg, maximum gross weight rises by 1,700kg, to 8,400kg and useful load is improved by 1,180kg, to 2,890kg. In the AH-1W's primary close-air-support mission, radius of action is more than tripled, to almost 280km (150nm), while deep-strike mission radius is boosted beyond 435km. Principal armament consists of Hellfire laser-guided anti-tank missiles, unguided rockets, AIM-9 Sidewinder air-to-air missiles and a 20mm gun.
Increased range
The improvements are even more dramatic with the upgraded UH-1N. Its empty weight is increased by 2,100kg, to 5,290kg, maximum gross weight rises by over 3,600kg, to 8,400kg and useful load goes up 1,520kg, to 3,100kg. Combat radius is increased to 205km with eight passengers, compared with 110km with four passengers for the UH-1N, and external fuel tanks boost its radius of more than 300km.
Bell is working on engineering and manufacturing development of the H-1 upgrade under contracts awarded in November 1996 for the 4BW and January 1997 for the 4BN. The Fort Worth, Texas-based company will modify three AH-1Ws and two UH-1Ns for the test programme. The first 4BW is scheduled to be flown in the fourth quarter of 2000, minus the new avionics, while the first 4BN is planned to be flown a few weeks later.
A low-rate initial production contract, for the remanufacture of five UH-1Ns by 2004 and five AH-1Ws by 2005, is scheduled to be awarded in February 2002. A contract for full-rate production is anticipated in February 2003, leading to remanufacture of the remaining 175 AH-1Ws and 95 UH-1Ns by 2013. Bell is also proposing to upgrade the USAir Force's UH-1Ns, and is already offering the improved AH-1W to international customers, Manning reveals.
Source: Flight International
