Graham Warwick/ATLANTA
BELL'S UH-1 HUEY HAS a distinguished history, and its AH-1 Cobra derivative defined the attack helicopter. Now US Marine Corps plans to upgrade its Hueys and Cobras promise to keep the H-1 in front-line service until 2020.
The USMC has received US Department of Defense approval to proceed with an ambitious programme to upgrade its AH-1 "Whiskeys" (AH-1Ws) and UH-1 "Novembers" (UH-1Ns) with four-blade rotors and other improvements. The four-blade Whiskey (4BW) and four-blade November (4BN) upgrade has been approved as an alternative to buying McDonnell Douglas (MDC) AH-64 attack and Sikorsky UH-60 assault helicopters.
USMC AH-1Ws and UH-1Ns are operated by joint light/attack helicopter squadrons, or HMLAs; AH-1s in anti-armour, anti-helicopter, escort, fire-support and reconnaissance roles; and UH-1s on assault, special-operations and other missions.
Capt Steven Fahrenkrog, head of the Marine H-1 upgrade programme, emphasises the commonality benefits within the HMLAs which will result from the 4BW/4BN upgrade. Not since the 1960s, he says, have Marine Corps Cobras and Hueys shared the same dynamic system. Successive upgrades have replaced the AH-1's original Lycoming T53 turboshaft with today's dual General Electric T700s, while the early UH-1's T53 has been replaced by Pratt & Whitney Canada's twin-turbine T400.
Using the same dynamic system - rotors, engines and transmission - on AH-1s and UH-1s flown by the same squadrons will reduce spares, maintenance and training, Fahrenkrog says. Few HMLA pilots are now cleared to fly both types, but similar handling qualities resulting from common dynamics should make cross-training easier, he believes.
Marine Corps helicopter-upgrade plans have a tortured history. Having decided, after the 1991 Gulf War, that the most urgent needs were to upgrade the AH-1W cockpit, to reduce crew workload, and the UH-1N rotor, to increase hot-and-high performance, planning became entangled in budgetary and political turmoil.
Plans to fit the Bell 412 four-blade rotor to the UH-1, to extend its life to 2010, were dropped in 1994 when it became clear that funding would not be available to replace the Huey in 2010. In addition, the hot-and-high performance provided by the rotor from the commercial Bell 412 was deemed inadequate.
Around the same time, Marine Corps AH-1W cockpit-upgrade plans became embroiled in Bell's bid to win the UK attack-helicopter competition. A deal was struck whereby the USA would fund a four-blade rotor if the UK paid for a new cockpit. Bell lost the UK contest, however, precipitating cancellation of the Marine Corps' cockpit upgrade.
ROTOR UPGRADE
Faced with a limited budget and slippage of its AH/UH-1 replacement programme to 2020, the Marine Corps decided in favour of a four-blade-rotor upgrade for both the AH-1W and the UH-1N. This more-substantial update will keep both aircraft in service until 2020, by which time it is hoped that they can be replaced by a common platform which will also supersede US Army AH-64s and UH-60s and US Navy Sikorsky SH-60s, Fahrenkrog says.
The AH-1W cockpit update is now back in the plan, he says, but will lag the rotor upgrade by two years, to stay within the funding available between 1997 and 1999. The Marine Corps plans to award Bell a single prime contract for the H-1 upgrade programme in late 1996, after which the manufacturer will conduct a cockpit-upgrade competition. Many of the bidders for the original Integrated Weapon System (IWS) cockpit upgrade are expected to compete.
The AH-1W SuperCobra was introduced in 1986. Earlier T400-powered AH-1Ts were upgraded to "Whiskeys" and, by 1994, the Marine Corps had an all-AH-1W force. The final six of a planned 206 aircraft will be purchased this year, giving the USMC a current inventory of around 180.
New AH-1Ws are equipped with the Israeli-developed night-targeting system (NTS) - a stabilised, steerable, forward-looking infra-red (FLIR), television camera and laser rangefinder. Older aircraft are being retrofitted, and the Marine Corps will have an all-NTS AH-1W fleet by 1999. The NTS is now being seen as phase one of a mid-life upgrade, with the four-blade rotor and cockpit upgrade as phase two.
The USMC's UH-1Ns were bought between 1971 and 1978, and around 108 remain of the 210 purchased. A night-capability upgrade is under way and will be completed in 1999, adding a navigation FLIR and improving the communication, navigation and electronic-countermeasures systems. This is now phase one of a mid-life upgrade, with the four-blade rotor and other improvements forming phase two.
BEARINGLESS MAIN ROTOR
The 4BW/4BN upgrade is centred on a derivative of Bell's Model 480 four-blade bearingless, hingeless main rotor. This all-composite rotor is used on Bell's latest Model 430 commercial helicopter, and features a flexible composite hub which allows pitch, flap and lead-lag motion of the blade without the bearings and hinges of conventional rotor-heads.
The upgraded dynamic system for both aircraft consists of the four-blade main rotor, a 1,960kW (2,625shp)-capacity transmission, T700 engines with infra-red suppressors, a new 90¡ gearbox in the tail and a four-blade pusher tail-rotor (replacing the present two-blade tractor tail-rotor). Both aircraft will receive auxiliary power units, and the uprated tail-rotor will be mounted on a strengthened tailboom with a more-effective elevator.
Upgraded UH-1Ns will be powered by T700-401Cs, and the Marine Corps is looking at the feasibility of replacing the AH-1W's existing T700-400s with these improved engines to provide commonality with the UH-1Ns and the US Navy's -401C-powered SH-60s.
In addition to the new dynamic system, the AH-1W will be upgraded to carry six wing stores-stations (from four) and the 1760 weapons databus will be introduced. The effect of the 4BW upgrade will be to increase hot-day maximum payload from 1,270kg to 1,770kg. Hot-day radius of action with a 450kg payload will increase from 240km (130nm) to 400km.
Changes to the UH-1N are more extensive, and the improvements more dramatic. As well as the new dynamic system, the fuselage will be stretched by 250-760mm "for centre-of-gravity reasons". The stretch will be used to house avionics and, with other changes, will increase cabin volume. The landing gear will be upgraded and crashworthy fuel-system and seats installed.
Fahrenkrog says that weight increases and operational restrictions have reduced the UH-1N's payload, from 1,770kg in 1971 to 1,270kg by 1995, with a projected reduction to 770kg by 2020, unless the aircraft is upgraded. In part, the problem results from a drop in allowable gross weight, from 4,770kg to 4,540kg, imposed after a UH-1N accident in March 1995, he acknowledges.
GREATER PAYLOAD
The 4BN upgrade will increase the UH-1N's hot-day payload from around 450kg to 1,450kg. The hot-day radius of action will be increased from 165km with no payload to almost 280km with a 680kg payload.
Upgrading both aircraft will result in zero-time airframes, with service lives being extended to 2020, according to Fahrenkrog. The dynamic systems, including the rotors, will have 10,000h lives, while the gearboxes will have 5,000h lives, he says.
Source: Flight International
