CUTAWAY: AH-1Z Viper enters production as substantially new aircraft

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  1. chex3009

    chex3009 Regular Member

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    CUTAWAY: AH-1Z Viper enters production as substantially new aircraft

    Initially envisioned as an effort to modernise the drive train of the US Marine Corps' (USMC) veteran fleet of Bell AH-1W Super Cobra helicopters, the AH-1Z Viper has essentially evolved into a new aircraft.
    The helicopter, which was developed alongside its close cousin, the UH-1Y, is a significant technological leap over its predecessor. The new airframe offers increased aerodynamic performance and exponentially more sophisticated avionics. The service hopes to procure some 226 AH-1Zs, including 58 new-build airframes and 168 machines remanufactured from the AH-1W.
    For the USMC, the appeal of the "Zulu" is focused on the logistical advantages of the UH-1Y/AH-1Z combination; there are those, however, who question the value of this arrangement.

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    The US Marine Corps' new-model attack helicopter can carry a mix of rockets, plus Hellfire and Sidewinder missiles

    "The H-1 programme originated largely because the Marines wanted to avoid ever taking any [Sikorsky] H-60s," says Richard Aboulafia, an analyst at the Teal Group, a Washington DC-based consultancy.

    "Taking H-60s would have been enormously sensible in terms of costs, capabilities and intra-service commonality, but it would have jeopardised the [Bell Boeing] V-22 requirement, which was the Marines' highest priority," Aboulafia says.

    Further, the US Army's Boeing AH-64D Apache, which is a direct competitor to the AH-1Z on the market, is arguably a superior attack platform.

    Comparatively, the Apache possesses roughly equal manoeuverability, but greater range and payload, although the Zulu is faster. More importantly, one experienced army aviator opines that the AH-64D also offers a superior sensor suite.

    The AH-1Z, which entered full-rate production on 28 November, has an estimated unit cost of $27 million. While this is projected to decline as production ramps up, the aircraft will still roughly match the $25 million price tag of the AH-64D.

    "I think the most important differences are not directly related to aircraft performance," Aboulafia says. "The Apache's much larger user base guarantees a more ambitious and robust product upgrade roadmap than the Zulu. It also guarantees easier and less costly logistics and training. And the Apache's heavier production volume means better manufacturing economics, which reduces some of the Zulu's original appeal as a less costly machine. On the other hand, a customer that preferred a strategic relationship with the US Marines over the army might find the Zulu an appealing product".

    OPERATIONAL REQUIREMENTS

    Col Harry Hewson, H-1 upgrades programme manager for the US Naval Air Systems Command, argues that the USMC, in nine separate studies - some as recent as 2006 - had concluded the UH-1Y/AH-1Z combination is the most cost-effective means to meet the service's unique operational requirements.

    Because a single squadron type operates both machines, commonality between the two airframes during USMC expeditionary operations is far more important than usually across the Department of Defense.

    "Eighty-four percent of the components are identical. The same part number can be used on one or the other. That's really one of the strong selling points for this programme," Hewson says. "The Marine Corps exists to operate in an expeditionary environment, being able to pack up and go some place and operate without a lot of support machines for extended periods. So getting your logistics footprint down to as small as possible is critical."

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    Increased commonality means that personnel costs can also be reduced, he argues. "Now you only have to train one flavour of avionics guy, or one flavour of rotor and powerplant guy. The skills sets focus down much more, which means when you go on some extended operation at some remote site, you can take fewer people."

    The reduced number of support troops and associated facilities helps to lower the operating cost of the aircraft over the course of its service life.

    While the AH-1Z retains the classic lines of its forebears, one change is immediately apparent to those familiar with the Cobra. Gone are the distinctive two-bladed metal rotors, instead the Zulu boasts a state-of-the-art four-bladed system.

    "It's all composite, basically carbon-fibre and epoxy. It's fully rigid," Hewson says, adding that the blades are connected to a bearing-less rotor hub. The rotor hub itself is composed of two fiberglass yokes, which accommodate blade flapping, lead-lag and pitch changes.

    The yokes allow for the elimination of all bearings, hinges and vibration absorbers, which would otherwise be required. The new system utilises 75% fewer parts than conventional articulated rotors, significantly reducing its weight. The new blades also provide tangible performance benefits.

    "It's an extremely responsive rotor system for manoeuverability, and, of course, a four-bladed system is quite a bit more aerodynamically efficient than a two-bladed system. We're getting quite a bit more performance out of them," Hewson says. While the new rotors boost the aircraft's manoeuverability, the system also increases the helicopter's cruise speed and improves handling characteristics.

    The new rotor system is not without its problems, however, he admits. Several rotor components are falling far short of the original 10,000h goal. The rotor cuff, for example, must be replaced after 1,200 flight hours. The programme will redesign the cuff and yoke to improve durability.

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    The legacy AH-1W's distinctive two-bladed rotor is replaced on the 'Zulu' version

    However, Hewson adds: "It remains a very high performance rotor head with very high response rates and minimal recurring maintenance."
    The Zulu replaces the twin General Electric T700-401 engines found on the AH-1W, which produce 1,680shp (1,250kW) each, with a pair of new T700-401Cs, each producing almost 1,830shp.

    While the new engines provide a combined total of almost 3,660shp, the aircraft's transmission is flat-rated for 2,350shp.

    "When you look at that, you say, jeez, the transmission can't handle everything the engines can give it," Hewson says. "However, that's at sea level on a standard day.

    Take it up high into the mountains, the power available running through the engines starts to be degraded by the thinner air, and at that point the transmission and engines match up pretty well." The Zulu can easily hover out of ground effect even in the high elevations and hot climate found in Afghanistan, he notes. Typically, the aircraft will cruise at around 135-140kt (250-260km/h) in a combat configuration while the maximum dash speed is "around 180kt," Hewson says.

    Above 180kt, the AH-1Z is limited by parasitic drag. Compared to the AH-1W, "you get either twice the payload in ordnance, or, you can trade some of that and you get twice the range in fuel carriage," according to Hewson.

    Another significant enhancement is the new automatic flight control system (AFCS), which stops short of a fly-by-wire system. The AFCS instead "beefs up" the hydraulically-assisted flight controls.

    More importantly, the ballistics tolerance of the control system has been significantly expanded, Hewson says. Materials published by Bell Helicopter suggest the controls can withstand 23mm cannon fire. The AFCS also incorporates a four-axis stability control augmentation system, which helps dampen attitude, roll, yaw and the collective.

    "In straight and level flight, you can engage that, it's basically an autopilot. You can take your hands off the controls and fly it comfortably hands-off," Hewson says.
    The aircraft's AFCS autopilot and navigation systems are precise enough to allow hands-free flight during the hover, which is typically the most difficult flight regime for helicopter pilots.

    Hewson, a veteran Cobra pilot, attributes the astonishing capability to the aircraft's advanced software and extremely sensitive embedded GPS/inertial navigation system.
    Inside the glass cockpit, most of the avionics hardware is common to both the UH-1Y and the AH-1Z, with only minor variations. The five-display layout includes two 152mm x 203mm (6in x 8in) multi-function screens for each pilot, plus a 102mm x 102mm screen.

    BINOCULAR VIEW

    The Thales Top Owl helmet, meanwhile, also displays information for heads-up flying in both day and night operations. The helmet display provides a 40e_SDgr binocular field of view and can display forward-looking infrared and video imagery to the pilot. The system can also overlay targeting data and navigational information directly into the pilot's line of sight.

    While the Top Owl is capable of 24h operations, the USMC has opted not to use this feature operationally in the fleet. "At night time, we still use conventional night vision goggles. It took a lot of testing and a lot of debate, but the resounding opinion across all Marine aviators is that there is nothing better out there than night vision goggles," Hewson says. "So that's what we decided to stick with."

    The AH-1Z also introduces the Lockheed Martin AAQ-30 Target Sight System (TSS), which incorporates a FLIR, digital colour TV camera and a laser designator. The sensor allows the AH-1Z to act as an armed reconnaissance platform in addition to its traditional role as an attack helicopter.

    While the TSS is built on a production line co-located with the Apache's Arrowhead sensor, the systems only share a few common components.

    The armaments package for the AH-1Z has not appreciably changed from what is currently found on the AH-1W. The aircraft carries a 20mm turret-mounted cannon, which can be slaved to the pilot's helmet-mounted sights. Additionally, the Zulu can also carry a mix of rocket pods, Lockheed AGM-114 Hellfires and Raytheon AIM-9 Sidewinder missiles. A total of 16 Hellfires can be carried, yielding a payload similar to the AH-64D.

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    In the future, additional weapons will be integrated onto the gunship, including the advanced precision kill weapon system and follow-on missiles.

    One area where the AH-1Z is lagging is in terms of its communications and networking systems. Hewson explains: "What we're doing right now is just voice. We can do all the digital encryption and talk on all the voice radios, but data itself, we're not linking. We've got some plans that we are doing some lab work on to come up with some good data link type stuff. But one thing we are doing that we are putting on AH-1W right now - the AH-1W is still going to be around for another 10, 12 years - we're putting something we call the tactical video data link on there. This will take the sensor video that's on the AH-1W and broadcast that down to a forward air controller who has a ROVER system. We can also receive video from another Cobra, a [Boeing] F/A-18 or [Boeing AV-8B] Harrier who has a Litening pod, or if we get a frequency match, we can look at what a UAV [unmanned air vehicle] is looking at, but not control it".

    For the future, new data links are very much on the agenda, Hewson says.

    http://www.flightglobal.com/articles/2010/12/20/351056/cutaway-ah-1z-viper-enters-production-as-substantially-new-aircraft.html
     
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