Peter Gray / Nas Patuxent River
Has Bell's rebuild of the AH-1 to the Z standard given it the combat potency to rival other modern attack helicopters? We fly it to find out
With more units deployed around the world, both on and offshore, than possibly any other military force, the US Marine Corps relies heavily on its light utility and attack helicopter fleets. But its Bell UH-1N Hueys and AH-1W SuperCobras are ageing, while requirements for readiness and capability are growing. Power available from engines and rotor systems is proving insufficient for the job, particularly when hot, high and heavy. Safety margins have eroded and survivability shown to be inadequate at times.
The USMC needed to improve its combat capabilities and had two choices - acquire new helicopters such as the Boeing AH-64 Apache and Sikorsky UH-60 Black Hawk or upgrade its existing aircraft. Studies showed the latter would save more than $3 billion over the next 20-30 years. Under the resulting H-1 upgrade programme, Bell will rebuild the USMC's aircraft to provide a fleet of zero-timed, highly common helicopters - 100 UH-1Y "Yankee" Hueys and 180 AH-1Z "Zulu" Cobras.
Common Power
Both aircraft are refitted with an identical dynamic system with new four-bladed main and tail rotors driven by twin General Electric T700 turboshafts. Replacing the Huey's Pratt & Whitney Canada T400 Twin-Pac - which produces 1,800shp (930kW) from twinned turboshafts - with two 1,800shp T700-401Cs overcomes the power inadequacy. The Cobras will retain their 1,700shp T700-401s until they are time-expired, when they will be replaced with the more powerful -401C model.
These modifications bring substantial increases in maximum all-up weight, payload, speed, range and agility along with reduced vibration levels. On a hot day, at high altitude, the UH-1Y will now hover out of ground effect with almost 2,730kg (6,000lb) of payload compared to 1,590kg for the UH-1N. Instead of carrying only four marines into a combat zone, theUH-1Y will carry eight and get them there at 150kt (277km/h) instead of 107kt.
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© USMC |
Bell says the new rotor system more than doubles the SuperCobra's payload, and increases the functional flight envelope by 80%. The Zulu Cobra can carry 16 Hellfire anti-armour missiles plus two Sidewinder air-to-air missiles on stub wings. At the same time, ballistic survivability has been improved and maintenance demands as well as operating costs reduced.
To reduce crew workload, both aircraft are fitted with a Northrop Grumman-developed integrated avionics system, built around dual mission computers, which includes glass-cockpit displays and controls, communications, navigation and weapon management systems. Each crew station is almost identical. Crews also have Thales TopOwl helmet-mounted displays, which provide the navigation, target designation and weapons aiming information needed to fly the aircraft by day and night in virtually all weathers.
Both aircraft have armoured crew seats, which are crash-resistant seats for all in the UH-1Z. Landing gear and fuselage crashworthiness has been increased to 20g vertically and longitudinally and 10g laterally. Other safety features are a crash-resistant fuel system that is also ballistically tolerant. Key systems such as electrical generators, hydraulic pumps and engines have redundancy. Gearboxes and engines can run after loss of oil for long enough to land safely.
A major feature of the upgrade programme is to get as much commonality between the two aircraft as possible. As well as the engines, drivetrain and main and tail rotors, the other common components are the avionics, electrics, hydraulics and controls. The tailboom and everything attached to it is identical in both the UH-1Y and AH-1Z. Bell says 85% commonality has been achieved, requiring 77% fewer spare parts to be held. The advantages claimed are lower maintenance and operating costs, more efficient crew and mechanic training, easier deployment and increased availability.
Both aircraft are fully marinised and capable of shipboard operations. Semi-automatic blade folding allows them to occupy minimum hangar or deck space. While the Cobra is the USMC's primary attack helicopter, the Huey is also capable of deploying offensive and defensive firepower, including 70mm rockets and machine guns.
The AH-1Z's first flight was in December 2000, followed in 2001 by the first UH-1Y. Three Zulus and two Yankees are involved in the first test programme, and Bell has begun remanufacturing the first production batches of UH-1Ys and AH-1Zs at its Amarillo, Texas plant.
With the H-1 upgrade programme in the final stages of engineering and manufacturing development, Flight International was invited by the US Marine Corps to provide the first civilian and first non-US citizen to fly the AH-1Z. USMC test pilot Maj Vic Argobright showed me round the aircraft.
Fewer Parts
The new all-composite main rotor head has 75% fewer parts than four-bladed articulated systems, says Bell. Two identical two-armed glassfibre reinforced plastic yokes stacked crosswise one on top of the other are used in lieu of the more common four-armed yoke. This allows higher flapping angles and reduces manufacturing complexity. Mounted on the pusher side of the tailboom, the four-blade tail rotor consists of two stacked, teetering rotors with titanium yokes and elastomeric bearings. Both the main and tail rotor blades have leading-edge abrasion strips. Design life of the main rotor blades and tail rotor hub is 10,000h.
The Zulu's nose is dominated by the Lockheed Martin AAQ-30 Hawkeye target sight system (TSS), incorporating a third-generation forward-looking infrared sensor, low-light colour television camera and eye-safe laser rangefinder, all stabilised on a five-axis gimbal. With its large-aperture optics, the TSS is designed to allow identification of targets up to three times farther away than is possible in the AH-1W. This greater standoff distance enhances survivability and allows Zulu crews to recognise and destroy targets they probably would not even see in the Whiskey Cobra.
Expanded Weapons
Under the TSS is the 20mm gun turret. This can be operated in three modes from either crew station, including slaving the turret to the helmet-mounted sight display. The three-barrel cannon can be fired by the trigger switch on the cyclic grip or action switch on the mission grip, which is used to control the TSS.
Much larger than on the AH-1W, the stub wings can carry a variety of weapons on six stores stations, including laser-guided Hellfires and heat-seeking Sidewinders, and double as fuel tanks. There are also two fuel cells inside the fuselage, for a total internal fuel capacity of 1,560 litres (412USgal). Auxiliary fuel tanks can be carried on the wing pylons. The aircraft can be pressure or gravity refuelled.
The engines are isolated from each other to provide protection in the event of loss or ballistic damage. The hover infrared suppression system mixes cooling air with the engine exhaust to reduce infrared signature, the exhausts turned outwards to prevent heating of the tailboom. For self-protection, the aircraft is fitted with a Northrop Grumman APR-39(V) 2 radar warning receiver, Alliant Techsystems AAR-47(V) 2 laser and missile warning system and BAE Systems ALE-47 countermeasures dispensers.
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Mounted above the engines, the Hamilton Sundstrand auxiliary power unit (APU) can be started using the aircraft's battery. In addition to providing air for engine starting, the APU drives a 200A, 28V DC generator that is capable of providing electrical power to all systems, including the gun turret. This allows them to be checked before engine start. If the engines cannot be started from the APU, there is a "buddy" system whereby the helicopter can receive compressed air from another aircraft alongside.
On the day of our flight, the outside air temperature of 10¡C (50¡F) at sea level gave us a density altitude of -1,000ft (-305m) at NAS Patuxent River, with a 10kt wind. Our take-off weight was 7,090kg - including 1,270kg of fuel, 180kg crew and 60kg of test equipment - 1,320kg below the maximum of 8,410kg. Bell says maximum take-off weight can be increased by at least another 450kg. Our 5,580kg empty weight was close to the published figure of 5,545kg, even though it was an instrumented test aircraft.
Climbing up into the narrow cockpit was easy, and Argobright gave me a thorough familiarisation. When I flew the AH-1W SuperCobra (Flight International, 4-10 January 1995), I noted the huge differences between the front and rear crew stations. On the AH-1Z, the cluttered instrument panels have been replaced in both cockpits with two side-by-side 200 x 150mm (8 x 6in) colour liquid-crystal multifunction displays (MFD), and a 105 x 105mm LCD dual-function display (DFD) and data-entry keyboard located on a stowable console in the centre of the crew station.
I had been briefed extensively in the avionics laboratory on the MFDs and DFD, the keyboard and the TSS. With the sensor looking out through the open laboratory window, we were able to use the sighting system in real time, locking on to moving targets and using the four fields of view: wide, medium, narrow and zoom.
One of the two MFDs is usually selected to the flight display. This presents side-by-side horizontal and vertical situation indicators for instrument flight. This information is coupled to the helmet display, so the crew need not even look at the MFD. The flight display also shows the status of certain critical components such as the drive train. The second MFD, meanwhile, can show whatever the crew requires, including:
* status of all critical systems such as engines, hydraulics and electrics;
* warnings, cautions and advisories - this page shows when a system limitation has been exceeded or a malfunction has occurred. The crew is prompted via their flight displays and helmet displays to select this page when a malfunction has occurred;
* voice and datalink communications information;
* digital moving map, driven by the aircraft's embedded global positioning/inertial navigation system - displays battlefield information, including the location and inter-visibility of threats;
* electronic-warfare display - provides warnings of radar, laser and missile threats and allows countermeasures to be set up;
* weapon display - graphically depicts the munitions on the aircraft and how to deploy them;
* target display - this shows the selected video, FLIR or colour TV imagery from the TSS as well as targeting information.
Display Suite
The DFD, a smaller LCD just below the instrument panel, can show get-you-home standby flight symbology if the MFDs fail. It displays aircraft attitude, altitude, heading and navigation information and can be stowed out of the way when not needed or when getting in and out of the cockpit.
Although the only crew position adjustment is to pedal reach, I was able to get comfortable. As in the AH-1W, there is a resting pad for the cyclic forearm. The cyclic stick is a stubby 150mm long, mounted on a right-hand ledge near the cockpit wall. On the AH-1W, the front cockpit stick has no trim release or adjust functions. To my delight, this one does. The Zulu and Yankee adhere to the philosophy of allowing the crew to do just about everything without removing their hands from the cyclic stick and collective lever. The helmet display enhances these capabilities, improving perception and control. The crew can change radio frequencies, select and fire weapons, and manage the automatic flight control system (AFCS) while flying hands on.
Visibility around and behind was good, but because of the lack of an up/down seat adjustment, forward visibility over the nose, especially in flight, is poor. When carrying out a steep approach to a pre-selected landing area during the flight, I had to cock the aircraft nose sideways to see it.
Argobright started the APU, carried out a number of system checks and started the first engine. This can be done from either cockpit, unlike in the Whiskey Cobra. I could not see the start buttons and other minor switches under my lever, but this is a combat cockpit with limited space. The engine start procedure is similar to that in the Bell 212, using the conventional twist-grip throttles. The second engine was started and the rotor brake released. As is usual with the T700, the starts were slow and cool. Engine control is not quite fully automatic and digital, but nearly so.
Easy Hover
I pulled up carefully into my first hover. It was easy and uneventful. The excellent power required and power available presentations on the flight display were simple to interpret. We had plenty of power in hand. This would also be so at maximum weight and at altitude, says Argobright. All the usual ground manoeuvres of hovering, sideways, backwards and spot turns were uneventful and easy, using the short stubby cyclic. The trim release and adjustment on the front cyclic made life easier than in the AH-1W. Our development aircraft, with only 347 flight hours, had some flight envelope restrictions so we were not able to go to maximums. At 22-25kt sideways flight, however, I still had plenty of pedal and engine power in hand. The auto-hover function of the four-axis AFCS held the aircraft steady in the 10kt of wind. Using the coolie-hat trim switch on the cyclic got the helicopter flying sideways or backwards at a steady rate on a constant heading - useful if shadowing a moving target. I detected no handling problems in hovers and landings at 90¡, 180¡ and 270¡ out of the 10kt wind.
We transitioned into forward flight, levelled out and did some upper-air work. I pulled maximum continuous power of 100% torque on the easy-to-read torque gauge. At 1,000ft pressure and density altitude, we achieved a steady 162kt, 7kt above the published speed. Our aircraft was speed restricted until further tests are done, but Argobright says the never-exceed speed is 200kt and the aircraft has been flown to VNE + 10% without any handling problems.
At 162kt the vibration levels were benign, including during steep turns. We then went to 60¡ of bank in both directions holding a steady 147kt. There was a slight increase of vibration levels, but nothing significant. Because of the flight envelope limitations we were not able to perform my usual check of closing one throttle and doing nothing else. But with a single-engine contingency power rating of 1,723shp for 2.5min, rotor droop should not be a big issue after a sudden engine failure. At my request, Argobright lowered the collective lever rapidly from a high power setting, then raised it from low to high while I watched the rotor RPM (NR). Doing both in quick succession resulted in an RPM change of ±3%, well within the generous NR limits. I noted the nose dropped when the lever was moved down quickly.
In a 160kt straight and level cruise, I invited Argobright to push over quickly, demonstrating the Zulu's increased negative g limit of -0.5. I felt my weight go negative and my body trying to come off the seat. The five-point harness held me in place.
I flew the aircraft "raw" with the AFCS and stability and control augmentation system (SCAS) switched off. This condition can often produce pilot-induced overcontrol, so I relaxed my control inputs and let the aircraft fly itself, which it did well. I was able to perform turns, climbs and descents with no problems, although my attention level was higher. The cyclic trim and trim release still functioned, which made control easier. I would be confident enough to fly the aircraft a long distance back to base in this degraded condition. Back at the airfield, I carried out an approach, hover and landing in the raw state with no difficulty.
Argobright demonstrated the AFCS heading, height, attitude and speed holds. This is not a programmable autopilot, but does allow hands-off flight to the parameters the pilot has selected. It is single channel, with no back-up, so the pilot should be aware of the aircraft's attitude and intended attitude, heading, height and speed in case of failure.
Back at the field, Argobright carried out a straightforward autorotation with power recovery. Control of the generous NR limits was easy - he did not have to move the lever to contain rotor speed. The rate of descent was 2,250ft/min (11.4m/s). Some other combat helicopters I have tested come down in autorotation like a falling piano. But this is not a major consideration in a helicopter that will spend its working life at low level, well below that height when an autorotation can be fully developed.
At the field, I tried a steep approach with the AFCS/SCAS switched off. Apart from the restricted visibility over the nose, which required me to cock the nose sideways to keep my intended landing spot in view, it was easy. Landing on a ship's helideck at night should not be a problem in such a condition. I went up vertically over the landing spot to 100ft radar altimeter height and back. The vertical rate of climb is impressive, although I did not pull the full 1,690shp 30min power available. A single engine will provide at least the same amount of power. Downwards visibility was limited, although I managed to arrive and hover over the designated landing spot. The aircraft was not yet cleared to land on slopes, but with its almost-rigid rotor system it should be able to take severe inclinations and stay there.
We finished off by going low level, below the tree tops at times, fast and agile. Argobright performed two simultaneous 90s - 90¡ of bank at 90kt then invited me to do the same. The manoeuvrability from the new rotor and powerful engines is excellent. The handling was crisp and accurate.
I believe the deficiencies of the previous model have been corrected. Cobra crews will benefit from the performance improvements, and their cockpit tasks will be much easier. The Zulu Cobra is a more potent fighting machine, and its survivability has been enhanced.
As the pair of upgraded H-1s enters operational testing with the USMC, Bell is looking to the export market for both helicopters. Whether remanufactured or new, the Zulu Cobra looks to be competitive with other attack helicopters on the market.
| Bell AH-1Z Supercobra Specifications | |||
| Overall length (rotors turning) | 17.7m | Main rotor diameter | 14.6m |
| Height | 4.02m | Weights: max gross take-off | 8,410kg |
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| empty | 5,590kg |
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| useful load | 2,820kg |
| Service ceiling | 20,000ft-plus | OGE ceiling, hot, high, & heavy | 16,900ft |
| Powerplant | 2 x GE T700-401 | Power: max continuous | 1,437shp |
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| 2 min 30s single engine | 1,723shp |
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| 30 min | 1,690shp |
| Internal fuel | 1,560 litres | Maximum endurance | 3.3h |
Source: Flight International
