|Royal Navy Merlin HM1 at the Royal International Air Tattoo, England|
|Type||Anti-submarine warfare & medium-lift transport / utility helicopter|
|Maiden flight||9 October 1987|
|Primary users||Royal Navy|
Royal Air Force
|Developed from||AgustaWestland AW101|
|Variants||CH-149 Cormorant |
The AgustaWestland Merlin is a medium-lift helicopter for military applications but also marketed for civil use. The helicopter was developed as a joint venture between Westland Aircraft in the UK and Agusta in Italy (now merged as AgustaWestland). The aircraft is manufactured at the AgustaWestland factories in Yeovil, England and Vergiate in Italy.
In spring 1977, the UK Ministry of Defence issued a requirement for an anti-submarine warfare (ASW) helicopter to replace the Royal Navy's Westland Sea Kings. Westland responded with a design designated the WG.34 that was then approved for development. Meanwhile, the Marina Militare (Italian Navy) was also seeking a replacement for its (Agusta-built) Sea Kings, leading Agusta to discussions with Westland about the possibility of a joint development. This culminated in the joint venture being finalised in November 1979 and a new company (EH Industries Limited [EHI], based in London) being formed in June the following year to manage the project.
As the design studies progressed, EHI became aware of a broader market for an aircraft with the same capabilities as those required by the British and Italian navies. On 12 June, 1981, the UK confirmed their participation, with an initial budget of £20 billion to develop nine pre-series examples. At the 1985 Paris Air Show at Le Bourget, Agusta showed a mock-up of a utility version of the new helicopter, leading to a more generalised design that could be customised. After a lengthy development, the first prototype flew on October 9 1987.
EHI was renamed AgustaWestland International Limited in January 2004 when parent companies merged. Consequently, in June 2007, the EH101 was re-branded as the AW101.
The modular aluminium-lithium alloy fuselage structure is damage and crash resistant, with multiple primary and secondary load paths. Active vibration control of the structural response (ACSR) uses a vibration-cancelling technique to reduce the stress on the airframe. The EH101 is rated to operate in temperatures ranging from -40 to +50 °C. High flotation tyres permit operation from soft or rough terrain. The main rotor blades are a derivative of the BERP blade design, which improves the aerodynamic efficiency at the blade tips, as well as reducing the blade's noise signature.
The cockpit is fitted with armoured seats for the crew, and can withstand an impact velocity of over 10 m/s. Dual flight controls are provided, though the EH-101 can be flown by a single person. The pilot's instrument displays include six full colour high-definition screens and an optional mission display. A digital map and Forward-Looking Infrared system display can also be installed.
The military version of the EH101 is powered by either three Rolls-Royce Turbomeca RTM322 turboshafts (UK, Japan, Denmark and Portugal), or three 1,491 kW General Electric CT7-6 turboshafts (Italy, Canada, Japan TMP). Engine inlet particle separator systems provide protection when operating in sandy environments. Each engine is supplied by a separate 1,074 litre self-sealing fuel tank using dual booster pumps. A fourth tank acts as a reservoir supply, topping up the main tanks during flight; while a fifth transfer tank can be added to increase range, as can airborne refuelling. The engines power an 18.59 metre diameter five-bladed main rotor. The rotor blades are constructed from carbon/glass with nomex honeycomb and rohacell foam, edged with titanium alloy. Computer control of the engines allows the EH101 to hover reliably in winds of over 80 km/h.
A chin FLIR is fitted to some variants. The EH101 is equipped with chaff and flare dispensers, directed infrared countermeasures, infrared jammers, missile approach warners, and a laser detection and warning system. It has two hard points for weapon carriers, on which the HM Mk1 model can carry four Sting Ray torpedoes or Mk 11 Mod 3 depth charges, though at present cannot use the Sea Skua missile. The Mk3 and 3a variants can mount General Purpose Machine Guns (GPMGs)in up to 5 locations in the main cabin pointing out of door or window apertures.
EH101 fuselage has a volume of 31.91 m² and the cargo compartment is 6.5 m in length, 2.3 m wide and 1.91 m high. The military version of the EH101 can accommodate up to 24 seated or 45 standing combat troops and their equipment. Alternative loads include a medical team and 16 stretchers, and cargo pallets. The cabin floor and rear ramp are fitted with flush tie-down points, a roller conveyor for palletized freight and a cargo winch. The ramp (1.91x2.3 m) can take a 3,050 kg load, allowing it to carry vehicles such as Land Rovers. A cargo hook under the fuselage can carry external loads of 5,440 kg. A rescue hoist and a hover trim controller are fitted at the cargo door.
The navigation system includes a GPS and inertial navigation system, VHF Omnidirectional Radio range (VOR) instrument landing system (ILS), tactical air navigation (TACAN) and automatic direction finding. The EH101 is equipped with helicopter management, avionics and mission systems linked by two 1553B multiplex databuses. A Smiths Industries OMI SEP 20 automatic flight control system provides dual redundant digital control, giving autostabilisation and four-axis auto-pilot operation.
The RN's final order was for 44 ASW machines, originally designated Merlin HAS.1 but soon changed to Merlin HM1. The first fully operational Merlin was delivered on May 17 1997, entering service on June 2 2000. All aircraft were delivered by the end of 2002, and are operated by five Fleet Air Arm squadrons, all based at RNAS Culdrose in Cornwall: 814 NAS, 820 NAS, 824 NAS, 829 NAS, and 700M NAS.
In March 2004 RN Merlins were grounded following an incident at RNAS Culdrose when the tail rotor failed on one of them. Investigations later revealed that this was due to tail rotor hub manufacturing defects. Flights resumed the following year.
To date, nine Type 23 frigates have been refitted to accept the Merlin HM1: HM Ships Somerset, Lancaster, Monmouth, Montrose, Westminster, Northumberland, Kent, Richmond, and Portland, although the squadron that operates Merlins from frigates, 829 NAS, currently only has six individual 'flights'. The Merlin HM1 has also been cleared to operate from the Royal Navy's aircraft carriers, amphibious assault ships and a number of RFA vessels including the Fort Victoria Class. The UK is considering the Merlin as a replacement for the Westland Sea King ASaC7 in the Airborne Early Warning (AEW) role.
Royal Air Force
RAF ordered 22 transport helicopters designated Merlin HC3, the first of which entered service with No. 28 Squadron RAF, based at RAF Benson, in January 2001.
The type is equipped with extended-range fuel tanks and is capable of air-to-air refuelling; however, due to the lack of a suitable UK tanker aircraft, this capability has not been cleared for use. It also differs from the Royal Navy version by having double-wheel main landing gear, whereas the RN version only has a single wheel on each of the main gears.
The first operational deployment was to the Balkans in early 2003. They are currently deployed to southern Iraq as part of Operation Telic.
To alleviate a shortfall in operational helicopters the British Ministry of Defence acquired six Merlins from Denmark in 2007. These were delivered to the RAF as the Merlin HC3A. As part of the deal, the UK Ministry of Defence has ordered six new-build replacements for the Royal Danish Air Force. In December 2007 a second Merlin squadron (No. 78 Squadron) was formed at Benson.
- Merlin HAS1
- Merlin HM1
- Merlin HC3
- Merlin HC3A
- Royal Navy
- 700M Naval Air Squadron (Operational Evaluation Unit)
- 814 Naval Air Squadron
- 824 Naval Air Squadron
- 829 Naval Air Squadron
- Royal Air Force
Notable accidents and incidents
- 27 October 2000 - British Royal Navy Merlin (ZH844) ditched near the Isle of Skye, Scotland after a hydraulic fire caused by the rotor brake being partially engaged.
- 30 March 2004 - British Royal Navy Merlin (ZH859) crashed on take-off from RNAS Culdrose due to tail rotor hub cracking.
- June 2007, during an airshow in the Irish city of Galway, a door detached from a hovering RAF Merlin and fell into the crowd of spectators below injuring three people. Investigators have concluded "...that a member(s) of the public had tampered with an emergency door handle, while the helicopter was being viewed at the static display park".
Specifications (Merlin HM1)
- Crew: 4
- 24 seated troops or
- 45 standing troops or
- 16 stretchers with medics
- Length: 74 ft 10 in (22.81 m)
- Rotor diameter: 61 ft 0 in (18.59 m)
- Height: 21 ft 10 in (6.65 m)
- Disc area: 2,992 ft² (271 m²)
- Empty weight: 23,150 lb (10,500 kg)
- Useful load: 12,000 lb (5,443 kg)
- Max takeoff weight: 32,188 lb (15,600 kg)
- Powerplant: 3× Rolls-Royce/Turbomeca RTM322-01 turboshafts, 2,312 shp (1,725 kW) each
- Never exceed speed: 167 knots (192 mph, 309 km/h)
- Range: 750 nm (863 mi, 1389 km)
- Service ceiling: 15,000ft (4575 m)
- Rate of climb: 2,000 ft/min (10.2 m/s)
- Disc loading: 53.8 kg/m² (11.01 lb/ft²)
- Power/mass: 0.174 shp/lb (284.9 W/kg)
- Guns: 5× general purpose machine guns
- Bombs: 2,116 lb (960 kg) of anti-ship missiles (up to 2), homing torpedoes (up to 4), depth charges and rockets
- Smiths Industries OMI SEP 20 dual-redundant digital automatic flight control system
- Navigation systems:
- BAE Systems LINS 300 ring laser gyro, Litton Italia LISA-4000 strapdown AHRS (naval variants)
- Tactical air navigation (TACAN), VHF Omnidirectional Radio range (VOR), instrument landing system (ILS)
- BAE Systems Blue Kestrel 5000 maritime surveillance radar (ASW RN EH101s)
- Eliradar MM/APS-784 maritime surveillance radar (ASW Italian EH101s)
- Eliradar HEW-784 air/surface surveillance radar (AEW variants)
- Officine Galileo MM/APS-705B search/weather radar (Italian Navy Utility EH101s)
- Telephonics RDR-1600 weather avoidance radar (Royal Danish Air Force EH101s)
- Galileo APS-717 search/surveillance radar (Portuguese Air Force EH101s)
- ↑ Flight International November issue 1978
- ↑ Aeronautica&Difesa n.14 dec 1987,pag.34
- ↑ Rotorcraft Report: AgustaWestland. Rotor & Wing. Access Intelligence, LLC (2007-08-01). Retrieved on 2007-08-11. “The company re-branded its medium-lift EH101 transport the AW101 to reflect...the full integration of its Agusta and Westland...”
- ↑ Prouty, Ray Helicopter Aerodynamics, Helobooks, 2003
- ↑ Probe continues into Merlin crash, BBC
- ↑ 28 Squadron
- ↑ 78 Squadron Operational
- ↑ Three hurt at airshow after chopper door falls into crowd by Brian McDonald, Irish Independent, 25th July 2007
- ↑ Air Accident Investigation UnitFull List of Reports
- AgustaWestland website
- EH101 VVIP
- EH101 Martime
- EH101 SAR
- EH101 Utility
- HMS Somerset embarks Merlin
- Royal Navy Merlin HM1 page
- RAF Merlin HC3 page
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