This is basically a Bell 212 but fitted with a new composite four-blade rotor. First flown in 1981, the 412 incorporated a new four-blade rotor system to replace the two-blade teetering rotor system. Bell had spent some time experimenting and developing their new family of composite blades. The new four-blade design gave the Bell 412 an improved performance with reduced noise and vibration. The first modified 412s flew in 1979. The new design had a steel and light alloy main rotor head with elastomeric bearings and dampers. The blades, fitted with a Nomex honeycomb core, are bonded together by glassfibre wrapping incorporating anti-icing heater mats and are interchangeable. The elastomeric bearings of the hub eliminate both mechanical hinges and heavy, viscous dampers. This improves the ride and also extends the rotor system life, while the flex beam yoke of the main rotor hub provides quick control response. The new bearings require no lubrication and require only a quick visual inspection to confirm integrity. In the drive system, five of the six-rotor drive shaft sections are interchangeable, reducing spares. Main transmission chip detectors help protect the system and will alert the pilot to possible problems. The four composite blades have an unlimited life and are exceptionally strong. Span wise variation of their chord, twist and thickness of airfoils give added turning and aerodynamic efficiency. The 412SP (Special Performance) is powered by Pratt & Whitney PT6T-3B-1 turbo Twin-Pacs developing around 1400shp and has a maximum speed of 260kph and a range of over 650km.

In 1986 Bell produced the 412 Attack Helicopter (AH) based on the Bell 412SP. It is armed with a nose-mounted Lucas Aerospace under-nose turret fitted with a 0.50 calibre machine-gun. The gun is slaved into a helmet-mounted sight produced by Sperry and can fire up to 875 rounds of ammunition. The 412AH has a maximum speed of 220kph and can also be armed with air-to-ground rockets.

P.Allen "The Helicopter", 1996

Under the designation Bell Model 412, the company has developed a version of the Model 212 which introduces a new four-bladed main rotor of advanced design. Each blade is constructed of glassfibre and Nomex honeycomb, incorporates a titanium abrasion strip on the leading edge, has lightning-protecting mesh included in the blade structure, and also has provisions for the inclusion of de-icing heater elements if required. The rotor hub is also of new design, being of steel and light alloy structure, with elastomeric bearings and dampers. Two new Model 212s were modified for use in the development prgramme of this new helicopter/with both IFR and VFR certification gained by 13 February 1980. The initial delivery of a VFR certificated aircraft was made on 18 January 1981, and two were delivered to the Venezuelan Air Force later in the year.

The latest production version is the Model 412SP, with a 55% increase in fuel capacity and other improvements. 100 of these are being built by IPTN in Indonesia, while Helikopter Services A/S is assembling 17 for the Royal Norwegian Air Force. By January 1989, 162 Model 412s had been delivered.

Agusta in Italy manufactures the type as the AB 412SP, and has delivered over 75. It has developed the Griffon, a strengthened version for military duties, the prototype flying in August 1982.

D.Donald "The Complete Encyclopedia of World Aircraft", 1997

Original 412 announced 8 September 1978; FAR Pt 29 VFR approval received 9 January 1981, IFR 13 February 1981; 213 built in USA; production (SP version) transferred to Canada February 1989; first delivery (civil) 18 January 1981. Production licences obtained by Dirgantara of Indonesia and Agusta of Italy.

VERSIONS:

• 412SP: Special Performance version with increased maximum T-O weight, new seating options and 55% greater standard fuel capacity. Superseded by 412HP early 1991.

• Military 412: Announced by Bell June 1986; fitted with Lucas Aerospace chin turret and Honeywell Head Tracker helmet sight similar to that in AH-1S; turret carries 875 rounds, weighs 188kg and can be removed in under 30 minutes; firing arcs ±110° in azimuth, +15° and -45° in elevation; other armament includes twin dual FN Herstal 7.62mm gun pods, single FN Herstal 12.7mm pod, pods of seven or nineteen 70mm rockets, M240E1 pintle-mounted door guns, FN Herstal four-round 70mm rocket launcher and a 12.7mm gun or two Giat M621 20mm cannon pods.

• 412HP: Improved transmission giving better OGE hover; FAR Pt 29 certification 5 February 1991, first delivery (c/n 36020) later that month.

• 412EP (Enhanced Performance): PT6T-3D engine, dual digital automatic flight control system (DDAFCS), three-axis in basic aircraft but customer option for four-axis and EFIS. Category A certification was imminent in late 1998. Also customer option for SAR fit. Now standard current model.

  Detailed description applies to Bell 412EP.

• 412CF (CH-146) Griffon: Canadian Forces C$700 million contract for 100 CH-146s (modified Bell 412EP) placed in 1992. Duties include armed support, troop/cargo transport, medevac, ASW, SAR and patrol; first flight (146000) 30 April 1994; deliveries began 14 October 1994; completed early 1998. Generally as commercial Bell 4I2EP except for avionics and mission equipment. Empty weight 3.402kg; maximum weight as civil version.

• 412EP Sentinel: First of two modified in 1998 by Heli-Dyne Systems with quick-change ASV and ASW mission packages; intended for Ecuadorean Navy, but order cancelled and aircraft became demonstrator. ASV equipment comprises Honeywell RDR-1500B chin radar, Hughes Starburst searchlight, radar warning receiver, Wescam sensor turret and possibly Penguin Mk 2 Mod 7 ASMs; ASW fit is L3 Ocean Systems AN/AQS-18A dipping sonar and Raytheon Mk 46 torpedo.

• 412SA: First three of 16 ordered by Royal Saudi Air-Force built in 2001 for manufacturer's trials. Equipment standard not disclosed, but sufficiently different from 412EP to warrant separate c/n sequence beginning 33501. Production continued in 2002-03.

• 412 Plus: Projected improved version under study in 1999 with MTOW increased to 5.647kg, uprated PT6C engines, new dynamic components and Rogerson-Kratos avionics. Development terminated in early 2001.

• NBell-412: Indonesia's Dirgantara has licence to produce up to 100 Model 412SPs.

CUSTOMERS: Some 635 Bell 412s of alI versions built in North America by early 2003, including 26 delivered in 1999 and in 2000; 22 in 2001 (including five to El Salvador) and in 2002 (including five to Saudi Arabia).

Military deliveries include Venezuelan Air Force (two), Botswana Defence Force (three), Public Security Flying Wing of Bahrain Defence Force (two), Sri Lankan armed forces (four), Nigerian Police Air Wing (two), Mexican government (two VIP transports), South Korean Coast Guard (one), Honduras (10), Royal Norwegian Air Force (19, of which 18 assembled by Helikopter Service, Stavanger, to replace UH-1Bs of 339 Squadron at Bardufoss and 720 Squadron at Rygge). Three 412EPs delivered to Slovenian Territorial Forces in 1995, for border patrol and rescue duties; four ordered by Philippine Air Force late in 1996, comprising two for VVIP transport and two SAR; first of nine 412EPs entered service in April 1997 as HT. Mk 1s with civilian-operated Defence Helicopter Flying School at RAF Shawbury, UK, within which they constitute No.60 (Reserve) Squadron, RAF; two more ordered in May 2002. together with four HAR. Mk 2s, latter replacing Wessex SAR helicopters of No.84 Squadron at Akrotiri, Cyprus, from April 2003. Four in SAR/utility fit delivered to Venezuelan Navy, 1999. Recent customers include the National Defence Secretariat of Mexico, which took delivery of four in mid-2002; Venezuelan Navy, which ordered four in SAR configuration in early 2002; and Khalifa Airways of Algeria, which took delivery of one 412EP in June 2002.

COSTS: Bell 412EP, VFR-equipped US$4,895 million (1999); Bell 412EP, lFR-equipped US$5.12 million (1999). Average direct operating cost US$746 per hour (1997).

DESIGN FEATURES: Four-blade main rotor with blades retained within central metal star fitting by single elastomeric bearings; shorter rotor mast than 212; blades can be folded; rotor brake standard; two-blade tail rotor; main rotor rpm 314.

FLYING CONTROLS: Fully powered hydraulic controls; gyroscopic stabiliser bar above main rotor; automatic tailplane incidence control.

STRUCTURE: Generally of conventional light metal. Main rotor blade spar unidirectional glass libre with 45° wound torque casing of glass fibre cloth; Nomex rear section core with trailing-edge of unidirectional glass fibre; leading-edge protected by titanium abrasion strip and replaceable stainless steel cap at tip; lightning protection mesh embedded; provision for electric de-icing heater elements; main rotor hub of steel and light alloy; all-metal tail rotor.

LANDING GEAR: High skid, emergency pop-out float or non-retractable tricycle gear optional. Spats optional for last-named.

POWER PLANT: Pratt & Whitney Canada PT6T-3D Turbo Twin-Ðàñ, rated at 1342kW for T-O and 1193kW maximum continuous. OEI ratings 850kW for 2 1/2 minutes, or 723kW for 30 minutes. Transmission rating 1,022kW for T-O, 828kW maximum continuous; OEI rating 850kW. Optional 30kW for accessory drives from main gearbox.

Seven interconnected rupture-resistant fuel cells, with automatic shutoff valves (breakaway fittings), have a combined usable capacity of 1,249 litres. Two 76 or 310.5 litre auxiliary fuel tanks, many combination, can increase maximum total capacity to 1.870 litres. Single-point refuelling on starboard side of cabin.

ACCOMODATION: Pilot and up to 14 passengers: one in front port seat and 13 in cabin. Dual controls optional. Accommodation heated and ventilated.

SYSTEMS: Dual hydraulic systems, pressure 69 bar each. 28V DC electrical system supplied by two completely independent 450VA inverters. 40Ah Ni/Cd battery.

AVIONICS: Comms: Optional IFR avionics include dual Bendix/King Gold Crown III.
Radar: Weather radar optional.
Flight: Dual KNR 660A VOR/LOC/RMI receivers. KDF 800 ADF, KMD 700A DME, KXP 750A transponder and KGM 690 marker beacon/glideslope receiver. Optional Honeywell AFCS.

EQUIPMENT: Optional equipment includes cargo sling and rescue hoist.

Jane's Helicopter Markets and Systems

On 8 September, 1978, Bell announced its intention to develop a four-bladed variant of its twin-turbine Model 212. Designated Model 412 (the figure 4 in the designation standing for 4-blade), this helicopter was the first four-blade rotor helicopter to be produced by Bell (multi-bladed aircraft already having been flown by Bell but only for research purposes). The new four-blade rotor improved the performance of the aircraft in many respects, first being the reduction of noise and vibration levels. The rotor head had elastomeric bearings that eliminated both mechanical hinges and viscous dampers. In mid-1984, the internal vibration level was further lowered by the introduction of a pendulum damper kit on production aircraft, but this was also available independently for retrofit to earlier machines.

Creation of the new Model was made on two newly built Model 212 airframes without costly redesign. Both aircraft served as development prototypes and for the certification programme. The Model 412 retained the same powerplant as the Model 212, the Pratt & Whitney Canada PT6-3B-1 Turbo Twin Pac delivering 1400hp for take-off and 1130hp for continuous operation. The first modified helicopter made its maiden flight in early August 1979, followed by the second machine in December of the same year. FAA type approval was given on 9 January, 1981, and IFR certification came on 13 February, 1981. Meanwhile, the first deliveries had taken place. On 18 January, 1981, ERA Helicopter Inc of Anchorage received its first aircraft (c/n 33001, N412EH), this company eventually acquiring up to nine Model 412s (c/n 33004/N164EH, 33007/ N414EH, 33009/N415EH, 33011/ N416EH, 33043/N419EH, 33068/ N422EH, 33069/N524EH and 33072/N356EH) to be operated alongside some sixteen Model 212s and fifty-two other Bell helicopters.

By the end of 1987, a total of 145 Model 412s had been delivered and, at the time of writing, some 200 machines have been manufactured.

Although the Model 412 is available in both civil and military configurations, up to now the majority of the operators are civil. Only a few machines have been sold to military customers: two aircraft to Bahrain Defence Force Air Wing with codes BPS-03 and 04; two to the Venezuelan Air Force (one is c/n 33013); three TO the Botswana Defence Force (with two more on order); one to Panama (c/n 33091, serialled FAP-1101); four to Sri Lanka's armed forces; two to the Nigerian Police Air Wing; an estimated seven to the Bangladesh Air Force and some aircraft to Peru to equip Escuadron 341 and Escuadrilla Presidencial.

An improved variant, know as the Model 412SP (SP for Special Performance), was later introduced. This Model had increased maximum take-off weight, a 55 per cent increase in fuel capacity and new interior seating options. This variant is also available to customers in both civil and military configurations. Up to now, several military operators have ordered Model 412SPs: Bahrain (the Public Security Flying Wing operates two), Botswana (five aircraft to be supplemented by two more in 1991), Honduras (ten), Nigeria (the Police Air Wing received two aircraft), Sri Lanka (four), Venezuela (two) and Norway (eighteen). Norway is assembling seventeen out of the eighteen machines ordered in Helikopter Services A/S workshops at Stavan-ger. These machines are due to replace ageing Bell UH-lBs operated by 339 and 720 Squadrons.

In June 1986, Bell proposed an armed version of the Model 412SP: the Model 412AH (AH standing for Attack Helicopter). The demonstrator aircraft (c/n 33119, N412AH) is equipped with a 0.50m machine-gun (carrying 875 rounds) in a Lucas Aerospace undernose turret aimed through a Sperry Head Tracker helmet sight system (as on the AH-1S) and had provision for nineteen air-to-ground rockets on each side of the cabin.

The Bell Model 412 is under production by Bell Helicopter Tex-tron in Canada (production was transferred in January 1989), and also by Industri Pesawat Terbang Nusantara (IPTN) in Bandung, Indonesia, and by Agusta in Italy. In November 1982, a licence agreement was signed with IPTN for the partial manufacture and complete assembly of more than one hundred Model 412s. The first of these Indonesian-built aircraft (designated NBell-412) flew for the first time in April 1986. Among the customers are the Indonesian armed forces and several private operators. Agusta began production of the Model 412 in 1981 and has since developed its own military variant designated AB 412 Griffon. This variant includes a high-energy-absorbing undercarriage, energy attenuating seats and crash resistant self-sealing fuel tanks. Armament can include a wide range of external weapons such as an 12.7mm gun and 25mm Oerlikon cannon under a swivelling turret, four to eight TOW missiles, 70mm rocket launchers, air-to-air missiles and air-to-surface Sea Skua missiles. The Griffon prototype flew for the first time in August 1982 and deliveries began in the following January. Among military customers for the AB 412 are the Italian Army, Carabinieri and Special Civil Protection, Capitanerie di Porto (four AB 412SP for coastal patrol and SAR duties), Dubai Central Military Command (three aircraft), Finnish Coast Guards (two), Ugandan Army and Zimbabwe Air Force (ten). A version for SAR and maritime surveillance is under development.

A.J.Pelletier "Bell Aircraft since 1935", 1992

- The Norwegian armed forces operate the 412SP from portable landing pads.

- Indonesia constructs the Model 412 under licence, as the NBell-412.