In 1959, the TRECOM (United States Army’s Transportation Research Command) set up a programme in order to determine various rotor systems and methods of drag reduction for helicopters. For this programme, Bell modified the first YH-40-BF service test model (s/n 56-6723) as a research test-bed which was known at Bell as the Model 533. Reworking was done on the airframe in order to reduce drag, including a cambered vertical tail surface to unload the tail rotor, streamlined fairing for the rotor head, flush air intakes located on each side of the new rotor fairing, redesigned cross-tubes for landing skids, and new hinges for the doors. The stabilising bar was removed and replaced by a variable-tilt rotor mast in order to maintain the fuselage in low-drag attitude. The 1400shp Lycoming T53-L-13 turboshaft was retained. Tests in NASA’s Ames wind tunnel showed that the aerodynamics of the airframe had been improved to such an extent that the equivalent flatplane area of the Huey had been reduced from 2.3sq.m to 1sq.m. Still with its original US Army serial number, the Model 533 made its maiden flight on Friday 10 August, 1962, and flight tests were conducted at Fort Worth in late 1962. In March 1963, the Model 533 flew at 278km/h and 302km/h was attained in a shallow dive. Several rotor types were tested (two-blade UH-1B-like rotor and rigid three-blade rotors) and two 765-kg Continental J69-T-9 turbojets were installed on each side of the fuselage. Take-off weight of the aircraft was now 3880kg. On 17 January, 1964, the helicopter achieved a speed of 338km/h in level flight using only 780shp from the 1100shp Lycoming T53-L-9A shaft-turbine, plus 568kg from the J69s. The next modification consisted of fitting two small sweptback fixed wings to convert the aircraft into a compound helicopter. On 11 May, 1964, it flew at 357km/h. The aircraft was then flown to San Antonio to have its J69-T-9s replaced by 765-kg J69-T-29s, and, on 15 October, 1964, the Model 533 was the first helicopter to break the 200 knots (370km/h) barrier by attaining 380km/h. On 6 April, 1965, the Model 533 flew at 402km/h in level flight and 409km/h in a shallow dive. It showed also its outstanding manoeuvrability in performing 2g turns and 60deg banks at speeds around 320km/h, and a Mach number of 0.985 was recorded by the advancing blades of the rotor. Early in 1968, a subsequent phase of the programme was the installation of two 1490-kg Pratt & Whitney JT12A-3 turbojets at the end of short stub wings. The first flight in this configuration was made in 1968, the machine gradually recording still higher speeds and, in May 1969, Bell announced that 508km/h had been attained.
Model 533 Rotor diameter: 13.41m Length of fuselage: 12.98m Normal take-off weight: 4173kg Maximum speed: 508km/h
The Bell 429 was the first model designed from scratch, since the Bell 222. A light-medium twin helicopter which received certification from Transport Canada Civil Aviation and the FAA on 1 July 2009. Five prototypes were used during certification. The first delivery was on July 7, in Iowa.
Launched as the New Light Twin (NLT) in February 1996 on signature of collaborative agreement with Samsung Aerospace Industries of South Korea. The Bell 427 prototype assembly began early 1997. An enlarged and lengthened by 13 inches version of Model 407 with wider cabin, centre-section fuel tank, OH-58D composite four-blade main rotor, and 2705kg TOGW, powered is from two 600shp Pratt & Whitney PW206D turboshafts. The first flight of the first prototype (C-GBLL) was on 11 December 1997 at Mirabel, Quebec. The second prototype (C-FCSS) was completed in February 1998 and the two prototypes undertook flight test programme, gaining Transport Canada certification on 19 November 1999, FAA VFR certification achieved in 24 January 2000, followed by Dual Pilot IFR (DPIFR) Category A certification on 24 May 2000. The first production aircraft (C-GDEJ) was flown in June 1998. Compared with prototypes, the production 427 has longer exhausts and revised upper surface contours. Similar in appearance to the Bell 407, with a cabin stretch of 33cm, the 427 is all-new design, incorporating twin-engine safety margins. Flight dynamics are based on the four-blade rotor system of Bell OH-58D Kiowa, allied to tail rotor of Bell 407, and folding main blades. A purpose-designed ‘flat pack’ main transmission, with direct input from both engines, has only four gear meshes to simplify design and operation. The transmission is attached to the airframe by four liquid-inertia vibration eliminators. It was the first Bell helicopter designed entirely with use of computer (Dassault CATIA programme).
The structure is generally as for the Bell 206, but extensive use of carbon/epoxy composites reduces airframe parts count by some 33%. Cabin floor and roof are flat panels for ease of manufacture; minimal use of curved panels elsewhere. Composites main and tail rotors; main blades have nickel-plated stainless steel leading-edges. Soft-in-plane hub of main rotor employs a composites flexbeam yoke and elastomeric joints, eliminating lubrication and maintenance requirements. Brake and main rotor blade folding optional. Composites cabins and rolled aluminium tailbooms built by Samsung; assembly in Canada, except for sales to Korea and China; Hexcel honeycomb as stiffener. The landing gear is twin skids with dynamically tuned cross tubes to reduce ground resonance. Low skids standard; optional high skids and emergency floats. Fuel is contained in three crash-resistant tanks; two forward, one aft, with a total usable capacity of 770 litres. One forward fuel tank can be removed in EMS configurations to provide additional stretcher space in cabin or to permit stretcher to extend into port side of cockpit. Oil capacity (total, both engines) 10.2 litres. Standard accommodation is for two crew in cockpit, on 20g energy-attenuating seats, and six passengers in cabin on two rows of three, seats in club configuration (all-forward-facing scats optional); all scats equipped with inertia-reel shoulder harnesses. Optional EMS interiors provide for carriage of one or two stretchers with up to two medical attendants, affording either full patient or head-only in-flight access, with single- or two-person crew. In cargo configuration, with all passenger seats removed, an optional removable flat cargo floor can be installed, equipped with integral tie-downs. Two forward-hinged doors each side; cabin doors, both sides, are forward-hinged, but port unit can be replaced by optional rearward-sliding door for cargo handling. External door on starboard side to rear baggage hold.
Orders for 22 were placed during the mockup’s first public display at Farnborough Air Show 1996, and 85 were on order by May 2000 from 50 customers. Deliveries began 2000 five delivered that year, 15 in 2001 and five in 2002.
Engines: Two Pratt & Whitney Canada PW207D turboshafts with FADEC, each 529kW for T-O (5 min) or 466kW max continuous OEI ratings: 611kW for 30 sec, 582kW for 2 min, 559kW for 30 min or 529kW max continuous. Twin-engine transmission rating: T-O & max continuous: 597kW. OEI transmission rating: 485kW for 30 sec: 451kW for 2 min; 343kW max continuous. Main rotor rpm: 395 Tail rotor rpm: 2,375 Main rotor diameter: 11.28m Fuselage length: 10.9m Take-off weight: 2722kg Empty weight: 1581kg Max speed at sea level: 252km/h Cruising speed at sea level: 240km/h Hovering ceiling, OGE: 4235m Hovering ceiling, IGE: 4940m Range at sea level: 663km Crew: 1 Passengers: 6-7
On 8 September, 1978, Bell announced its intention to develop a four-bladed variant of its twin-turbine Model 212. Designated Model 412, this helicopter was the first four-blade rotor helicopter to be produced by Bell. 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.
Two newly built Model 212 airframes 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 blades, fitted with a Nomex honeycomb core, are bonded together by glassfibre wrapping incorporating anti-icing heater mats and are interchangeable. The rotor mast is shorter than the 212, with blades that can be folded ans a rotor brake as standard. The main rotor rpm is 314. Equipped with a two-blade tail rotor. 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. The four composite blades have an unlimited life and span wise variation of their chord, twist and thickness of airfoils give added turning and aerodynamic efficiency. Generally of conventional light metal. Main rotor blade spar unidirectional glass libre with 45degree 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. The undercarriage is high skid, emergency pop-out float or non-retractable tricycle gear optional. Spats optional. Fuel in in 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. The cabin hold a pilot and up to 14 passengers: one in front port seat and 13 in cabin. Dual controls optional. Accommodation heated and ventilated. The first modified helicopter made its maiden flight in early August 1979, followed by the second machine in December of the same year. FAA Pt 29 type approval was given on 9 January, 1981, and IFR certification came on 13 February, 1981. 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. Two were delivered to the Venezuelan Air Force later in the year. By the end of 1987, a total of 145 Model 412s had been delivered. 213 were built in USA before production (SP version) was transferred to Canada in February 1989. A 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, 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. 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.This variant was also available in both civil and military configurations. 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).
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. Norway is assembling seventeen out of the eighteen machines ordered in Helikopter Services A/S workshops at Stavanger for the Royal Norwegian Air Force.
Agusta in Italy began production of the Model 412 in 1981, and manufactures the type as the AB 412SP, and has delivered over 75. Agusta 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). In June 1986 Bell produced the 412 Attack Helicopter (AH) based on the Bell 412SP.
The demonstrator aircraft (c/n 33119, N412AH) was 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 412AH has a maximum speed of 220kph. By January 1989, 162 Model 412s had been delivered. The Bell 412 is operated by the RAF as the Griffin. The Bell 412EP Griffin HT.1 being the training variant. 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).
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 110deg in azimuth, +15deg and –45deg 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.
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.
AB.412 Griffon Agusta’s multirole military development of the Bell 412 which first flew in August 1982, and is suitable for troop transport, fire-support, scout and reconnaissance, SAR, medevac and maritime surveillance. Armament options include 25mm Oerlikon cannon, machine-gun pods, rocket pods, and Sea Skua ASMs.
Specifications:
412 Engine: 2 x P&W PT6T-3B, 900 shp, 1342kW TBO: 2500 hr Main rotor: 46 ft / 14.02m Seats: 15 Length: 56 ft Length with rotors turning: 17.07m Height: 10.7 ft Max ramp weight: 11,600 lb Max takeoff weight: 11,600 lb Standard empty weight: 6267 lb / 2823kg Max useful load: 5333 lb Max landing weight: 11,600 lb Max sling load: 5000 lb Disc loading: 7 lbs/sq.ft Power loading: 6.4 lbs/hp Max usable fuel: 1455 lb Service ceiling: 20,000 ft Hover in ground effect: 4100 ft Hover out of ground effect: 2000 ft Max speed: 142 kt Normal cruise @ 3000 ft: 125 kt Fuel flow @ normal cruise: 758 pph Endurance @ normal cruise: 1.7 hr
412EP Engine: 1 x P&WC PT6T-3D Twin Pac, 1342kW for T-O / 1193kW max continuous OEI ratings: 850kW for 2 1/2 min / 723kW for 30 min Transmission rating: 1,022kW for T-O, 828kW max continuous OEI rating: 850kW Instant pwr: 1342 kW Rotor dia: 14 m MTOW: 5402 kg Payload: 2319 kg Useful load: 2271 kg Max speed: 140 kt Max cruise: 130 kt Max range: 782 km HIGE (@ MAUW): 10,200 ft HOGE (@MAUW): 5200 ft Service ceiling: 13,100 ft Crew: 1 Seats: 14
412HP Engine: 2 x P&WC PT6T-3BE Instant pwr: 1340 kW Rotor dia: 14 m MTOW: 5400 kg Payload: 2395 kg Useful load: 2395 kg Max speed: 140 kt Max cruise: 130 kt Max range: 745 km HIGE (@MAUW): 10,200 ft HOGE (@MAUW): 5200 ft Service ceiling: 17,000 ft Seats: 15
AB.412 Griffon Engine: 1 x P&WC PT6T-3BE Twin Pac Instant pwr: 764 kW Rotor dia: 14 m Fuselage length: 12.7 m No. Blades: 4 Empty wt: 2840 kg MTOW: 5400 kg Payload: 2290 kg Max speed: 125 kts Max cruise: 122 kts ROC: 440 m/min Ceiling: 5180 m Fuel cap (+aux): 820 lt ( 680 lt ) Range: 480 km Max range: 656 km HIGE: 10,200 m HOGE: 5200 m Crew: 1 Pax: 14
In November 1972 the Army called for design proposals for a new Advanced Attack Helicopter (AAH) intended for the all-weather anti-armor role. The Army’s specifications required that the aircraft be powered by twin General Electric T700 turboshaft engines and armed with up to sixteen Hellfire or TOW anti-tank missiles in addition to a single 30mm cannon. Preliminary design proposals were submitted by Boeing-Vertol, Bell, Hughes, Lockheed, and Sikorsky, and in June 1973 Bell and Hughes were selected as finalists and were each awarded contracts for the construction of two prototype aircraft. The contract was awarded to Bell on 22 June, 1973, for design, construction and qualification (Phase 1) of two flying prototypes (YAH-63A-BF) and a ground test vehicle (GTV). Bell’s 409, military designation YAH-63, was based largely on the earlier 309 King Cobra. The YAH-63 seated its two man crew in tandem within a narrow fuselage, though Bell put the pilot in front in order to improve the aircraft’s low-level ‘nap-of-the-earth’ (NOE) flight capabilities. In accordance with the Army’s specifications the YAH-63 was powered two widely separated 1536shp GE T700-GE-700 engines and was intended to carry its anti-tank ordnance load on short stub wings fixed to either side of the fuselage below the engine air intakes. The engines driving wide-chord, two-bladed semi-rigid main and tail rotors. Main rotor blade chord was 1.08m and an FX-69-H-083 aerofoil was used. The wide-chord had been selected mainly because it met performance requirements, permitted the spar separation required for 23mm survivability and was less complex by a factor of two. The ‘flat-pack’ transmission had large slow turning herringbone gears for increased survivability, reduced noise and a 30-minute fly-dry capability. The main rotor mast quickly retracted into the transmission for air transport. The YAH-63 had wheeled tricycle landing gear and a distinctive T-tail. The YAH-63 had a high flotation tricycle wheeled undercarriage with oleo struts equipped with ‘strut cutter’ crash energy absorber to meet the design impact velocity of 12.8m/sec. The weapon ‘systems consisted of a chin turret-mounted triple-barrel 30mm XM-188 rotary cannon (fire rate 600 to 1800rpm) mounted ahead of the stabilised sight to minimize damaging muzzle blast effects, and up to sixteen Rockwell AGM-114A Hellfire air-to-ground missiles or seventy-six 70mm FFAR rockets could be carried on the four wing stores. The first proroype YAH-63 (s/n 73-22246) first flew on 1 October, 1975, and the second prototype (s/n 73-22247) followed it into the air two months later. On 4 June, 1976, the first prototype experienced a heavy emergency landing and suffered minor damage. It was repaired in time to take part in the evaluation of the two contenders which was made at the Army Engineering Flight Activity (AEFA) from June to September 1976. The comparative tests between YAH-63 and YAH-64 led eventually to the selection of the Hughes design on 10 December, 1976. All flight testing with the YAH-63 then ceased and plans were made to continue work with the T700 powerplant. One Bell YAH-63 (s/n 73-22247) survives and is preserved by the US Army Aviation Museum, at Fort Rucker, Alabama.
AH-63 Engine: 2 x General Electric T700-GE-700 turboshaft, 1145kW Main rotor diameter: 15.54m Length with rotors turning: 18.51m Height: 3.73m Take-off weight: 7237kg Max speed: 325km/h Hovering ceiling: 1980m Crew: 2
The Bell ARH-70 helicopter was developed for the US Army as a possible direct replacement to the successful but aged Kiowa Warrior series of light armed reconnaissance mounts. In an effort to keep production and acquisition costs down for the US Army, the project attempted to develop a product using existing yet proven components. The Bell ARH was essentially a militarized form of the Bell 407. The ARH-70 came from the US Army’s Armed Reconnaissance Helicopter (ARH) program after the official cancellation of the RAH-66 Comanche light attack helicopter. Initial production forms would have been given the designation of ARH-70A.
In December of 2004, the requirement was sent out by the US Army and interested parties responded with their proposals. Chief among the returns was the Bell Model 407 (billed as an upgraded OH-58 Kiowa Warrior) and a Boeing response. Bell eventually won out and was awarded the multi-billion dollar production contract on July 29th, 2005. The contract called for some 368 production examples and required two prototypes along with two preproduction samples, this later changed to require four pre-production examples instead.
First flight of a demonstrator ARH was achieved on June 3rd, 2005. Further flights ensued and ultimately included additional avionics, mission-specific systems and the selected Honeywell HTS900-2 series turboshaft engine. The engine was trialed only on demonstrators and on the ground to verify its base qualities to this point. After some program delays, the first true ARH-70 prototype (Prototype #2) went airborne on July 20th, 2006, less than one year since the awarding of the Army contract. Prototype #4 was of note for it was forced to make a crash landing at a gold course after suffering an engine failure, this recorded on February 21st, 2007. Though neither of the pilots was harmed in the crash, the airframe was deemed a complete loss and a setback for the ARH program.
Ultimately, delays and product costs soon crept up on the ARH-70. The US Army halted the project, giving Bell one month to get its act in order. For the interim, Bell used its own money to further develop the systems until the US Army agreed to pick up the project once again by the middle of 2007. The rising costs forced an automatic and direct DoD review of the program under the existing Nunn-McCurdy Act. In the 2008 Defense Budget, no money was deviated to furthering the ARH-70. A final attempt to offer the ARH-70 as an export product to help recover some cost fell to naught and the ARH-70 remained in limbo for the time being. At one point, it was expected that some 512 total systems could be purchased by the US military alone, the additional examples over the original agreed upon total being delivered for use by the Army National Guard to replace their aged AH-64 Apaches.
The ARH-70 program proved too much to be a viable option for the US Army, despite the mount reaching all required performance parameters. The Army Acquisition Executive Office for Aviation called for the DoD contract to be terminated in full. The US Department of Defense officially acknowledged the request and did not promote the multi-million dollar expenditure to the US Congress, effectively killing hope for Bell and their new little machine. By this time, a single ARH-70 example had nearly doubled in per-unit cost to an estimated $14.5 million USD. According to Bell, the contract was 53 percent complete at the time of its cancellation on October 16th, 2008, with some 1,500 test flight hours having been recorded.
Design of the ARH-70 followed suit with the OH-58 series family of light helicopters. The two-man crew was seated in a side-by-side arrangement well-forward in the fuselage. Each position featured redundant controls and large, transparent, bulging forward windshields offering excellent visibility. Each pilot maintained their own automobile-style doors, hinged at two points forward, for entry and exit into their respective cockpit seats. Optics and special mission equipment could be mounted externally under the chin portion of the fuselage. The passenger cabin was located directly behind the cockpit and accessed via side access doors. Weapon stub pylons emerged from the fuselage underside and could carry limited offensive munitions. Landing skids were affixed to either fuselage underside and supported at two fixed points. The single engine was fitted high atop the fuselage above and behind the crew cabin. Exhaust jettisoned upwards at the rear of the engine compartment. The engine drove a four-bladed main rotor and a two-bladed tail rotor. The empennage was raised at the rear of the crew cabin and engine compartment, capped by a tall vertical tail fin. Additional vertical fins were set along the sides of the tail system along horizontal planes. The tail rotor was set to face the portside of the aircraft.
Crew accommodations amounted to two pilots in the forward cockpit and up to six passengers in the main cabin.
Power for the ARH-70 was supplied from a single Honeywell HTS900-2 turboshaft engine of 970 shaft horsepower. This powerplant could supply the airframe a top speed of 161 miles per hour with a cruise speed of about 130 miles per hour. Her range was listed at 186 miles with a service ceiling equal to 20,000 feet. Empty weight registered at 2,598lbs with a maximum take-off weight equal to 5,000lbs.
As an armed reconnaissance helicopter and as in the OH-58D before it, the ARH-70 was intended to carry a rather modest arrangement of weaponry. Primary hitting power was to be supplied y a 1 x GAU-19 series 0.50 caliber Gatling gun fitted to an outboard pylon as well as Hydra 70 2.75-inch (70mm) rockets, also on an outboard pylon.
Although referred to in a few official media reports under the designation of ‘Arapaho’, this name was never officially assigned to the ARH-70 product.
Bell ARH-70A (Arapaho) Engine: 1 x Honeywell HTS900-2 turboshaft, 970shp Rotor: four-blade main rotor and two-blade tail rotor. Length: 34.68ft (10.57m) Height: 11.68ft (3.56m) Empty Weight: 2,597lbs (1,178kg) Maximum Take-Off Weight: 5,000lbs (2,268kg) Maximum Speed: 161mph (259kmh; 140kts) Maximum Range: 186miles (300km) Service Ceiling: 20,000ft (6,096m) Accommodation: 2 + 6 Hardpoints: 2
With the design definition launched in 1993, the Bell 407, developed from the 206L-4 offered wider cabin, 815 shp 250-C47B derated to 675 shp for takeoff and four main rotor blades. From the windscreen pillars the cabin swells outwards to a width 178 mm more than the LongRanger’s, not tapering in again until it meets the baggage compartment forward bulkhead. Aft of that it’s normal LongRanger, although with a different tail rotor system. The extra width is gained through curved door pillars and skins of carbon fibre composites. Cabin windows are greatly enlarged, coming down to the level of the windscreen and curving well up towards the cabin roof. The doors are interchangeable between 407s, handles are flush-mounted car-type.
The LongRanger’s extra left-hand cabin door is retained for loading a stretcher, with the aft-facing left-hand seat wider than its counterpart behind the pilot. The rear seat usually takes three passengers, but in the VIP configuration the centre space is taken by a folding armrest and there’s adequate room for four passengers in the main cabin. Lap and inertia reel shoulder harness is supplied for all passenger seats.
Bell used the four-blade main rotor and complete tail rotor drive train from the OH-58D Kiowa Warrior, and the transmis¬sion also comes from the OH-58D, with larger bearings and redesigned gears to increase fatigue life. The four 255 mm chord composite blades (Nomex honeycomb core, glass fibre reinforced plastic spar and skin) have tapered tips and unlimited fatigue life, and are attached to a flexible GFRP yoke which accom-modates flapping motion, with elastomeric dampers and bearings for lead-lag and pitch-change motion. A Frahm damper on top of the hub takes care of rotor vibration, and the transmission is attached to the airframe by SAVITAD (system for attenuating vibration independent of tuning and damping) which comprises two beams with elastomeric mounts and retained by springs.
The “avoid curve” is at 800 ft or 70 kts, almost twice that of the JetRanger. The low-inertia rotor also leads to a restriction in climb rate to 2000 ft/min. Although the 407 is capable of much more, over 4000 ft/min. Although the tail rotor system is taken from the OH-58D, the Kevlar/Nomex blades are longer and give enough authority to allow takeoffs in 35 kt winds from any direction. Tail rotor control is also hydraulic. Normal MTOW is 2267 kg, increased to 2499 kg with an external jettisonable load, as the gross weight is dictated by the landing skids and structure. Maximum external load is 1200 kg, but for normal passenger use it can take full fuel and seven people with light baggage and still be under gross weight.
The Rolls-Royce Allison 250-C47B turboshaft is controlled by a full-authority digital engine control system, the first to be fitted to a single¬ turbine light helicopter.
The 407 can handle slopes 5 degrees nose down or 10 degrees nose up or to either side, due in part to a pivoted rear undercarriage cross member.
A proof of concept demonstrator featuring bulged cabin door, a four blade rotor system (off the 406) and Allison 250-C47 turboshaft. A Law Enforcement demostrator was demonstrated in 2002, with a Rolls-Royce/Allison 250-C47B engine.
The concept demonstrator 407 (N407LR) was first flown on 21 April 1994 (standard Bell 206L-3 modified with tailboom and dynamic system of military OH-58D, plus sidewall fairings to simulate broader fuselage), and the programme was first revealed at Heli-Expo ’95, Las Vegas, January 1995. Two prototype/ pre-production 407s (C-GFOS and C-FORS) were first flown on 29 June and 13 July 1995, respectively.
The first producrion airframe (C-FWQY/N407BT) was flown 10 November 1995 and Transport Canada certification was received on 9 February 1996 with FAA certification following on 23 February. The first customer delivery was at Heli-Expo ’96, Dallas, in February 1996. A MoU of June 1996 provided for licensed assembly and marketing by Dirgantara (formerly IPTN) of Indonesia.
After extensive flight testing in the wake of three accidents, Transport Canada and the FAA approved an increase in the Bell 407’s maximum speed to 130 kt. from 100 kt., and company officials expected to restore the light helicopter’s 140-kt. never exceed speed (Vne) by the third quarter of 1999.
The latest approval is predicated on compliance with a Bell Helicopter Textron Alert Service Bulletin (ASB) that calls for installation of a redesigned tail rotor hub and blades as well as addition of mechanical stops on the anti-torque pedals. A Bell official said the stops restrict left pedal travel to 20.75 deg. from 28 deg., but right pedal travel remains at 14 deg.
In addition, the hub design moves the tail rotor centerline outboard 0.86 in. and provides an additional 2.4 in. of clearance between the tail boom and the tail rotor blades at maximum flapping angle. The chief performance penalty is reduced tail rotor authority at high altitudes, a Bell official said. The company has begun incorporating the changes into production 407s at its facilities in Mirabel, Quebec.
Bell also plans to provide parts to complete the modifications at no expense to operators in the field. According to the official, there were more than 350 of the single-engine 407s in operation worldwide in 1999. The helicopter entered service in 1996.
Company engineers and test pilots developed ancl evaluated the latest fix during a series of special flight tests in March and April that exceeded normal Transport Canada certification requirements by a significant margin, the official said. The tests centered on flying a 407 at 130 kt. indicated airspeed and using each anti-torque pedal to its mechanical stop in less than 0.4 sec. Although the abrupt applications were applied repeatedly, the tail rotor blades did not contact the tail boom structure and several inches of clearance were maintained, he said.
The 130-kt. approval comes about two months after Bell began conducting a series of special flight tests to increase Vne above a 100-kt. limit imposed on the aircraft early in 1999. The restriction was imposed after the tail booms of three 407s were severed following left pedal inputs. The first accident occurred in 1997 in the U.S., the second in 1998 in South Africa, and the third occurred in Brazil.
According to a Bell official, investigation has revealed that each f the accidents was cause by a sudden, full input of the left tail rotor pedal at cruise airspeed.” The sudden input “caused exceptional flapping (deflection) of the tail rotor” blades that damaged pitch stops and the pitch control links. As a result, the blades struck the tail boom aft of the horizontal stabilizers, severing it. The cause of the pedal input, however, has not been fully explained but pilot error is not being ruled out.
To reinstate the 407’s original 140-kt. Vne, Bell was instrumenting a 407, at its Mirabel site, in preparation for beginning flight tests of a solenoid-operated airspeed sensing system that will automatically engage/disengage the pedal stops depending on airspeed. If the helicopter is flying below 50 kt. the stops will be retracted to permit 28 deg. of left pedal travel and maximum tail rotor authority. Above 55 kt., the solenoid will engage the stops and limit left pedal travel to 20.75 deg.
The system, which is redundant and features a mechanical override, will be standard equipment in the twin-engine Bell 427. That aircraft was completing certification by Transport Canada and FAA.
The 500th production Bell 407 was delivered in October 2001 to Pabst Air, Germany, and 550 had been delivered to operators in 45 countries by early 2003; fleet time then totalled more than 745,000 hours. Total of 62 delivered in 1999, 62 in 2000, 47 in 2001 and 33 in 2002. COSTS: US$1.37 million (1999) flyaway. Development cost were estimated as US$50 million, of which US$9 million provided by Canadian government.
Bell 407 Engine: One Rolls-Royce 250-C47B turboshaft, 606kW for T-O, 523kW Max continuous pwr: 630 shp Transmission rating: 503kW for T-O, 470kW continuous op Main rotor diameter: 10.7m Rotor speed: 413 rpm Length: 12.7m Height: 3.7m Take-off weight: 2267kg Empty weight: 1178kg Useful load: 1058 kg. Standard usable fuel: 484 lt Optional aux fuel: 72 lt Max speed at sea level: 252km/h Vne: 204km/h / 140 kts Max cruise: 133 kt. LR cruise: 121 kt Hovering ceiling, OGE: 2470m / 12,200 ft Hovering ceiling, IGE: 3440m / 10,450 ft Service ceiling: 5460m Max ROC: 2000 fpm Range: 608km Loiter @ 60 kt: 3.8 hr. Internal payload: 1089kg External payload: 1200kg Crew: 1 Passengers: 6
In February 1981 the US Army’s Applied Technology Laboratory announced that Bell Helicopter and the Sikorsky Aircraft Division of United Technologies had both been awarded contracts for the design, construction, and initial flight testing of composite airframe research helicopters as part of the Advanced Composite Airframe Programme (ACAP). The programme is the development of an all-composite helicopter fuselage lighter and cheaper to build, per production airframe, than conventional machines. Bell and Sikorsky were each awarded contracts for the production of three machines; a tool-proof vehicle, a static test vehicle, and a flight test vehicle. Bell’s ACAP machine, which carries the company model number D292, made its first hover flight on 30 August, 1985. By mid-January 1986 the aircraft had completed twelve of its projected fifty flight test hours.
The D292 was based on Bell’s commercial Model 222 twin- turbine light helicopter and used that machine’s Avco Lycoming engines, transmission, and two-bladed main and tail rotors. The ACAP’s tailboom, vertical fin, and rotor pylon are almost identical in appearance to those of the 222, though the D292’s entire elongated pod-and-boom airframe is constructed of glass-reinforced plastic (GRP), graphite, and Kevlar. The use of a particular composite material for a specific aircraft component is determined by the strength, flexibility or other primary characteristic required of that component. The D292’s basic load-bearing structure is thus constructed primarily of graphite or graphite/epoxy, while the flooring and most of the craft’s exterior ‘skin’ is made of a more ballistically-tolerant Kevlar/ epoxy or glassfiber/epoxy blend. The seats for the helicopter’s two crew members and two passengers are of Kevlar/epoxy and are designed to absorb the high vertical loads of a forty-foot- per-second crash landing, as are the legs of the craft’s non-retracting tailwheel landing gear. In addition to 15 hours of ground running and 50 hours of flight testing, which were completed in October 1985, the D-292 was used for shake testing and controls proof loading. A five-phase militarisation test and evaluation programme (MT&E) began in 1985 and was completed in 1988, following evaluation of undercarriage crashworthiness, lightning protection system, internal acoustics and additional repairability demonstrations. This programme included dropping the helicopter airframe from 12m in September 1987 at the NASA Langley Research Centre to demonstrate the capability of meeting stringent military crash survivability requirements. This included a 15m/s impact velocity at an aircraft attitude of ten degrees roll and ten degrees nose up pitch without any apparent serious injuries to the four dummy occupants (this impact velocity was comparable to a free fall from a three-storey building). Another major advancement demonstrated by the Bell ACAP design during these tests was the fuel system which totally contained the fuel during the drop test, thus reducing the risk of post-crash fires. But the main purpose of the ACAP programme was to achieve the US Army’s goal of reducing weight and cost, as well as improving military helicopter characteristics, by demonstrating the application of advanced composite materials. In this sphere, the Bell D-292 featured a weight reduction of 22% in the airframe structure, a 17% saving in cost, survivability in a vertical crash, and reduced radar signature. These comparisons were made possible because Bell and Sikorsky each also designed a duplicate aircraft of current conventional metal construction.
In February 1983, Bell announced the both commercial and military, single and twin-engined, Model 400 TwinRanger. This seven-seat aircraft was in the 1800-2700kg gross weight class. The Model 400 was powered by two 443shp Allison 250-C20R turboshaft engines, had a four-blade soft-in-plane main rotor, an advanced technology transmission and drive system with ‘run-dry’ capability. The aircraft entered development in 1983 with wind-tunnel testing with a one-quarter scale model and flight testing of the dynamic components on a specially modified Model 206LM LongRanger (c/n 45003, N206N) which served as test-bed and flew in March 1983. This aircraft had the four-bladed OH-58D AHIP rotor, a strengthened tail boom, a ring guard tail rotor and a deepened fuselage to increase fuel capacity. The first prototype Model 400 (c/n 48001, N3185K) flew on 30 June, 1984, powered by Allison engines. Three pre-production Model 400 TwinRangers (c/n 48002/ 48004) were built, the first of which (N3185L) flew for the first time on 4 July, 1985, the second (N3185U) in May and the third (N400BH) in June 1985. The first aircraft was later used as a ground test vehicle. It was expected that the Canadian factory, at Mirabel, Montreal, would undertake production of the Model 400 and develop the Model 400A, a variant of the Model 400 powered by a single 1000shp Pratt & Whitney Canada PW209T turboshaft engine, and employing major composites components. The programme was suspended indefinitely pending a market situation that would support an annual sales rate of about 120 aircraft. The four existing aircraft have been cancelled from the register and put in storage by Bell Helicopter Textron Canada, at Mirabel.
Model 400 Rotor diameter: 11.30m Overall length: 13.39m Length of fuselage: 11.02m Height overall: 3.56m Maximum take-off weight: 2495kg Empty weight: 1427kg Maximum speed: 278km/h Maximum cruising speed at 1525m: 244km/h Initial rate of climb: 464m/min Service ceiling: 6100m Hover ceiling outside ground effect: 3110m Hover ceiling in ground effect: 4360m Maximum range: 834km
Bell announced the development of a new combat helicopter on 28 September 1971, derived from the Model 209 and 211, with company funds, with a 1.10m longer fuselage supporting a larger diameter rotor measuring 14.63m. Both the main and tail rotors had wider chord blades and the main rotor blades had double swept tips to reduce noise levels and improve performance at high speed. The nose was also modified to accept new apparatus, the available space for ammunition was increased, and the wing span was taken to 3.96m. A redesigned tail assembly was used with a lower fin for improved longitudinal stability. It also had the transmission, wide-chord two-blade main rotor and drive train of the Model 211 HueyTug. Design work was begun by a team led by Joe Tilley and construction started in January 1971. Two prototypes of the Model 309 Kingcobra were built. The first (c/n 2503, registered N309J), which flew on 10 September 1971 at Fort Worth with Gene Colvin at the controls, was offered to the Marines with Turbo Twin Pack T400-CP-400 engines, while the second prototype (which flew in January 1972) was offered to the Army with a 2890shp Lycoming T55-L7C turbine of the Model 211, derated to 2050 on take-off. The KingCobra incorporated new avionics and systems to fulfill its anti-tank mission (inertial navigation system, APN-198 radar altimeter, fire-control computer, multi-sensor sight, head-up display, helmet sighting system, FL-33 FLIR, low-light level television and, of course TOW guidance system). Armament included provision for sixteen TOW missiles under extended stub wings and a General Electric chin-turret housing a three-barelled 20mm Gatling gun with 1345 rounds. On 11 April 1972, the first prototype was damaged in an accident. To meet future Army needs it was decided to convert the twin-engined 309 into single-engined configuration. As expected, on 9 August, 1972, the Army finally cancelled the Cheyenne programme and in due course two helicopter manufacturers, Sikorsky and Bell, submitted proposals for a less sophisticated aircraft, the Model S-67 and the Model 309 respectively. Tests and demonstrations were successfully conducted with both aircraft, but the Army set up new requirements and opened a new contest within the Advanced Attack Helicopter programme (AAH) which would eventually lead to the selection of the MDD/Hughes AH-64 Apache. The Bell Model 309 (N309J) is now preserved by the US Army Aviation Museum in Fort Rucker, Alabama.
Bell 309 Kingcobra Engine: 1 x Lycoming T55-L7C turboshaft, 2155kW Main rotor diameter: 14.63m Length: 14.63m Height: 4.11m Take-off weight: 4510kg Empty weight: 2890kg Gross weight: 6350kg Max speed: 330km/h
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