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Bell 407

 

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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.

 

Bell-407


A fter 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



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