|Bell Model 406 / OH-58D "Kiowa Warrior"|
The latest Bell OH-58D is the result of a 1981 proposal by the US Army for a scout helicopter capable of working alongside the AH-64 Apache. This would include working in the forward battle area, being capable of designating targets by laser for the Apache's Hellfire missiles, close combat aerial reconnaissance and intelligence gathering plus artillery spotting. The OH-58D resulted from the Army Helicopter Improvement Program (AHIP). The result for Bell was the first flight in October 1983 of their OH-58D. The new OH-58 was fitted with the new four-blade composite rotors developed by Bell and a mast-mounted sight. A more powerful 650shp Allison 250-C30R turboshaft engine was fitted and also cockpit multi-function displays. The mast-mounted sight allows the helicopter to stay out of sight and gives added protection in forward areas. The sight contains 12 x magnification TV camera, auto-focusing infra-red thermal imaging sensor and laser range finder/designator, automatic target tracking and in-flight bore sighting. In the scout role the OH-58D can be equipped with Stinger missiles for air-to-air combat. The OH-58D has a maximum speed of 230kph and a range of 495km.
In May 1984 Bell developed the Model 406CS (Combat Scout). This increased the capability of the OH-58D and provided a quick change weapons package. Designed as a force multiplyer, the 406CS can accept any of the roof-mounted sights in production or under development, with growth provisions for laser target designation, FLIR and video thermal tracker. Bell is also under contract with the US Government for an all-composite airframe program (ACAP) which will lead to expanded use of composite materials for all Bell helicopters, including future scout helicopters. The power-plant fitted to the 406CS is the Allison 250-C30 turboshaft developing 650shp with built-in particle separation system fitted to a 510shp transmission with elastomeric vibration isolation, fail-safe four-point mounting and a thirty minute run dry capability.
P.Allen "The Helicopter", 1996
Bell won US Army Helicopter Improvement Program (AHIP) 21 September 1981; first flight of OH-58D 6 October 1983; deliveries started December 1985; first based in Europe June 1987. First OH-58D(I) retrofit contract awarded January 1992. First 117 conversions at Amarillo, Texas; then Fort Worth; produced as Kiowa Warrior from 202nd aircraft. Production completed in 2000.
OH-58D (I) Kiowa Warrior: Armed version, to which all planned OH-58Ds are being modified; integrated weapons pylons, uprated transmission and engine, lateral CG limits increased, raised gross weight, EMV protection of avionics bays, localised strengthening, RWR, IR jammer, video recorder, SINCGARS radios, laser warning receiver and tilting vertical fin, armament same as Prime Chance, integrated avionics and lightened structure.
Prime Chance: Fifteen special armed OH-58Ds modified from September 1987 under Operation Prime Chance for use against Iranian high-speed boats in Gulf; delivery started after 98 days, in December 1987; firing clearance for Stinger, Hellfire, 0.50 in gun and seven-tube rocket pods completed in seven days. Further conversion for development trials.
MultiPurpose Light Helicopter (MPLH) : Further modification of Kiowa Warrior; features include squatting landing gear, quick-folding rotor blades, horizontal stabiliser and tilting fin to allow helicopter to be transported in cargo aircraft and flown to cover 10 minutes after unloading from C-130. Later additions include cargo hook for up to 907kg (2,000 lb) slung load and fittings for external carriage of six outward-facing troop seats or two stretchers. All Kiowa Warriors have MPLH capability.
Further modifications for Warrior, currently under consideration, include improved SINCGARS (secure speech) radios; improved data modem; improved master processor and mast-mounted sight processor; video cross-link; INS/GPS; digital map display.
OH-58X Light Utility Variant: Contender for anticipated US Army requirement; fourth development OH-58D (69-16322) modified in 1992 with partial stealth features (including chisel nose); concept subsequently discarded.
CUSTOMERS: US Army: initial plan to modify 592 OH-58A to OH-58D reduced to 477; reduced again to 207, but Congressionally mandated re-orders increased total to 398 (excluding five prototypes) by 1996 from new goal of 507. Taiwan ordered 12 OH-58Ds in February 1992, plus 14 options, subsequently converted to firm orders. Deliveries started in July 1993.
COSTS: US$7.46 million (1993) programme unit cost.
DESIGN FEATURES: Four-blade Bell soft in plane rotor with carbon composites yoke, elastomeric bearings and composites blades. Transmission rating: Kiowa 339kW continuous; Kiowa Warrior 410kW continuous. Main rotor 395 rpm; tail rotor 2,381 rpm. McDonnell Douglas/Northrop mast-mounted sight containing TV and IR optics and laser designator/ranger; Honeywell integrated control of mission functions, navigation, communications, systems and maintenance functions based on large electronic primary displays for pilot and observer/gunner; hands-on cyclic and collective controls for all combat functions; airborne target handover system in all OH-58Ds operates air-to-air as well as air-to-ground using digital frequency-hopping; system indicates location and armament state of other helicopters; some OH-58Ds have real-time video downlink capable of relaying of US Army and Air Force aircraft to headquarters 40km away or, via satellite, to remote locations.
FLYING CONTROLS: Fully powered controls, including tail rotor, with four-way trim and trim release; Stability and Control Augmentation System (SCAS) using AHRS gyro signals; automatic bob-up and return to hover mode; Doppler blind hover guidance mode; co-pilot/observer's cyclic stick can be disconnected from controls and locked centrally.
STRUCTURE: Basic OH-58 structure reinforced; armament cross-tube fixed above rear cabin floor; avionics occupy rear cabin area, baggage area and nose compartment.
LANDING GEAR: Light-alloy tubular skids bolted to extruded cross-tubes.
POWER PLANT: One Allison 250-C30R (T703-Ad-700) turboshaft, (C30R/3 with improved diffuser in Kiowa Warrior) with an intermediate power rating of 485kW at S/L, ISA, FADEC. Transmission rating: Kiowa 339kW continuous; Kiowa Warrior 410kW continuous. One self-sealing crash-resistant fuel cell, capacity 424 litres located aft of the cabin area. Refuelling point on starboard side of fuselage. Oil capacity 5.7 litres.
ACCOMMODATION: Pilot and co-pilot/observer seated side by side. Door on each side of fuselage. Accommodation is heated and ventilated.
SYSTEMS: Single hydraulic system with three-axis SCAS, pressure 69 bars, for main and tail rotor controls. Maximum flow rate 11.34 litres/min. Open-type reservoir. Primary electrical power provided by 10 kVA 400Hz three-phase 120/208V AC alternator with 200A 28V DC transformer-rectifier unit for secondary DC power. Back-up power provided by 500VA 400Hz single-phase 115V AC solid-state inverter and 200A 28V DC starter/generator.
AVIONICS: Comms: Five com transceivers, datalink and secure voice equipment. Phase 1 additions, introduced on production line in 1991 in preparation for Kiowa Warrior, include AN/ARC-201 SINCGARS secure voice/data radio and Have Quick II radio.
EQUIPMENT: NBC mask in Phase 1 and Warrior aircraft.
ARMAMENT: Four Stinger air-to-air or Hellfire air-to-surface missiles, or two seven-round 70mm in rocket pods, or one 12.7mm machine gun, mounted on outriggers on cabin sides; port side only for gun.
Jane's Helicopter Markets and Systems
At the end of the 1970s, the US Army set up the Army Helicopter Improvement Program (AHIP) to provide a near-term scout helicopter (NTSH) as an interim aircraft pending development of a new design (in fact the LHX). After several proposals had been examined, Bell's Model 406 proposal was declared the winning contender in the AHIP competition and, on 21 September, 1981, the US Army announced that the Model 406 had been selected. A $151 million contract called for Bell to design, modify and test five prototype aircraft. The dynamic components were tested in March 1983 on the Model 206LM LongRanger c/n 45003 (N206N). The first of these five prototypes flew on 6 October, 1983, and was used for manual validation and training. The second and fifth prototypes were employed in flight testing at Bell's Flight Research Center in Arlington, while the third prototype was equipped with the mast mounted sight and sent to Yuma for mission equipment package evaluation. The fourth aircraft was used for avionics and electro-magnetic compatibility.
The qualification programme was completed by June 1984 and operational tests were conducted at Yuma and Edwards in February 1985 and completed by March of the same year.
The Model 406 incorporated several refinements: a new power-plant, advanced avionics and systems as well as extended armament capabilities. The powerplant was a 650shp Allison 250-C30R (T703-AD-700) turboshaft driving a four-blade soft-in-plane rotor, in place of the 420shp Allison T63-A-720 turboshaft driving the classic two-blade rotor of the OH-58C. The OH-58D, as it was officially designated, was equipped with a McDonnell Douglas/Northrop mast-mounted sight (MMS) capable of operating in day/night and limited visibility and with a Honeywell Sperry cockpit control and display subsystem. The MMS brings together a lot of sophisticated technology. It is a combination of television camera, thermal imaging sensor, boresight system and laser range finder/ designator. Automatically, the system focuses and tracks the area and points targets. This system provides commanders with a survivable real time combat information, command and control, reconnaissance, security, aerial observation and target acquisition/designation system to operate with attack helicopters, air-cavalry and field artillery units during day, night and reduced visibility. The MMS enhances survivability by allowing the crew to accomplish its mission while hovering behind trees and hilltops. By day, the MMS provides long-range target acquisition with television in a 2deg by 8deg field of view, and at night with thermal imaging in a 3deg by 10deg field of view. It also provides laser designation at stand-off ranges for Hellfire, M172 Copperhead and other Army and Air Force laser guided munitions (LGM).
Armament of the OH-58D includes four FIM-92A Stinger air-to-air missiles, or four Hellfire air-to-surface missiles, or two rocket pods, or two 12.7mm machine-gun pods, mounted on outriggers on the cabin sides. Qualification tests for these armaments were conducted during November and December 1987.
Under the AHIP programme, 578 OH-58Ds were expected to be procured over the 1985-91 period at an estimated cost of $2.000 million. An initial batch of 171 aircraft had been funded during FY88, in five lots (16, 44, 39, 36 and 36 aircraft). A further thirty-six aircraft have been requested in FY89. In 1987, deliveries totalled eighty-seven OH-58Ds among which several were of the armed version. Responding to the Army's desire to field an initial armed helicopter, Bell modified fifteen OH-58Ds to the attack configuration known as Kiowa Warrior or simply Warrior. By July 1987, sixty-four were on the US Army inventory and the first shipment to units stationed in Europe began on 11 June, 1987, when twelve OH-58Ds were loaded on board a single Lockheed C-5A Galaxy.
Deliveries of the armed version began during the spring of 1988 to the 18th Airborne Corps Brigade at Fort Bragg. The Warriors were shipped to the Persian Gulf where they were stationed to protect the vital sea lanes for the world's oil supply. Because of the success of the Persian Gulf operation, the Secretary of the Army ordered that 243 OH-58Ds be reconfigured to the armed Warrior version. Eighty-one of these aircraft will also be equipped as the Multi-purpose Light Helicopter (MPLH), capable of carrying troops externally, litter patients or cargo on a sling. First operational deployment of the US Army OH-58Ds occurred during operation 'Desert Storm' when aircraft were deployed by the Aviation Battalion of the 101st Airborne Division and the 82nd Aviation Brigade of the 82nd Airborne Division.
A.J.Pelletier "Bell Aircraft since 1935", 1992
Technical data for OH-58D
Engine: 1 x Allison 250-C30R rated at 485kW, main rotor diameter: 10.67m, length with rotors turning: 15.85m, fuselage length: 10.48m, height: 3.93m, take-off weight: 2360kg, empty weight: 1380kg, max speed: 241km/h, cruising speed: 204km/h, hovering ceiling, OGE: 3415m, range: 555km