Bell OH-58 Kiowa
The Bell OH-58 Kiowa is a family of single-engine single-rotor military helicopters used for observation, utility, and direct fire support. It was produced by the American manufacturer Bell Helicopter and is closely related to the Model 206A JetRanger civilian helicopter.
The OH-58 was originally developed during the early 1960s as the D-250 for the Light Observation Helicopter. While the rival Hughes OH-6 Cayuse was picked over Bell's submission in May 1965, the company refined its design to create the Model 206A, a variant of which it successfully submitted to the reopened LOH competition two years later. The initial model, designated by the service as the OH-58A, was introduced in May 1969. Successive models followed, often with uprated engines, enhanced protection systems, and other improvements, culminating in the OH-58F. Additional improvements, such as the OH-58X, were proposed but not pursued.
During the 1970s, the US Army became interested in pursuing an advanced scout helicopter, for which the OH-58 would be further developed, evaluated, and ultimately procured as the OH-58D Kiowa Warrior. The OH-58D is equipped to perform armed reconnaissance missions and to provide fire support to friendly ground forces; it is equipped with a distinctive Mast Mounted Sight containing various sensors for target acquisition and laser designation. Another visible feature present on most OH-58s are knife-like extensions above and below the cockpit that form part of the passive wire strike protection system. The early-build OH-58s were equipped with a two-bladed main rotor, while the OH-58D and newer variants have a four-bladed rotor.
The OH-58 was primarily produced for the United States Army, and deployed in the Vietnam War two months after its entry to service. The US Army made extensive use of various OH-58 models across numerous war zones over the decades, seeing active combat during the Gulf War, the invasion of Panama, and the War in Afghanistan among others. In 2017, the US Army withdrew its remaining OH-58s, using alternative rotorcraft such as the Boeing AH-64 Apache and unmanned aerial vehicles, to fill the role. The OH-58 has been exported to Austria, Canada, Croatia, the Dominican Republic, Taiwan, Saudi Arabia, and Greece. It has also been produced under license in Australia.
Development
Light Observation Helicopter (LOH)
On 14 October 1960, the United States Navy approached 25 helicopter manufacturers to request on behalf of the Army the submission of proposals for a Light Observation Helicopter. Bell Helicopter was one of the manufacturers approached, and chose to enter the competition along with 12 other manufacturers, including Hiller Aircraft and Hughes Tool Co., Aircraft Division. Bell's design was internally referred to as the D-250, and would be officially designated as the YHO-4. On 19 May 1961, Bell and Hiller were announced as winners of the design competition.Bell developed the D-250 design into the Model 206, while the HO-4 designation was changed to YOH-4A in 1962, and produced five prototype aircraft for the Army's test and evaluation phase. On 8 December 1962, the first prototype performed its maiden flight. The YOH-4A was also called the Ugly Duckling in comparison to other contending aircraft. After a fly off of the Bell, Hughes and Fairchild-Hiller prototypes, the Hughes OH-6 Cayuse was selected in May 1965.
When the YOH-4A was rejected by the Army, Bell went about solving the problem of marketing the aircraft. In addition to the image problem, the helicopter lacked cargo space and only provided cramped quarters for the planned three passengers in the back. The solution was a fuselage redesigned to be more sleek and aesthetic, adding of cargo space in the process. The redesigned aircraft was designated as the Model 206A, and Bell President Edwin J. Ducayet named it the JetRanger denoting an evolution from the popular Model 47J Ranger.
In 1967, the Army reopened the LOH competition for bids because Hughes Tool Co. Aircraft Division could not meet the contractual production demands. Bell resubmitted for the program using the Bell 206A. Fairchild-Hiller failed to resubmit their bid with the YOH-5A, which they had successfully marketed as the FH-1100. In the end, Bell underbid Hughes to win the contract and the Bell 206A was designated as the OH-58A. Following the U.S. Army's naming convention for helicopters, the OH-58A was named Kiowa in honor of the Native American tribe.
Advanced Scout Helicopter
In the 1970s, the U.S. Army began evaluating the need to improve the capabilities of their scout aircraft. Anticipating the AH-64A's replacement of the venerable AH-1, the Army began shopping the idea of an Aerial Scout Program to stimulate the development of advanced technological capabilities for night vision and precision navigation equipment. The stated goals of the program included prototypes that would:...possess an extended target acquisition range capability by means of a long-range stabilized optical subsystem for the observer, improved position location through use of a computerized navigation system, improved survivability by reducing aural, visual, radar, and infrared signatures, and an improved flight performance capability derived from a larger engine to provide compatibility with attack helicopters.
During March 1974, the Army created a special task force at Fort Knox to develop the system requirements; by the following year, the task force had devised the requirements for an Advanced Scout Helicopter program. The requirements were formulated around an rotorcraft capable of performing in day, night, and adverse weather, and compatible with all advanced weapons systems planned for development and fielding into the 1980s. The program was approved by the System Acquisition Review Council and the Army prepared for competitive development to begin the next year. However, as the Army tried to get the program off the ground, Congress declined to provide funding in the fiscal year 1977 budget and the ASH Project Manager's Office was closed on 30 September 1976.
While no development occurred for some years, the program survived as a requirement without funding. On 30 November 1979, the decision was made to defer development of an advanced scout helicopter in favor of modifying existing airframes in inventory as a near term scout helicopter option. The development of a mast-mounted sight would be the primary focus to improve the ability to perform reconnaissance, surveillance, and target acquisition missions while remaining hidden behind trees and terrain. Both the UH-1 and the OH-58 were evaluated as NTSH candidates, but the UH-1 was dropped from consideration due to its larger size and ease of detection. The OH-58, on the other hand demonstrated a dramatic reduction in detectability with a Mast-Mounted Sight.
On 10 July 1980, the Army decided that the NTSH would be a competitive modification program based on developments in the commercial helicopter sector, particularly Hughes Helicopters' Hughes 500D, which had made major improvements over the OH-6.
Army Helicopter Improvement Program (AHIP)
The Army's decision to acquire the NTSH resulted in the "Army Helicopter Improvement Program ". Both Bell Helicopter and Hughes Helicopters redesigned their scout aircraft to compete for the contract. Bell offered a more robust version of the OH-58 in their Model 406, and Hughes offered an upgraded version of the OH-6. On 21 September 1981, Bell Helicopter Textron was awarded a development contract. On 6 October 1983, the first prototype performed its maiden flight, and the aircraft entered service two years later as the OH-58D.Initially intended for attack, cavalry, and artillery roles, the Army only approved a low initial production level and confined the OH-58D's role to field artillery observation. The Army also directed that a follow-on test be conducted to further evaluate it due to perceived deficiencies. On 1 April 1986, the Army formed a task force at Fort Rucker, Alabama, to remedy deficiencies in the AHIP. During 1988, the Army had planned to discontinue the OH-58D and focus on the LHX; however, Congress approved $138 million to expand the program, calling for the AHIP to operate with the Apache as a hunter/killer team; the AHIP would locate targets and the Apache would destroy them in a throwback to the traditional OH-58/AH-1 relationship.
The Secretary of the Army directed instead that the aircraft's armament systems be upgraded, based on experience with Task Force 118's performance operating armed OH-58Ds in the Persian Gulf in support of Operation Prime Chance, and that the type be used primarily for scouting and armed reconnaissance. The armed aircraft would be known as the OH-58D Kiowa Warrior, denoting its new armed configuration. Beginning with the 202nd aircraft in May 1991, all remaining OH-58Ds were produced in the Kiowa Warrior configuration. During January 1992, Bell received its first retrofit contract to convert all remaining OH-58Ds to the Kiowa Warrior configuration.
Production
Overall 2,325 OH-58 were produced, with an additional 56 Bell 206B-1 also built. Production of new airframes for the A and B models ended in 1977, and the D model in 2000. Conversions of early models to the D standard continued afterward.Design
The Bell OH-58 Kiowa is a family of single-engine single-rotor military helicopters principally used for observation, utility, and direct fire support. The primary role of the original OH-58A was to identify targets for other platforms, such as the Bell AH-1 Cobra attack helicopter and ground artillery; it lacked any armaments and weighed 1,451 kg when fully loaded, being able to carry a small amount of cargo or up to two passengers. While initial examples were reliant on the crew to conduct observations, later models were furnished with sophisticated sensors to precisely determine a target's location. Payload capacity was also increased considerably on later-build rotorcraft, the OH-58D Kiowa was designed to carry a maximum load of 2,495 kg, 72% more capacity than the original version.Early Kiowas were fitted with a flexible twin-bladed main rotor; starting with the OH-58D, a four-bladed rigid main rotor was used. This was entirely composed of composite materials, the OH-58D was the first US Army rotorcraft to incorporate an all-composite main rotor hub. Later models were outfitted as light gunships, being equipped with various armaments, such as Stinger air-to-air missiles, a.50-caliber machine gun, podded 70mm Hydra rockets and AGM-114 Hellfire air to ground missiles. Other areas of improvement were the avionics and the cockpit; new navigation and communication systems were installed along with new and larger flight instrumentation, while all light sources were redesigned for compatibility with Night Vision Goggles. Later versions were outfitted with a glass cockpit, which retained conventional instrumentation as a fallback measure.
File:OH-58D.webm|thumb|right|upright=1.25|OH-58D firing its.50 caliber machine gun and Hydra 70 rockets
The OH-58D introduced perhaps the most distinctive feature of the Kiowa family — the Mast Mounted Sight, which resembles a beach ball perched above the rotor system. The MMS by Ball Aerospace & Technologies has a gyro-stabilized platform containing a television system, a thermal imaging system, and a laser range finder/designator. These features gave the OH-58D the additional mission capability of target acquisition and laser designation in day or night, limited-visibility and adverse weather. In combination with the 1553 databus, the OH-58D being first US Army helicopter to be fielded with such equipment, target data from the sensors could be directly passed to precision-guided weapons.
The MMS was developed by the McDonnell Douglas Corp. in Huntington Beach, CA. Production took place primarily at facilities in Monrovia, CA. As a result of a merger with Boeing, and a later sale of the business unit, the program is currently owned and managed by DRS Technologies, with engineering support based in Cypress, CA, and production support taking place in Melbourne, FL. On the OH-58F, the MMS was removed, its functions having been replaced by the AAS-53 Common Sensor Payload, which is mounted on the chin.
File:OH-58D 2.jpg|thumb|right|An OH-58D Kiowa Warrior takes off armed with an AGM-114 Hellfire and 7 Hydra 70 rockets.
One distinctive feature of operational OH-58s are the knife-like extensions above and below the cockpit which are part of the passive wire strike protection system; it protects 90% of the frontal area of the helicopter from wire strikes that can be encountered at low altitudes by directing wires to the upper or lower blades before they can entangle the rotor blade or landing skids. The OH-58 was the first helicopter to test this system, after which the system was adopted by the US Army for the OH-58 and most of their other helicopters. Various other defensive and survivability measures were incorporated, such as ballistic floor armor, a missile warning system, crashworthy seats, and infrared suppression systems for the engine exhaust.