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127-649: 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 (LOH). While

254-505: A fantail ), and MD Helicopters ' NOTAR . The number of rotors is also important, many helicopters have two rotors in a single line, and another configuration is 4 rotors. An example of two-blade rotor is the Bell 212 , and four blade version of this helicopter is the Bell 412 . An example of the effect of rotor blade number is the UH-72 ( EC145 variant ); the A model had four blades, but

381-579: A missile warning system , crashworthy seats, and infrared suppression systems for the engine exhaust. In May 1969, the first OH-58A Kiowa was officially received at a ceremony held at Bell Helicopter's Fort Worth plant, officiated by Major General John Norton , commanding general of the Army Aviation Materiel Command (AMCOM). Two months later, on 17 August 1969, production OH-58A helicopters arrived in South Vietnam for

508-479: A 92 percent fully mission capable rate. The Kiowa Warrior had the lowest ratio of maintenance hours to flight hours of any combat helicopter in the war. The "Army attack helicopters" also worked jointly with close air support and support aircraft such as the USAF A-10As , F-16A/Cs , EF-111As , EC-130H Compass Call , RF-4G Phantom II ' Wild Weasel ,' and E-8 Joint STARS . In 1989, Congress mandated that

635-409: A common flapping or teetering hinge at the rotor shaft. This allows the blades to flap together in opposite motions like a seesaw . This underslinging of the blades below the teetering hinge, combined with an adequate dihedral or coning angle on the blades, minimizes variations in the radius of each blade's center of mass from the axis of rotation as the rotor turns, which in turn reduces the stress on

762-400: A composite yoke. This yoke is attached to the mast and runs through the blade grips between the blades and the shear bearing inside the grip. This yoke does transfer some movement of one blade to another, usually opposing blades. While this is not fully articulated, the flight characteristics are very similar and maintenance time and cost are reduced. The term rigid rotor usually refers to

889-468: A conventional design the rotor blades' angle of attack is reduced via a collective pitch control. Slowing the rotor instead can reduce drag during this phase of flight and thus improve fuel economy. Most helicopters have a single main rotor but require a separate rotor to overcome torque. This is accomplished through a variable-pitch antitorque rotor or tail rotor. This is the design that Igor Sikorsky settled on for his VS-300 helicopter, and it has become

1016-447: A direction opposite that of the main rotor's rotation, thereby countering the torque effect created by the main rotor. Tail rotors are simpler than main rotors since they require only collective changes in pitch to vary thrust. The pitch of the tail rotor blades is adjustable by the pilot via the anti-torque pedals, which also provide directional control by allowing the pilot to rotate the helicopter around its vertical axis, thereby changing

1143-502: A ducted fan can have a smaller size than a conventional tail rotor. The Fenestron was used for the first time at the end of the 1960s on the second experimental model of Sud Aviation's SA 340 and produced on the later model Aérospatiale SA 341 Gazelle . Besides Eurocopter and its predecessors, a ducted fan tail rotor was also used on the canceled military helicopter project, the United States Army 's RAH-66 Comanche , as

1270-593: A flexible hub, which allows for blade bending (flexing) without the need for bearings or hinges. These systems, called flexures , are usually constructed from composite material. Elastomeric bearings may also be used in place of conventional roller bearings . Elastomeric bearings are constructed from a rubber type material and provide limited movement that is perfectly suited for helicopter applications. Flexures and elastomeric bearings require no lubrication and, therefore, require less maintenance. They also absorb vibration, which means less fatigue and longer service life for

1397-566: 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

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1524-690: A four-bladed rotor. The OH-58 was primarily produced for the United States Army . Only two months after the type's entry to service, it was first deployed into the Vietnam War . The US Army would make 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. During 2017,

1651-480: A helicopter are long, narrow airfoils with a high aspect ratio , a shape that minimizes drag from tip vortices (see the wings of a glider for comparison). They generally contain a degree of washout that reduces the lift generated at the tips, where the airflow is fastest and vortex generation would be a significant problem. Rotor blades are made out of various materials, including aluminium, composite structure, and steel or titanium , with abrasion shields along

1778-409: A helicopter. Twin rotors turn in opposite directions to counteract the torque effect on the aircraft without relying on an antitorque tail rotor. This lets the aircraft apply the power that would have driven a tail rotor to the main rotors, increasing lifting capacity. Primarily, three common configurations use the counterrotating effect on rotorcraft. Tandem rotors are two rotors—one mounted behind

1905-548: A hingeless rotor system with blades flexibly attached to the hub. Irv Culver of Lockheed developed one of the first rigid rotors, which was tested and developed on a series of helicopters in the 1960s and 1970s. In a rigid rotor system, each blade flaps and drags about flexible sections of the root. A rigid rotor system is mechanically simpler than a fully articulated rotor system. The aerodynamic and mechanical loads from flapping and lead/lag forces are accommodated through rotor blades flexing, rather than through hinges. By flexing,

2032-417: A minimum. This stability is achieved by keeping the center of pressure virtually unchanged as the angle of attack changes. Center of pressure is the imaginary point on the chord line where the resultant of all aerodynamic forces are considered to be concentrated. Today, designers use thinner airfoils and obtain the required rigidity by using composite materials. Some airfoils are asymmetrical in design, meaning

2159-408: A narrow range of a few percent), but a few experimental aircraft used variable speed rotors . Unlike the small diameter fans used in turbofan jet engines, the main rotor on a helicopter has a large diameter that lets it accelerate a large volume of air. This permits a lower downwash velocity for a given amount of thrust. As it is more efficient at low speeds to accelerate a large amount of air by

2286-470: A negative effect of limiting the crew's forward view, a previous strength of the original design. The aircraft was also equipped with a larger instrument panel, roughly one–third bigger than the OH-58A panel, which held larger flight instruments. The panel was also equipped with Night Vision Goggle (NVG) compatible cockpit lighting. The OH-58C were also the first U.S. Army scout helicopter to be equipped with

2413-506: 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

2540-416: A small degree than a small amount of air by a large degree, a low disk loading (thrust per disc area) greatly increases the aircraft's energy efficiency, and this reduces the fuel use and permits reasonable range. The hover efficiency ("figure of merit") of a typical helicopter is around 60%. The inner third length of a rotor blade contributes very little to lift due to its low airspeed. The blades of

2667-474: A tandem configuration. An advantage of quad rotors on small aircraft such as drones is the opportunity for mechanical simplicity. A quadcopter using electric motors and fixed-pitch rotors has only four moving parts. Pitch, yaw and roll can be controlled by changing the relative lift of different rotor pairs without changing total lift. The two families of airfoils are Symmetrical blades are very stable, which helps keep blade twisting and flight control loads to

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2794-575: A training aircraft. On 9 July 2020, the US Army retired the last OH-58Cs from service. The OH-58D (Bell Model 406) was the result of the Army Helicopter Improvement Program (AHIP). An upgraded transmission and engine gave extra power, needed for nap-of-the-earth flight profiles, and a four-bladed main rotor made it quieter than the two-bladed OH-58C. The OH-58D introduced the distinctive Mast-Mounted Sight (MMS) above

2921-512: Is an increased mechanical complexity of the rotor system because it requires linkages and swashplates for two rotor systems. Also, because the rotors must rotate in opposite directions, the mast is more complex, and control linkages for pitch changes to the upper rotor system must pass through the lower rotor system. An example of coaxial design in a compound helicopter was the Sikorsky Skyraider X , which also had pusher prop at

3048-711: 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. One distinctive feature of operational OH-58s are the knife-like extensions above and below the cockpit which are part of

3175-400: Is equipped with a distinctive Mast Mounted Sight (MMS) 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

3302-401: Is gradual and visible. The metal-to-metal contact of older bearings and the need for lubrication is eliminated in this design. The third hinge in the fully articulated system is called the feathering hinge about the feathering axis. This hinge is responsible for the change in pitch of rotor blades excited via pilot input to the collective or cyclic. A variation of the fully articulated system is

3429-446: Is powered by the engine, through the transmission, to the rotating mast. The mast is a cylindrical metal shaft that extends upward from—and is driven by—the transmission. At the top of the mast is the attachment point (colloquially called a Jesus nut ) for the rotor blades called the hub. The rotor blades are then attached to the hub, and the hub can have 10-20 times the drag of the blade. Main rotor systems are classified according to how

3556-470: Is simple and eliminates torque reaction, prototypes that have been built are less fuel efficient than conventional helicopters. Except for tip jets driven by unburnt compressed air, very high noise levels is the single most important reason why tip jet powered rotors have not gained wide acceptance. However, research into noise suppression is ongoing and may help make this system viable. There are several examples of tip jet powered rotorcraft. The Percival P.74

3683-452: Is that the center of pressure changes with changes in angle of attack. When the center of pressure lifting force is behind the pivot point on a rotor blade, it tends to cause the rotor disc to pitch up. As the angle of attack increases, the center of pressure moves forward. If it moves ahead of the pivot point, the pitch of the rotor disc decreases. Since the angle of attack of the rotor blades is constantly changing during each cycle of rotation,

3810-483: Is the most common tandem rotor helicopter. Coaxial rotors are a pair of rotors mounted one above the other on the same shaft and turning in opposite directions. The advantage of the coaxial rotor is that, in forward flight, the lift provided by the advancing halves of each rotor compensates for the retreating half of the other, eliminating one of the key effects of dissymmetry of lift: retreating blade stall . However, other design considerations plague coaxial rotors. There

3937-608: 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

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4064-755: The AH-64E Apache Guardian was the most capable immediate solution. One proposal was to transfer all Army National Guard and Army Reserve AH-64s to the active Army for use as scouts to divest the OH-58. The Apache costs 50 percent more than the Kiowa to operate and maintain; studies note that had it been used in place of the Kiowa in Iraq and Afghanistan, total operating costs would have risen by $ 4 billion, but also saved $ 1 billion per year in operating and sustainment costs. UH-60 Black Hawks would transfer from

4191-627: The Army National Guard would take part in the country's War on Drugs , enabling them to aid federal, state and local law enforcement agencies with "special congressional entitlements". In response, the Army National Guard Bureau created the Reconnaissance and Aerial Interdiction Detachments (RAID) in 1992, consisting of aviation units in 31 states with 76 specially modified OH-58A helicopters to assume

4318-609: The Austrian Air Force . Austria plans to replace the OH-58B by the end of 2030. Equipped with a more robust engine, the OH-58C was supposed to solve issues regarding the Kiowa's power. In addition to the improved engine, it had unique IR suppression systems mounted on its exhaust. Early OH-58Cs had flat-panel windscreens as an attempt to reduce glint from the sun, which could reveal its location to enemies. The windscreens had

4445-631: 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

4572-681: The Focke-Achgelis Fa 223 , as well as the world's largest helicopter ever built, the Mil Mi-12 . It is also the configuration found on tiltrotors such as the Bell-Boeing V-22 Osprey and the AgustaWestland AW609 . A quad rotor or quadrotor comprises four rotors in an "X" configuration. Rotors to the left and right are in a transverse configuration while those in the front and to the rear are in

4699-556: The Future Attack Reconnaissance Aircraft (FARA) program to fill the capability gap left by the retirement of the OH-58. On 9 July 2020, the US Army retired its last OH-58Cs from active service at Fort Polk . In February 2024, FARA was cancelled; by this point, there were three abandoned attempts to replace the OH-58 at a cost in excess of $ 9 billion. The armed scout role has been filled by the AH-64 and

4826-807: The M134 Minigun , a 7.62 mm electrically operated machine gun. The Australian Army leased eight OH-58As in 1971 in Vietnam for eight months. The Australian Government procured the OH-58A for the Australian Army and Royal Australian Navy as the CAC CA-32 . Licensed produced in Australia by Commonwealth Aircraft Corporation , the CA-32 was the equivalent of the 206B-1 (uprated engine and longer rotor blades). The first twelve of 56 were built in

4953-520: The Native American tribe . 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

5080-605: The OH-58F . Additional improvements, such as the OH-58X , were proposed but ultimately 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

5207-479: The United States Navy approached 25 helicopter manufacturers to request on behalf of the Army the submission of proposals for a Light Observation Helicopter (LOH). 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

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5334-417: The Vietnam War due to combat losses and accidents. One of the last combat losses in the theatre was of an OH-58A (s/n 68-16888) from A Troop, 3-17th Cavalry , flown by First Lieutenant Thomas Knuckey. On 27 May 1971, Lieutenant Knuckey was also flying a battle damage assessment mission when his aircraft came under machine gun fire and exploded. Knuckey and his observer, Sergeant Philip Taylor, both died in

5461-548: The lead-lag hinge or drag hinge , allows the blade to move back and forth. This movement is called lead-lag, dragging, or hunting. Dampers are usually used to prevent excess back and forth movement around the drag hinge. The purpose of the drag hinge and dampers is to compensate for acceleration and deceleration caused by the difference in drag experienced by the advancing and retreating blades. Later models have switched from using traditional bearings to elastomeric bearings. Elastomeric bearings are naturally fail-safe and their wear

5588-414: The soft-in-plane rotor system. This type of rotor can be found on several aircraft produced by Bell Helicopter, such as the OH-58D Kiowa Warrior . This system is similar to the fully articulated type in that each blade has the ability to lead/lag and hunt independently of the other blades. The difference between a fully articulated system and soft-in-plane system is that the soft-in-plane system utilises

5715-567: 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 (PM-ASH) was closed on 30 September 1976. While no development occurred for some years,

5842-515: The 202nd aircraft (s/n 89-0112) 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. 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

5969-466: The 2030s. In December 2013, the U.S. Army had 338 Kiowas in its active-duty force and 30 in the Army National Guard . The Army considered retiring the Kiowa as part of a wider restructuring to cut costs and reduce the variety of helicopters operated. The Analysis of Alternatives for the AAS program found that operating the Kiowa alongside RQ-7 Shadow UAVs was the most affordable and capable solution, while

6096-544: The AN/APR-39 radar detector, which alerted the crew to active anti-aircraft radar systems nearby. Some OH-58Cs were armed with two AIM-92 Stingers and are sometimes referred to as OH-58C/S, the "S" referring to the Stinger addition. Called Air-To-Air Stinger (ATAS), the weapon system was intended to provide an air defense capability. The OH-58C was the final Kiowa variant in service with the U.S. Army, with it being used as

6223-406: 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 (ASH) 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

6350-537: 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

6477-602: 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

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6604-573: The D model in 2000. Conversions of early models to the D standard continued afterward. 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 (3,200 lb) when fully loaded, being able to carry

6731-568: The FANTAIL. NOTAR, an acronym for no ta il r otor , is a helicopter anti-torque system that eliminates the use of the tail rotor on a helicopter. Although the concept took some time to refine, the NOTAR system is simple in theory and provides antitorque the same way a wing develops lift by using the Coandă effect . A variable pitch fan is enclosed in the aft fuselage section immediately forward of

6858-565: The Kiowa family — the Mast Mounted Sight (MMS), 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 (TVS), a thermal imaging system (TIS), and a laser range finder / designator (LRF/D). 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

6985-448: The Kiowa's last deployment in U.S. Army service; during the following year, the unit reequipped with AH-64s. In January 2017, the last Kiowa Warrior performed their last live fire maneuver before retirement. Ex-U.S. Army OH-58Ds were made available through Excess Defense Article and foreign military sales (FMS) programs. In November 2014, Croatia sent a letter of intent for the acquisition of 16 OH-58Ds. In 2016, Croatia and Tunisia became

7112-474: The Navy. In November 1988, the number of OH-58D helicopters that supported Task Force 118 was reduced. However, the rotorcraft continued to operate from the Navy's Mobile Sea Base Hercules , the frigate Underwood , and the destroyer Conolly . OH-58D operations primarily entailed reconnaissance flights at night, and depending on maintenance requirements and ship scheduling, Army helicopters usually rotated from

7239-779: The OH-58 was the RAH-66 Comanche of the Light Helicopter Experimental program, which was canceled in 2004. Airframe age and losses led to the Armed Reconnaissance Helicopter program and the Bell ARH-70 , which was canceled in 2008 due to cost overruns. The third replacement effort was the Armed Aerial Scout program. Due to uncertainty in the AAS program and fiscal restraints, the OH-58F's planned retirement

7366-543: The OH-6. The Army's decision to acquire the NTSH resulted in the "Army Helicopter Improvement Program (AHIP)". 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,

7493-521: The U.S. and radio-control aeromodeler Dieter Schlüter in Germany, found that flight stability for helicopters could be achieved with a stabilizer bar, or flybar. The flybar has a weight or paddle (or both for added stability on smaller helicopters) at each end to maintain a constant plane of rotation. Through mechanical linkages, the stable rotation of the bar mixes with the swashplate movement to damp internal (steering) as well as external (wind) forces on

7620-580: The U.S. then partially disassembled and shipped to Australia, where they were reassembled. Helicopters in the naval fleet were retired in 2000. A total of 74 OH-58As were delivered to the Canadian Armed Forces as COH-58A and later redesignated CH-136 Kiowa . As many as 12 surplus Kiowas were sold to the Dominican Republic Air Force, and others sold privately in Australia. In 1978, OH-58As began to be converted to

7747-551: 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 (MMS). 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

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7874-554: The UH-72B was changed to five blades which reduced vibration. Other blade numbers are possible, for example, the CH-53K , a large military transport helicopter has a seven blade main rotor. The tail rotor is a smaller rotor mounted so that it rotates vertically or near-vertically at the end of the tail of a traditional single-rotor helicopter. The tail rotor's position and distance from the center of gravity allow it to develop thrust in

8001-592: The US Army opted to withdraw its remaining OH-58s, making use of alternative rotorcraft, such as the Boeing AH-64 Apache and Eurocopter UH-72 Lakota , as well as increasing use of unmanned aerial vehicles (UAVs), to fill the role. Furthermore, 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. On 14 October 1960,

8128-511: The United States. Examples of hazards faced by Helicopters, includes ones common to aircraft such as bird-strikes , but also a number of others depending on the design of the helicopter and conditions. This includes but its not limited to: Dynamic rollover , Ground resonance , Loss of tail-rotor effectiveness , Retreating blade stall , Dynamic stall , Vortex ring state , Servo transparency , Mast bumping, and Tailstrike . Because

8255-413: The active Army to reserve and Guard units. The aim was to retire older helicopters and retain those with the best capabilities to save money. Retiring the Kiowa would fund Apache upgrades. The Army placed 26 out of 335 OH-58Ds in non-flyable storage during 2014. In anticipation of divestment, the Army looked to see if other military branches, government agencies, and foreign customers had interest in buying

8382-424: The advantage of easy reconfiguration and fewer mechanical parts. Most helicopter rotors spin at constant speed. However slowing the rotor in some situations can bring benefits. As forward speed increases, the advancing rotor tip speed soon approaches the speed of sound . To reduce the problem, the speed of rotation may be slowed, allowing the helicopter to fly faster. To adjust the rotor lift at slower speeds, in

8509-426: The amount of airflow from the rotorwash. This is augmented by a direct jet thruster which also provides directional yaw control, with the presence of a fixed-surface empennage near the end of the tail, incorporating vertical stabilizers. Development of the NOTAR system dates back to 1975 when engineers at Hughes Helicopters began concept development work. In December 1981, Hughes flew an OH-6A fitted with NOTAR for

8636-413: 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 (NVG). Later versions were outfitted with a glass cockpit , which retained conventional instrumentation as a fallback measure. The OH-58D introduced perhaps the most distinctive feature of

8763-607: The barge returned to the United States. For the next few months, the AHIP helicopters on the Wimbrown VII shared patrol duties with the SEABAT team on the Hercules. Coordination proved difficult, despite frequent requests from TF-160, the SEABAT team on the Hercules was not replaced by an AHIP detachment until June 1988. The OH-58D helicopter crews involved in the operation received deck landing and underwater survival training from

8890-467: The blades from lead and lag forces caused by the Coriolis effect . Secondary flapping hinges may also be used to provide sufficient flexibility to minimize bouncing. Feathering is accomplished by the feathering hinge at the blade root, which allows changes to the pitch angle of the blade. Modern rotor systems may use the combined principles of the rotor systems mentioned above. Some rotor hubs incorporate

9017-460: The blades tend to flap, feather, lead, and lag to a greater degree. Hexacopter is a popular configuration for unmanned drone helicopters, and ways to manage and improve the control of multirotor drones has been studied. The octocopter configuration is used notably in NASA's planned Dragonfly probe , designed to fly in the atmosphere of Saturn 's Moon Titan . A manned multirotor helicopter that

9144-451: The blades themselves compensate for the forces that previously required rugged hinges. The result is a rotor system that has less lag in control response because of the large hub moment typically generated. The rigid rotor system thus eliminates the danger of mast bumping inherent in semirigid rotors. The semirigid rotor can also be referred to as a teetering or seesaw rotor. This system is normally composed of two blades that meet just under

9271-501: The conflict. On 27 March 1970, an OH-58A Kiowa (s/n 68-16785) was shot down over South Vietnam, one of the first OH-58A losses of the war. The pilot, Warrant Officer Ralph Quick Jr., was flying Lieutenant Colonel Joseph Benoski Jr. as an artillery spotter. After completing a battle damage assessment for a previous fire mission, the aircraft was damaged by .51 inch (13 mm) machine gun fire and crashed, killing both crew members. Approximately 45 OH-58A helicopters were destroyed during

9398-568: 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

9525-656: The crew had been spying. Five days of negotiations resulted in the North Koreans turning over Hilemon's body to U.S. authorities. The negotiations failed to secure Hall's immediate release. After 13 days in captivity, Hall was freed on 30 December, uninjured. The U.S. Army employed the OH-58D during Operation Iraqi Freedom in Iraq and Operation Enduring Freedom in Afghanistan . Between a combination of combat and accidents, over 35 airframes have been lost, resulting in

9652-439: The deaths of 35 pilots. Their presence was also anecdotally credited with saving lives, having been used to rescue wounded despite their small size. In Iraq, OH-58Ds reportedly flew 72 hours per month, while in Afghanistan, the type flew 80 hours per month. During April 2013, Bell stated that the OH-58 collectively accumulated 820,000 combat hours, and had achieved a 90% mission capable rate. The U.S. Army's first attempt to replace

9779-468: The designs has not fully settled, with eVTOL being a popular name, also manned drone, or even flying car being used, or in certain cases Air Taxi. As an aircraft, the FAA has worked to refine the regulations surrounding eVTOL designs, which is oriented towards traditional Helicopters and airplanes, but in 2024 finalized airworthiness criteria as it resolves how to classify and certify these types of aircraft in

9906-423: The direction the craft is pointed. Fenestron and FANTAIL are trademarks for a ducted fan mounted at the end of the tail boom of the helicopter and used in place of a tail rotor. Ducted fans have between eight and eighteen blades arranged with irregular spacing so that the noise is distributed over different frequencies. The housing is integral with the aircraft skin and allows a high rotational speed; therefore,

10033-466: The end of wings or outriggers perpendicular to the body of the aircraft. Similar to tandem rotors and intermeshing rotors, the transverse rotor also uses differential collective pitch. But like the intermeshing rotors, the transverse rotors use the concept for changes in the roll attitude of the rotorcraft. This configuration is found on two of the first viable helicopters, the Focke-Wulf Fw 61 and

10160-429: The engine turns the rotor creates a torque effect that causes the body of the helicopter to turn in the opposite direction of the rotor. To eliminate this effect, some sort of antitorque control must be used with a sufficient margin of power available to allow the helicopter to maintain its heading and provide yaw control. The three most common controls used today are the tail rotor, Eurocopter's Fenestron (also called

10287-598: The explosion. During early 1988, it was decided that armed OH-58D (AHIP) helicopters from the 118th Aviation Task Force would be phased in to replace the SEABAT ( AH-6/MH-6 ) teams of Task Force 160th to carry out Operation Prime Chance , the escort of oil tankers during the Iran–Iraq War . On 24 February 1988, two AHIP helicopters reported to the Mobile Sea Base Wimbrown VII, and the helicopter team ("SEABAT" team after their callsign) stationed on

10414-496: The first nations to request the helicopters, ordering 16 and 24, respectively. Croatia received the first batch of 5 OH-58Ds at the Zadar-Zemunik air base on 30 June 2016. In early 2018, Greece was granted 70 OH-58Ds via an FMS arrangement, the type has been initially stationed at Hellenic Army Aviation air base at Stefanovikio . In March 2020, the U.S. Army selected the Bell 360 Invictus and Sikorsky Raider X as part of

10541-421: 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,

10668-486: The first time. A more heavily modified prototype demonstrator first flew in March 1986 and successfully completed an advanced flight-test program, validating the system for future application in helicopter design. There are currently three production helicopters that incorporate the NOTAR design, all produced by MD Helicopters. This antitorque design also improves safety by eliminating the possibility of personnel walking into

10795-556: The first time; their deployment was accompanied by a New Equipment Training Team (NETT) comprising personnel from both the US Army and Bell Helicopters. Although the Kiowa production contract had replaced the LOH contract with Hughes, the OH-58A did not automatically replace the OH-6A in operations; subsequently, the Kiowa and the Cayuse would continue operating in the same theater until the end of

10922-479: The front of the cabin, and positioned close to the 180° view unobstructed Lexan "bubble" windscreen. A single bench seat at the rear of the cabin spanned its entire width and allowed for a passenger capacity limited by weight to typically 3 or 4 adults. In March 1957 two Bell 47Js were bought by the United States Air Force as presidential transport and designated H-13J . On 13 July 1957 a H-13J

11049-402: The front rotor tilts right and the rear rotor tilts left. To pivot left, the front rotor tilts left and the rear rotor tilts right. All rotor power contributes to lift, and it is simpler to handle changes in the center of gravity fore-aft. However, it requires the expense of two large rotors rather than the more common one large main rotor and a much smaller tail rotor. The Boeing CH-47 Chinook

11176-470: The helicopter components. Controls vary the pitch of the main rotor blades cyclically throughout rotation. The pilot uses this to control the direction of the rotor thrust vector , which defines the part of the rotor disc where the maximum thrust develops. Collective pitch varies the magnitude of rotor thrust by increasing or decreasing thrust over the whole rotor disc at the same time. These blade pitch variations are controlled by tilting, raising, or lowering

11303-429: The individual blades through pitch links and pitch horns. The non-rotating plate is connected to links that are manipulated by pilot controls—specifically, the collective and cyclic controls. The swash plate can shift vertically and tilt. Through shifting and tilting, the non-rotating plate controls the rotating plate, which in turn controls the individual blade pitch. A number of engineers, among them Arthur M. Young in

11430-595: The leading edge. Rotorcraft blades are traditionally passive; however, some helicopters include active components on their blades. The Kaman K-MAX uses trailing edge flaps for blade pitch control and the Hiller YH-32 Hornet was powered by ramjets mounted on the blade ends. As of 2010 , research into active blade control through trailing edge flaps is underway. Tips of some helicopter blades can be specially designed to reduce turbulence and noise and to provide more efficient flying. An example of such tips are

11557-414: The main rotor blades are attached and move relative to the main rotor hub. There are three basic classifications: rigid, semirigid, and fully articulated, although some modern rotor systems use a combination of these classifications. A rotor is a finely tuned rotating mass, and different subtle adjustments reduce vibrations at different airspeeds. The rotors are designed to operate at a fixed RPM (within

11684-434: The main rotor is vital to keeping a helicopter in the air, any damage to can have disastrous consequences. Because the tip is usually the farthest extremity helicopters flying in formation have be careful to keep their distance and not touch tips or tail rotors, or with surroundings. Bell 47J Ranger The Bell 47J Ranger is an American single-engine single-rotor light helicopter manufactured by Bell Helicopter . It

11811-483: The main rotor, and a mixed glass cockpit with traditional instruments as "standby" for emergencies. The Bell 406CS "Combat Scout" was based on the OH-58D (sometimes referred to as the MH-58D ). Fifteen aircraft were sold to Saudi Arabia. A roof-mounted Saab HeliTOW sight system was opted for in place of the MMS. The 406CS also had detachable weapon hardpoints on each side. Helicopter rotor The helicopter rotor

11938-698: The mobile sea base and other combatant ships to a land base every seven to fourteen days. On 18 September 1989, an OH-58D crashed during night gunnery practice and sank, but with no loss of personnel. When the Mobile Sea Base Hercules was deactivated in September 1989, all but five OH-58D helicopters redeployed to the continental United States. During Operation Desert Shield (the build-up to Operation Desert Storm ) U.S. Army OH-58Ds would exercise alongside USMC AH-1Ws and assist with targeting and laser spotting. However while this tactic worked and

12065-495: The most unusual design of this type was the Rotary Rocket Roton ATV , which was originally envisioned to take off using a rocket-tipped rotor. The French Sud-Ouest Djinn used unburnt compressed air to drive the rotor, which minimized noise and helped it become the only tip jet driven rotor helicopter to enter production. The Hughes XH-17 had a tip jet-driven rotor, which remains the largest rotor ever fitted to

12192-495: The other. Coaxial rotors are two rotors mounted one above the other on the same axis. Intermeshing rotors are two rotors mounted close to each other at a sufficient angle to let the rotors intermesh over the top of the aircraft. Another configuration—found on tiltrotors and some early helicopters—is called transverse rotors, where a pair of rotors are mounted at each end of a wing-type structure or outrigger. Tandem rotors are two horizontal main rotor assemblies mounted one behind

12319-480: The other. Tandem rotors achieve pitch attitude changes to accelerate and decelerate the helicopter through a process called cyclic pitch. To pitch forward and accelerate, both rotors increase the pitch at the rear and reduce the pitch at the front (cyclic) keeping torque the same on both rotors, flying sideways is achieved by increasing the pitch on one side and reducing pitch on the other. Yaw control develops through opposing cyclic pitch in each rotor. To pivot right,

12446-471: The others. These rotor systems usually have three or more blades. The blades are allowed to flap, feather, and lead or lag independently of each other. The horizontal hinge, called the flapping hinge , allows the blade to move up and down. This movement is called flapping and is designed to compensate for dissymmetry of lift . The flapping hinge may be located at varying distances from the rotor hub, and there may be more than one hinge. The vertical hinge, called

12573-522: 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,

12700-537: The planned three passengers in the back. The solution was a fuselage redesigned to be more sleek and aesthetic, adding 16 cubic feet (0.45 cubic metres) 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

12827-479: 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,

12954-468: 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 (NTSH) 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

13081-585: The rear. Intermeshing rotors on a helicopter are a set of two rotors turning in opposite directions with each rotor mast mounted on the helicopter with a slight angle to the other so that the blades intermesh without colliding. This configuration is sometimes referred to as a synchropter. Intermeshing rotors have high stability and powerful lifting capability. The arrangement was pioneered in Nazi Germany in 1939 with Anton Flettner 's successful Flettner Fl 265 design, and later placed in limited production as

13208-406: The recognized convention for helicopter design, although designs do vary. When viewed from above, most American helicopter rotors turn counter-clockwise; French and Russian helicopters turn clockwise. Another type of rotorcraft is the tiltrotor , which has many similarities to helicopter main rotors when in mode of powered lift . With a single main rotor helicopter, the creation of torque as

13335-631: The reconnaissance/interdiction role in the fight against illegal drugs. During 1994, 24 states conducted more than 1,200 aerial counterdrug reconnaissance and interdiction missions, conducting many of these missions at night. Eventually, the program was expanded to cover 32 states and consisting of 116 aircraft, including dedicated training aircraft at the Western Army Aviation Training Site (WAATS) in Marana, Arizona . The RAID program's mission has now been expanded to include

13462-550: 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 would follow, often with uprated engines, enhanced protection systems, and other improvements, culminating in

13589-404: The rotor. The Lockheed rotor system used a control gyro, similar in principle to that of the Bell stabilizer bar, but designed for both hands-off stability and rapid control response of the hingeless rotor system. In fly-by-wire helicopters or Remote Control (RC) models, a microcontroller with gyroscope sensors and a Venturi sensor can replace the stabilizer. This flybar-less design has

13716-417: The rotor. This makes it easier for the pilot to maintain control of the aircraft. Stanley Hiller arrived at a similar method to improve stability by adding short stubby airfoils, or paddles, at each end. However, Hiller's "Rotormatic" system also delivered cyclic control inputs to the main rotor as a sort of control rotor, and the paddles provided the added stability by damping the effects of external forces on

13843-588: The same engine and dynamic components as the OH-58C. In 1992, 76 OH-58A were modified with another engine upgrade, a thermal imaging system, a communications package for law enforcement, enhanced navigational equipment and high skid gear as part of the Army National Guard's (ARNG) Counter-Drug RAID program. The U.S. Army retired its last OH-58A in November 2017. The OH-58B was an export version for

13970-595: The securing of Fort Amador in Panama . The OH-58 was fired upon by Panama Defense Force soldiers and crashed 100 yards (90 m) away, in the Bay of Panama . The pilot was rescued, but the co-pilot was killed in action. On 17 December 1994, Army Chief Warrant Officers (CWO) David Hilemon and Bobby Hall left Camp Page, South Korea on a routine training mission along the Demilitarized Zone (DMZ). Their flight

14097-673: The successful Flettner Fl 282 Kolibri , used by the German Kriegsmarine in small numbers (24 airframes produced) as an experimental light anti-submarine warfare helicopter. During the Cold War , an American company, Kaman Aircraft , produced the HH-43 Huskie for USAF firefighting and rescue missions. The latest Kaman model, the Kaman K-MAX , is a dedicated sky crane design. Transverse rotors are mounted on

14224-410: The swash plate with the flight controls. The vast majority of helicopters maintain a constant rotor speed (RPM) during flight, leaving the angle of attack of the blades as the sole means of adjusting thrust from the rotor. The swash plate is two concentric disks or plates. One plate rotates with the mast, connected by idle links, while the other does not rotate. The rotating plate is also connected to

14351-438: The tail boom and is driven by the main rotor transmission. To provide the sideways force to counteract the clockwise torque produced by a counterclockwise-spinning main rotor (as seen from above the main rotor), the variable-pitch fan forces low pressure air through two slots on the right side of the tailboom, causing the downwash from the main rotor to hug the tailboom, producing lift and thus a measure of antitorque proportional to

14478-498: The tail rotor. A predecessor (of sorts) to this system existed in the form of Great Britain's Cierva W.9 helicopter, a late 1940s aircraft using the cooling fan from its piston engine to push air through a nozzle built into the tailboom to counteract rotor-torque. The main rotor may be driven by tip jets. Such a system may be powered by high pressure air provided by a compressor. The air may or may not be mixed with fuel and burnt in ram-jets, pulse-jets, or rockets. Though this method

14605-563: The tips of the BERP rotors created during the British Experimental Rotor Programme. Description of a simple rotor: Juan de la Cierva developed the fully articulating rotor for the autogyro . The basis of his design permitted successful helicopter development. In a fully articulated rotor system, each rotor blade is attached to the rotor hub through a series of hinges that let the blade move independently of

14732-564: The type. The Kiowas were considered to be well priced for foreign countries with limited resources; Bell had not yet agreed to support them if sold overseas. Media expected OH-58s to go to foreign militaries rather than civil operators due to high operating cost. By 2015, the Army had divested 33 OH-58Ds. By January 2016, the Army had divested all but two OH-58D squadrons. In June 2016, members of 1st Squadron, 17th Cavalry Regiment, 82nd Combat Aviation Brigade , arrived in South Korea as part of

14859-404: The unarmed RQ-7 Shadow UAV; this combination reportedly accomplished 80% of the scouting mission, while also providing greater firepower, durability, and speed. The OH-58A Kiowa is a four-place observation helicopter. It has two-place pilot seating, although the controls in the left seat are designed to be removed to carry a passenger up front. During its Vietnam development, it was fitted with

14986-405: The upper and lower surfaces do not have the same camber. Normally these airfoils would not be as stable, but this can be corrected by bending the trailing edge to produce the same characteristics as symmetrical airfoils. This is called "reflexing." Using this type of rotor blade allows the rotor system to operate at higher forward speeds. One of the reasons an asymmetrical rotor blade is not as stable

15113-591: The war against terrorism and supporting U.S. Border Patrol activities in support of homeland defense. The National Guard RAID units' Area of Operation (AO) is the only one in the Department of Defense that is wholly contained within the borders of the United States . During Operation Just Cause in 1989, a team consisting of an OH-58 and an AH-1 were part of the Aviation Task Force during

15240-596: 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

15367-424: Was an executive variant of the highly successful Bell 47 and was the first helicopter to carry a United States president. The 47J was a four-seat variant of the earlier three-seat Bell 47H. The 47H was a deluxe variant of the 47G with a fully clad fuselage and an enclosed cabin. The 47H proved to be too small, so Bell developed the 47J. The 47J was a single pilot aircraft with the pilot seat and controls centered in

15494-500: Was effective, there is little evidence that this tactic was used, likely to a lack of OD-58Ds. During Operation Desert Storm, 130 deployed OH-58D helicopters worked alongside the other Army attack helicopters, 145 AH-1 Cobras and 277 AH-64 Apaches , and participated in a wide variety of critical combat ground forces mission. During Operation Desert Shield and Operation Desert Storm , the Kiowas collectively flew nearly 9,000 hours with

15621-481: Was extended from 2025 to 2036. The Kiowa's scout role was supplemented by tactical unmanned aerial vehicles , the two platforms often acting in conjunction to provide reconnaissance to expose crews to less risk. The OH-58F had the ability to control UAVs directly to safely perform scout missions. In 2011, the Kiowa was scheduled to be replaced by the light version of the Future Vertical Lift aircraft in

15748-433: Was flying in the 2010s had 18 electrically powered rotors; the single seat aircraft is powered by batteries. The first aerobatic manned drone, as this type of electrically powered multi-rotor helicopter is known, had 12 rotors and could carry 1-2 people. Manned drones or eVTOL as they are called typically multirotor designs powered by batteries gained increasing popularity and designs in the 2020s. The naming of some of

15875-655: Was intended to be to a point known as Checkpoint 84, south of the DMZ "no-fly zone", but the OH-58C Kiowa strayed nearly four miles (6 km) into the Kangwon Province, inside North Korean airspace, due to errors in navigating the snow-covered, rugged terrain. The helicopter was shot down by North Korean troops and CWO Hilemon was killed. CWO Hall was held captive and the North Korean government insisted that

16002-516: Was the first helicopter used by a United States president when it carried Dwight D. Eisenhower from the White House . In March 1962 the two helicopters were moved from presidential duties but were used as VIP transports for the next five years until retired in July 1967. Two Bell 47J-2s were used during the 1966 film production of Paradise, Hawaiian Style starring Elvis Presley . Throughout

16129-418: Was under-powered and could not fly. The Hiller YH-32 Hornet had good lifting capability but performed poorly otherwise. Other aircraft used auxiliary thrust for translational flight so that the tip jets could be shut down while the rotor autorotated. The experimental Fairey Jet Gyrodyne , 48-seat Fairey Rotodyne passenger prototypes and McDonnell XV-1 compound gyroplanes flew well using this method. Perhaps

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