The North American Rockwell OV-10 Bronco is a turboprop-driven light attack and cargo aircraft. Although it is a fixed-wing aircraft, its mission capabilities more resemble a sort of impossibly fast, long-range, inexpensive and reliable ultra-heavy attack helicopter. It flies 350mph, carries 3 tons of external munitions, and easily loiters for 3 or more hours. It is prized for its versatility, redundancy, load, wide field of view, short-field ability, low operational costs and ease of maintenance. In most cases, it flies acceptably on a single engine.
The Bronco has its problems. An engine failure on takeoff can cause the other engine to spin the whole aircraft around a couple of times. An immediate ejection is recommended when this happens. The Bronco is also said to be dangerous to ditch. In most reported incidents the aircraft came apart on contact with the ground or water. Ejections often failed, even with zero-altitude ejection seats.
Although the United States military no longer flies the Bronco, other countries continue to operate it. It is in the active inventory of the Philippines, Colombia, Indonesia, Thailand and Venezuela, where it is used primarily for light attack counterinsurgent (COIN) missions, and utility missions such as border patrols, anti-piracy patrols, forward air control, surveillance, defense mapping and search-and-rescue.
A number of Broncos are in civilian use. The large cargo capacity makes the airframe well suited to dumping liquids. It is used for anti-drug crop-spraying aircraft (22, U.S. State Depts and BATF) and light fire-fighting tankers (9 active, 7 spares, California Dept. of Forestry). NASA has a few air-frames it uses for noise and stability research. By sheer accident, the Bronco's propellors revolve at a constant 2,000 RPM, simplifying noise research. It's also well-suited to some stability and vortex studies because either turboprop can be easily refitted to revolve either direction.
New air-frames are no longer produced, and spares are difficult to locate. Most operators keep several airframes to cannibalize.
Visually, it has a central nacelle containing pilots and cargo, and twin booms containing twin turboprop engines. The visually-distinctive item of the aircraft is the combination of the twin booms, with the horizontal stabilizer that connects them. The North Vietnamese nickname for a Bronco was "pig sty," perhaps because it resembled a fenced enclosure.
It can perform short take-offs and landings on aircraft carriers without using catapults. The cockpit has extremely good visibility for a tandem pilot and co-pilot provided by a wrap-around 'greenhouse.' With the second seat removed, it can carry 7,040kg (3,200lbs) of cargo, five paratroopers or two litter patients and an attendant. Its rear fuselage compartment can carry 7,040kg (3,200lbs) of cargo, five combat-equipped troops, or two litter patients and a medical attendant. Gross dry weight was 18172kg (8,260lbs). Normal operating fueled weight, with two crew was 22,308kg (10,140lbs). Maximum take-off weight was 31,680kg (14,400lbs).
The bottom of the fuselage contains sponsons with four 7.62mm M-60C machine guns. The M-60Cs were accessed through a large forward-opening hatch on the top of each sponson. The sponsons also had four racks to carry bombs, pods or fuel. The wings outboard of the engines contain two additional racks, one per side.
Sponsons are "stub wings" underneath the fuselage. The sponsons were mounted horizontally on the prototype. Testing caused them to be redesigned for production aircraft. The downward angle assured that stores carried on the sponsons jettisoned cleanly. The sponsons are easy to remove, and this improves flight performance by decreasing aerodynamic drag. Most unarmed Broncos have now had their sponsons removed. Indonesia and Thailand have removed the light machine guns and retrofitted heavy .50 calibre machine guns.
Racked armament in the Vietnam War was usually seven-shot 2.75 inch rocket pods with marker or high-explosive rockets, or 5-inch four-shot Zuni rocket pods. Bombs, ADSIDS air-delivered seismic sensors, Mk-6 battlefield illumination flares, and other stores were carried as well.
One of the most interesting uses of the Bronco was that in Vietnam, the U.S. Navy successfully operated fourteen OV-10A Broncos and a small support unit as a "Light Attack Squadron" designated VAL-4. The Broncos patrolled and scrambled in groups of two. After the first few weeks, most patrols carried a central fuel pod to extend their loitering time, a 4-missile Zuni pod outboard on each wing as their heavy weapons, the four light machine guns for suppressive fire, and a flare dispenser.
The efficient turboprops and wings gave the Bronco low operational expenses and a unique operational mode, not shared by either jets or helicopters: long loiter times from forward air bases. The result was that patrolling Broncos were often much more quickly available to the troops on the ground. Troops in fact, began asking for the Broncos, who were often available 40 minutes or more before conventional fast attack jets.
The Broncos' radio utilization was significant. Most use occurred on the radios used by ground troops: VHF-FM. The squadron officially wished for a direction finder for this type of radio, to locate ground troops needing help. The UHF radio was used for tower directions, and occasionally for finding downed airmen. The HF long-haul radio was rarely used.
In Vietnam there was a divided command in air support, so there was significant confusion between U.S. Air-Force forward air controllers (FAC), tactical aircraft deployments, and the Broncos. With their low speeds and great visibilitiy, the Broncos self-controlled very well, and often finished a requested fire-mission and left before the USAF TACAIR jets arrived. FACs said that the Broncos had a tighter turning radius than their little Cessna O-1s, and this caused difficulty for the FACs- they had to loiter near the outer edge of a target area to keep all aircraft in sight.
The Broncos were vulnerable to massed machine-gun fire, anti-aircraft artillery and light antiaircraft rockets. However, the aircraft's simplicity and redundancy rewarded careful flying. Over 7 months of combat by VAL-4, at 655 sorties per month (~4,550sorties), only four aircraft were downed.
In August 1969, VAL-4 reported availability at 85 hours per aircraft per month, with 1105 flight hours, 656 sorties and 12 aircraft. Doctrines required all flights to have two aircraft. An author of this aritcle calculated average sortie times of about 3.2 hours, with about two sorties per day per aircraft.
The popular weapons were a 20mm gun pod (always in short supply) and the Zuni 5" rocket, single-fired at targets of opportunity. Ripple firing was possible, but rarely used. All Vietnamese insurgent targets could be destroyed with these weapons: sampans, light structures, bunkers and troop concentrations. The 7.62 machine guns and 2.75" rockets were used for antipersonnel and suppressive fire.
With the 5 inch (7cm) Zuni rockets, the Navy pilots did not want heavy gravity bombs. The Zuni had good operational flexibility because it had forward fuses (good for attacking material, and adequate for troops and vehicles), rear fuses (perfect for bunkers- a rear-fused Zuni would penetrate 4 feet into earth), and proximity fuses (exploding at 6 meters above ground, these were best for antipersonnel, and satisfactory for light structures and vehicles). The only problem with the Zuni was its 500 meter fragmentation radius, which, though usually an advantage, sometimes damaged aircraft and caused friendly fire casualties on the ground.
Flares were very useful for night attacks, and all patrols began to carry flare dispensers after the first few weeks.
The U.S. Marine Corps and U.S. Air Force operated the Bronco as an armed observation platform, usually manned by a forward-air controller and a pilot. Although more survivable and useful than a little O-1 or O-2, some authorities believe that this use was too limited, given the capabilities of the air-frame.
This lack of vision is probably what led to the end of deployment.
The Bronco has 6,400 lbs of cargo capacity, but its nacelle is not tall enough for easy cargo handling. A commercial version of the aircraft would have fixed this, possibly producing an excellent bush aircraft, given that the Bronco was designed for amphibious and short-runway operation. The Bronco is quite fast (more than 350mph), and has good fuel efficiency and range. Many air forces have adapted it to utility roles.
The Bronco began with a specification approved by the U.S. Navy, Air Force and Army, a "tri-service" specification called "LARA" (the Light Armed Reconnaissance Aircraft), issued at the end of 1963. LARA was based on a perceived need for a new type of "jungle fighting" versatile light attack and observation aircraft. Existing aircraft (the O-1 and O-2) were perceived as obsolescent, with too small a cargo capacity for this flexible role.
The specification called for a twin-engined, two-man aircraft that could carry at least 2,400 lbs. of cargo, six paratroops or stretchers, and be stressed for +8 and -3 Gs (basic aerobatic ability). It also had to be launchable from an aircraft carrier, fly at least 350mph, take off in 800 feet and convert to an amphibian.
Various armament had to be carried, including four 7.62mm machine guns with 2,000 rounds, and external weapons including a 20mm gun pod and Sidewinder missiles.
Eleven proposals were submitted, and seven made the first cut: the Beech PD 183, Douglass D.855, General Dynaics/Convair Model 48 Charger, the Helio 1320, the Lockheed CL-760, a Martin design and the North American/Rockwell NA300.
In August 1964, the NA300 was selected. A contract for seven prototype aircraft was issued in October 1964.
General Dynamics/Convair protested the decision and built a prototype of the Model 48 Charger anyway, which first flew on November 29, 1964. This was also a twin-boom aircraft that had a broadly similar layout to the Bronco. The Charger, while capable of outperforming the OV-10 in some respects, crashed on October 19, 1965 after 196 test flights. Convair dropped out of contention.
The Bronco started flying midway through the Charger's test program on July 16, 1965 and became the premiere COIN (COunter INsurgence) aircraft of the next thirty years.
The Bronco performed observation, forward air control, helicopter escort, armed reconnaissance, gunfire spotting, utility light air transport and limited ground attack. The Bronco has also performed aerial radiological reconnaissance, tactical air observation, artillery and naval gunfire spotting and airborne control of tactical air support operations, and front line, low-level aerial photography.
It was first acquired by the U.S. Marine Corps. Each of the Marine Corps' two observation squadrons had 18 aircraft, 9 OV-10As and 9 OV-10Ds night observation aircraft. There was also a Marine Air Reserve squadron. The OV-10 was phased out of the Marine Corps in 1995.
Technical Data
Doctrine: Fire Support
Doctrine: Forward Air Control
Doctrine: Utility
History
Operation as forward air controllers in the U.S. Marines continued through July 1994, when the Broncos were decommissioned. Doctrines changed as smart bombs were integrated with the force structure. Forward air control passed mostly to elite ground units with laser designators and digital radios. The concept of using loitering Broncos to deliver munitions was not explored. No one realized that they could deliver smart weapons more cheaply and promptly than jets. Most operational U.S. Broncos were reassigned to civil governments in the U.S. Some were sold to other countries.
The USAF acquired the Bronco primarily as a forward air control (FAC) aircraft. The first USAF OV-10As for combat arrived in Vietnam on July 31, 1968. At least 157 OV-10As were delivered to the USAF before production ended in April 1969.
In 1970, one USAF squadron's Broncos received PAVE NAIL modifications. NAIL was the radio handle of the squadron. PAVE was Loral Aerospace's pod, mounted under the fuselage, containing a Loran-C navigational radio, a laser designator and electronics to integrate them. PAVE NAIL illuminated targets for laser-guided precision bombs. The program was successful, but the equipment was removed after Vietnam.
The Air-Force generally disliked the Bronco because it flew low and slow compared to a jet, and when acting as a forward air control, it was vulnerable to anti-aircraft artillery. It therefore did not fit any of the perceived U.S. Air Force missions of the 1980s, and was removed from service.
Bronco pilots were fond of pulling up next to F-4s, and then turning their propellers slightly in reverse, so the Bronco would drift backwards as the F-4 ran up its engine during preflight checkout. Often the F-4 pilots would think their brakes had failed, and panic.
The NAVY unit, VAL-4, formed in January 3, 1969, and operated in Vietnam from April through October, 1970. The NAVY used the Bronco OV-10Aa as a light ground attack aircraft, for interdiction of enemy logistics, and fire-support of marines, SEALs and river boats. It succeeded in this role.
Indonesia and Thailand still fly COIN operations similar to the U.S. Navy's Vietnam missions with their Broncos, but have retrofitted .50-calibre Browning heavy machine guns in place of the light 7.62 mm (.30 calibre) machine guns. Reportedly Broncos won most Thai bombing competitions until heavily automated F-15s became available. At one time Thailand even flew Broncos as air-defense.
The Philipines flys Broncos on search-and-rescue and COIN operations in the Jolo islands.