The North American Aviation Rockwell OV-10 Bronco is a turboprop light attack and observation aircraft. It was developed in the 1960s as a special aircraft for counter-insurgency (COIN) combat, and one of its primary missions was as a forward air control (FAC) aircraft. It can carry up to three tons of external munitions, and loiter for three or more hours.
The aircraft was initially conceived in the early 1960s through an informal collaboration between W.H. Beckett and Colonel K.P. Rice, U.S. Marine Corps, who met at Naval Air Weapons Station China Lake, California, and who also happened to live near each other. The original concept was for a rugged, simple, close air support aircraft integrated with forward ground operations. At the time, the U.S. Army was still experimenting with armed helicopters, and the U.S. Air Force was not interested in close air support.
The concept aircraft was to operate from expedient forward air bases using roads as runways. Speed was to be from very slow to medium subsonic, with much longer loiter times than a pure jet. Efficient turboprop engines would give better performance than piston engines. Weapons were to be mounted on the centerline to get efficient unranged aiming like the Lockheed P-38 Lightning and North American F-86 Sabre aircraft. The inventors' favored strafing weapons were self-loading recoilless rifles, which could deliver aimed explosive shells with less recoil than cannons, and a lower per-round weight than rockets. The airframe was to be designed to avoid the back blast.
Beckett and Rice developed a basic platform meeting these requirements, then attempted to build a fiberglass prototype in a garage. The effort produced enthusiastic supporters and an informal pamphlet describing the concept. W.H. Beckett, who had retired from the Marine Corps, went to work at North American Aviation to sell the aircraft.
"The military definition of STOL (500 ft to a 50 ft obstacle) allows takeoff and landing in most of the areas in which limited war might be fought. In addition, the airplane was designed to use roads so that operation would even be possible in jungle areas where clearings are few and far between. As a result the wingspan was to be limited to twenty feet and a heavy trailing arm type landing gear with a tread of 6.5 ft was provided for operation from roads. Float operation was to be feasible... "
"...it is quite feasible to design the various components so that it can be disassembled easily and stored in a box that would fit in a 6x6 truck bed together with the equipment needed for re-assembly in the field. It could thus be transported by amphibious shipping and either heli-lifted or driven ashore by a 6x6 truck."
Light Armed Reconnaissance Aircraft
A "tri-service" specification for the Light Armed Reconnaissance Aircraft (LARA) was approved by the U.S. Navy, Air Force and Army and was issued in late 1963. The LARA requirement was based on a perceived need for a new type of "jungle fighting" versatile light attack and observation aircraft. Existing military aircraft in the observation role, such as the Cessna O-1 Bird Dog and Cessna O-2 Skymaster, were perceived as obsolescent, with too slow a speed and too small a load capacity for this flexible role.
The specification called for a twin-engine, two-man aircraft that could carry at least 2,400 pounds (1,100 kg) of cargo, six paratroopers or stretchers, and be stressed for +8 and -3 gs (basic aerobatic ability). It also had to be able to operate from an aircraft carrier, fly at least 350 miles per hour (560 km/h), take off in 800 feet (240 m) and convert to an amphibian. Various armament had to be carried, including four 7.62 mm (0.300 in) machine guns with 2,000 rounds, and external weapons including a 20 mm (0.79 in) gun pod and AIM-9 Sidewinder air-to-air missiles.
Eleven proposals were submitted, nine of them were: the Grumman Model 134R tandem-seat version of the already fielded U.S. Army's OV-1 Mohawk (the U.S. Marine Corps dropped out of the Mohawk program in 1958), Goodyear GA 39, Beechcraft PD-183, Douglas D-855, Convair Model 48 Charger, Helio 1320, Lockheed CL-760, a Martin design, and the North American/Rockwell NA-300.
In August 1964, the NA-300 was selected. A contract for seven prototype aircraft was issued in October 1964. Convair protested the decision and built a small-wing prototype of the Model 48 Charger anyway, which first flew on 29 November 1964. This was also a twin-boom aircraft that had a broadly similar layout to the OV-10. The Charger, while capable of outperforming the OV-10 in some respects, crashed on 19 October 1965 after 196 test flights. Convair subsequently dropped out of contention.
The Bronco started flying midway through the Charger's test program on 16 July 1965, and became one of the premier counter-insurgency (COIN) aircraft of the next 30 years. It failed to live up to Rice's L2 VMA concept because the DoD insisted on 40-foot (12 m) long wings which made it depend on airbases. Rice concludes:
"The original concept of a small, simple aircraft that could operate close to the supported troops had been almost completely eviscerated by the 'system.' The ability to operate from roads (20 ft span and 6.5 tread) had been ignored, and performance compromised by the short 30 ft span, the extra 1,000 lb for the rough field landing gear and another 1000 lb of electronics. The 'light, simple' airplane also had a full complement of instruments, ejection seats and seven external store stations. The concept of using ground ordnance and a bomb bay had been ignored, although it did have provisions for four M60
[medium] machine guns. In spite of this growth (almost double the size and weight of our home built), the YOV-10 still had great potential. It would not achieve the advantages of integration with the ground scheme of maneuver, but it did have capabilities at the low end of the performance envelope that were still valuable and unique."
The Bronco performed observation, forward air control, helicopter escort, armed reconnaissance, utility light air transport and limited ground attack. The Bronco has also performed aerial radiological reconnaissance, tactical air observation, artillery and naval gunfire spotting, airborne control of tactical air support operations and front line, low-level aerial photography. A prototype in Vietnam designed to lay smoke was extremely successful, kept in service by evaluators for several months, and only reluctantly released, was not purchased due to a perceived lack of mission.
Possible modernized variant
Boeing has recently put together plans internally to build a modernized, improved version of the OV-10 Bronco, called the OV-10X, to satisfy a possible Air Force requirement for a light attack plane. According to Pentagon and industry officials, while the aircraft would maintain much of its 1960s-vintage rugged external design, the 21st century modernizations would include a computerized glass cockpit, intelligence sensors and smart-bomb-dropping capabilities. Boeing indicates that international interest in restarting production is growing, to compete with other light attack aircraft such as the T-6B Texan II, A-67 Dragon and EMB 314 Super Tucano.
On 3 February 2010, during the Singapore Air Show, Boeing announced that the international interest for the aircraft was such, that it would go on with its development even in the case it failed to win the USAF tender for 100 Light Attack/Armed Reconnaissance aircraft.
Engine installation on OV-10B Bronco
An OV-10A Bronco from VMO-1 takes off from the flight deck of the USS Nassau (LHA-4)
Visually, the OV-10 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 aircraft's design supports effective operations from forward bases. The OV-10 can perform short takeoffs and landings, including on aircraft carriers and large deck amphibious assault ships without using catapults or arresting wires. Further, the OV-10 was designed to takeoff and land on unimproved sites. Repairs can be made with ordinary tools. No ground equipment is required to start the engines. And, if necessary, the engines will operate on high-octane automobile fuel with only a slight loss of power.
The aircraft has responsive handling and can fly for five and a half hours with external fuel tanks. The cockpit has extremely good visibility for a tandem pilot and co-pilot provided by a wrap-around "greenhouse" that is wider than the fuselage. With the second seat removed, it can carry 3,200 pounds (1,500 kg) of cargo, five paratroopers or two litter patients and an attendant. Empty weight was 6,970 pounds (3,161 kg). Normal operating fueled weight with two crew was 9,910 pounds (4,494 kg). Maximum takeoff weight was 14,446 pounds (6,553 kg).
The bottom of the fuselage contains sponsons or "stub wings" that improve flight performance by decreasing aerodynamic drag 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. Normally four .30 in (7.62 mm) M60C machine guns were carried on the sponsons with the M60Cs 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.
Racked armament in the Vietnam War was usually seven-shot 2.75 in (70 mm) rocket pods with marker or high-explosive rockets, or 5 in (127 mm) four-shot Zuni rocket pods. Bombs, ADSIDS air-delivered seismic sensors, Mk-6 battlefield illumination flares, and other stores were carried as well.
Operational experience showed that there were some weaknesses in the OV-10's design. It is seriously underpowered. This contributed to crashes in Vietnam in sloping terrain because the pilots could not climb fast enough. While specifications state that the aircraft could reach 26,000 feet (7,900 m), in Vietnam the aircraft could reach only 18,000 feet (5,500 m). Also, no OV-10 pilot survived ditching the aircraft.
The OV-10 served in the U.S. Air Force, U.S. Marine Corps, and U.S. Navy, as well as in the service of a number of other countries. A total of 81 OV-10 Broncos were ultimately lost to all causes during the course of the Vietnam War, with the Air Force losing 64, the Navy 7 and the Marines 10.