North American Rockwell OV-10 Bronco
Design & Development

The original vision was developed by an informal collaboration of W.H. Beckett and Col. K.P. Rice, who met at China Lake Naval Test Station. It was for a rugged, simple close air support aircraft integrated with forward ground operations. At the time, the Army had not yet developed armed helicopters, and the Air Force was uninterested in close air support.

The aircraft was to operate from expedient forward air bases using roads as runways. Even in jungles, roads would be available. So, it needed a 20 ft wing span and a 6.5 ft tread. Speed was to range from very slow, to medium subsonic, with much longer loiter times than a jet. Efficient turboprop engines would give better performance than piston aircraft. Weapons were to be mounted on the centerline to get efficient unranged aiming like a P-38. 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 would avoid the back blast.

They developed a basic platform meeting the 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 retired from the Marine Corps, and went to work at North American to sell the aircraft.

Rice states: "The military definition of STOL (500' to a 50' 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."

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. Retired Marine Corps aviators K.P. Rice and William H. Beckett originated the LARA concept as an aircraft with very small wingspans of around 20 feet that could land in nearly any small clearing and use the same ammunition and fuel as ground troops used. His "L2 VMA" concept also would have the aircraft ground-mobile so it could be co-located with ground units and not require runways and air bases.

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 Bird Dog and O-2 Skymaster) 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 lb (1,100 kg) 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 350 mph (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 machine guns with 2,000 rounds, and external weapons including a 20 mm gun pod and Sidewinder missiles.

Eleven proposals were submitted, nine of them were the Grumman Model 134R tandem-seat version of the already fielded OV-1 Mohawk observation/attack aircraft (the Marine Corps dropped out of the program in 1958), Goodyear GA 39, the Beech PD-183, Douglas D-855, General Dynamics/Convair Model 48 Charger, the Helio 1320, the 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.

General Dynamics/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 Bronco. The Charger, while capable of outperforming the OV-10 in some respects, crashed on 19 October 1965 after 196 test flights. Convair dropped out of contention.

General Dynamics/Convair Model 48 Charger.

The Bronco started flying midway through the Charger's test program on 16 July 1965, and became one of the premiere COIN (COunter INsurgence) aircraft of the next 30 years. It failed to live up to Rice's L2 VMA concept because DoD insisted on 40 ft 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 1000 lbs for the rough field landing gear and another 1000 lbs 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, 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. 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.

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 North Vietnamese nickname for an OV-10 was chuong lon or "pigpen", perhaps because its tail empennage resembled a traditional Vietnamese pig enclosure.

The OV-10 can perform short takeoffs 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 1,452 kg (3,200 lb) of cargo, five paratroopers or two litter patients and an attendant. Empty weight was 3,161 kg (6,969 lb). Normal operating fueled weight, with two crew was 4,494 kg (9,908 lb). Maximum takeoff weight was 6,563 kg (14,466 lb).

The bottom of the fuselage contains sponsons or "stub wings" that improves 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 7.62 mm M60C machine guns were carried on the sponsons with the M-60Cs 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. The sponsons are easy to remove, and most unarmed Broncos have now had their sponsons removed.

Racked armament in the Vietnam War was usually seven-shot 2.75 inch (70 mm) rocket pods with marker or high-explosive rockets, or 5 inch (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.

Wikipedia: OV-10 Bronco