Boeing Vertol BV-347

Development of the BV-347 began in January 1969, when Boeing Vertol was contracted by the United States Army to develop an improved CH-47 Chinook. The Army loaned a single CH-47A, serial number 65-7992, to be modified in exchange for exclusive rights to the project's research data. The modifications, which were funded by Boeing, were carried out in two phases.[1] Phase I began with redesigned rotors, which had four blades of increased diameter compared to the Chinook's three-blade rotors, as well as a 30-degree offset flapping hinge.[2] The fuselage was stretched by 110 inches (280 cm), reducing the rotor overlap from 35% on the original Chinook to 22%, and provisions were added to mount small wings to the upper fuselage at a later time. The rear pylon was raised 30 inches (76 cm) to increase rotor clearance and decrease noise. The engines were replaced with uprated T55-L-11s, which would later be standard on the CH-47C.[1][3] The cockpit layout was improved, with thicker glass being added, as well as a bulkhead with an entrance door and other improvements to reduce cockpit noise.[1]

For Phase II, a pair of small wings was added to the fuselage. These wings served to provide extra lift and allowed the BV-347 to achieve a 60 degree banked turn. They had a variable incidence from 10 degrees down to 85 degrees up, and featured full-span flaps. During hover, the wings would be tilted to 85 degrees to minimize interference with the rotor downwash.[1]

BV-347 at the US Army Aviation Museum in Fort Rucker (now Fort Novosel) in Alabama

The BV-347 made its first flight in Phase I configuration on May 27, 1970.[1] During Phase I test flights, the BV-347 demonstrated a transmission-limited maximum true airspeed of 177 knots (204 mph; 328 km/h), excellent stability and flight characteristics, and low vibration and sound levels. Flight testing of the Phase II configuration began in December 1971.[1]

Boeing Vertol used the BV-347 as part of the development of its XCH-62. As part of the program, the BV-347's hydro-mechanical rotor control system was replaced with a fly-by-wire system, becoming the first helicopter in history to be controlled with such a system. The BV-347 was also fitted with a retractable ventral gondola, with its own set of controls, which was used to operate the load recovery system. A sidearm controller originally developed for the XCH-62 was installed in the gondola. The new control system was noted to be easy for novice pilots to fly. During demonstrations in Washington DC, the BV-347 was flown by over 125 pilots, 100 of which had never flown an aircraft of any kind before, with some even being capable of performing normally difficult maneuvers.[1]

Flight testing of the BV-347 was completed in 1975.[3] Although the Army could not feasibly upgrade its entire CH-47 fleet with the stretched fuselage and wings of the BV-347, the latter did influence some of the improvements made to the CH-47D, such as the flight control systems and reliability improvements.[1][2]

BV-347 Phase I

Original configuration with stretched fuselage.

BV-347 Phase II

Fitted with small wings on the mid-fuselage.

Civil BV-347

A civil variant of the BV-347 considered by NASA.[4]

Following the completion of the test program, the sole BV-347 was retired and donated to the United States Army Aviation Museum at Fort Rucker (now Fort Novosel) in Alabama.[1]

Data from [1]

General characteristics

• Wingspan: 45 ft (14 m)
• Wing area: 340 sq ft (32 m²)
• Powerplant: 2 × Lycoming T55-L-11 turboshaft engine
• Main rotor diameter: 2 × 60 ft 0 in (18.29 m)

Related development

• Boeing CH-47 Chinook
• Boeing Vertol XCH-62

Aircraft of comparable role, configuration, and era

• Kamov V-100
• Lockheed AH-56 Cheyenne
• Piasecki 16H Pathfinder
• Sikorsky S-67 Blackhawk

Wikimedia Commons has media related to Boeing Vertol BV-347.

• BV-347 Phase II final report