In today’s Sydney Flyer article we are delighted to welcome back author Anthony Coleiro and the most recent instalment of his X-Files series. For those of you not aware, Anthony has already written 133 articles under the ‘X-Files’ series for the club magazine. What a record!
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FILE X133: BELL XV-3
The Bell Helicopter Company began developing helicopters back in 1941 and flew its first aircraft two years later. In 1953, Bell for the first time dabbled in the field of Vertical Take-Off and Landing (VTOL) aircraft. The aircraft they came up with was originally designated the model 200 XH-33, it was later changed to the XV-3 under a joint US Army and Air Force contract. The XV-3 was a convertiplane, i.e. the lifting rotors were tilted from the vertical for take-off and landing to the horizontal for forward flight. The military signed up to investigate the engineering challenges with such an aircraft.
Two XV-3s were built. The aircraft’s layout was conventional except that it had skids for landing gear and a relatively short wing. A pair of electrically tiltable helicopter counter-rotating 3-bladed rotors were fitted, one on each wing tip. The cabin was designed to accommodate four occupants. Power was supplied by a 450 hp Pratt & Whitney R-985 radial piston engine mounted behind the cabin. The two rotors were connected to the single engine by the use of transmission shafts and gears. In the event of an engine failure, the rotors would be tilted to the vertical so that the aircraft could autorotate just like a conventional helicopter.
Ground testing commenced on 10 February 1955 and after an extensive programme, the first prototype made its first vertical take-off on 23 August 1955. Progressive way was being made to full horizontal flight but it was written off after a heavy landing in October of the following year, the rotors only having achieved 15° of tilt.
The second prototype continued on with the test programme but with different rotors. The 3-bladed fully articulated rotors were replaced by 2-bladed semi-rigid type. On 18 December 1958 the first full transition flight took place and a speed of 115 kts was achieved at 4,000 feet. It took 10-15 seconds to fully tilt the rotors and they could be tilted to any angle. In April of the following year the first gearshift was achieved. This was when, after having tilted the rotors to the horizontal position, the rotors shifted gear to a reduced RPM by some 40% for maximum efficiency in the forward cruise.
In the following month the aircraft was handed over to the USAF for evaluation. It was while with them that the aircraft made its power-off reconversion under simulated engine failure conditions, this was where the rotors were tilted to the vertical position for autorotation. When the USAF had finished with it, NASA obtained it for their own testing. By the end of 1962, the aircraft had clocked up 450 hours, made over 100 full conversion flights up to altitudes of 12,000 feet with speeds ranging from –24 kph to 290 kph, yes that was negative 24 kph, like a hummingbird, this aircraft could fly backwards.
The XV-3 was never intended to go into production but rather to be a proof of concept for the Bell XV-15 that went on to fly in 1976.
The last surviving XV-3 can be seen at the Wright-Patterson Air Force Base in Dayton Ohio at the USAF museum.
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