Bell XV-3

https://en.wikipedia.org/wiki/Bell_XV-3

The Bell XV-3 (Bell 200) is an American tiltrotor aircraft developed by Bell
Helicopter for a joint research program between the United States Air Force and
the United States Army in order to explore convertiplane technologies. The XV-3
featured an engine mounted in the fuselage with driveshafts transferring power
to two-bladed rotor assemblies mounted on the wingtips. The wingtip rotor
assemblies were mounted to tilt 90 degrees from vertical to horizontal, designed
to allow the XV-3 to take off and land like a helicopter but fly at faster
airspeeds, similar to a conventional fixed-wing aircraft.

The XV-3 was first flown on 11 August 1955. Although it was limited in
performance, the aircraft successfully demonstrated the tiltrotor concept,
accomplishing 110 transitions from helicopter to airplane mode between December
1958 and July 1962. The XV-3 program ended when the remaining aircraft was
severely damaged in a wind tunnel accident on 20 May 1966. The data and
experience from the XV-3 program were key elements used to successfully develop
the Bell XV-15, which later paved the way for the V-22 Osprey.

In 1951, the Army and Air Force announced the Convertible Aircraft Program and
released the Request for Proposals (RFP) to solicit designs from the aircraft
industry. In October 1953, Bell Helicopter was awarded a development contract to
produce two aircraft for testing purposes. The original military designation was
XH-33, classifying it as a helicopter, but its designation was changed to XV-3
in the convertiplane series. The designation was changed once again in 1962 to
XV-3A when the V-prefix was changed to mean VTOL. The leading designers were Bob
Lichten and Kenneth Wernicke.

The first XV-3 (serial number 54-147) flew on 11 August 1955 with Bell Chief
Test Pilot Floyd Carlson at the controls. On 18 August 1955, the aircraft
experienced a hard landing when the rotor developed dynamic instability. Bell
attempted to remedy the situation, and flight testing resumed on 29 March 1956
after additional ground runs. Bell continued to expand the flight envelope of
the XV-3, but on 25 July 1956, the same rotor instability occurred again. Flight
testing of the XV-3 resumed in late September 1956. Then, on 25 October 1956,
the aircraft crashed when the test pilot blacked out due to extremely high
cockpit vibrations. The vibrations resulted when the rotor shafts were moved 17
degrees forward from vertical. The test pilot, Dick Stansbury, was seriously
injured, and the aircraft was damaged beyond repair.

Bell modified the second XV-3 (serial number 54-148) by replacing the
three-bladed rotors with two-bladed rotors, and after taking extensive
precautions, the second XV-3 began testing at the National Advisory Committee
for Aeronautics' (NACA) Ames Aeronautical Laboratory wind tunnel facility on 18
July 1957. Flight testing for aircraft #2 began on 21 January 1958 at Bell's
facility. By April, the aircraft had expanded the flight envelope to 127 miles
per hour (204 km/h) as well as demonstrating full autorotation landings and
30-degrees forward transitions with the rotor pylons. On 6 May 1958, another
instance of rotor instability occurred when the pylons were advanced to
40-degrees forward pylon angle, and the XV-3 was grounded once more. The XV-3
returned to the Ames wind tunnel in October 1958 to collect more data before it
could be flown again. As a result of the wind tunnel testing, the rotor diameter
was reduced, wing structure was increased and strengthened, and the rotor
controls were stiffened.

The XV-3 resumed flight testing at Bell's facility on 12 December 1958. On 18
December 1958, Bell test pilot Bill Quinlan accomplished the first dynamically
stable full conversion to airplane mode, and on 6 January 1959, Air Force
Captain Robert Ferry became the first military pilot to complete a tiltrotor
conversion to airplane mode. Flight testing at the Bell facilities was completed
on 24 April 1959, and the aircraft was shipped to Edwards Air Force Base. The
military flight testing of the XV-3 began on 14 May 1959. Promoted to the rank
of Major, Robert Ferry would coauthor the report on the military flight
evaluations, conducted from May to July 1959, noting that despite the
deficiencies of the design, the "fixed-wing tilt-prop," or tiltrotor, was a
practical application for rotorcraft.


Role
Experimental VTOL aircraft

National origin
United States

Manufacturer
Bell Helicopter

First flight
11 August 1955

Status
Display

Number built
2

In April 1966, Bell Helicopter aerodynamicist Dr. Earl Hall published an
analysis of the XV-3 program data explaining the tiltrotor aircraft pylon whirl
instability. In order to establish Hall's findings and develop a computer model,
NASA agreed to conduct wind tunnel testing at the Ames 40 × 80 wind tunnel. As
the engineers were completing the last planned test, a wingtip failure caused
both rotors to fail, resulting in severe damage of the XV-3 and damage to the
wind tunnel. On 14 June 1966, NASA Ames Research Center announced the completion
of XV-3 testing. The XV-3 had accomplished a total of 250 flights, accumulated
125 flight hours, and completed 110 full conversions.

Specifications (XV-3)

General characteristics
Crew: one
Length: 30 ft 4 in (9.2 m)
Wingspan: 31 ft 4 in (9.5 m)
Main rotor diameter: 2× 25 ft 0 in (7.6 m)
Height: 13 ft 3 in (4.0 m)
Wing area: 116 ft2 (10.8 m2)
Empty weight: 4,205 lb (1,907 kg)
Gross weight: 4,890 lb (2,218 kg)
Powerplant: 1 × Pratt & Whitney R-985-AN-1 radial engine, 450 hp (336 kW)

Performance
Maximum speed: 184 mph (296 km/h)
Cruise speed: 167 mph (269 km/h)
Range: 255 miles (411 km)
Service ceiling: 15,000 ft (4,600 m)
Rate of climb: 1,260 ft/min (6.3 m/s)




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