Bell X-5

https://en.wikipedia.org/wiki/Bell_X-5

The Bell X-5 was the first aircraft capable of changing the sweep of its wings
in flight. It was inspired by the untested wartime P.1101 design of the German
Messerschmitt company. In contrast with the German design which could only have
its wing sweepback angle adjusted on the ground, the Bell engineers devised a
system of electric motors to adjust the sweep in flight.

The incomplete Messerschmitt P.1101 fighter prototype recovered by United States
troops in 1945 from the experimental facility at Oberammergau, Germany, was
brought back to the United States. Although damaged in transit, the innovative
fighter prototype was delivered to the Bell factory at Buffalo, New York where
company engineering staff studied the design closely, and, led by Chief Designer
Robert J. Woods, submitted a proposal for a similar design.

Although superficially similar, the X-5 was much more complex than the P.1101,
with three sweep positions: 20°, 40° and 60°, creating an inflight
"variable-geometry" platform. A jackscrew assembly moved the wing's hinge along
a set of short horizontal rails, using disc brakes to lock the wing into its
inflight positions. Moving from full extension to full sweep took less than 30
seconds. The articulation of the hinge and pivots partly compensated for the
shifts in center of gravity and center of pressure as the wings moved.

Even so, the X-5 had vicious spin characteristics arising from the aircraft's
flawed aerodynamic layout, particularly a poorly positioned tail and vertical
stabilizer which, in some wing positions, could lead to an irrecoverable spin.
This violent stall / spin instability would eventually cause the destruction of
the second aircraft and the death of its Air Force test pilot in 1953.

The unfavorable spin characteristics also led to the cancellation of tentative
plans by the United States Air Force to modify the X-5's design into a low-cost
tactical fighter for NATO and other foreign count.


Role
Research aircraft

Manufacturer
Bell Aircraft Corporation

Designer
Robert J. Woods

First flight
20 June 1951

Retired
December 1958

Primary users
United States Air Force
National Advisory Committee for Aeronautics

Number built
2

Two X-5s were built (serial numbers 50-1838 and 50-1839). The first was
completed 15 February 1951, and the two aircraft made their first flights on 20
June and 10 December 1951. Almost 200 flights were made at speeds up to Mach 0.9
and altitudes of 40,000 ft (12,000 m). One aircraft was lost on 14 October 1953,
when it failed to recover from a spin at 60° sweepback. Air Force Captain Ray
Popson died in the crash at Edwards Air Force Base. The other X-5 remained at
Edwards and continued active testing until 1955, and remained in service as a
chase plane until 1958.

The X-5 successfully demonstrated the advantage of a swing-wing design for
aircraft intended to fly at a wide range of speeds. Despite the X-5's stability
problems, the concept was later successfully implemented in such aircraft as the
General Dynamics F-111 and Grumman F-14 Tomcat, the Mikoyan Gurevich MiG-23 and
MiG-27, the Sukhoi Su-17/20/22 and Su-24, the Tupolev Tu-22M and Tu-160, the
Panavia Tornado and the Rockwell B-1 Lancer.

Specifications (Bell X-5)

General characteristics
Crew: 1
Length: 33 ft 4 in (10.1 m)
Wingspan:
Unswept: 33 ft 6 in (10.2 m)
60° sweep: 20 ft 10 in (6.5 m)

Height: 12 ft (3.6 m)
Wing area: 175 sq. ft. (16.26 m².)
Empty weight: 6,336 lb (2,880 kg)
Max. takeoff weight: 9,980 lb (4,536 kg)
Powerplant: 1 × Allison J35-A-17 turbojet, 4,900 lbf (21.8 kN)

Performance
Maximum speed: 716 mph (1,150 km/h)
Range: 750 mi (1,207 km)
Service ceiling: 49,900 ft (15,200 m)
Thrust/weight: 0.50:1




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