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From: Miloch <Miloch_member@newsguy.com>
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Subject: Northrop X-4 Bantam
Date: 23 Oct 2018 07:10:25 -0700
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https://en.wikipedia.org/wiki/Northrop_X-4_Bantam
The Northrop X-4 Bantam was a prototype small twinjet aircraft manufactured by
Northrop Corporation in 1948. It had no horizontal tail surfaces, depending
instead on combined elevator and aileron control surfaces (called elevons) for
control in pitch and roll attitudes, almost exactly in the manner of the
similar-format, rocket-powered Messerschmitt Me 163 of Nazi Germany's Luftwaffe.
Some aerodynamicists had proposed that eliminating the horizontal tail would
also do away with stability problems at fast speeds (called shock stall)
resulting from the interaction of supersonic shock waves from the wings and the
horizontal stabilizers. The idea had merit, but the flight control systems of
that time prevented the X-4 from any success.
Two X-4s were built by the Northrop Corporation, but the first was found to be
mechanically unsound and after ten flights it was grounded and used to provide
parts for the second. While being tested from 1950 to 1953 at the NACA
High-Speed Flight Research Station (now Edwards Air Force Base), the X-4's
semi-tailless configuration exhibited inherent longitudinal stability problems
(porpoising) as it approached the speed of sound. It was concluded that (with
the control technology available at the time) tailless craft were not suited for
transonic flight.
It was believed in the 1940s that a design without horizontal stabilizers would
avoid the interaction of shock waves between the wing and stabilizers. These
were believed to be the source of the stability problems at transonic speeds up
to Mach 0.9. Two aircraft had already been built using a semi-tailless
British de Havilland DH.108 Swallow built after the war. The United States Army
Air Forces signed a contract with the Northrop Aircraft Company on 11 June 1946,
to build two X-4s. Northrop was selected because of its experience with flying
wing designs, such as the N-9M, XB-35 and YB-49 aircraft.
The resulting aircraft was very compact, only large enough to hold two
Westinghouse J30 jet engines, a pilot, instrumentation, and a 45-minute fuel
supply. Nearly all maintenance work on the aircraft could be done without using
a ladder or footstool. A person standing on the ground could easily look into
the cockpit. The aircraft also had split flaps, which doubled as speed brakes.
Role
Tailless aircraft prototype
Manufacturer
Northrop
First flight
15 December 1948
Status
Preserved
Number built
Two
The first X-4 (serial number 46-676) was delivered to Muroc Air Force Base,
California, in November 1948. It underwent taxi tests and made its first flight
on December 15, 1948, with Northrop test pilot Charles Tucker at the controls.
Winter rains flooded Rogers Dry Lake soon after, preventing additional X-4
flights until April 1949. The first X-4 proved mechanically unreliable, and made
only ten flights. Walt Williams, the head of the NACA Muroc Flight Test Unit
(now Dryden Flight Research Center) called the aircraft a "lemon". The second
X-4 (serial number 46-677) was delivered during the halt of flights, and soon
proved far more reliable. It made a total of 20 contractor flights. Despite
this, the contractor flight program dragged on until February 1950, before both
aircraft were turned over to the Air Force and the NACA. The first X-4 never
flew again, used as spare parts for the second aircraft.
The NACA instrumented the second X-4 to conduct a short series of flights with
Air Force pilots. These included Chuck Yeager, Frank Kendall Everest, Jr., Al
Boyd, Richard Johnson, Fred Ascani, Arthur Murray and Jack Ridley. The flights
were made in August and September 1950. The first flight by an NACA pilot was
made by John H. Griffith on September 28, 1950.
The initial NACA X-4 flights, which continued from late 1950 through May of
1951, focused on the aircraft's sensitivity to pitch. NACA pilots Griffith and
Scott Crossfield noted that as the X-4's speed approached Mach 0.88, it began a
pitch oscillation of increasing severity, which was likened to driving on a
washboard road. Increasing speeds also caused a tucking phenomenon, in which the
nose pitched down, a phenomenon also experienced by the Me 163A Anton prototypes
in 1941. More seriously, the aircraft also showed a tendency to "hunt" about all
three axes. This combined yaw, pitch and roll, which grew more severe as the
speed increased, was a precursor to the inertial coupling which would become a
major challenge in the years to come.
The X-4's primary importance involved proving a negative, in that a swept-wing
semi-tailless design was not suitable for speeds near Mach 1, although the F7U
first aircraft to demonstrate stores separation above Mach 1. Aircraft designers
were thus able to avoid this dead end. It was not until the development of
computer fly-by-wire systems that such designs could be practical. Semi-tailless
designs appeared on the X-36, Have Blue, F-117, and Bird of Prey, although these
aircraft all differed significantly in shape from the X-4. The trend during its
test program was already towards delta and modified delta aircraft such as the
Douglas F4D, the Convair F-102A derived from the XF-92A, and the Avro Vulcan.
Specifications (X-4)
General characteristics
Crew: one
Length: 22 ft 3 in (7.09 m)
Wingspan: 26 ft 10 in (8.18 m)
Height: 14 ft 10 in (4.52 m)
Wing area: 200 sq ft (18.6 m2)
Aspect ratio: 3.6:1
Empty weight: 5,507 lb (2,500 kg)
Max. takeoff weight: 7,820 lb (3,550 kg)
Performance
Maximum speed: 625 mph (543 knots, 1,006 km/h)
Range: 420 mi (365 nmi, 676 km)
Service ceiling: 42,300 ft (12,900 m)
Rate of climb: 7,700 ft/min (39.1 m/s)
*
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