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
An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...
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
A shock stall is a stall created when the airflow over an aircraft's wings is disturbed by shock waves formed when flying at or above the aircraft's drag divergence Mach number The drag-divergence Mach number (not to be confused with critical Mach ...
) resulting from the interaction of
supersonic
Supersonic speed is the speed of an object that exceeds the speed of sound ( Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately . Speeds greater than five times ...
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 achieving any success.
Development
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.
[Wilkinson, Stephan. "Northrop X-4". ''Air & Space Smithsonian.'' Vol.29 No.2. June/July 2014.]
While being tested from
1950
Events January
* January 1 – The International Police Association (IPA) – the largest police organization in the world – is formed.
* January 5 – 1950 Sverdlovsk plane crash, Sverdlovsk plane crash: ''Aeroflot'' Lisunov Li-2 cr ...
to
1953
Events
January
* January 6 – The Asian Socialist Conference opens in Rangoon, Burma.
* January 12 – Estonian émigrés found a Estonian government-in-exile, government-in-exile in Oslo.
* January 14
** Marshal Josip Broz Tito i ...
at the
NACA High-Speed Flight Research Station (now
Edwards Air Force Base
Edwards Air Force Base (AFB) is a United States Air Force installation in California. Most of the base sits in Kern County, but its eastern end is in San Bernardino County and a southern arm is in Los Angeles County. The hub of the base is E ...
), 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 design—the
rocket-powered
Me 163B ''Komet'' flown in combat by
Nazi Germany's
Luftwaffe in
World War II, and the turbojet-powered
British de Havilland DH.108 Swallow
The de Havilland DH 108 "Swallow" was a British experimental aircraft designed by John Carver Meadows Frost in October 1945. The DH 108 featured a tailless, swept wing with a single vertical stabilizer, similar to the layout of the wartime Ge ...
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
The Northrop YB-35, Northrop designation N-9 or NS-9, were experimental heavy bomber aircraft developed by the Northrop Corporation for the United States Army Air Forces during and shortly after World War II. The airplane used the radical a ...
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.
Operational history
The first X-4 (serial number 46-676) was delivered to
Muroc Air Force Base
Edwards Air Force Base (AFB) is a United States Air Force installation in California. Most of the base sits in Kern County, but its eastern end is in San Bernardino County and a southern arm is in Los Angeles County. The hub of the base is Ed ...
,
California, in November
1948
Events January
* January 1
** The General Agreement on Tariffs and Trade (GATT) is inaugurated.
** The Constitution of New Jersey (later subject to amendment) goes into effect.
** The railways of Britain are nationalized, to form British ...
. 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
Events
January
* January 1 – A United Nations-sponsored ceasefire brings an end to the Indo-Pakistani War of 1947. The war results in a stalemate and the division of Kashmir, which still continues as of 2022.
* January 2 – Luis ...
. The first X-4 proved mechanically unreliable, and made only ten flights.
Walter C. Williams
Walter Charles Williams (July 30, 1919 – October 7, 1995) was an American engineer, leader of the National Advisory Committee for Aeronautics (NACA) group at Edwards Air Force Base in the 1940s and 1950s, and a NASA deputy associate administra ...
, 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.
Brigadier General Frank Kendall "Pete" Everest Jr. (August 9, 1920 – October 1, 2004) was a U.S. Air Force officer who is best remembered as an aeroengineer and test pilot during the 1950s.
Early years
Everest was born August 9, 1920, i ...
,
Al Boyd,
Richard Johnson,
Fred Ascani
Fred J. Ascani (born Alfredo John Ascani; May 29, 1917 – March 28, 2010) was an American major general and test pilot of the United States Air Force. He was one of the "Men of Mach 1" and was considered the father of systems engineering at Wrig ...
,
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
John H. Griffith was a test pilot for the National Advisory Committee for Aeronautics, one of the pilots of the Bell X-1.
Griffith grew up in Homewood, Illinois. He joined the United States Army Air Corps in November 1941, and served in the South ...
on September 28, 1950.
The initial NACA X-4 flights, which continued from late 1950 through May of
1951
Events
January
* January 4 – Korean War: Third Battle of Seoul – Chinese and North Korean forces capture Seoul for the second time (having lost the Second Battle of Seoul in September 1950).
* January 9 – The Government of the United ...
, 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.
To correct the poor stability, project engineers decided to increase the flap/speed brake trailing edge thickness.
Balsa wood strips were added between the upper and lower hinged "clamshell"-style flap/speed brake halves, causing them to remain open at a 5° angle. The first test of the blunt trailing edge was flown on 20 August 1951 by NACA pilot
Walter Jones. A second test was made by Crossfield in October. The results were positive, with Jones commenting that the X-4's flight qualities had been greatly improved, and the aircraft did not have pitch control problems up to a speed of Mach 0.92.
The balsa strips were removed, and the X-4 then undertook a long series of flights to test landing characteristics. By opening the speed brakes, the
lift-to-drag ratio of the aircraft could be reduced to less than 3:1. This was for data on future rocket-powered aircraft. The tests continued through October 1951, until wing tank fuel leaks forced the aircraft to be grounded until March
1952
Events January–February
* January 26 – Black Saturday in Egypt: Rioters burn Cairo's central business district, targeting British and upper-class Egyptian businesses.
* February 6
** Princess Elizabeth, Duchess of Edinburgh, becomes m ...
, when the landing tests resumed. NACA pilots
Joe Walker,
Stanley Butchard
Stanley may refer to:
Arts and entertainment
Film and television
* ''Stanley'' (1972 film), an American horror film
* ''Stanley'' (1984 film), an Australian comedy
* ''Stanley'' (1999 film), an animated short
* ''Stanley'' (1956 TV series) ...
, and
George Cooper were also checked out in the aircraft.
The thickened flap/speed brake tests had been encouraging, so balsa wood strips were reinstalled on both the flap/speed brake and the elevons. The first flight was made by Jones on 19 May 1952, but one of the engines was damaged during the flight, and it was August before a replacement J30 could be found. When the flights resumed, they showed that the modifications had improved stability in both pitch and yaw, and delayed the nosedown trim changes from Mach 0.74 to Mach 0.91. Above Mach 0.91, however, the X-4 still oscillated.
In May 1953, the balsa wood strips were again removed, and the X-4's dynamic stability was studied in the original flap/speed brake and elevon configuration. These flights were made by Crossfield and
John B. McKay
John Barron McKay (December 8, 1922 – April 27, 1975) was an American naval officer, World War II pilot, aeronautical engineer, test pilot, and astronaut. He was one of twelve pilots who flew the North American X-15, an experimental spaceplane ...
. This was the final project for the X-4, which made its 81st and final NACA flight on September 29, 1953. Both aircraft survived the test program. The first X-4, AF serial number 46-676, was transferred to the
United States Air Force Academy,
Colorado Springs, Colorado
Colorado Springs is a home rule municipality in, and the county seat of, El Paso County, Colorado, United States. It is the largest city in El Paso County, with a population of 478,961 at the 2020 United States Census, a 15.02% increase since ...
, before being returned to Edwards Air Force Base.
46-676 has been restored as of August 2012, and is currently being held in storage pending placement in the Edwards Museum. The second X-4 went to the
National Museum of the United States Air Force at
Wright-Patterson Air Force Base near
Dayton, Ohio, where it remains on display.
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
Vought's
F7U Cutlass proved to be something of a counterexample—the developed version was the 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
The McDonnell Douglas (later Boeing) X-36 ''Tailless Fighter Agility Research Aircraft'' was an American stealthy subscale prototype jet designed to fly without the traditional empennage found on most aircraft. This configuration was designed ...
,
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.
Aircraft on display
*The surviving X-4, tail number 6677, is on display at the
National Museum of the United States Air Force in
Dayton, Ohio.
Specifications (X-4)
See also
References
Notes
Bibliography
*
* Pelletier, Alain J. "Towards the Ideal Aircraft: The Life and Times of the Flying Wing, Part Two". ''
Air Enthusiast'', No. 65, September–October 1996, pp. 8–19. .
NASA-Dryden X-4 Fact Sheet
{{x-planes
X-4 Bantam
Edwards Air Force Base
1940s United States experimental aircraft
Tailless aircraft
Mid-wing aircraft
Twinjets
Aircraft first flown in 1948