The Northrop X-4 Bantam was a prototype small twinjetaircraft 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 supersonicshock 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.
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.[1] 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.[2]
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 Britishde 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.
Operational history
Preparing for flight
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 pilotCharles 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. Walter C. Williams, the head of the NACA Muroc Flight Test Unit (now Dryden Flight Research Center) called the aircraft a "lemon".[1] 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 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 Mach0.88, 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 Mach0.92.
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, when the landing tests resumed. NACA pilots Joe Walker, Stanley Butchard, 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 Mach0.91. Above Mach0.91, 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. 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, before being returned to Edwards Air Force Base.[1] 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.[1]
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 Mach1. 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.
A flying wing is a tailless fixed-wing aircraft that has no definite fuselage, with its crew, payload, fuel, and equipment housed inside the main wing structure. A flying wing may have various small protuberances such as pods, nacelles, blisters, booms, or vertical stabilizers.
The Bell X-1 is a rocket engine–powered aircraft, designated originally as the XS-1, and was a joint National Advisory Committee for Aeronautics–U.S. Army Air Forces–U.S. Air Force supersonic research project built by Bell Aircraft. Conceived during 1944 and designed and built in 1945, it achieved a speed of nearly 1,000 miles per hour in 1948. A derivative of this same design, the Bell X-1A, having greater fuel capacity and hence longer rocket burning time, exceeded 1,600 miles per hour in 1954. The X-1 aircraft #46-062, nicknamed Glamorous Glennis and flown by Chuck Yeager, was the first piloted airplane to exceed the speed of sound in level flight and was the first of the X-planes, a series of American experimental rocket planes designed for testing new technologies.
The Douglas D-558-2 Skyrocket is a rocket and jet-powered research supersonic aircraft built by the Douglas Aircraft Company for the United States Navy. On 20 November 1953, shortly before the 50th anniversary of powered flight, Scott Crossfield piloted the Skyrocket to Mach 2, or more than 1,290 mph (2076 km/h), the first time an aircraft had exceeded twice the speed of sound.
Elevons or tailerons are aircraft control surfaces that combine the functions of the elevator and the aileron, hence the name. They are frequently used on tailless aircraft such as flying wings. An elevon is not part of the main wing, but instead is a separate tail surface, is a stabilator.
The Douglas X-3 Stiletto was a 1950s United States experimental jet aircraft with a slender fuselage and a long tapered nose, manufactured by the Douglas Aircraft Company. Its primary mission was to investigate the design features of an aircraft suitable for sustained supersonic speeds, which included the first use of titanium in major airframe components. Douglas designed the X-3 with the goal of a maximum speed of approximately 2,000 mph (3,200 km/h), but it was seriously underpowered for this purpose and could not even exceed Mach 1 in level flight. Although the research aircraft was a disappointment, Lockheed designers used data from the X-3 tests for the Lockheed F-104 Starfighter which used a similar trapezoidal wing design in a successful Mach 2 fighter.
Joseph Albert Walker was an American World War II pilot, experimental physicist, NASA test pilot, and astronaut who was the first person to fly an airplane to space. He was one of twelve pilots who flew the North American X-15, an experimental spaceplane jointly operated by the Air Force and NASA.
Albert Scott Crossfield was an American naval officer and test pilot. In 1953, he became the first pilot to fly at twice the speed of sound. Crossfield was the first of twelve pilots who flew the North American X-15, an experimental spaceplane jointly operated by the United States Air Force and NASA.
Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's pitch, and therefore the angle of attack and the lift of the wing. The elevators are usually hinged to the tailplane or horizontal stabilizer. They may be the only pitch control surface present, and are sometimes located at the front of the aircraft or integrated into a rear "all-moving tailplane", also called a slab elevator or stabilator.
The Convair XF-92 was an American, delta wing, first-generation jet prototype. Originally conceived as a point-defence interceptor, the design was later used purely for experimental purposes and only one was built. However, it led Convair to use the delta-wing on a number of designs, including the F-102 Delta Dagger, F-106 Delta Dart, B-58 Hustler, the US Navy's F2Y Sea Dart as well as the VTOL FY Pogo.
The Northrop XP-79, USAAF project number MX-365, was a rocket and jet-powered flying wing fighter aircraft, designed by Northrop. The pilot operated the aircraft in a prone position, permitting him to withstand much greater g-forces in pitch. It also used a welded magnesium monocoque structure instead of riveted aluminum.
The Northrop N-1M, also known by the nickname "Jeep", is a retired American experimental aircraft used in the development of the flying wing concept by Northrop Aircraft during the 1940s.
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 German Messerschmitt Me 163 Komet. Initially designed to evaluate swept wing handling characteristics at low and high subsonic speeds for the proposed early tailless design of the Comet airliner, three examples of the DH 108 were built to Air Ministry specifications E.18/45. With the adoption of a conventional tail for the Comet, the aircraft were used instead to investigate swept wing handling up to supersonic speeds. All three prototypes were lost in fatal crashes.
An aircraft stabilizer is an aerodynamic surface, typically including one or more movable control surfaces, that provides longitudinal (pitch) and/or directional (yaw) stability and control. A stabilizer can feature a fixed or adjustable structure on which any movable control surfaces are hinged, or it can itself be a fully movable surface such as a stabilator. Depending on the context, "stabilizer" may sometimes describe only the front part of the overall surface.
The Armstrong Whitworth A.W.52 was an early flying wing aircraft designed and produced by British aircraft manufacturer Armstrong Whitworth Aircraft.
The Short SB.4 Sherpa was an experimental aircraft designed and produced by the British aircraft manufacturer Short Brothers. Only a single example was ever produced.
In aeronautics, a tailless aircraft is an aircraft with no other horizontal aerodynamic surface besides its main wing. It may still have a fuselage, vertical tail fin, and/or vertical rudder.
The General Dynamics X-62 VISTA is an experimental aircraft, derived from the F-16D Fighting Falcon, which was modified as a joint venture between General Dynamics and Calspan for use by the United States Air Force (USAF). Originally designated NF-16D, the aircraft was redesignated X-62A on 14 June 2021 as part of an upgrade to a Skyborg, with System for Autonomous Control of Simulation (SACS).
The SZD-6x Nietoperz was a single-seat tail-less experimental glider aircraft that was designed and built in Poland at Szybowcowy Zakład Doświadczalny in Bielsko-Biała in 1951. Only one example was constructed.
The NRC tailless glider, also called the NRL tailless glider, was a two-seat tailless research glider designed by the National Research Council of Canada and built by the National Research Laboratories, at the instigation of G.T.R. Hill who had previously designed the British Westland-Hill Pterodactyl series of tailless aircraft.
References
Wikimedia Commons has media related to Northrop X-4.
Notes
1 2 3 4 Wilkinson, Stephan. "Northrop X-4". Air & Space Smithsonian. Vol.29 No.2. June/July 2014.
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. ISSN0143-5450.
1 Not assigned •2 Assigned to multiple types •3 Unofficial
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
