The Rockwell-Messerschmitt-Bölkow-Blohm X-31 was an experimental jet fighter designed to test fighter
thrust vectoring
Thrust vectoring, also known as thrust vector control (TVC), is the ability of an aircraft, rocket, or other vehicle to manipulate the direction of the thrust from its engine(s) or motor(s) to control the attitude or angular velocity of the v ...
technology.
It was designed and built by
Rockwell and
Messerschmitt-Bölkow-Blohm
Messerschmitt-Bölkow-Blohm (MBB) was a West German aerospace manufacturer. It was formed during the late 1960s as the result of efforts to consolidate the West German aerospace industry; aircraft manufacturer Messerschmitt AG merged with the civi ...
(MBB), as part of a joint US and German ''Enhanced Fighter Maneuverability'' program to provide additional control authority in pitch and yaw, for significantly more maneuverability than most conventional fighters. An advanced
flight control system
A conventional fixed-wing aircraft flight control system consists of flight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight. Aircraft ...
provided controlled flight at high
angles of attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
where conventional aircraft would
stall or lose control. Two aircraft were built, of which only one has survived.
Design and development
The X-31 design was essentially an all-new airframe design, although it borrowed heavily on design elements and sometimes actual parts of previous production, prototype, and conceptual aircraft designs, including the British Aerospace
Experimental Airplane Programme (choice of wing type with canards, plus underfuselage intake), the German
TKF-90 (wing planform concepts and underfuselage intake),
F/A-18 Hornet
The McDonnell Douglas F/A-18 Hornet is an all-weather, twinjet, twin-engine, supersonic aircraft, supersonic, carrier-based aircraft, carrier-capable, Multirole combat aircraft, multirole combat aircraft, designed as both a Fighter aircraft, ...
(forebody, including cockpit, ejection seat, and canopy; electrical generators),
F-16 Fighting Falcon
The General Dynamics F-16 Fighting Falcon is a single-engine multirole fighter aircraft originally developed by General Dynamics for the United States Air Force (USAF). Designed as an air superiority day fighter, it evolved into a successful ...
(landing gear, fuel pump, rudder pedals, nosewheel tires, and emergency power unit),
F-16XL
The General Dynamics F-16XL is a derivative of the F-16 Fighting Falcon, with a cranked-arrow delta wing. It was originally conceived as a technology demonstrator, later entered in the United States Air Force's (USAF) Enhanced Tactical Fighter ...
(leading-edge flap drives),
V-22 Osprey
The Bell Boeing V-22 Osprey is an American multi-mission, tiltrotor military aircraft with both vertical takeoff and landing (VTOL) and short takeoff and landing (STOL) capabilities. It is designed to combine the functionality of a convention ...
(control surface actuators),
Cessna Citation
The Cessna Citation is a family of business jets by Cessna that started in 1972 with the entry into service of the first model. In the fifty years following the 1969 first flight, more than 7,500 Citations were delivered, forming the largest b ...
(main landing gear's wheels and brakes),
F-20 Tigershark
The Northrop F-20 Tigershark (initially F-5G) is a light fighter, designed and built by Northrop. Its development began in 1975 as a further evolution of Northrop's F-5E Tiger II, featuring a new engine that greatly improved overall performa ...
(hydrazine emergency air-start system, later replaced) and
B-1 Lancer
The Rockwell B-1 Lancer is a supersonic variable-sweep wing, heavy bomber used by the United States Air Force. It is commonly called the "Bone" (from "B-One"). It is one of three strategic bombers serving in the U.S. Air Force fleet along with ...
(spindles from its control vanes used for the canards). This was done on purpose, so that development time and risk would be reduced by using flight-qualified components. To reduce the cost of tooling for a production run of only two aircraft, Rockwell developed the "fly-away tooling" concept (perhaps the most successful spinoff of the program), whereby 15 fuselage frames were manufactured via
CNC
Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a computer. A CNC machine processes a p ...
, tied together with a holding fixture, and attached to the factory floor with survey equipment. That assembly then became the tooling for the plane, which was built around it, thus "flying away" with its own tooling.
Two X-31s were built, with the first flying on October 11, 1990. Over 500 test flights were carried out between 1990 and 1995. The X-31 is a
canard delta
Delta commonly refers to:
* Delta (letter) (Δ or δ), a letter of the Greek alphabet
* River delta, at a river mouth
* D ( NATO phonetic alphabet: "Delta")
* Delta Air Lines, US
* Delta variant of SARS-CoV-2 that causes COVID-19
Delta may also ...
, a delta wing aircraft which uses canard foreplanes for primary pitch control, with secondary thrust-vectoring control. The canard delta had earlier been used on the
Saab Viggen
The Saab 37 Viggen ( Swedish for ''"the Bolt"'' or ''"the Tufted Duck"'' ( see name)) is a retired Swedish single-seat, single-engine, short-medium range combat aircraft. Development work on the type was initiated at Saab in 1952 and, follow ...
strike fighter, and has since become common on fighters such as the
Eurofighter Typhoon
The Eurofighter Typhoon is a European multinational twin-engine, canard delta wing, multirole fighter. The Typhoon was designed originally as an air-superiority fighter and is manufactured by a consortium of Airbus, BAE Systems and Leonardo ...
,
Dassault Rafale
The Dassault Rafale (, literally meaning "gust of wind", and "burst of fire" in a more military sense) is a French twin-engine, canard delta wing, multirole fighter aircraft designed and built by Dassault Aviation. Equipped with a wide ran ...
and
Gripen
The Saab JAS 39 Gripen (; English: ''griffin'') is a light single-engine multirole fighter aircraft manufactured by the Swedish aerospace and defense company Saab AB. The Gripen has a delta wing and canard configuration with relaxed stabilit ...
which were all designed and flew several years before the X-31. The X-31 featured a cranked-delta wing (similar to the
Saab 35 Draken
The Saab 35 Draken (; 'The Kite' or 'The Dragon') is a Swedish fighter-interceptor developed and manufactured by Svenska Aeroplan Aktiebolaget (SAAB) between 1955 and 1974. Development of the Saab 35 Draken started in 1948 as the Swedish air fo ...
and the F-16XL prototype), and fixed
strakes along the
aft fuselage, as well as a pair of movable computer-controlled
canards to increase stability and maneuverability. There are
no moveable horizontal tail surfaces, only the vertical fin with
rudder
A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally aircraft, air or watercraft, water). On an aircraft the rudder is used primarily to ...
.
Pitch and roll are controlled by the canard with the aid of the three paddles directing the exhaust (thrust vectoring). Eventually, simulations and flight tests on one of the X-31s showed that flight would be stable without the vertical fin, because the thrust-vectoring nozzle provided sufficient yaw and pitch control.
During flight testing, the X-31 aircraft established several milestones. On November 6, 1992, the X-31 achieved controlled flight at a 70° angle of attack. On April 29, 1993, the second X-31 successfully executed a rapid minimum-radius, 180° turn using a
post-stall
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', p. 486. Aviation Supplies & Academics, 1997. This occurs when the ...
maneuver, flying well outside the range of angle of attack normal for conventional aircraft. This maneuver has been called the "
Herbst maneuver
The Herbst maneuver (also known as a J-turn"Turn and Burn." Fulghum, D. A.; Fabey, M. J. ''Aviation Week & Space Technology''. January 8, 2007. " after Dr. Wolfgang Herbst, an MBB employee and proponent of using post-stall flight in air-to-air combat.
Herbst was the designer of the Rockwell SNAKE, which formed the basis for the X-31.
In the mid-1990s, the program began to revitalize and so the US and Germany signed a Memorandum of Understanding in April 1999 to start collaboration on the $53 million VECTOR program to capitalize on this previous investment. VECTOR is a joint venture that includes the US Navy, Germany's defense procurement agency BWB, Boeing's
Phantom Works
Boeing Phantom Works is the advanced prototyping arm of the defense and security side of Boeing. Its primary focus is developing advanced military products and technologies, many of them highly classified.
Founded by McDonnell Douglas, the res ...
, and
DASA
''Dasa'' ( sa, दास, Dāsa) is a Sanskrit word found in ancient Indian texts such as the ''Rigveda'' and ''Arthasastra''. It usually means "enemy" or "servant" but ''dasa'', or ''das'', also means a "servant of God", "devotee," "votary" or "o ...
; it was initially expected to involve Sweden, which pulled out due to fiscal constraints. As the site for the flight testing,
Naval Air Station Patuxent River
Naval Air Station Patuxent River , also known as NAS Pax River, is a United States naval air station located in St. Mary’s County, Maryland, on the Chesapeake Bay near the mouth of the Patuxent River.
It is home to Headquarters, Naval Air Sys ...
in Maryland was chosen. From 2002 to 2003, the X-31 flew extremely short takeoff and landing approaches first on a virtual runway at in the sky, to ensure that the
Inertial Navigation System
An inertial navigation system (INS) is a navigation device that uses motion sensors (accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity (dire ...
/
Global Positioning System
The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
accurately guides the aircraft with the centimeter accuracy required for on the ground landings. The program then culminated in the first ever autonomous landing of a manned aircraft with high angle of attack (24 degree) and short landing. The technologies involved a differential GPS System based on
pseudolite
Pseudolite is a contraction of the term "pseudo-satellite," used to refer to something that is not a satellite which performs a function commonly in the domain of satellites. Pseudolites are most often small transceivers that are used to create ...
technology from Integrinautics and a miniaturized flush air data system from Nordmicro.
Serial numbers
* BuNo 164584, 292 flights – crashed on January 19, 1995, north of
Edwards AFB
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. The crash was caused by ice inside the pitot tube, sending incorrect airspeed data to the flight control computers. Contributing factors included the replacement of a heated pitot tube with an unheated
Kiel probe, and ground crew/pilot ignorance of an option to override computer control. The pilot ejected safely. NASA issued in 2005 a film, "X-31: Breaking the Chain," reviewing the events.
[Archived a]
Ghostarchive
and th
Wayback Machine
The novelty of the X-31 trials was computer control of its revolutionary flight controls (the canard wing and engine baffles) to effect maneuvers impossible for conventional jet fighters. The film discusses at length the combination of independent errors (e.g. that the accompanying chase pilot could not hear the test pilot's radio conversation with his base) in prompting loss of control, when the test pilot (correctly) ejected to save his life. Film of the crash shows the aircraft in unusual attitudes as the computer applied its false data to attempt to control flight after the pilot ejected.
* BuNo 164585, 288 flights, the last one being in 2003. Put on Permanent Display at
Deutsches Museum Flugwerft Schleissheim
Flugwerft Schleissheim is an aviation museum located in the German town of Oberschleißheim near Munich, it forms part of the Deutsches Museum collection and complements the aviation exhibits on display at the main site. The museum was opened on ...
in Germany''.
Specifications (X-31)
See also
Gallery
References
Bibliography
*
* Jenkins, Dennis R., Tony Landis, and Jay Miller
SP-2003-4531, "American X-Vehicles, An Inventory—X-1 to X-50" NASA, June 2003.
*
* USAF & NATO Report RTO-TR-015 AC/323/(HFM-015)/TP-1 (2001)
External links
NASA X-31 image galleryvideo of crash and investigation
{{DEFAULTSORT:Rockwell-Mbb X-31
Canard aircraft
Edwards Air Force Base
X-31
The Rockwell-Messerschmitt-Bölkow-Blohm X-31 was an experimental jet fighter designed to test fighter thrust vectoring technology.
It was designed and built by Rockwell and Messerschmitt-Bölkow-Blohm (MBB), as part of a joint US and German ' ...
NASA aircraft
X-31
The Rockwell-Messerschmitt-Bölkow-Blohm X-31 was an experimental jet fighter designed to test fighter thrust vectoring technology.
It was designed and built by Rockwell and Messerschmitt-Bölkow-Blohm (MBB), as part of a joint US and German ' ...
X-31, Rockwell-MBB
Delta-wing aircraft
Single-engined jet aircraft
Articles containing video clips
Aircraft first flown in 1990
1990s German experimental aircraft
Three dimension thrust vectoring aircraft
1990s international aircraft
Germany–United States military relations