X-3 Stiletto
Encyclopedia
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. It was, however, seriously underpowered for its purpose and could not even exceed Mach
1 in level flight. Though the research aircraft was a disappointment, Lockheed designers used data from the X-3 tests for the F-104 Starfighter
which used a similar wing design in a successful Mach 2 fighter.
s, and the large-scale use of titanium in aircraft structures.
Construction of a pair of X-3s was approved on 30 June 1949. During development, the X-3's planned Westinghouse J46
engines were unable to meet the thrust, size and weight requirements, so lower-thrust Westinghouse J34
turbojets were substituted, producing only 4,900 lbf (21.8 kN) of thrust with afterburner rather than the planned 7,000 lbf (31.3 kN). The first aircraft was completed and delivered to Edwards Air Force Base
, California
, on 11 September 1952.
The X-3 featured an unusual, rakish shape of a long cylindrical fuselage with tiny trapezoidal wing
s. One of the design considerations was to create the smallest and "thinnest" shape possible in order to achieve a streamlined planform. The extended nose was to allow for the provision of test equipment while the semi-buried cockpit and windscreen was designed to alleviate the effects of "thermal thicket" conditions. The low aspect ratio, unswept wings were designed for high speed and later the Lockheed
design team used data from the X-3 tests for the similar F-104 Starfighter
wing design. Due to both engine and airframe problems, the partially completed second aircraft was cancelled, and its components were used for spare parts.
William Bridgeman. During a high-speed taxi test, Bridgeman lifted the X-3 off the ground and flew it about 1 mi (1.6 km) before settling back onto the lakebed. The official first flight was made by Bridgeman on 20 October, and lasted about 20 minutes. He made a total of 26 flights (counting the hop) by the end of the Douglas tests in December 1953. These showed that the X-3 was severely underpowered and difficult to control. Its takeoff speed was an unusually high 260 kts (482 km/h). More seriously, the X-3 did not approach its planned top speed. Its first supersonic flight required that the airplane make a 15° dive to reach Mach 1.1. The X-3's fastest flight, made on 28 July 1953, reached Mach 1.208 in a 30° dive. A plan to re-engine the X-3 with rocket motors was considered but eventually dropped.
With the completion of the contractor test program in December 1953, the X-3 was delivered to the United States Air Force
. The poor performance of the X-3 meant only an abbreviated program would be made, to gain experience with low-aspect ratio wings. Lieutenant Colonel
Frank Everest and Major
Chuck Yeager
each made three flights. Although flown by Air Force pilots, these were counted as NACA
flights. With the last flight by Yeager in July 1954, NACA made plans for a limited series of research flights with the X-3. The initial flights looked at longitudinal stability and control, wing and tail loads, and pressure distribution.
NACA pilot Joseph A. Walker
made his pilot checkout flight in the X-3 on 23 August 1954, then conducted eight research flights in September and October. By late October, the research program was expanded to include lateral and directional stability tests. In these tests, the X-3 was abruptly rolled at transonic
and supersonic speeds, with the rudder kept centered. Despite its shortcomings, the X-3 was ideal for these tests. The mass of its engines, fuel and structure was concentrated in its long, narrow fuselage, while its wings were short and stubby. As a result, the X-3 was "loaded" along its fuselage, rather than its wings. This was typical of the fighter aircraft then in development or testing.
These tests would lead to the X-3's most significant flight, and the near-loss of the aircraft. On 27 October 1954, Walker made an abrupt left roll at Mach 0.92 and an altitude of 30,000 ft (9,144 m). The X-3 rolled as expected, but also pitched up 20° and yawed 16°. The aircraft gyrated for five seconds before Walker was able to get it back under control. He then set up for the next test point. Walker put the X-3 into a dive, accelerating to Mach 1.154 at 32,356 ft (9,862 m), where he made an abrupt left roll. The aircraft pitched down and recorded an acceleration of -6.7 g (-66 m/s²), then pitched upward to +7 g (69 m/s²). At the same time, the X-3 side-slipped, resulting in a loading of 2 g (20 m/s²). Walker managed to bring the X-3 under control and successfully landed.
The post-flight examination showed the fuselage had been subjected to its maximum load limit. Had the acceleration been higher, the aircraft could have broken up. Walker and the X-3 had experienced "roll inertia coupling," in which a maneuver in one axis will cause an uncommanded maneuver in one or two others. At the same time, several F-100 Super Sabre
s were involved in similar incidents. A research program was started by NACA to understand the problem and find solutions.
For the X-3, the roll coupling flight was the high point of its history. The aircraft was grounded for nearly a year after the flight, and never again explored its roll stability and control boundaries. Walker made another 10 flights between 20 September 1955 and the last on 23 May 1956. The aircraft was subsequently retired to the U.S. Air Force Museum
. Although the X-3 never met its intention of providing aerodynamic data in Mach 2 cruise, its short service was of value. It showed the dangers of roll inertia coupling
, and provided early flight test data on the phenomena. Its wing planform
was used in the Lockheed F-104 Starfighter, and it was one of the first aircraft to use titanium. Finally, the X-3's very high takeoff and landing speeds required improvements in tire technology.
Douglas Aircraft Company
The Douglas Aircraft Company was an American aerospace manufacturer, based in Long Beach, California. It was founded in 1921 by Donald Wills Douglas, Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas...
X-3 Stiletto was a 1950s United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
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
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
in major airframe components. It was, however, seriously underpowered for its purpose and could not even exceed Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
1 in level flight. Though the research aircraft was a disappointment, Lockheed designers used data from the X-3 tests for the F-104 Starfighter
F-104 Starfighter
The Lockheed F-104 Starfighter is a single-engine, high-performance, supersonic interceptor aircraft originally developed for the United States Air Force by Lockheed. One of the Century Series of aircraft, it served with the USAF from 1958 until 1969, and continued with Air National Guard units...
which used a similar wing design in a successful Mach 2 fighter.
Design and development
The Douglas X-3 Stiletto was the sleekest of the early experimental aircraft, but its research accomplishments were not those originally planned. It was originally intended for advanced Mach 2 turbojet propulsion testing, but it fell largely into the category of configuration explorers, as its performance (due to inadequate engines) never met its original performance goals. The goal of the aircraft was ambitious — it was to take off from the ground under its own power, climb to high altitude, maintain a sustained cruise speed of Mach 2, then land under its own power. The aircraft was also to test the feasibility of low-aspect ratio wingAspect ratio (wing)
In aerodynamics, the aspect ratio of a wing is essentially the ratio of its length to its breadth . A high aspect ratio indicates long, narrow wings, whereas a low aspect ratio indicates short, stubby wings....
s, and the large-scale use of titanium in aircraft structures.
Construction of a pair of X-3s was approved on 30 June 1949. During development, the X-3's planned Westinghouse J46
Westinghouse J46
|-References:...
engines were unable to meet the thrust, size and weight requirements, so lower-thrust Westinghouse J34
Westinghouse J34
-See also:-External links:* http://www.arkairmuseum.org/engines/engine-westinghouse.php* http://www.globalsecurity.org/military/systems/aircraft/systems/j34.htm...
turbojets were substituted, producing only 4,900 lbf (21.8 kN) of thrust with afterburner rather than the planned 7,000 lbf (31.3 kN). The first aircraft was completed and delivered to Edwards Air Force Base
Edwards Air Force Base
Edwards Air Force Base is a United States Air Force base located on the border of Kern County, Los Angeles County, and San Bernardino County, California, in the Antelope Valley. It is southwest of the central business district of North Edwards, California and due east of Rosamond.It is named in...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, on 11 September 1952.
The X-3 featured an unusual, rakish shape of a long cylindrical fuselage with tiny trapezoidal wing
Trapezoidal wing
The trapezoidal or diamond wing is a high-performance wing configuration. It is a short tapered wing having little or no overall sweep, such that the leading edge sweeps back and the trailing edge sweeps forwards. The trapezoidal design allows for a thin wing with low drag at high speeds, while...
s. One of the design considerations was to create the smallest and "thinnest" shape possible in order to achieve a streamlined planform. The extended nose was to allow for the provision of test equipment while the semi-buried cockpit and windscreen was designed to alleviate the effects of "thermal thicket" conditions. The low aspect ratio, unswept wings were designed for high speed and later the Lockheed
Lockheed Corporation
The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1912 and later merged with Martin Marietta to form Lockheed Martin in 1995.-Origins:...
design team used data from the X-3 tests for the similar F-104 Starfighter
F-104 Starfighter
The Lockheed F-104 Starfighter is a single-engine, high-performance, supersonic interceptor aircraft originally developed for the United States Air Force by Lockheed. One of the Century Series of aircraft, it served with the USAF from 1958 until 1969, and continued with Air National Guard units...
wing design. Due to both engine and airframe problems, the partially completed second aircraft was cancelled, and its components were used for spare parts.
Operational history
The first X-3 "hop" was made on 15 October 1952, by Douglas test pilotTest pilot
A test pilot is an aviator who flies new and modified aircraft in specific maneuvers, known as flight test techniques or FTTs, allowing the results to be measured and the design to be evaluated....
William Bridgeman. During a high-speed taxi test, Bridgeman lifted the X-3 off the ground and flew it about 1 mi (1.6 km) before settling back onto the lakebed. The official first flight was made by Bridgeman on 20 October, and lasted about 20 minutes. He made a total of 26 flights (counting the hop) by the end of the Douglas tests in December 1953. These showed that the X-3 was severely underpowered and difficult to control. Its takeoff speed was an unusually high 260 kts (482 km/h). More seriously, the X-3 did not approach its planned top speed. Its first supersonic flight required that the airplane make a 15° dive to reach Mach 1.1. The X-3's fastest flight, made on 28 July 1953, reached Mach 1.208 in a 30° dive. A plan to re-engine the X-3 with rocket motors was considered but eventually dropped.
With the completion of the contractor test program in December 1953, the X-3 was delivered to the United States Air Force
United States Air Force
The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...
. The poor performance of the X-3 meant only an abbreviated program would be made, to gain experience with low-aspect ratio wings. Lieutenant Colonel
Lieutenant colonel
Lieutenant colonel is a rank of commissioned officer in the armies and most marine forces and some air forces of the world, typically ranking above a major and below a colonel. The rank of lieutenant colonel is often shortened to simply "colonel" in conversation and in unofficial correspondence...
Frank Everest and Major
Major
Major is a rank of commissioned officer, with corresponding ranks existing in almost every military in the world.When used unhyphenated, in conjunction with no other indicator of rank, the term refers to the rank just senior to that of an Army captain and just below the rank of lieutenant colonel. ...
Chuck Yeager
Chuck Yeager
Charles Elwood "Chuck" Yeager is a retired major general in the United States Air Force and noted test pilot. He was the first pilot to travel faster than sound...
each made three flights. Although flown by Air Force pilots, these were counted as NACA
National Advisory Committee for Aeronautics
The National Advisory Committee for Aeronautics was a U.S. federal agency founded on March 3, 1915 to undertake, promote, and institutionalize aeronautical research. On October 1, 1958 the agency was dissolved, and its assets and personnel transferred to the newly created National Aeronautics and...
flights. With the last flight by Yeager in July 1954, NACA made plans for a limited series of research flights with the X-3. The initial flights looked at longitudinal stability and control, wing and tail loads, and pressure distribution.
NACA pilot Joseph A. Walker
Joseph A. Walker
Joseph Albert "Joe" Walker was an American NASA test pilot, and member of the U.S. Air Force Man In Space Soonest program. In 1963, he made two X-15 Experimental rocket aircraft flights beyond the altitude of 100 kilometers - at the edge of outer space...
made his pilot checkout flight in the X-3 on 23 August 1954, then conducted eight research flights in September and October. By late October, the research program was expanded to include lateral and directional stability tests. In these tests, the X-3 was abruptly rolled at transonic
Transonic
Transonic speed is an aeronautics term referring to the condition of flight in which a range of velocities of airflow exist surrounding and flowing past an air vehicle or an airfoil that are concurrently below, at, and above the speed of sound in the range of Mach 0.8 to 1.2, i.e. 600–900 mph...
and supersonic speeds, with the rudder kept centered. Despite its shortcomings, the X-3 was ideal for these tests. The mass of its engines, fuel and structure was concentrated in its long, narrow fuselage, while its wings were short and stubby. As a result, the X-3 was "loaded" along its fuselage, rather than its wings. This was typical of the fighter aircraft then in development or testing.
These tests would lead to the X-3's most significant flight, and the near-loss of the aircraft. On 27 October 1954, Walker made an abrupt left roll at Mach 0.92 and an altitude of 30,000 ft (9,144 m). The X-3 rolled as expected, but also pitched up 20° and yawed 16°. The aircraft gyrated for five seconds before Walker was able to get it back under control. He then set up for the next test point. Walker put the X-3 into a dive, accelerating to Mach 1.154 at 32,356 ft (9,862 m), where he made an abrupt left roll. The aircraft pitched down and recorded an acceleration of -6.7 g (-66 m/s²), then pitched upward to +7 g (69 m/s²). At the same time, the X-3 side-slipped, resulting in a loading of 2 g (20 m/s²). Walker managed to bring the X-3 under control and successfully landed.
F-100 Super Sabre
The North American F-100 Super Sabre was a supersonic jet fighter aircraft that served with the United States Air Force from 1954 to 1971 and with the Air National Guard until 1979. The first of the Century Series collection of USAF jet fighters, it was the first USAF fighter capable of...
s were involved in similar incidents. A research program was started by NACA to understand the problem and find solutions.
For the X-3, the roll coupling flight was the high point of its history. The aircraft was grounded for nearly a year after the flight, and never again explored its roll stability and control boundaries. Walker made another 10 flights between 20 September 1955 and the last on 23 May 1956. The aircraft was subsequently retired to the U.S. Air Force Museum
National Museum of the United States Air Force
The National Museum of the United States Air Force is the official museum of the United States Air Force located at Wright-Patterson Air Force Base northeast of Dayton, Ohio. The NMUSAF is the world's largest and oldest military aviation museum with more than 360 aircraft and missiles on display...
. Although the X-3 never met its intention of providing aerodynamic data in Mach 2 cruise, its short service was of value. It showed the dangers of roll inertia coupling
Inertia coupling
Inertia coupling is a potentially lethal phenomenon of high-speed flight in which the inertia of the heavier fuselage overpowers the aerodynamic stabilizing forces of the wing and empennage...
, and provided early flight test data on the phenomena. Its wing planform
Planform
In aviation, a planform is the shape and layout of a fixed-wing aircraft's fuselage and wing. Of all the myriad planforms used, they can typically be grouped into those used for low-speed flight, found on general aviation aircraft, and those used for high-speed flight, found on many military...
was used in the Lockheed F-104 Starfighter, and it was one of the first aircraft to use titanium. Finally, the X-3's very high takeoff and landing speeds required improvements in tire technology.
Survivors
- The sole X-3 was transferred in 1956 to the National Museum of the United States Air ForceNational Museum of the United States Air ForceThe National Museum of the United States Air Force is the official museum of the United States Air Force located at Wright-Patterson Air Force Base northeast of Dayton, Ohio. The NMUSAF is the world's largest and oldest military aviation museum with more than 360 aircraft and missiles on display...
at Wright-Patterson Air Force BaseWright-Patterson Air Force BaseWright-Patterson Air Force Base is a United States Air Force base in Greene and Montgomery counties in the state of Ohio. It includes both Wright and Patterson Fields, which were originally Wilbur Wright Field and Fairfield Aviation General Supply Depot. Patterson Field is located approximately...
, Ohio. it is on display in the Museum's Research & Development Gallery.
Specifications (X-3)