X-3 Stiletto
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The Douglas X-3 Stiletto is a 1950s
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experimental
jet aircraft A jet aircraft (or simply jet) is an aircraft (nearly always a fixed-wing aircraft) propelled by one or more jet engines. Whereas the engines in Propeller (aircraft), propeller-powered aircraft generally achieve their maximum efficiency at much ...
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 speed Supersonic speed is the speed of an object that exceeds the speed of sound (Mach number, 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 tha ...
s, which included the first use of
titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
in major
airframe The mechanical structure of an aircraft is known as the airframe. This structure is typically considered to include the fuselage, undercarriage, empennage and wings, and excludes the propulsion system. Airframe design is a field of aeros ...
components. Douglas designed the X-3 with the goal of a maximum speed of approximately , but it was seriously underpowered for this purpose and could not even exceed
Mach The Mach number (M or Ma), often only Mach, (; ) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a Boundary (thermodynamic), boundary to the local speed of sound. It is named after the Austrian physi ...
1 in level flight. Although the
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was a disappointment, Lockheed designers used data from the X-3 tests for the
Lockheed F-104 Starfighter The Lockheed F-104 Starfighter is an American single-engine, supersonic interceptor. Created as a day fighter by Lockheed as one of the " Century Series" of fighter aircraft for the United States Air Force (USAF), it was developed into an ...
which used a similar
trapezoidal wing In aeronautics, a trapezoidal wing is a straight-edged and tapered wing planform. It may have any aspect ratio and may or may not be swept.G. Dimitriadis; ''Aircraft Design'Lecture 2: Aerodynamics Université de Liège. (retrieved 30 November 2 ...
design in a successful
Mach The Mach number (M or Ma), often only Mach, (; ) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a Boundary (thermodynamic), boundary to the local speed of sound. It is named after the Austrian physi ...
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 it never met its original performance goals due to inadequate engines. 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 wings, and the large-scale use of titanium in aircraft structures. The design of the Douglas X-3 Stiletto is the subject of U.S. Design Patent #172,588 granted on July 13, 1954, to Frank N. Fleming and
Harold T. Luskin Harold may refer to: People * Harold (given name), including a list of persons and fictional characters with the name * Harold (surname), surname in the English language * András Arató, known in meme culture as "Hide the Pain Harold" Arts ...
and assigned to the Douglas Aircraft Company, Inc. Construction of a pair of X-3s was approved on 30 June 1949. During development, the X-3's planned
Westinghouse J46 The Westinghouse J46 is an afterburning turbojet engine developed by the Westinghouse Aviation Gas Turbine Division for the United States Navy in the 1950s. It was primarily employed in powering the Convair F2Y Sea Dart and Vought F7U Cutlass. T ...
engines were unable to meet the thrust, size and weight requirements, so lower-thrust
Westinghouse J34 The Westinghouse J34, company designation Westinghouse 24C, was a turbojet engine developed by Westinghouse Aviation Gas Turbine Division in the late 1940s. Essentially an enlarged version of the earlier Westinghouse J30, the J34 produced 3,000 ...
turbojet The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and ...
s were substituted, producing only of thrust with afterburner rather than the planned . The first aircraft was built and delivered to
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,
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, on 11 September 1952. The X-3 featured an unusual slender, streamlined shape having a very long, gently-tapered nose and small
trapezoidal wing In aeronautics, a trapezoidal wing is a straight-edged and tapered wing planform. It may have any aspect ratio and may or may not be swept.G. Dimitriadis; ''Aircraft Design'Lecture 2: Aerodynamics Université de Liège. (retrieved 30 November 2 ...
s. The aim was to create the thinnest and most slender shape possible in order to achieve low drag at supersonic speeds. The extended nose was to allow for the provision of test equipment while the semi-buried cockpit and windscreen were 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.Winchester 2005, p. 89.


Operational history

The first X-3 "hop" was made on 15 October 1952, by Douglas
test pilot A test pilot is an aircraft pilot with additional training to fly and evaluate experimental, newly produced and modified aircraft with specific maneuvers, known as flight test techniques.Stinton, Darrol. ''Flying Qualities and Flight Testin ...
Bill Bridgeman William Barton Bridgeman (June 25, 1916 – September 29, 1968) was an American test pilot who broke aviation records while working for the Douglas Aircraft Company, testing experimental aircraft. In July 1951, the United States Navy announced t ...
. During a high-speed taxi test, Bridgeman lifted the X-3 off the ground and flew it about one mile (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 unusually high—. 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 United States Air Force (USAF) is the Air force, air service branch of the United States Department of Defense. It is one of the six United States Armed Forces and one of the eight uniformed services of the United States. Tracing its ori ...
. 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 Brigadier general (United States), Brigadier General Charles Elwood Yeager ( , February 13, 1923December 7, 2020) was a United States Air Force officer, flying ace, and record-setting test pilot who in October 1947 became the first pilot in his ...
each made three flights. Although flown by Air Force pilots, these were counted as
NACA The National Advisory Committee for Aeronautics (NACA) was a United States federal agency that was founded on March 3, 1915, to undertake, promote, and institutionalize aeronautical research. On October 1, 1958, the agency was dissolved and its ...
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 Albert Walker (February 20, 1921 – June 8, 1966) ( Capt, USAF) 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 pilot ...
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 (or transsonic) flow is air flowing around an object at a speed that generates regions of both subsonic and Supersonic speed, supersonic airflow around that object. The exact range of speeds depends on the object's critical Mach numb ...
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 . 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 , where he made an abrupt left roll. The aircraft pitched down and recorded an acceleration of -6.7 ''g'' (-66 m/s²), then pitched upwards 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 that 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 aeronautics, inertia coupling, also referred to as inertial coupling and inertial roll coupling, is a potentially catastrophic phenomenon of high-speed flight in a long, thin aircraft, in which an intentional rotation of the aircraft about one ...
," in which a maneuver in one axis will cause an uncommanded maneuver in one or two others. At the same time, several
North American F-100 Super Sabre The North American F-100 Super Sabre is an American supersonic jet fighter aircraft designed and produced by the aircraft manufacturer North American Aviation. The first of the Century Series of American jet fighters, it was the first United ...
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 ten flights between 20 September 1955 and the last on 23 May 1956. The aircraft was subsequently retired to the
National Museum of the United States Air Force The National Museum of the United States Air Force (formerly the United States Air Force Museum) is the official museum of the United States Air Force located at Wright-Patterson Air Force Base, northeast of Dayton, Ohio. The NMUSAF is ...
. 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 In aeronautics, inertia coupling, also referred to as inertial coupling and inertial roll coupling, is a potentially catastrophic phenomenon of high-speed flight in a long, thin aircraft, in which an intentional rotation of the aircraft about on ...
, and provided early flight test data on the phenomenon. Its small, highly loaded unswept wing 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.


Production

Two aircraft were ordered, but only one was built, completing 51 test flights.


Aircraft on display

*The X-3 was transferred in 1956 to the
National Museum of the United States Air Force The National Museum of the United States Air Force (formerly the United States Air Force Museum) is the official museum of the United States Air Force located at Wright-Patterson Air Force Base, northeast of Dayton, Ohio. The NMUSAF is ...
at
Wright-Patterson Air Force Base Wright-Patterson Air Force Base (WPAFB) is a United States Air Force base and census-designated place just east of Dayton, Ohio, in Greene County, Ohio, Greene and Montgomery County, Ohio, Montgomery counties. It includes both Wright and Patte ...
, Ohio.''United States Air Force Museum Guidebook'' 1975, p. 88. , it is on display in the museum's Research & Development Gallery.


Specifications (X-3)


See also


References

* ''United States Air Force Museum Guidebook''. Wright-Patterson AFB, Ohio: Air Force Association, 1975 edition. * Winchester, Jim. "Douglas X-3." ''Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft''. Kent, UK: Grange Books plc, 2005. .


External links


NASA Dryden X-3 photo collection



Global Aircraft: X-3 Stiletto
{{Authority control X-3 Stiletto Edwards Air Force Base NASA aircraft X-03 Stiletto Aircraft first flown in 1952 Low-wing aircraft Twinjets