Lockheed XF-104
Encyclopedia
The Lockheed XF-104 was a single-engine, high-performance, supersonic
interceptor
prototype
for a United States Air Force
(USAF) series of lightweight and simple fighters. Only two aircraft were built, one aircraft was used primarily for aerodynamic research and the other served as an armament testbed. Both prototypes were destroyed in accidents during testing. The XF-104 was the forerunner of over 2,500 Lockheed F-104 Starfighters.
During the Korean War, USAF fighter pilots were outclassed by MiG-equipped Soviet pilots. Lockheed engineers, led by Kelly Johnson, designed and submitted a novel design to the Air Force. The design was notable for its sleekness, particularly its thin wings and missile-shaped fuselage, as well as a novel pilot ejection system.
The XF-104's maiden flight
came in February 1954. The flight test program encountered problems, some of which were resolved; however, the XF-104 performance proved better than estimates. Both prototypes were lost through accidents. Nevertheless, the USAF ordered 17 service-test F-104s. Internationally, the production F-104 Starfighters proved popular, serving as front-line fighters with a number of countries.
Skunk Works
, visited Korea
in December 1951 and talked to fighter pilots about what sort of aircraft they wanted. At the time U.S. Air Force pilots were confronting the MiG-15 "Fagot"
in their F-86 Sabre
s, and many of the pilots felt that the MiGs were superior to the larger and more complex American design. The pilots requested a small and simple aircraft with excellent performance. One pilot in particular, Colonel Gabby Gabreski
was quoted as saying; "I'd rather sight with a piece of chewing gum stuck on the windscreen" and told Johnson that radar "was a waste of time".
On his return to the U.S., Johnson immediately started the design of just such an aircraft realising that an official requirement would soon be published. In March 1952 his team was assembled, and they sketched several different aircraft proposals, ranging from small designs at 8,000 lb (3.6 t), to fairly large ones at 50,000 lb (23 t). The L-246 as the design became known remained essentially identical to the "Model L-083 Starfighter" as eventually delivered.
The design was presented to the Air Force in November 1952, who were interested enough to create a new proposal, inviting several companies to participate. Three additional designs were received: the Republic
AP-55, an improved version of its prototype XF-91 Thunderceptor
; the North American
NA-212, which would eventually evolve into the F-107; and the Northrop
N-102 Fang, a new General Electric J79-powered design. Although all were interesting, Lockheed had an insurmountable lead and was granted a development contract in March 1953.
Test data from the earlier Lockheed X-7
unmanned ramjet/rocket program proved invaluable for aerodynamic research since the XF-104 would share the X-7's wing and tail planform
and airfoil
sections.
Experience gained from the Douglas
X-3 Stiletto
was also used in the design phase of the XF-104. Over 400 surplus instrumented artillery rockets were launched to test various airfoils and tail designs; from which the camera film and telemetry were recovered by parachute.
Work progressed quickly, with a wooden mock-up ready for inspection at the end of April, and work started on two prototypes late in May. At the time, the J79 engine was not ready; so, both prototypes were designed to use the Wright J65
engine instead, a licensed built version of the Armstrong Siddeley Sapphire. Construction of the first prototype XF-104 (US serial number
53-7786, FG-786) began in summer 1953 at Lockheed's Burbank, California
factory. This aircraft was powered by a non-afterburning Buick
-built Wright J65-B-3 turbojet. The first prototype was completed by early 1954, and started flying in March. The total time from award of the contract to first flight was only one year, a very short time even then, and unheard of today, when ten to 15 years is more typical. Construction of the second prototype (s/n 53-7787) proceeded at a slower pace.
efficient airframe
possible around a single powerful engine. The emphasis was on minimizing drag
and mass
.
The XF-104 had a radical wing design. Most jet fighters of the period (and to this day) used a swept-wing or delta-wing planform
. This allowed a reasonable balance between aerodynamic performance, lift
, and internal space for fuel and equipment. Lockheed's tests, however, determined that the most efficient shape for high-speed, supersonic
flight was a very small, straight, mid-mounted, trapezoid
al wing. The low-aspect ratio wing was extremely thin, with a thickness-to-chord
ratio of only 3.4%. The leading edge
s of the wing were so thin (0.016 in/0.41 mm) and so sharp that they presented a hazard to ground crews, and protective guards had to be installed during ground operations. The thinness of the wings meant that fuel tanks and landing gear
had to be contained in the fuselage. The hydraulic actuators driving the ailerons were only one inch (25 mm) thick to fit into the available space and were known as Piccolo
actuators because of their resemblance to this musical instrument. The wings had electrically driven leading and trailing edge flaps
to increase lift at low speed. The XF-104 did not feature the Boundary Layer Control System
of the production aircraft.
After extensive wind tunnel
testing, the stabilator
was mounted at the top of the fin for optimum stability and control about the pitch
axis. Because the vertical tail fin was only slightly shorter than the length of each wing and nearly as aerodynamically effective, it could act as a wing on rudder
application (a phenomenon known as "Dutch roll
"). To offset this effect, the wings were angled downward to give 10° anhedral. The rudder was manually operated and supplemented by a small yaw damper
surface mounted at the bottom of the fin.
The fuselage
of the XF-104 had a high fineness ratio
, i.e., tapering sharply towards the nose, and a small frontal area of 25 sq ft (2.3 m²). The fuselage was tightly packed, containing the cockpit
, avionics
, cannon, all internal fuel, landing gear, and engine. The air intakes, designed by Ben Rich
, were of fixed geometry without inlet cones, since the J65-powered aircraft was incapable of Mach
2 performance. They were similar to those of the F-94 Starfire, being mounted slightly away from the fuselage, with an inner splitter plate for the boundary layer
bleed air. The combination of these features provided extremely low drag except at high angle of attack
, at which point induced drag became very high.
The XF-104 featured an unusual downward-ejecting Stanley B
seat. It was feared that contemporary ejection seat designs would not have enough explosive power to clear the high "T" tail assembly. In the event of the seat not firing, it was possible to manually release the lower fuselage hatch and then exit the aircraft via gravity. The F-104 series aircraft would later convert to upward-ejecting seats but the fuselage hatch was retained as a useful maintenance feature.
The first XF-104 (Lockheed 083-1001, s/n 53-7786) was transported to Edwards AFB amidst high secrecy during the night of 24–25 February where Lockheed test pilot Tony LeVier
was to do the initial testing. On 28 February 1954, the XF-104 made a planned hop of about five ft off the ground during a high-speed taxi, but its first official flight took place on 4 March 1954. During that flight, the landing gear did not retract, and LeVier landed after a low-speed flight of about 20 minutes. Adjustments and further flights discovered that the problem was low pressure in the hydraulic system. Bad weather kept the XF-104 on the ground until 26 March when further flights were carried out with the landing gear retracting normally.
The second prototype (Lockheed 083-1002, s/n 53-7787), fitted with the afterburning J65 from the start, first flew on 5 October 1954. Since it was to be the armament test bed, it was fitted with the 20 mm (.79 in) M61 Vulcan
cannon and was equipped with an AN/ASG-14T-1 fire control system. XF-104 #2 achieved a top speed of Mach 1.79 at 60000 feet (18,288 m) on 25 March 1955, piloted by Lockheed test pilot J. Ray Goudey. This was the highest speed achieved by the XF-104.
XF-104 #1 was subsonic in level flight when powered by the non-afterburning J65, but Mach 1 could be easily exceeded during a slight descent. In July 1954, the J65-B-3 was replaced by the afterburning J65-W-7 turbojet. With this engine installed, the performance of the XF-104 was greatly improved. Maximum level speed was Mach 1.49 at 41000 ft (12,496.8 m), and an altitude
of 55000 ft (16,764 m) could be attained in a zoom climb, while Mach 1.6 could be attained in a dive. The first XF-104 was accepted by the USAF in November 1955.
Initial aerial firing tests with the Vulcan cannon on the second aircraft were successful, but on 17 December, there was an explosion during a firing burst and the J65 engine suffered severe compressor stall
s. Tony LeVier immediately shut down the engine and glided back to make a successful deadstick landing
at Rogers Dry Lake
. An investigation later showed that one of the 20 mm cannon rounds had exploded in the breech
, blowing the bolt
out the rear of the gun and through the structure into the forward fuselage fuel cell. Jet fuel had run into the gun bay, and leaked out of the compartment door seals and into the left engine air intake. The engine immediately flooded with fuel, causing the compressor stalls.
XF-104 53-7787 was lost on 14 April 1955 after accumulating over 1,000 flying hours when test pilot Herman Salmon
was forced to eject during gun firing trials at 50000 ft (15,240 m). The gun malfunctioned during a test firing, and severe vibrations began to build up which knocked loose the ejection hatch below the cockpit. Cabin pressure
was lost with Salmon's pressure suit
inflating and covering his face so that he could not see. Recalling LeVier's harrowing experience with the exploding cannon shell the previous December, Salmon believed that the same thing had happened to him and that he had no option but to eject. He later found out that he could have saved 53-7787 by simply bringing it down to a lower altitude
and waiting for his pressure suit to deflate. With the loss of the armament testbed
, Lockheed engineers were forced to find an alternative, and armament trials were continued on a modified Lockheed F-94C Starfire. The two XF-104s amassed an approximate total of 250 flight hours.
fighters being developed at the time. The XF-104's ceiling at 60000 ft (18,288 m) was 7000 ft (2,133.6 m) higher than predicted, and it exceeded estimated speed and drag figures by two to three percent. It was noted however that the low thrust of the J65 engine did not enable the full performance potential of the type to be realized.
A number of minor problems surfaced, but were readily fixed. The yaw damper
of the XF-104 was found to be ineffective and the rudder did not positively center, these problems were corrected by revising the rudder control system. The unpowered rudder did not provide adequate directional control at high air speeds (remedied by using hydraulic power on all subsequent versions of the F-104) and some concern was expressed over poor subsonic
maneuverability at higher altitudes.
During a later interview, Kelly Johnson was asked about his opinion on the aircraft, "Did it come up to my designs? In terms of performance, yes. In terms of engine, we went through a great many engine problems, not with the J65s but with the J79s." For his part in designing the F-104 airframe, Johnson was jointly awarded the Collier Trophy
in 1958, sharing the honor with General Electric (engine) and the U.S. Air Force (Flight Records).
Visible changes from the XF-104 to production versions of the Starfighter include a longer fuselage (to accommodate the J79 engine and extra internal fuel) and a forward-retracting nose landing gear (except two-seat versions) to increase clearance for the downward-ejecting seat. A ventral fin for increased stability was added during the YF-104A test program. Inlet shock cones and a fuselage spine fairing between the canopy and fin that housed fuel piping were further added features. Production aircraft would also feature a redesigned fin structure using stainless steel
spars
to eliminate the flutter problem.
Since the internal fuel capacity was low limiting the useful range of the aircraft, extra capacity was provided on later versions by lengthening the forward fuselage.
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
interceptor
Interceptor aircraft
An interceptor aircraft is a type of fighter aircraft designed specifically to prevent missions of enemy aircraft, particularly bombers and reconnaissance aircraft. Interceptors generally rely on high speed and powerful armament in order to complete their mission as quickly as possible and set up...
prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
for a 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...
(USAF) series of lightweight and simple fighters. Only two aircraft were built, one aircraft was used primarily for aerodynamic research and the other served as an armament testbed. Both prototypes were destroyed in accidents during testing. The XF-104 was the forerunner of over 2,500 Lockheed F-104 Starfighters.
During the Korean War, USAF fighter pilots were outclassed by MiG-equipped Soviet pilots. Lockheed engineers, led by Kelly Johnson, designed and submitted a novel design to the Air Force. The design was notable for its sleekness, particularly its thin wings and missile-shaped fuselage, as well as a novel pilot ejection system.
The XF-104's maiden flight
Maiden flight
The maiden flight of an aircraft is the first occasion on which an aircraft leaves the ground of its own accord. This is similar to a ship's maiden voyage....
came in February 1954. The flight test program encountered problems, some of which were resolved; however, the XF-104 performance proved better than estimates. Both prototypes were lost through accidents. Nevertheless, the USAF ordered 17 service-test F-104s. Internationally, the production F-104 Starfighters proved popular, serving as front-line fighters with a number of countries.
Development
Clarence L. "Kelly" Johnson, chief engineer at Lockheed'sLockheed 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:...
Skunk Works
Skunk works
Skunk Works is an official alias for Lockheed Martin’s Advanced Development Programs , formerly called Lockheed Advanced Development Projects. Skunk Works is responsible for a number of famous aircraft designs, including the U-2, the SR-71 Blackbird, the F-117 Nighthawk, and the F-22 Raptor...
, visited Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...
in December 1951 and talked to fighter pilots about what sort of aircraft they wanted. At the time U.S. Air Force pilots were confronting the MiG-15 "Fagot"
Mikoyan-Gurevich MiG-15
The Mikoyan-Gurevich MiG-15 was a jet fighter developed for the USSR by Artem Mikoyan and Mikhail Gurevich. The MiG-15 was one of the first successful swept-wing jet fighters, and it achieved fame in the skies over Korea, where early in the war, it outclassed all straight-winged enemy fighters in...
in their F-86 Sabre
F-86 Sabre
The North American F-86 Sabre was a transonic jet fighter aircraft. Produced by North American Aviation, the Sabre is best known as America's first swept wing fighter which could counter the similarly-winged Soviet MiG-15 in high speed dogfights over the skies of the Korean War...
s, and many of the pilots felt that the MiGs were superior to the larger and more complex American design. The pilots requested a small and simple aircraft with excellent performance. One pilot in particular, Colonel Gabby Gabreski
Gabby Gabreski
Francis Stanley "Gabby" Gabreski was the top American fighter ace in Europe during World War II, a jet fighter ace in Korea, and a career officer in the United States Air Force with more than 26 years service.Although best known for his credited destruction of 34½ aircraft in aerial combat and...
was quoted as saying; "I'd rather sight with a piece of chewing gum stuck on the windscreen" and told Johnson that radar "was a waste of time".
The design was presented to the Air Force in November 1952, who were interested enough to create a new proposal, inviting several companies to participate. Three additional designs were received: the Republic
Republic Aviation Company
The Republic Aviation Corporation was an American aircraft manufacturer based in Farmingdale, Long Island, New York. Originally known as the Seversky Aircraft Company, the company was responsible for the design and production of many important military aircraft, including the P-47 Thunderbolt, F-84...
AP-55, an improved version of its prototype XF-91 Thunderceptor
XF-91 Thunderceptor
|-See also:-References:NotesBibliography* Jenkins, Dennis R. and Tony R. Landis. Experimental & Prototype U.S. Air Force Jet Fighters. North Branch, Minnesota, USA: Specialty Press, 2008. ISBN 978-1-58007-111-6....
; the North American
North American Aviation
North American Aviation was a major US aerospace manufacturer, responsible for a number of historic aircraft, including the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F-86 Sabre jet fighter, the X-15 rocket plane, and the XB-70, as well as Apollo Command and Service...
NA-212, which would eventually evolve into the F-107; and the Northrop
Northrop Corporation
Northrop Corporation was a leading United States aircraft manufacturer from its formation in 1939 until its merger with Grumman to form Northrop Grumman in 1994. The company is known for its development of the flying wing design, although only a few of these have entered service.-History:Jack...
N-102 Fang, a new General Electric J79-powered design. Although all were interesting, Lockheed had an insurmountable lead and was granted a development contract in March 1953.
Test data from the earlier Lockheed X-7
Lockheed X-7
-See also:-External links:*...
unmanned ramjet/rocket program proved invaluable for aerodynamic research since the XF-104 would share the X-7's wing and tail 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...
and airfoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
sections.
Experience gained from the Douglas
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
X-3 Stiletto
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...
was also used in the design phase of the XF-104. Over 400 surplus instrumented artillery rockets were launched to test various airfoils and tail designs; from which the camera film and telemetry were recovered by parachute.
Work progressed quickly, with a wooden mock-up ready for inspection at the end of April, and work started on two prototypes late in May. At the time, the J79 engine was not ready; so, both prototypes were designed to use the Wright J65
Wright J65
|-See also:-External links:*...
engine instead, a licensed built version of the Armstrong Siddeley Sapphire. Construction of the first prototype XF-104 (US serial number
United States military aircraft serials
In the United States, all military aircraft display a serial number to identify individual aircraft. Because these numbers are located on the aircraft tail, they are sometimes referred to unofficially as "tail numbers"...
53-7786, FG-786) began in summer 1953 at Lockheed's Burbank, California
Burbank, California
Burbank is a city in Los Angeles County in Southern California, United States, north of downtown Los Angeles. The estimated population in 2010 was 103,340....
factory. This aircraft was powered by a non-afterburning Buick
Buick
Buick is a premium brand of General Motors . Buick models are sold in the United States, Canada, Mexico, China, Taiwan, and Israel, with China being its largest market. Buick holds the distinction as the oldest active American make...
-built Wright J65-B-3 turbojet. The first prototype was completed by early 1954, and started flying in March. The total time from award of the contract to first flight was only one year, a very short time even then, and unheard of today, when ten to 15 years is more typical. Construction of the second prototype (s/n 53-7787) proceeded at a slower pace.
Design
In order to achieve the desired performance, Lockheed chose a minimalist approach: a design that would achieve high performance by wrapping the lightest, most aerodynamicallyAerodynamics
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...
efficient airframe
Airframe
The airframe of an aircraft is its mechanical structure. It is typically considered to include fuselage, wings and undercarriage and exclude the propulsion system...
possible around a single powerful engine. The emphasis was on minimizing drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
and mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
.
The XF-104 had a radical wing design. Most jet fighters of the period (and to this day) used a swept-wing or delta-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...
. This allowed a reasonable balance between aerodynamic performance, lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
, and internal space for fuel and equipment. Lockheed's tests, however, determined that the most efficient shape for high-speed, supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
flight was a very small, straight, mid-mounted, trapezoid
Trapezoid
In Euclidean geometry, a convex quadrilateral with one pair of parallel sides is referred to as a trapezoid in American English and as a trapezium in English outside North America. A trapezoid with vertices ABCD is denoted...
al wing. The low-aspect ratio wing was extremely thin, with a thickness-to-chord
Chord (aircraft)
In aeronautics, chord refers to the imaginary straight line joining the trailing edge and the center of curvature of the leading edge of the cross-section of an airfoil...
ratio of only 3.4%. The leading edge
Leading edge
The leading edge is the part of the wing that first contacts the air; alternatively it is the foremost edge of an airfoil section. The first is an aerodynamic definition, the second a structural one....
s of the wing were so thin (0.016 in/0.41 mm) and so sharp that they presented a hazard to ground crews, and protective guards had to be installed during ground operations. The thinness of the wings meant that fuel tanks and landing gear
Landing Gear
Landing Gear is Devin the Dude's fifth studio album. It was released on October 7, 2008. It was his first studio album since signing with the label Razor & Tie. It features a high-profile guest appearance from Snoop Dogg. As of October 30, 2008, the album has sold 18,906 copies.-Track...
had to be contained in the fuselage. The hydraulic actuators driving the ailerons were only one inch (25 mm) thick to fit into the available space and were known as Piccolo
Piccolo
The piccolo is a half-size flute, and a member of the woodwind family of musical instruments. The piccolo has the same fingerings as its larger sibling, the standard transverse flute, but the sound it produces is an octave higher than written...
actuators because of their resemblance to this musical instrument. The wings had electrically driven leading and trailing edge flaps
Flap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...
to increase lift at low speed. The XF-104 did not feature the Boundary Layer Control System
Blown flap
Blown flaps are a powered aerodynamic high-lift device invented by the British and used on the wings of certain aircraft to improve low-speed lift during takeoff and landing. The process is sometimes called a boundary layer control system . They were a popular design feature in the 1960s, but fell...
of the production aircraft.
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
testing, the stabilator
Stabilator
A stabilator is an aircraft control surface that combines the functions of an elevator and a horizontal stabilizer...
was mounted at the top of the fin for optimum stability and control about the pitch
Flight dynamics
Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in three dimensions about the vehicle's center of mass, known as pitch, roll and yaw .Aerospace engineers develop control systems for...
axis. Because the vertical tail fin was only slightly shorter than the length of each wing and nearly as aerodynamically effective, it could act as a wing on rudder
Rudder
A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...
application (a phenomenon known as "Dutch roll
Dutch roll
Dutch roll is a type of aircraft motion, consisting of an out-of-phase combination of "tail-wagging" and rocking from side to side. This yaw-roll coupling is one of the basic flight dynamic modes...
"). To offset this effect, the wings were angled downward to give 10° anhedral. The rudder was manually operated and supplemented by a small yaw damper
Yaw damper
A yaw damper is a device used on many aircraft to damp the rolling and yawing oscillations due to Dutch roll mode. It involves yaw rate sensors and a processor that provides a signal to an actuator connected to the rudder...
surface mounted at the bottom of the fin.
The fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
of the XF-104 had a high fineness ratio
Fineness ratio
Fineness ratio is a term used in naval architecture and aerospace engineering to describe the overall shape of a streamlined body. Specifically, it is the ratio of the length of a body to its maximum width; shapes that are "short and fat" have a low fineness ratio, those that are "long and skinny"...
, i.e., tapering sharply towards the nose, and a small frontal area of 25 sq ft (2.3 m²). The fuselage was tightly packed, containing the cockpit
Cockpit
A cockpit or flight deck is the area, usually near the front of an aircraft, from which a pilot controls the aircraft. Most modern cockpits are enclosed, except on some small aircraft, and cockpits on large airliners are also physically separated from the cabin...
, avionics
Avionics
Avionics are electronic systems used on aircraft, artificial satellites and spacecraft.Avionic systems include communications, navigation, the display and management of multiple systems and the hundreds of systems that are fitted to aircraft to meet individual roles...
, cannon, all internal fuel, landing gear, and engine. The air intakes, designed by Ben Rich
Ben Rich
Benjamin Robert Rich was the second director of Lockheed's Skunk Works from 1975 to 1991, succeeding its founder, Kelly Johnson. Regarded as the "father of stealth," Ben Rich was responsible for leading the development of the F-117, the first production stealth aircraft...
, were of fixed geometry without inlet cones, since the J65-powered aircraft was incapable of 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...
2 performance. They were similar to those of the F-94 Starfire, being mounted slightly away from the fuselage, with an inner splitter plate for the boundary layer
Boundary layer
In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...
bleed air. The combination of these features provided extremely low drag except at high angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
, at which point induced drag became very high.
The XF-104 featured an unusual downward-ejecting Stanley B
Stanley Aviation
Stanley Aviation is an aerospace company started by Robert M Stanley, the aviation pioneer, in Buffalo, New York in 1948.The company has since acquired several other companies and has been most recently acquired by Eaton Corporation....
seat. It was feared that contemporary ejection seat designs would not have enough explosive power to clear the high "T" tail assembly. In the event of the seat not firing, it was possible to manually release the lower fuselage hatch and then exit the aircraft via gravity. The F-104 series aircraft would later convert to upward-ejecting seats but the fuselage hatch was retained as a useful maintenance feature.
Testing and evaluation
Tony LeVier
Anthony W. "Tony" LeVier was an air racer and test pilot for the Lockheed Corporation from the 1940s to the 1970s.- Early life :...
was to do the initial testing. On 28 February 1954, the XF-104 made a planned hop of about five ft off the ground during a high-speed taxi, but its first official flight took place on 4 March 1954. During that flight, the landing gear did not retract, and LeVier landed after a low-speed flight of about 20 minutes. Adjustments and further flights discovered that the problem was low pressure in the hydraulic system. Bad weather kept the XF-104 on the ground until 26 March when further flights were carried out with the landing gear retracting normally.
The second prototype (Lockheed 083-1002, s/n 53-7787), fitted with the afterburning J65 from the start, first flew on 5 October 1954. Since it was to be the armament test bed, it was fitted with the 20 mm (.79 in) M61 Vulcan
M61 Vulcan
The M61 Vulcan is a hydraulically or pneumatically driven, six-barreled, air-cooled, electrically fired Gatling-style rotary cannon which fires 20 mm rounds at an extremely high rate. The M61 and its derivatives have been the principal cannon armament of United States military fixed-wing aircraft...
cannon and was equipped with an AN/ASG-14T-1 fire control system. XF-104 #2 achieved a top speed of Mach 1.79 at 60000 feet (18,288 m) on 25 March 1955, piloted by Lockheed test pilot J. Ray Goudey. This was the highest speed achieved by the XF-104.
XF-104 #1 was subsonic in level flight when powered by the non-afterburning J65, but Mach 1 could be easily exceeded during a slight descent. In July 1954, the J65-B-3 was replaced by the afterburning J65-W-7 turbojet. With this engine installed, the performance of the XF-104 was greatly improved. Maximum level speed was Mach 1.49 at 41000 ft (12,496.8 m), and an altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
of 55000 ft (16,764 m) could be attained in a zoom climb, while Mach 1.6 could be attained in a dive. The first XF-104 was accepted by the USAF in November 1955.
Compressor stall
A compressor stall is a situation of abnormal airflow resulting from a stall of the aerofoils within the compressor of a jet engine. Stall is found in dynamic compressors, particularly axial compressors, as used in jet engines and turbochargers for reciprocating engines.Compressor stalls result in...
s. Tony LeVier immediately shut down the engine and glided back to make a successful deadstick landing
Deadstick landing
A deadstick landing, also called a dead-stick landing is a type of forced landing when an aircraft loses all of its propulsive power and is forced to land. The term is often misunderstood, as the flight controls in the majority of aircraft are either fully or partially functional, even with no...
at Rogers Dry Lake
Rogers Dry Lake
Rogers Dry Lake is an endorheic desert salt pan in the Mojave Desert of Kern County, California. The lake derives its name from the Anglicization from the Spanish name, Rodriguez Dry Lake. It is the central part of Edwards Air Force Base as its hard surface provides a natural extension to the...
. An investigation later showed that one of the 20 mm cannon rounds had exploded in the breech
Breech-loading weapon
A breech-loading weapon is a firearm in which the cartridge or shell is inserted or loaded into a chamber integral to the rear portion of a barrel....
, blowing the bolt
Bolt (firearm)
A bolt is a mechanical part of a firearm that blocks the rear of the chamber while the propellant burns.In manually-operated firearms, such as bolt-action, lever-action, and pump-action rifles and shotguns, the bolt is held fixed by its locking lugs during firing, forcing all the expanding gas...
out the rear of the gun and through the structure into the forward fuselage fuel cell. Jet fuel had run into the gun bay, and leaked out of the compartment door seals and into the left engine air intake. The engine immediately flooded with fuel, causing the compressor stalls.
Crashes
XF-104 53-7786 was lost in a crash on 11 July 1957 when it developed an uncontrollable tail flutter while flying chase for F-104A flight tests. The entire tail group was ripped from the airframe, and Lockheed test pilot Bill Park was forced to eject. Vertical fin flutter was a known problem and the aircraft had been limited to speeds of no more than Mach 0.95 at the time of the accident. Tony LeVier had attempted to have the aircraft removed from flight status and placed in a museum, arguing that its performance was not suitable for chase duties.XF-104 53-7787 was lost on 14 April 1955 after accumulating over 1,000 flying hours when test pilot Herman Salmon
Herman Salmon
Herman R. Salmon , nicknamed "Fish", was a barnstormer, air racer, and test pilot for the Lockheed Corporation. He started work at Lockheed in 1940 ferrying Hudsons to Montreal for the Royal Air Force...
was forced to eject during gun firing trials at 50000 ft (15,240 m). The gun malfunctioned during a test firing, and severe vibrations began to build up which knocked loose the ejection hatch below the cockpit. Cabin pressure
Cabin pressurization
Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.-Need for cabin pressurization:...
was lost with Salmon's pressure suit
Pressure suit
A pressure suit is a protective suit worn by high-altitude pilots who may fly at altitudes where the air pressure is too low for an unprotected person to survive, even breathing pure oxygen at positive pressure. Such suits may be either full-pressure or partial-pressure...
inflating and covering his face so that he could not see. Recalling LeVier's harrowing experience with the exploding cannon shell the previous December, Salmon believed that the same thing had happened to him and that he had no option but to eject. He later found out that he could have saved 53-7787 by simply bringing it down to a lower altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
and waiting for his pressure suit to deflate. With the loss of the armament testbed
Testbed
A testbed is a platform for experimentation of large development projects. Testbeds allow for rigorous, transparent, and replicable testing of scientific theories, computational tools, and new technologies.The term is used across many disciplines to describe a development environment that is...
, Lockheed engineers were forced to find an alternative, and armament trials were continued on a modified Lockheed F-94C Starfire. The two XF-104s amassed an approximate total of 250 flight hours.
Testing conclusions
Flight testing proved that performance estimates were accurate and that even when fitted with the low powered J65 engine, the XF-104 flew faster than the other Century SeriesCentury series
The Century Series is a popular name for a group of US fighter aircraft representing models designated between F-100 and F-106 which went into full production...
fighters being developed at the time. The XF-104's ceiling at 60000 ft (18,288 m) was 7000 ft (2,133.6 m) higher than predicted, and it exceeded estimated speed and drag figures by two to three percent. It was noted however that the low thrust of the J65 engine did not enable the full performance potential of the type to be realized.
Yaw damper
A yaw damper is a device used on many aircraft to damp the rolling and yawing oscillations due to Dutch roll mode. It involves yaw rate sensors and a processor that provides a signal to an actuator connected to the rudder...
of the XF-104 was found to be ineffective and the rudder did not positively center, these problems were corrected by revising the rudder control system. The unpowered rudder did not provide adequate directional control at high air speeds (remedied by using hydraulic power on all subsequent versions of the F-104) and some concern was expressed over poor subsonic
Subsonic aircraft
A subsonic aircraft is an aircraft with a maximum speed less than the speed of sound ....
maneuverability at higher altitudes.
During a later interview, Kelly Johnson was asked about his opinion on the aircraft, "Did it come up to my designs? In terms of performance, yes. In terms of engine, we went through a great many engine problems, not with the J65s but with the J79s." For his part in designing the F-104 airframe, Johnson was jointly awarded the Collier Trophy
Collier Trophy
The Collier Trophy is an annual aviation award administered by the U.S. National Aeronautics Association , presented to those who have made "the greatest achievement in aeronautics or astronautics in America, with respect to improving the performance, efficiency, and safety of air or space...
in 1958, sharing the honor with General Electric (engine) and the U.S. Air Force (Flight Records).
F-104 production
Official approval of the XF-104 design led to a contract for 17 YF-104A service test aircraft and a production run of over 2,500 aircraft built both in the United States and under license worldwide.Visible changes from the XF-104 to production versions of the Starfighter include a longer fuselage (to accommodate the J79 engine and extra internal fuel) and a forward-retracting nose landing gear (except two-seat versions) to increase clearance for the downward-ejecting seat. A ventral fin for increased stability was added during the YF-104A test program. Inlet shock cones and a fuselage spine fairing between the canopy and fin that housed fuel piping were further added features. Production aircraft would also feature a redesigned fin structure using stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
spars
Spar (aviation)
In a fixed-wing aircraft, the spar is often the main structural member of the wing, running spanwise at right angles to the fuselage. The spar carries flight loads and the weight of the wings whilst on the ground...
to eliminate the flutter problem.
Since the internal fuel capacity was low limiting the useful range of the aircraft, extra capacity was provided on later versions by lengthening the forward fuselage.
Specifications (XF-104)
See also
External links
- XF-104 page on USAF National Museum site
- First flight of the XF-104 on YouTube.
- Baugher's U.S. Military Aircraft page on the XF-104
- F-104 Flight International.
- XF-104 on Vectorsite.net