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Subject: Lockheed XF-104
Date: 19 Jun 2018 05:39:04 -0700
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https://en.wikipedia.org/wiki/Lockheed_XF-104
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 aircraft being destroyed in accidents during testing. The XF-104s were
forerunners of over 2,500 production 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, notable for its sleekness, particularly its
thin wings and missile-shaped fuselage, as well as a novel pilot ejection
system.
Flight testing of the XF-104s began with the first flight in March 1954,
encountering several problems, some of which were resolved; however, performance
of the XF-104 proved better than estimates and despite both prototypes being
lost through accidents, the USAF ordered 17 service-test/pre-production
YF-104As. Production Starfighters proved popular, both with the USAF and
internationally, serving with a number of countries, including Jordan, Turkey,
and Japan.
Clarence L. "Kelly" Johnson, chief engineer at Lockheed's 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 North American F-86 Sabres, 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 general
design of the X-7's wing and tail. 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.
The wooden mock-up was ready for inspection at the end of April, and work
started on two prototypes late in May. The J79 engine was not yet ready, so both
prototypes were instead designed to use the Wright J65, a licensed built version
of the Armstrong Siddeley Sapphire. Construction of the first prototype XF-104
(US serial number 53-7786, Buzz number 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,
second prototype (s/n 53-7787) proceeded at a slower pace.
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 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.
The XF-104 had a radical wing design. Most supersonic jets use a swept or delta
wing. This allows a reasonable balance between aerodynamic performance, lift,
and internal space for fuel and equipment. However the most efficient shape for
high-speed, supersonic flight had been found to be a small, straight,
mid-mounted, trapezoidal wing of low aspect ratio and high wing loading. The
wing was extremely thin, with a thickness-to-chord ratio of only 3.4%. The
leading edges 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.
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 Series fighters being developed at the time. The XF-104's ceiling
at 60,000 ft (18,000 m) was 7,000 ft (2,100 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.
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).
Specifications (XF-104)
General characteristics
Crew: 1
Length: 49 ft 2 in (15 m)
Wingspan: 21 ft 11 in (6.69 m)
Height: 13 ft 6 in (4.1 m)
Airfoil: Bi-convex 3.36%
Empty weight: 11,500 lb (5,216 kg)
Loaded weight: 16,700 lb (7,575 kg)
Max. takeoff weight: 15,700 lb (7,120 kg)
Thrust with afterburner: 10,300 lbf (45.82 kN)
Performance
Maximum speed: 1,151 kn (1,324 mph, 2,131 km/h)
Stall speed: 139 kn (160 mph, 257 km/h)
Range: 695 nmi (800 mi, 1,290 km)
Service ceiling: 50,500 ft (15,500 m)
Armament
*
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