Northrop YF-17
The Northrop YF-17 Cobra was a prototype fighter aircraft designed for the U.S. Air Force's Light Weight Fighter (LWF) technology evaluation program as a lightweight day fighter. It was the culmination of a long line of Northrop designs, beginnin with the N-102 Fang in 1956, continuing through the F-5 series. Though it lost the LWF competition, it would form the basis for the F/A-18 Hornet adopted by the U.S. Navy and U.S. Marine Corps.[1]
History
The aircraft's main design elements were begun in early 1965 with the internal Northrop project N-300, based on the F-5E with a stretched fuselage, small leading-edge root extensions (LERX), and more powerful GE15-J1A1 turbojets, rated at 9,000 pound force (lbf) each. The wing was moved higher on the fuselage to increase ordnance flexibility. The N-300 further evolved the P530 Cobra, utilizing 13,000 lbf GE15J1A5 engines, with a very small .25 bypass ratio. The bypass effectively was only a cooling stream for the rear of the engine, leading to the nickname "leaky turbojet", allowing the engine bay to constructed of lighter, cheaper materials.[1]
The P530's wing planform was similar to the F-5, with a trapezoidal shape formed by a sweep of 20° at the quarter-chord line, and an unswept trailing edge, but was over double the area, with 400 square feet as opposed to the 186 of the F-5E. Initially shoulder mounted, the wings was gradually shifted down to the mid position. It's most distinctive new feature were the LERXs, that tapered into the fuselage under the cockpit. They enabled maneuveraing at angles of attack exceeding 50°, by providing about 50% additionally lift. The extensions also smoothed airflow into the engine inlets at high angles of attack. The resemblence to the head of a cobra lead to the adoption of the nickname "Cobra", also adopted for the YF-17. Studies showed a single vertical stabilizer was insufficient at high angles of attack, and it was changed to twin vertical stabilizers, canted at 45°. The result was an aircraft that had relaxed longitudinal stability, enhancing maneuverability. However, Northrop was not yet confident in fly-by-wire controls and retained mechanically signaled flight controls. The resulting aircraft, unveiled on 28 January 1971, advertised with a max weight of 40,000 pounds and maxomum speed of Mach 2, but stirlled little interest among foreign buyers.
In 1972 the United States Air Force sought proposals for a light fighter that was small, low-cost, lightweight and easy to maintain, in response to the soaring costs and projected limited production run of the brand-new F-15 Eagle (an issue that would resound decades later in the development of the Joint Strike Fighter project in response to the cost and time overruns of the F-22 Raptor). Northrop had experience with such requirements through its very successful F-5 Freedom Fighter and T-38 Talon.
When the Light Weight Fighter program was announced in 1971, Northrop modified the P530 into the P600 design that would be designated the YF-17A. Whereas the P530 was intended as a multi-role aircraft, the P600 was to be strictly an air-to-air demonstrator, and consequently the cannon moved from the underside of the fuselage, to the upper part. Design of the YF-17 and the prototype YJ101 engine (a development of the GE15 engine), consumed over a million man-hours, and 5,000 hours of wind tunnel testing.
The first prototype (tail number 72-1569) was rolled out at Hawthorne on 4 April 1974, and made its first flight at Edwards AFB on 9 July. The second (72-1570) first flew on 21 August. Through 1974, the YF-17 competed against the General Dynamics YF-16 Eagle. The two prototypes flew 288 test flights, totaling 345.5 hours. It attained a top speed of Mach 1.95, a peak load factor of 9.4g, and a maximum altitude of over 50,000 feet. It could attain a sustained 34° angle of attack in level flight, and 63° in a climb at 50 knots.
The U.S. Navy was a small participant on the LWF program. In August 1974, the Navy directed the Navy to make maximum use of the technology and hardware of the LWF for its new lightweight strike fighter, the VFAX. As neither contractor had experience with naval fighters, they sought partners to provide that expertise. General Dynamics teamed with LTV; Northrop with McDonnell Douglas. Each submitted revised designs in line with the Navy needs for a long-range radar and multirole capabilities.[2]
Through Northrop was expected to be the winner based on years of light fighter experience, and the extensive history of the P530 design, the Air Force, in January 1975, selected the YF-16, which was slightly faster and used a common engine with the Air Force's F-15. The Navy did not believe the YF-16's single engine and narrow landing gear were suitable or easily adapted to carrier operations, and refused to adopt the design. In May 1975, the Navy secured approval to develop its own aircraft based on the YF-17. As this now became a purely naval project, the Navy designated McDonnell Douglas the prime contractor. As the Navy requirements were quite different from the Air Force's, the aircraft was significantly modified and the resulting F/A-18 would share no dimensions or structures with the YF-17 demonstrators.
Design Characteristics
The YF-17 was primarily constructed of aluminum, in conventional semimonocoque stressed-skin construction, though over 900 pounds of its structure were graphite/epoxy composite. The small nose contained a simple ranging radar. The cockpit sported an ejection seat inclined at 18°, a bubble canopy, and a heads-up display. The thin wings carried no fuel, and in areas such as the leading and trailing edge and the LERX, contained a Nomex honeycomb core with composite facesheets. The rear of the aircraft sported twin all-moving stabilators of aluminum over a honeycomb core, and twin vertical stabilizers of a conventional construction. Like the wings, the leading and trailing edges were constructed of composite facesheets over honeycomb core. A composite speedbrake was located above and between the engines.
The aircraft was powered by a pair of 14,400-lbf General Electric YJ101-GE-110 turbofans, a development of the GE15, mounted next to each other to minimize asymmetry in the event of an engine loss. The engines are mounted in a steady-rest that allows removal from below the aircraft, without disturbing the empennage controls, for ease of maintentance. Each engine drove an independent hydraulic system. Unlike the P530, the YF-17 sported a partial fly-by-wire control scheme, formally called the electronic control augmentaion system (CAS), utilizing ailerons, rudders, and stabilators for primarly flight control.
Specifications (YF-17 Cobra)
Vorlage:Aircraft specifications
References
- ↑ a b Dennis R. Jenkins: F/A-18 Hornet: A Navy Success Story. McGraw-Hill, New York 2000, ISBN 0-07-134696.
- ↑ Kent Lee, Capt. E.T. Wooldridge, U.S. Navy, editor: Into the Jet Age: Conflict and change in Naval Aviation, 1945-1970. Naval Institute Press, 1995.
