YF-17 Cobra
Encyclopedia
The Northrop YF-17 (nicknamed "Cobra") was a prototype
lightweight fighter aircraft
designed for the United States Air Force
's Lightweight Fighter (LWF) technology evaluation program. The LWF was initiated because many in the fighter community believed that aircraft like the F-15 Eagle were too large and expensive for many combat roles. The YF-17 was the culmination of a long line of Northrop
designs, beginning with the N-102 Fang in 1956, continuing through the F-5 family.
Although it lost the LWF competition to the F-16 Fighting Falcon, the YF-17 was selected for the new Naval Fighter Attack Experimental (VFAX
) specification. In enlarged form, the F/A-18 Hornet was adopted by the United States Navy
and United States Marine Corps
to replace the A-7 Corsair II and F-4 Phantom II, complementing the more expensive F-14 Tomcat. This design, conceived as a small and lightweight fighter, was scaled up to the Boeing F/A-18E/F Super Hornet, which is similar in size to the original F-15.
(LERX), and more powerful GE15-J1A1 turbojets, rated at 9,000 lbf
(40 kN) each. The wing was slightly elevated to increase ordnance flexibility. The N-300 further evolved into the P-530 Cobra, which uses 13000 lbf (57.8 kN) GE15-J1A5 engines, with a very small .25 bypass ratio
leading to the nickname "leaky turbojet". The bypass effectively was only a cooling stream for the rear of the engine, allowing the engine bay to be constructed of lighter, cheaper materials.
The P-530's wing planform and nose section 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 sq ft (37.2 m²) as opposed to 186 sq ft (17.3 m²) of the F-5E. Initially shoulder mounted, the wings were gradually shifted down to the mid position. Its most distinctive new feature were the LERXs that tapered into the fuselage under the cockpit. They enabled maneuvering at angles of attack
exceeding 50°, by providing about 50% additional lift. The extensions also trapped airflow under them at high angles of attack, ensuring airflow into the engines. The resemblance to the head of a cobra
lead to the adoption of the nickname "Cobra", often unofficially used for the YF-17.
The YF-17 was primarily constructed of aluminum
, in conventional semi-monocoque
stressed-skin construction, though over 900 lb (408 kg) 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 head-up display
(HUD). The thin wings carried no fuel, and in areas such as the leading and trailing edge and the LERX, were composed of a Nomex
honeycomb core with composite facesheets. The rear of the aircraft featured 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 14400 pound-forces (64.1 kN) General Electric
YJ101-GE-100
turbofans, a development of the GE15, mounted next to each other to minimize thrust asymmetry in the event of an engine loss. For ease of maintenance, the engines are mounted in a steady-rest that allows removal from below the aircraft, without disturbing the empennage controls. Each engine drove an independent hydraulic system. Unlike the P-530, the YF-17 sported a partial fly-by-wire control scheme, formally called the electronic control augmentation system (ECAS), utilizing ailerons, rudders, and stabilators for primary flight control.
Studies showed a single vertical stabilizer was insufficient at high angles of attack, and it was changed to twin vertical stabilizer
s, canted at 45°, resulting in a "relaxed longitudinal stability" design, which enhances maneuverability. 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 a maximum weight of 40,000 lb (18,144 kg) and maximum speed of Mach
2, but stirred little interest among foreign buyers.
When the Lightweight Fighter program was announced in 1971, Northrop modified the P-530 into the P-600 design that would be designated the YF-17A. Whereas the P-530 was intended as a multi-role aircraft, the P-600 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 (serial number
72-1569) was rolled out at Hawthorne on 4 April 1974; its first flight
at Edwards AFB came on 9 June with Henry "Hank" Chouteau at the controls. The second YF-17 (s/n 72-1570) first flew on 21 August. Through 1974, the YF-17 competed against the General Dynamics
YF-16
. The two YF-17 prototypes flew 288 test flights, totaling 345.5 hours. The YF-17 attained a top speed of Mach 1.95, a peak load factor of 9.4 g, and a maximum altitude of over 50000 ft (15,240 m). It could attain a sustained 34° angle of attack in level flight, and 63° in a climb at 50 kt (58 mph, 93 km/h).
. As neither contractor had experience with naval fighters, they sought partners to provide that expertise. General Dynamics teamed with LTV Aerospace
for the F-16N; Northrop with McDonnell Douglas
for the F-18. Each submitted revised designs in line with the Navy needs for a long-range radar and multirole capabilities.
Prototype YF-17 72-1569 was sent to NASA's Dryden Research Center
for base drag studies from 27 May to 14 July 1976 prior to the first F/A-18 prototype under development.
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 ,...
lightweight fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...
designed for 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...
's Lightweight Fighter (LWF) technology evaluation program. The LWF was initiated because many in the fighter community believed that aircraft like the F-15 Eagle were too large and expensive for many combat roles. The YF-17 was the culmination of a long line of 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...
designs, beginning with the N-102 Fang in 1956, continuing through the F-5 family.
Although it lost the LWF competition to the F-16 Fighting Falcon, the YF-17 was selected for the new Naval Fighter Attack Experimental (VFAX
VFAX
VFAX for Naval Fighter Attack Experimental was actually two specifications for two US Naval fighter projects. The first was for a low cost lightweight complement for the F-111B which could replace the F-4 Phantom II for air superiority, escort, and ground attack missions in the early 1960s. This...
) specification. In enlarged form, the F/A-18 Hornet was adopted by the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
and United States Marine Corps
United States Marine Corps
The United States Marine Corps is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States...
to replace the A-7 Corsair II and F-4 Phantom II, complementing the more expensive F-14 Tomcat. This design, conceived as a small and lightweight fighter, was scaled up to the Boeing F/A-18E/F Super Hornet, which is similar in size to the original F-15.
Design and development
The aircraft's main design elements date to early 1965, from the internal Northrop project N-300. The N-300 was itself derived from the F-5E, and features a longer fuselage, small leading-edge root extensionsLeading edge extension
A leading edge extension is a small extension to an aircraft wing surface, forward of the leading edge. Different kinds of extensions have been used for different reasons.-Leading edge slats:...
(LERX), and more powerful GE15-J1A1 turbojets, rated at 9,000 lbf
Pound-force
The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...
(40 kN) each. The wing was slightly elevated to increase ordnance flexibility. The N-300 further evolved into the P-530 Cobra, which uses 13000 lbf (57.8 kN) GE15-J1A5 engines, with a very small .25 bypass ratio
Bypass ratio
The term bypass ratio relates to the design of turbofan engines, commonly used in aviation. It is defined as the ratio between the mass flow rate of air drawn in by the fan bypassing the engine core to the mass flow rate passing through the engine core....
leading to the nickname "leaky turbojet". The bypass effectively was only a cooling stream for the rear of the engine, allowing the engine bay to be constructed of lighter, cheaper materials.
The P-530's wing planform and nose section 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
Trailing edge
The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential control surfaces are attached here to redirect the air flow and exert a controlling force by changing its momentum...
, but was over double the area, with 400 sq ft (37.2 m²) as opposed to 186 sq ft (17.3 m²) of the F-5E. Initially shoulder mounted, the wings were gradually shifted down to the mid position. Its most distinctive new feature were the LERXs that tapered into the fuselage under the cockpit. They enabled maneuvering at angles 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...
exceeding 50°, by providing about 50% additional lift. The extensions also trapped airflow under them at high angles of attack, ensuring airflow into the engines. The resemblance to the head of a cobra
Cobra
Cobra is a venomous snake belonging to the family Elapidae. However, not all snakes commonly referred to as cobras are of the same genus, or even of the same family. The name is short for cobra capo or capa Snake, which is Portuguese for "snake with hood", or "hood-snake"...
lead to the adoption of the nickname "Cobra", often unofficially used for the YF-17.
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, in conventional semi-monocoque
Monocoque
Monocoque is a construction technique that supports structural load by using an object's external skin, as opposed to using an internal frame or truss that is then covered with a non-load-bearing skin or coachwork...
stressed-skin construction, though over 900 lb (408 kg) 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
Bubble canopy
A bubble canopy is a canopy made like a soap bubble, which attempts to provide 360° vision to the pilot.-History:Bubble canopies have been in use since World War II. The British had already developed the "Malcolm hood", which was a bulged canopy, but the British Miles M.20 was one of the first...
, and a head-up display
Head-Up Display
A head-up display or heads-up display is any transparent display that presents data without requiring users to look away from their usual viewpoints...
(HUD). The thin wings carried no fuel, and in areas such as the leading and trailing edge and the LERX, were composed of a Nomex
Nomex
Nomex is a registered trademark for flame resistant meta-aramid material developed in the early 1960s by DuPont and first marketed in 1967.- Properties:...
honeycomb core with composite facesheets. The rear of the aircraft featured 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 14400 pound-forces (64.1 kN) General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
YJ101-GE-100
General Electric YJ101
|-See also:-External links:*...
turbofans, a development of the GE15, mounted next to each other to minimize thrust asymmetry in the event of an engine loss. For ease of maintenance, the engines are mounted in a steady-rest that allows removal from below the aircraft, without disturbing the empennage controls. Each engine drove an independent hydraulic system. Unlike the P-530, the YF-17 sported a partial fly-by-wire control scheme, formally called the electronic control augmentation system (ECAS), utilizing ailerons, rudders, and stabilators for primary flight control.
Studies showed a single vertical stabilizer was insufficient at high angles of attack, and it was changed to twin vertical stabilizer
Vertical stabilizer
The vertical stabilizers, vertical stabilisers, or fins, of aircraft, missiles or bombs are typically found on the aft end of the fuselage or body, and are intended to reduce aerodynamic side slip. It is analogical to a skeg on boats and ships.On aircraft, vertical stabilizers generally point upwards...
s, canted at 45°, resulting in a "relaxed longitudinal stability" design, which enhances maneuverability. Northrop was not yet confident in fly-by-wire
Fly-by-wire
Fly-by-wire is a system that replaces the conventional manual flight controls of an aircraft with an electronic interface. The movements of flight controls are converted to electronic signals transmitted by wires , and flight control computers determine how to move the actuators at each control...
controls and retained mechanically-signaled flight controls. The resulting aircraft, unveiled on 28 January 1971, advertised a maximum weight of 40,000 lb (18,144 kg) and maximum speed 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, but stirred little interest among foreign buyers.
Operational history
The first prototype (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"...
72-1569) was rolled out at Hawthorne on 4 April 1974; its first 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....
at Edwards AFB came on 9 June with Henry "Hank" Chouteau at the controls. The second YF-17 (s/n 72-1570) first flew on 21 August. Through 1974, the YF-17 competed against the General Dynamics
General Dynamics
General Dynamics Corporation is a U.S. defense conglomerate formed by mergers and divestitures, and as of 2008 it is the fifth largest defense contractor in the world. Its headquarters are in West Falls Church , unincorporated Fairfax County, Virginia, in the Falls Church area.The company has...
YF-16
F-16 Fighting Falcon
The General Dynamics F-16 Fighting Falcon is a multirole jet fighter aircraft originally developed by General Dynamics for the United States Air Force . Designed as an air superiority day fighter, it evolved into a successful all-weather multirole aircraft. Over 4,400 aircraft have been built since...
. The two YF-17 prototypes flew 288 test flights, totaling 345.5 hours. The YF-17 attained a top speed of Mach 1.95, a peak load factor of 9.4 g, and a maximum altitude of over 50000 ft (15,240 m). It could attain a sustained 34° angle of attack in level flight, and 63° in a climb at 50 kt (58 mph, 93 km/h).
Naval Fighter Attack Experimental
Initially, the U.S. Navy was not heavily involved as a participant in the LWF program. In August 1974, Congress directed the Navy to make maximum use of the technology and hardware of the LWF for its new lightweight strike fighter, the VFAXVFAX
VFAX for Naval Fighter Attack Experimental was actually two specifications for two US Naval fighter projects. The first was for a low cost lightweight complement for the F-111B which could replace the F-4 Phantom II for air superiority, escort, and ground attack missions in the early 1960s. This...
. As neither contractor had experience with naval fighters, they sought partners to provide that expertise. General Dynamics teamed with LTV Aerospace
Vought
Vought is the name of several related aerospace firms. These have included, in the past, Lewis and Vought Corporation, Chance Vought, Vought Sikorsky, LTV Aerospace , Vought Aircraft Companies, and the current Vought Aircraft Industries. The first incarnation of Vought was established by Chance M...
for the F-16N; Northrop with McDonnell Douglas
McDonnell Douglas
McDonnell Douglas was a major American aerospace manufacturer and defense contractor, producing a number of famous commercial and military aircraft. It formed from a merger of McDonnell Aircraft and Douglas Aircraft in 1967. McDonnell Douglas was based at Lambert-St. Louis International Airport...
for the F-18. Each submitted revised designs in line with the Navy needs for a long-range radar and multirole capabilities.
Prototype YF-17 72-1569 was sent to NASA's Dryden Research Center
Dryden Flight Research Center
The Dryden Flight Research Center , located inside Edwards Air Force Base, is an aeronautical research center operated by NASA. On March 26, 1976 it was named in honor of the late Hugh L. Dryden, a prominent aeronautical engineer who at the time of his death in 1965 was NASA's deputy administrator...
for base drag studies from 27 May to 14 July 1976 prior to the first F/A-18 prototype under development.
Aircraft on display
- YF-17 Cobra, s/nUnited States military aircraft serialsIn 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"...
72-1569, is on display at the Western Museum of FlightWestern Museum of FlightThe Western Museum of Flight is an aviation museum located at Zamperini Field, the municipal airport in Torrance, California. WMOF is operated by the Southern California Historical Aviation Foundation....
in Torrance, CaliforniaTorrance, CaliforniaTorrance is a city incorporated in 1921 and located in the South Bay region of Los Angeles County, California, United States. Torrance has of shore-front beaches on the Pacific Ocean, quieter and less well-known by tourists than others on the Santa Monica Bay, such as those of neighboring...
. - YF-17 Cobra, s/n 72-1570 is on display at the Battleship Memorial ParkBattleship Memorial ParkBattleship Memorial Park is a military history park and museum located on the western shore of Mobile Bay in Mobile, Alabama. It has a collection of notable aircraft and museum ships including the South Dakota-class battleship USS Alabama and Gato-class submarine USS Drum...
in Mobile, AlabamaMobile, AlabamaMobile is the third most populous city in the Southern US state of Alabama and is the county seat of Mobile County. It is located on the Mobile River and the central Gulf Coast of the United States. The population within the city limits was 195,111 during the 2010 census. It is the largest...
.