Northrop YF-17

The Northrop YF -17 Cobra was a prototype under the " Lightweight Fighter " program of the U.S. Air Force. This was initiated because it was thought that the F- 15 Eagle is too expensive to produce them in sufficient quantities can. However, economic policy interests played a role, especially in relation to the export market. The YF -17, which is in the broadest sense is a development of the F -5, lost the LWF program of its competitor, the YF- 16th

After losing the LWF program the YF -17 from McDonnell Douglas under the new " Naval Fighter Attack Experimental" program ( VFAX ) for the F/A-18 Hornet was developed. The larger F-18 finally went with the U.S. Navy and the U.S. Marine Corps in service and replaced there, as a complement to the F- 14 Tomcat, A-7 Corsair II and F- 4 Phantom II

  • 2.1 armament



The basic construction of the YF -17 was designed under the firm internal Northropprojektes N -300 1965. When N- 300 is to use boost in a derivative of the F- 5E Tiger II, in which the fuselage was extended by the more powerful GE15 - J1A1 -jets with up to 40 kN. To counteract the resulting weight increases, the wing was enlarged which should reduce the increase in wing loading. However, the N -300 concept was never realized, but further developed into the P -530. The primary difference between the concepts is the change to the GE15 - J1A5 engines with up to 58 kN thrust, which have a very low bypass ratio of 0.25. This brought the engines the nickname "leaky turbojet " (engl.: " leaky jet engines " ), since the small side stream could at best cool the engines. In fact, the temperature in the engine bays could be kept low by the interpretation as turbofan, and the designers have been in the construction in this range of cells allows aluminum as a material without additional heat protection measures to use.

The P -530 design has an identical configuration in the region of the wing to the F- 5. These fall again trapezoidal and assign a sweep of 20 °, but with 37 m² approximately twice as large. Also, " nose " of the machine was nearly unchanged from the F -5. To move the center of gravity of the machine, the bearing surfaces should be centrally mounted on the hull in the P -530. The biggest technical innovation was announced the installation of the " Leading Edge Extension" (LEX), better than strakes. With these the airflow at high angles of attack is affected and to make the machine more controllable and thus ultimately also allow higher angle of attack. These design features, along with the black painted nose, led to the later YF -17 was nicknamed "Cobra". It is controversial, however, whether this really is an official designation.

The YF -17 aluminum was used for the construction and largely dispensed with new production methods that has to do with the cost reduction in the first place. The aluminum parts were mounted on a conventional honeycomb structure. Something unusual was the use of only about 400 kg of a graphite - epoxy composite. In the narrow nose of the machine a simple radar was installed. The engines are placed close to each other to reduce the asymmetry in the event of a failure. In the cockpit of the ejection seat was tilted by 18 °, and for the first time used a head-up display (HUD ). The wings were too thin, than this could carry fuel. Thus, the tanks were only in the front and rear edge, and in the strakes.

In the final drafts of the YF- 17, the General Electric was relatively short YJ101 -GE- 100 turbofan engines with up to 67 kN thrust used (other sources give the thrust of 64 kN ). Although this had been developed from the GE15 jet engines, these were not yet mature, which should prove in the final selection later as a disadvantage. The decision led to numerous design changes that had to be carried out under considerable time pressure. For easy maintenance, the engines are fixed to the lower rear part and can be lowered with this change to the engine without disassembly of the tail is necessary. In contrast to P -530, the YF -17 was already wearing a partial fly-by -wire controls.

Originally they wanted to take over the simple vertical tail of the F- 5 for the YF -17, but studies showed that this is inefficient at high angles of attack. Therefore, Northrop decided now to mount two side fins and these must be angled slightly. Interim attempts to mount them even at a 45 ° angle and for giving up the elevator, however, were discarded.

Flight testing

As the LWF program was initiated in 1971, Northrop developed the P -530 to P -600 concept further, then emerged the YF- 17 from the. The P -530 was originally designed as a multi-role combat aircraft, the P -600, however, was strictly designed as a pure fighter, so the Vulcan cannon has now been placed in the forward fuselage area, rather than in a separate tank weapons. The YF -17 was powered by the half-baked YJ101 engines, a further development of the GE15. Over 5000 hours in the wind tunnel were needed for the design of the YF -17.

The first prototype (S / N 72-1569 ) was presented on April 4, 1974 in Hawthorne and was used for the first rolling tests. The first flight finally took place on June 9 of the same year. The second YF -17 ( S / N 72-1570 ) was followed on 21 August. The two prototypes completed a total of 288 test flights and from which arise 345 flight hours. During the test program, a top speed of Mach 1.95 was reached, the maximum load was 9.4 g and the maximum altitude at about 15,000 m. It has a maximum angle of 34 ° and 63 ° in Horizentalflug climb are achieved ( at 93 km / h).

As on 13 January 1975, the U.S. Secretary of the Air Force John L. McLucas, announced the decision in favor of the YF -16 and YF -17 against, the flight testing of the Cobra was discontinued. The reason he mentioned that the YJ101 engines were not yet mature, and thus constitute an unnecessary risk development. It is assumed that the lower operating costs are likely to have (due to the single-beam design ) played a role, and thus potentially better export opportunities.


Originally, the U.S. Navy was not involved in the LWF program. However, the Congress initiated in August 1974 that the Navy should use as many technologies and experience from the LWF program for their own fighter program, the VFAX. As Northrop had no experience with trägergestützen fighter planes, closed one with McDonnel Douglas together, which from then on took over the development of the YF- 17 to the F/A-18 Hornet. Similarly acted General Dynamics F- 16 could develop together with LTV Aerospace the F- 16N, to adapt it to the needs of the Navy. In contrast to the U.S. Air Force, the Navy decided now but for the F/A-18, which is located to the present in the service and is used as F/A-18E/F Super Hornet also produced by Boeing.

For the VFAX program, the first YF -17 prototype (S / N 72-1569 ) before the first F/A-18 was reactivated by the NASA Dryden Research Center and used from 27 May to 14 July 1976 studies, prototype was able to resume flight testing.


Both prototypes are now exhibited publicly and can be visited:

  • The YF -17 Cobra (S / N 72-1569 ) is located in the Western Museum of Flight in Torrance, California.
  • The YF -17 Cobra (S / N 72-1570 ) is on the Battleship Memorial Park in Mobile, Alabama.



  • A 20 mm M61A1 Vulcan cannon machine
  • Two AIM-9 Sidewinder air - to-air missiles