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	Boeing or Lockheed Martin Joint Strike Fighter Multi-Role Fighter

DESCRIPTION: The Joint Strike Fighter program was started to replace a myriad of aircraft for the US Air Force, US Navy, US Marines, and the British Royal Navy beginning around 2010. Since each branch hoping to acquire the JSF has different needs, each variant of the aircraft is tailored to the requirements of that service. The USAF initially planned to acquire 1,760 conventional takeoff attack fighter variants to replace the F-16 and A-10 while the Navy and Marines need to replace older models of the F/A-18. The Navy's approximately 300 to 480 aircraft are generally similar to the Air Force model but carry more fuel for greater range. The Marines also need 480 to 640 vertical/short takeoff and landing (V/STOL) aircraft to replace its fleet of F-18 Hornets and AV-8B Harriers, so its version features a ducted lift-fan to assist in vertical flight. The Royal Navy also plans to purchase up to 60 V/STOL models to replace the Sea Harrier while the Royal Air Force plans to acquire another 90 to replace its Harrier II fleet. The origins of the JSF project can be traced to 1986 when a combined US and UK study explored a potential supersonic replacement for the Harrier and Sea Harrier. The simplest approach studied considered adding plenum chamber burning to each of the Harrier's four rotating nozzles, but this idea was rejected due to problems with ground erosion and hot gas being reingested by the engine. The study also rejected other advanced thrust vectoring approaches as being too complicated, too heavy, or too risky. A completely unrelated project began in 1990 when the Advanced Research Project Agency (ARPA) commenced the Common Affordable Lightweight Fighter (CALF) study. The purpose of CALF was to propose options for a multi-service aircraft, including a variant with vertical flight capability. This project eventually led to the Supersonic Strike Fighter study of 1991 through 1994 in which several aircraft and engine manufacturers were contracted to explore fighter and propulsion concepts for a future multi-role combat plane. CALF focused primarily on development of a supersonic short/vertical takeoff and landing (STOVL) aircraft, but an additional project underway at the time studied the feasibility of a joint combat aircraft for the US Air Force and US Navy. Supported by the US Department of Defense, this effort was known as the Joint Advanced Strike Technology (JAST) project. JAST had resulted from a merger of the Navy's Attack/Fighter-Experimental (A/F-X) program that followed the cancellation of the A-12 Avenger with the Air Force's Multi-Role Fighter (MRF) study intended to develop a replacement for the F-16. CALF was also merged into JAST in 1994, and the project was later renamed Joint Strike Fighter (JSF). The goal of JSF was to develop a common aircraft for the USAF, USN, USMC, and RN. Since the designation X-32 had already been set aside for a CALF STOVL demonstrator and X-35 for an advanced fighter demonstrator, these were reallocated to two Joint Strike Fighter demonstrators to compete for a production contract. Manufacturers began considering design concepts in 1994 and the official request for proposals was released in 1996. The three design teams expressing interest included: McDonnell Douglas, Northrop Grumman, and British Aerospace: a relatively conventional design except it did away with standard horizontal and vertical tails in favor of a flat-angle butterfly control surface. The STOVL version employed a separate lift fan installed aft of the cockpit coupled with a clam-shell to divert the main engine exhaust to two rotating nozzles for vertical flight. In forward flight, the clam-shell was opened and the exhaust flowed through the aft nozzle. The conventional models replaced this lift engine with an additional fuel tank. Boeing: a delta wing design with a V-tail, and a scoop jet intake under the nose. The STOVL version drove thrust from the engine forward to a pair of vectored lift nozzles under the aircraft's center of gravity. The nose intake scoop hinged forward to allow greater airflow. Lockheed Martin: conventional design, resembling a single-engined version of the F-22 Raptor. The STOVL version featured a lift fan behind the cockpit, driven by a shaft off the main engine, plus a vectored exhaust and two exhaust ducts, extending from each side of the engine to exit in the bottom of the wings. Following evaluation in 1996, the McDonnell Douglas design was rejected as too complex. Boeing and Lockheed were awarded contracts to build prototypes of their respective X-32 and X-35 submissions. These were not true prototypes participating in a competitive flyoff, as with the YF-22 and YF-23, but technology demonstrators showing different approaches to producing a common aircraft for the three armed forces. Nonetheless, the Lockheed X-35 design was judged superior in 2001, and the company began additional development leading to full production of an operational fighter to begin entering service in the early 2010s. For detailed information on each of the competitors, see the Boeing X-32 and Lockheed Martin X-35 entries as well as the F-35. Last modified 28 August 2010

SOURCES: Boeing X-32 site (no longer available) Lockheed Martin F-35 site Spick, Mike. Brassey's Modern Fighters: The Ultimate Guide to In-Flight Tactics, Technology, Weapons, and Equipment. Washington, DC: Brassey's, 2000, p. 136-139. Spohrer, Jennifer and Frase, Tuesday. Jane's Combat Simulations: ATF Gold Users Manual. San Mateo, CA: Electronic Arts, 1997, p. 9.39. US Military JSF site