| F-16XL | |
|---|---|
_in_flight_060905-F-1234S-049.jpg) The F-16XL which competed with the F-15E for the USAF's Enhanced Tactical Fighter contract in 1984 | |
| General information | |
| Type | Experimental fighter |
| National origin | United States |
| Manufacturer | General Dynamics |
| Primary users | United States Air Force |
| Number built | 2 |
| History | |
| First flight | 3 July 1982 |
| Retired | 2009 |
| Developed from | General Dynamics F-16 Fighting Falcon |
TheGeneral Dynamics F-16XL is a derivative of theF-16 Fighting Falcon with acranked-arrow delta wing. It entered theUnited States Air Force's (USAF)Enhanced Tactical Fighter (ETF) competition in 1981 but lost to theF-15E Strike Eagle. The two prototypes were shelved until being turned over toNASA for additional aeronautical research in 1988. Both aircraft were fully retired in 2009 and stored atEdwards Air Force Base; one of the two aircraft has since been placed on display.
Shortly after winning thelightweight fighter program,General Dynamics Fort Worth began investigating possibleF-16 derivatives with the goal of enhancing both air-to-air and air-to-ground mission capabilities while retaining parts commonality with theF-16A.[1] Under the leadership ofHarry Hillaker (designer of the originalF-16), the Supersonic Cruise and Maneuver Prototype (SCAMP) project was started. Several wing designs were considered, including one using aforward-swept wing, but the large "cranked-arrow" wing (similar to that of theSaab 35 Draken)[note 1] was pursued due to its much more efficientlift-to-drag ratio at supersonic speeds.[2]
The company worked closely with NASA'sLangley Research Center[3] and invested significantR&D funds for wind tunnel testing. Over several years the design was refined which led to the finalF-16XL design by late 1980.[4]
In 1980, the USAF signed on as a partner,[5] providing the fuselages of the third[note 2] and fifth[note 3] productionF-16s for conversion. These two fuselages became the only examples of theF-16XL.[6]
In March 1981, the USAF announced theEnhanced Tactical Fighter (ETF) program to procure a replacement for theF-111 Aardvark.[7] The concept envisioned an aircraft capable of launching deepinterdiction missions without requiring additional support in the form of fighter escorts or jamming support. General Dynamics submitted theF-16XL, whileMcDonnell Douglas submitteda variant of the F-15 Eagle. Though the two aircraft were competing for the same role, they had fairly different design approaches. TheF-15E required very few alterations from its baseF-15B or D, while theF-16XL had major structural and aerodynamic differences from the originalF-16.[8] As such, theF-16XL would have required much more effort, time, and money to put into full production.[9] Additionally, theF-15E had two engines, which gave it a much highermaximum takeoff weight and redundancy in the case of engine failure.[9][note 4]
In February 1984, the USAF awarded the ETF contract to McDonnell Douglas.[10][11][12] The twoF-16XLs were returned to the Air Force and placed in storage atEdwards Air Force Base.[13] Had General Dynamics won the competition, theF-16XL would have gone into production as theF-16E/F (E for single seat, F for two seats).[14]
The wing and rear horizontal control surfaces of the baseF-16A were replaced with a cranked-arrow delta wing 115% larger than the original wing.[15] Extensive use ofgraphite-bismaleimide composites allowed the savings of 595 pounds (270 kg) of weight,[16] but theF-16XL-1 andXL-2 were 4,100 pounds (1,900 kg) and 5,600 pounds (2,500 kg) heavier respectively than the originalF-16A.[17][note 5]
Less noticeable is that the fuselage was lengthened by 56 inches (140 cm) by the addition of two sections at the joints of the main fuselage sub-assemblies.[15] With the new wing design, the tail section had to be canted up 3.16°,[18] and the ventral fins removed, to prevent them from striking the pavement during takeoff and landing.[19] TheF-16XL-2 also received a larger inlet which would go on to be included in laterF-16 variants.[20]
These changes resulted in a 25% improvement inlift-to-drag ratio in supersonic flight[21] while remaining comparable in subsonic flight,[22] and a plane that reportedly handled smoothly at high speeds and low altitudes.[23] The enlargements increased internal fuel capacity by 4,350 pounds (1,970 kg), or about 65%.[15][note 6] TheF-16XL could carry twice the ordnance of theF-16A and deliver it 50% farther.[26] The enlarged wing and strengthened hardpoints allowed for a highly configurable payload:[27]
In 1988, the two aircraft were turned over to NASAAmes-Dryden Flight Research Facility for supersoniclaminar flow research for theHigh Speed Civil Transport (HSCT) program.[28] The F-16XL was considered ideal for these tests because of its cranked-arrow wing and high-speed, high-altitude capabilities.[29] The tests were carried out by a NASA and industry team[note 10] and were intended to achieve laminar flow over the wings, validatecomputational fluid dynamics (CFD) design methodology, and test active suction systems.[30] These tests involved the installation of either passive or active suction aerodynamic gloves. The active suction glove was intended to suck awayturbulent airflow over the wings during supersonic flight, restoring laminar flow and reducingdrag.[31][32][33] The NASALangley Research Center developed and coordinatedF-16XL experiments.[34]
F-16XL-1 was fitted with an active suction glove encasing the left wing.[35] Designed and built byNorth American Aviation, it had laser-cut holes that were nominally 0.0025 inches (0.064 mm) diameter at a uniform 2,500 per square inch (390/cm2) spacing.[35] The suction was provided by aConvair 880 air-conditioning turbocompressor where the 20mm cannon's ammunition had been.[31][35] The glove covered over 5 square feet (0.46 m2) of the wing. Overall,F-16XL-1 completed 31 test flights for these tests from May 1990 to September 1992.[32] Afterwards, it was used to test takeoff performance, engine noise, and sonic boom phenomena.[36]
F-16XL-2 had its engine replaced with the more powerfulGeneral Electric F110-129.[12][37] It achieved limitedsupercruise, a design goal of theF-16XL that was never attained in ETF testing, when it reachedMach 1.1 at 20,000 feet (6,100 m) on full military power.[38] It was mounted with a passive glove on the right wing and an active suction glove on the left wing.[32] The passive glove was fitted with instruments to measure the flow characteristics over the wing.[39] The active suction glove was designed and fabricated by Boeing; it was made of titanium and had over 12 million laser-cut holes, each 0.0025 inches (0.064 mm) in diameter, spaced 0.010 to 0.055 inches (0.025 to 0.140 cm) apart.[40][31][41] Suction was provided by a cabin-air pressurization turbocompressor from aBoeing 707, installed where the 20mm ammunition drum had been, which exhausted above the right wing.[42][32][33] Overall,F-16XL-2 performed 45 test flights from October 1995 to November 1996.[43][31]
While "significant progress" was made towards achieving laminar flow at supersonic speeds, neither aircraft achieved the requisite laminar flow characteristics at intended speeds and altitudes.[44][45][46] Nonetheless, NASA officials considered the test program to have been successful.[32] NASA briefly investigated using aTupolev Tu-144 which would more closely resemble the high-speed civil transport aircraft to continue supersonic laminar flow research, but did not pursue the idea due to a limited budget.[47]
At the conclusion of their test programs in 1999, bothF-16XLs were placed into storage at NASA Dryden.[12] In 2007, Boeing and NASA studied the feasibility of returningF-16XL-1 to flight status and upgrading it with many of the improvements found in the USAF'sF-16 Block 40 in order to further test sonic boom mitigation technology.[48]F-16XL-1 was taxi tested at Dryden and given systems checks.[48] However, bothF-16XLs were retired in 2009 and stored at Edwards AFB.[49]
Data from Darling,[51] F-16.net,[52] Piccirillo[53]
General characteristics
Performance
Armament
Related development
Aircraft of comparable role, configuration, and era
Related lists
