General Dynamics F-16XL
Template:Short description Template:Good article Template:Infobox aircraft
The General Dynamics F-16XL is a derivative of the F-16 Fighting Falcon with a cranked-arrow delta wing. It entered the United States Air Force's (USAF) Enhanced Tactical Fighter (ETF) competition in 1981 but lost to the F-15E Strike Eagle. The two prototypes were shelved until being turned over to NASA for additional aeronautical research in 1988. Both aircraft were fully retired in 2009 and stored at Edwards Air Force Base; one of the two aircraft has since been placed on display.
Development
SCAMP
Shortly after winning the lightweight fighter program, General Dynamics Fort Worth began investigating possible F-16 derivatives with the goal of enhancing both air-to-air and air-to-ground mission capabilities while retaining parts commonality with the F-16A.[1] Under the leadership of Harry Hillaker (designer of the original F-16), the Supersonic Cruise and Maneuver Prototype (SCAMP) project was started. Several wing designs were considered, including one using a forward-swept wing, but the large "cranked-arrow" wing (similar to that of the Saab 35 Draken)Template:NoteTag was pursued due to its much more efficient lift-to-drag ratio at supersonic speeds.Template:Sfn
The company worked closely with NASA's Langley Research CenterTemplate:Sfn and invested significant R&D funds for wind tunnel testing. Over several years the design was refined which led to the final F-16XL design by late 1980.Template:Sfn
Enhanced Tactical Fighter competition
In 1980, the USAF signed on as a partner,Template:Sfn providing the fuselages of the thirdTemplate:NoteTag and fifthTemplate:NoteTag production F-16s for conversion. These two fuselages became the only examples of the F-16XL.[2]
In March 1981, the USAF announced the Enhanced Tactical Fighter (ETF) program to procure a replacement for the F-111 Aardvark.Template:Sfn The concept envisioned an aircraft capable of launching deep interdiction missions without requiring additional support in the form of fighter escorts or jamming support. General Dynamics submitted the F-16XL, while McDonnell Douglas submitted a variant of the F-15 Eagle. Though the two aircraft were competing for the same role, they had fairly different design approaches. The F-15E required very few alterations from its base F-15B or D, while the F-16XL had major structural and aerodynamic differences from the original F-16.[3] As such, the F-16XL would have required much more effort, time, and money to put into full production.[4] Additionally, the F-15E had two engines, which gave it a much higher maximum takeoff weight and redundancy in the case of engine failure.[4]Template:NoteTag
In February 1984, the USAF awarded the ETF contract to McDonnell Douglas.Template:Sfn[5][6] The two F-16XLs were returned to the Air Force and placed in storage at Edwards Air Force Base.Template:Sfn Had General Dynamics won the competition, the F-16XL would have gone into production as the F-16E/F (E for single seat, F for two seats).Template:Sfn
Design
The wing and rear horizontal control surfaces of the base F-16A were replaced with a cranked-arrow delta wing 115% larger than the original wing.[7] Extensive use of graphite-bismaleimide composites allowed the savings of Template:Convert of weight,Template:Sfn but the F-16XL-1 and XL-2 were Template:Convert and Template:Convert heavier respectively than the original F-16A.[8]Template:NoteTag
Less noticeable is that the fuselage was lengthened by Template:Convert by the addition of two sections at the joints of the main fuselage sub-assemblies.[7] With the new wing design, the tail section had to be canted up 3.16°,Template:Sfn and the ventral fins removed, to prevent them from striking the pavement during takeoff and landing.Template:Sfn The F-16XL-2 also received a larger inlet which would go on to be included in later F-16 variants.Template:Sfn
These changes resulted in a 25% improvement in lift-to-drag ratio in supersonic flight[9] while remaining comparable in subsonic flight,[10] and a plane that reportedly handled smoothly at high speeds and low altitudes.[11] The enlargements increased internal fuel capacity by Template:Convert, or about 65%.[7]Template:NoteTag The F-16XL could carry twice the ordnance of the F-16A and deliver it 50% farther.Template:Sfn The enlarged wing and strengthened hardpoints allowed for a highly configurable payload:[12]
- 16× Template:Convert wing hardpoints
- 5× Template:Convert wing hardpoints
- 4× semi-recessed AIM-120 AMRAAM stations under fuselageTemplate:NoteTag
- 2× wingtip stations
- 1× centerline stationTemplate:NoteTag
- 2× wing "heavy/wet" stationsTemplate:NoteTag
- 2× chin LANTIRN stations
NASA testing
In 1988, the two aircraft were turned over to NASA Ames-Dryden Flight Research Facility for supersonic laminar flow research for the High Speed Civil Transport (HSCT) program.Template:Sfn The F-16XL was considered ideal for these tests because of its cranked-arrow wing and high-speed, high-altitude capabilities.Template:Sfn The tests were carried out by a NASA and industry teamTemplate:NoteTag and were intended to achieve laminar flow over the wings, validate computational fluid dynamics (CFD) design methodology, and test active suction systems.Template:Sfn These tests involved the installation of either passive or active suction aerodynamic gloves. The active suction glove was intended to suck away turbulent airflow over the wings during supersonic flight, restoring laminar flow and reducing drag.[13][14]Template:Sfn The NASA Langley Research Center developed and coordinated F-16XL experiments.[15]
F-16XL-1 was fitted with an active suction glove encasing the left wing.Template:Sfn Designed and built by North American Aviation, it had laser-cut holes that were nominally Template:Convert diameter at a uniform Template:Convert spacing.Template:Sfn The suction was provided by a Convair 880 air-conditioning turbocompressor where the 20mm cannon's ammunition had been.[13]Template:Sfn The glove covered over Template:Convert of the wing. Overall, F-16XL-1 completed 31 test flights for these tests from May 1990 to September 1992.[14] Afterwards, it was used to test takeoff performance, engine noise, and sonic boom phenomena.Template:Sfn
F-16XL-2 had its engine replaced with the more powerful General Electric F110-129.[6]Template:Sfn It achieved limited supercruise, a design goal of the F-16XL that was never attained in ETF testing, when it reached Mach 1.1 at Template:Convert on full military power.[16] It was mounted with a passive glove on the right wing and an active suction glove on the left wing.[14] The passive glove was fitted with instruments to measure the flow characteristics over the wing.Template:Sfn The active suction glove was designed and fabricated by Boeing; it was made of titanium and had over 12 million laser-cut holes, each Template:Convert in diameter, spaced Template:Convert apart.Template:Sfn[13]Template:Sfn Suction was provided by a cabin-air pressurization turbocompressor from a Boeing 707, installed where the 20mm ammunition drum had been, which exhausted above the right wing.Template:Sfn[14]Template:Sfn Overall, F-16XL-2 performed 45 test flights from October 1995 to November 1996.Template:Sfn[13]
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.Template:SfnTemplate:SfnTemplate:Sfn Nonetheless, NASA officials considered the test program to have been successful.[14] NASA briefly investigated using a Tupolev 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.Template:Sfn
At the conclusion of their test programs in 1999, both F-16XLs were placed into storage at NASA Dryden.[6] In 2007, Boeing and NASA studied the feasibility of returning F-16XL-1 to flight status and upgrading it with many of the improvements found in the USAF's F-16 Block 40 in order to further test sonic boom mitigation technology.[17] F-16XL-1 was taxi tested at Dryden and given systems checks.[17] However, both F-16XLs were retired in 2009 and stored at Edwards AFB.[18]
F-16XL aircraft on display
- 75-0747 – Museum Air Park, Air Force Flight Center Museum, Edwards AFB, California[19]
- 75-0749 – in storage at the Air Force Flight Center Museum, Edwards AFB, California[19]
Specifications (F-16XL number 2)
See also
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Related development
Aircraft of comparable role, configuration, and era
Related lists
References
Citations
Notes
Bibliography
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External links
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Template:Convair aircraft Template:USAF fighters Template:F-16 Fighting Falcon variants
- ↑ Script error: No such module "Footnotes".: "These were oriented to extending range and payload, expanding basic missions, and developing advanced versions or derivative configurations of the aircraft. Importantly, these were intended to enhance both air-to-air and air-to-ground capabilities while retaining the maximum possible commonality with the basic F-16 design."
- ↑ Script error: No such module "Footnotes".
- ↑ Script error: No such module "Footnotes".: "...the F-16E required major changes to the basic F-16 airframe. ... Changes required for the F-15E were not considered by the GAO to be as great as those needed for the F-16E, and mainly consisted of structural modifications to the wings as well as a strengthened landing gear."
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- ↑ Script error: No such module "Footnotes".: "As speed approached Mach 1.0, the F-16XL's comparative cruise efficiency improved, and at Mach 1.4, the F-16XL had a 25-percent-higher lift-to-drag ratio than that of the F-16C."
- ↑ Script error: No such module "Footnotes".: "...the L/D ratios of the cranked-arrow, canard-delta, and baseline F-16 were essentially equal at subsonic speeds..."
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- ↑ Script error: No such module "Footnotes".: "F-16XL-2 was also able to demonstrate limited supercruise performance by maintaining Mach 1.1 at an altitude of 20,000 feet in full military power without resorting to the use of afterburner."
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