Válvulas de expansión

In articles in military journals, in professional society papers and presentations, and during interviews with the aviation press, General Dynamics strongly advocated the improved capabilities incorporated into the F-16XL. In particu-lar, they emphasized that the cranked-arrow design chosen for their aircraft would lead to significant improvements in range and payload compared to the standard F-16 while also addressing other aspects of fighter mission success.

The cranked-arrow wing was said to retain the advantages of the conventional delta wing for high-speed flight while overcoming its disadvantages. These advantages partially resulted from the cranked-arrow wing’s less highly swept outboard wing panels, which provided excellent low-speed characteristics while minimizing the trim drag penalties of a more conventional tailless delta design.

Although the wing area of the F-16XL was more than double that of the standard F-16, GD showed that the overall drag on the aircraft was actually reduced. Despite the fact that the F-16XL’s skin friction drag was larger than the standard F-16 (due to its much greater surface area), the other compo-nents of total drag (supersonic wave drag, interference drag, and trim drag) were actually lower. This resulted from the F-16XLs streamlined aerodynamic configuration and the geometrical arrangement and semiconformal carriage of its external stores. Thus, while the larger F-16XL in a clean configuration had an overall drag that was slightly lower than that of a standard F-16 at high subsonic speeds, its drag was 40 percent lower when comparing each type carrying bombs and missiles. Although, because of weight gain (as previously discussed), the thrust-to-weight ratio of the F-16XL was lower than that of the F-16, its excess thrust was actually greater due to the F-16XL’s lower total drag, especially at higher subsonic and supersonic speeds.²⁴

But in actuality, this only held true for 1-g (straight and level) flight, and it partially accounted for the improved range and payload capabilities of the F-16XL. For example, on an air-to-surface mission, the F-16XL could carry twice the payload of the F-16 up to 40 percent farther without having to carry eternal tanks. With equal payloads and carrying external tanks, the XL mission radius was nearly double that of the F-16. A fully loaded F-16XL had a speed

advantage of up to 80 knots calibrated airspeed (KCAS) in military power at sea level over the F-16 with a similar payload.²⁵ However, during high-AoA sustained subsonic maneuvering, the F-16XL (like delta configurations gener-ally) had a much higher induced drag penalty. This was a natural result of the aerodynamics of its very-low-aspect-ratio cranked-arrow wing. During the latter Air Force flight-test program, this higher induced drag would prove to cause a rapid loss of excess energy. This, in turn, was manifested by a rapid loss of airspeed and altitude during sustained subsonic high-g turns as compared to the standard F-16. In the “real world” of fighter-versus-fighter combat, this constituted a major performance deficit, given potential opponents such as the powerful and highly agile Soviet Mikoyan MiG-29 Fulcrum and Sukhoi Su-27 Flanker.²⁶

In their briefings and marketing literature, General Dynamics emphasized that the F-16XL had two additional advantages that would contribute to increased overall effectiveness and survivability in combat situations. These were its improved instantaneous maneuvering capability and its reduced radar cross section, as compared to the standard F-16.

In an attempt to offset the reduced performance capabilities of the F-16XL during sustained hard-maneuvering combat, GD highlighted its excellent instantaneous turning performance. This, they claimed, would enable an F-16XL pilot to quickly change direction and get his missiles off before an enemy was able to react and adjust his tactics. In this regard, the F-16XL with its much lower wing loading did have a distinct instantaneous turning advantage, for it was able to reach 5 g’s in less than 1 second and 9 g’s in about 2 seconds.

Both times were less than half those of the standard F-16A. Also, then-recent advances in infrared guided missile target seekers provided the capability to engage enemy aircraft from all aspect angles, rather than just the aft quartering region where infrared energy was strongest. This reduced the dependence on sus-tained high-g maneuvering to

gain an effective firing posi-tion on an enemy aircraft in fighter-versus-fighter combat.

This was certainly true for the AIM-9L version of the classic Sidewinder infrared-guided missile then being carried on USAF F-15s and F-16s.

The United States had rap-idly supplied the AIM-9L to the British during the

spring 1982 Falkland Islands The F-16XL-2 during radar signature testing conducted by General Dynamics. (Lockheed Martin)

conflict with Argentina. The all-aspect target engagement capabilities of the AIM-9L were widely acknowledged as a major factor in Britain successfully regaining control over the Falklands.²⁷

The F-16XL’s radar signature (usually termed its RCS) was somewhat lower than that of the standard F-16 when measured head on without air-to-ground ordnance, drop tanks, and Low Altitude Navigation Targeting Infra-Red Night (LANTIRN) navigation and targeting pods. RCS was reported as being 50 percent lower than that of the standard F-16 during testing conducted by GD.²⁸ Since the detection range of an enemy radar varies with the forth root of its target’s radar cross section, halving the radar signature of the target air-craft reduces its detectability (detection range) to enemy radars by about 16 percent.²⁹ However, frontal signature reduction would have been negligible when the aircraft was loaded with the external stores mentioned above for the air-to-ground mission.

Endnotes

1. D.R. Kent, vice president and program director, F-16XL program, General Dynamics Fort Worth Division, letter to Brig. Gen. G.L.

Monahan, ASD, Aeronautical Systems Division, January 7, 1981.

2. Under U.S. Federal Acquisition Regulations (FARs), IRAD efforts must fall within one of the following four categories: Basic Research, Applied Research, Development, or Systems/Concept Formulation Studies. Allowable IRAD costs are limited to those projects deter-mined to be of potential interest to the DoD based on their contri-butions to the criteria listed below.

• Enable superior performance of future U.S. weapon system and components.

• Reduce acquisition costs and life-cycle costs of military systems.

• Strengthen the defense industrial and technology base of the United States.

• Enhance the industrial competitiveness of the United States.

• Promote the development of technologies identified as critical.

• Increase the development and promotion of efficient and effective applications of dual-use technologies.

• Provide efficient and effective technologies for achieving environ-mental benefits.

In various ways, the F-16XL initiative clearly met all of these criteria.

3. Harry J. Hillaker, “F-16XL Flight Test Program Overview”;

Aronstein and Piccirillo, “The Lightweight Fighter Program: A Successful Approach to Fighter Technology Transition.”

4. K.R. Hinman, “F-16E Point Paper,” General Dynamics Corporation, July 27, 1981.

5. Kent, letter.

6. The Program Objective Memorandum is the primary document used by the military services within the Department of Defense to submit their programming proposals. The POM includes an analysis of missions, objectives, alternative methods to accomplish objec-tives, and allocation of resources. It presents planned activities and the personnel and budget obligation authority required over a 5-year period to build, operate, and maintain the proposed program.

7. Harry J. Hillaker, “F-16XL Presentation to the Lone Star Aero Club,” Arlington, TX, September 3, 1998.

8. Wetherall, “F-16XL First Flight Anniversary Celebration.”

9. Lt. Gen. Lawrence A. Skantze, USAF, Headquarters Aeronautical Systems Division (AFSC), letter to Richard E. Adams, vice president

and general manager, General Dynamics Corporation, October 15, 1980; Hinman, “F-16E Point Paper.”

10. Skantze, “Letter to Richard E. Adams.”

11. Mark J. Bulban, “Mach 2.2 F-16 Development Underway,” Aviation Week & Space Technology (July 21,1980): pp. 20–22.

12. David P. Garino, “General Dynamics to Spend $53 Million on Two Versions of its F16 Fighter Plane,” The Wall Street Journal, December 8, 1980.

13. Author not identified, “General Dynamics Developing F-16XL Hardware,” Aviation Week & Space Technology (April 6, 1981): 57.

14. F. Clifton Berry, Jr., “The Revolutionary Evolution of the F-16XL,”

Air Force Magazine 66, no. 11 (November 1983); Wetherall interview.

15. Both of these technology areas would later be investigated by NASA using suitably modified F-16XL subscale wind tunnel models, but they never became part of the full-scale flight-test program with the aircraft.

16. H.J. Hillaker, vice president and deputy program manager, F-16XL, memo to D.R. Kent, December 15, 1980.

17. The initial release of F-16XL engineering drawings occurred on December 18, 1980, only 17 days after program go-ahead. These drawings were released quickly because they were relatively straight-forward changes to the existing engine installation in the F-16.

Robert Wetherall, correspondence with author, July 14, 2012.

18. Kent, letter to Monahan.

19. Wetherall, “F-16XL First Flight Anniversary Celebration”; D.R.

Kent, “F-16XL Program Organization,” General Dynamics Fort Worth Division, F-16XL Program Directive Memorandum No.

2, November 25, 1980; C.E. Hart, “F-16XL Fighter Engineering Organization Assignment of Responsibilities,” General Dynamics Fort Worth Division, Project Engineering Memorandum (PEM) No. 19-1.1, November 20, 1980, Revision A, December 30, 1980.

20. C.E. Hart, chief engineer, F-16XL program, “Memo to F-16XL Engineering Personnel: F-16XL Weight Saving,” General Dynamics, Fort Worth Division, F-16XL-ENG-48, April 10, 1981.

21. “A source of some frustration to GD was the fact that “the Air Force would not allow us to use the GE F110 engine in our pro-posal even though the No. 2 XL, the 2-place version, was powered by a F110 engine and provided better performance than the P&W F100 engine.” Robert Wetherall correspondence with the author, December 20, 2012.

22. Wetherall, “F-16XL First Flight Anniversary Celebration.”

23. Ibid.

24. Hillaker,“F-16XL Presentation to the Lone Star Aero Club”;

“General Dynamics F-16XLC/D MULTIROLE FIGHTER”;

General Dynamics Corporation Marketing Brochure, Fort Worth Division (undated, circa 1983).

25. Hillaker, “General Dynamics F-16XLC/D MULTIROLE FIGHTER.”

26. Talty, “F-16XL Demonstrates New Capabilities.”

27. During the relatively brief Falklands conflict, Royal Navy British Aerospace Sea Harrier FRS 1 fighters launched AIM-9L Sidewinder missiles during 23 air-to-air engagements with Argentine aircraft.

The AIM-9L accounted for 19 confirmed kills for an overall success rate of 82 percent. See Jeffrey Ethell and Alfred Price, Air War South Atlantic (New York: Macmillan Publishing Company, 1983).

28. Wetherall, “F-16XL First Flight Anniversary Celebration”; C.A.

Robinson, Jr., “USAF Studies Fighters for Dual-Role, All-Weather Operations,” Aviation Week & Space Technology (January 3, 1983) p. 39.

29. Eugene F. Knott, John F. Schaeffer, and Michael T. Tulley, Radar Cross Section: Its Prediction Measurement and Reduction (Norwood, MA: ARTECH House, Inc., 1985), p. 35.

By the early 1980s, General Dynamics released detailed illustrations and descrip-tions of the F-16XL configuration. They noted that the cranked-arrow-wing design had both aerodynamic and configuration benefits and significant poten-tial for increased combat range. The cranked F-16XL arrow wing had an area that was 115 percent larger than that of the standard F-16A wing. The resulting larger internal wing volume enabled much more fuel to be carried—5,000 pounds as compared to about 1,150 pounds in the standard F-16 wing. The two fuselage plugs resulted in a new fuselage that was 56 inches longer than that of the standard F-16. This enabled the F-16XL to carry over 7,600 pounds of fuel inside its fuselage compared to slightly over 5,800 pounds carried in the standard F-16’s fuselage.¹ Wing camber and twist were optimized to minimize drag during high-speed cruise and level acceleration. Supersonic wave drag was