General Dynamics began the SCAMP effort by evaluating the performance potential of cranked-arrow wings. These derived from concepts that had been evaluated earlier during the NASA Langley Supersonic Cruise Aerodynamics Research (SCAR) effort. Analytical and experimental data from the SCAR work was considered for potential application to a modified F-16 to provide supersonic cruise capability as well as improvements in the areas of subsonic performance, maneuverability, and aircraft handling qualities. GD proposed to, with NASA assistance, conduct wing optimization studies that would con-sider various aspects of wing design that could be important to improving F-16 performance. These included determination of the effects of noncranked and cranked leading edges, assessments of various leading-edge sweep combi-nations, variations in wing
aspect ratio and wing area, and determination of the resultant internal wing fuel volumes. Issues associated with adequate aircraft con-trol, including methods to provide effective pitch and roll control on very highly swept wings, were to be evaluated. An important concern was dealing with rapidly varying trim require-ments resulting from the aft movement of the center of lift as speed increased from subsonic to supersonic.
By late 1977, the com-bined NASA-GD effort led to a configuration based on
This SCAMP concept featured an all-moving vertical tail and full-span leading-edge flaps on both the inboard and outboard wing segments of its highly swept cranked-arrow wing. (Lockheed Martin)
an F-16 stretched fuselage mated with a cranked-arrow wing. Two 20-inch plugs, one aft of the cockpit and one just forward of the lower vertical fin, increased fuselage length by 40 inches. The new extended fuselage was 51.8 feet long. The highly swept cranked-arrow wing had a span of 30 feet 10 inches and an aspect ratio of 1.38. Total wing area was 600 square feet, double the area of the standard F-16 wing. Leading-edge sweep angles were 76.6 degrees (inboard) and 66.6 degrees (outboard). To provide good maneuverability and handling qualities, full-span leading-edge flaps, capable of being deflected up to 60 degrees, were mounted on both inboard and outboard wing segments.
Trailing-edge flaps were mounted on the aft inboard wing segments with addi-tional flap power provided by outboard elevons (essentially, combination eleva-tors and ailerons). These served as elevaeleva-tors for pitch control and ailerons for roll control. Other characteristics of this design concept were an all-moving vertical tail and a variable-geometry single-ramp engine inlet. This would be used to control the airflow entering the engine out to speeds of Mach 2.2 (the standard F-16 used a fixed-geometry inlet). This design concept was also intended to be used to evaluate additional performance enhancements that might be possible by incorporating a two-dimensional thrust-vectoring nozzle.
A modified version of this arrow-wing concept was tested in the NASA Langley Unitary Plan Wind Tunnel. This 1/15-scale model had leading-edge wing-sweep angles of 71 degrees on the inboard wing segments and 57 degrees on the outboard segments.
By 1978, the NASA-GD collaboration had resulted in a refined cranked-arrow-wing configuration with the fuselage now lengthened by 52 inches.
Leading-edge sweep angles were revised to 70 degrees on the inboard section and 50 degrees on the outboard (cranked) section of the wing. The wing crank was relocated from
its earlier 63 percent out-board position (measured from the aircraft center-line) to 70 percent out-board. The trailing edge of the wing now featured a uniform sweep angle of –8.6 degrees. This was somewhat reduced from that of the earlier SCAR-derived arrow-wing plan-form discussed above.
This new wing proved to
be a better choice than Test model of an interim SCAMP concept mounted in the NASA Langley Unitary Plan Wind Tunnel in 1978. (NASA)
the earlier arrow-wing configuration. The smaller aft movement of its mean aerodynamic center (MAC) as the Mach number changed from subsonic to supersonic minimized flight control issues.13 This aft shift in mean aerodynamic center was reduced to a much more manageable 10.5 percent. This compared to a rearward shift in MAC of as much as 26 percent during transition from subsonic to supersonic flight for the standard F-16. This was due largely to the reduced leading-edge sweep angle on the cranked outboard portions of the wing. The revised wing also provided major improvements in low-speed roll control as well as significant supersonic rolling capabilities. GD claimed this newer wing design would provide a 9-g instantaneous maneuvering capability at Mach 2.0 at an altitude of 50,000 feet using the maximum available up-elevon deflection angle of 20 degrees.14
As initially conceived,
vertical tail (that would have provided relaxed static directional stability) as well as all-movable wingtips for both pitch trim and roll control.15
The existing horizontal tail surfaces from the production F-16A were stud-ied for possible use as both an all-movable tailfin and as all-moveable wingtips.
The all-movable vertical tailfin and all-movable wingtips would be dropped from the final SCAMP–F-16XL configuration. This reportedly resulted after negative feedback during discussions between GD engineering and Air Force engineers from the Aeronautical Systems Division who perceived these items as creating unnecessarily high technical risk.16 This negative position was rein-forced by subsequent NASA wind tunnel testing in the 30- by 60-foot Full-Scale Tunnel with a matrix model fitted with these features. This revealed that the all-movable wingtip control surfaces did not provide adequate aircraft Although bearing a general resemblance, this SCAMP design concept, circa September 1977, was still somewhat removed from the eventual F-16XL configuration in a number of significant respects. (Lockheed Martin)
control during low-speed, high-angle-of-attack maneuvering. Another impor-tant negative consideration was that all-movable wingtips prevented the use of wingtip-mounted AIM-9 Sidewinder infrared guided air-to-air missiles, as used on the standard F-16. The all-moving vertical fin was eliminated due to reduced effectiveness at higher angles of attack due to its low height as well as the risk of stall at high deflections in sideslip conditions.
Key members of the General Dynamics SCAMP design team at this time (1977) were Harry J. Hillaker, program manager; Roger Marquardt, chief aerodynamicist; Kenneth H. Barnes, stability and control lead; and James A. Gordon, SCAMP lead engineer. Kenny Barnes was a very key player on the GD SCAMP team, effectively leading efforts focused on modifying the F-16 fly-by-wire flight control system to adapt to the requirements of the radically different SCAMP–F-16XL configuration. These cooperative efforts would eventually provide effective flight control at much higher angles of attack than were ever possible with the basic F-16 configuration. During the SCAMP cooperative effort, Andrew Lewis and the General Dynamics aerodynamics group worked closely and effectively with NASA Langley researchers in evolv-ing major aspects of the SCAMP aerodynamic configuration and its associated wing planform. These included selection of the eventual airfoil, the wing twist, and the highly sophisticated camber that reduced transonic and supersonic Key members of the GD SCAMP development team with a matrix model circa late 1977. From the left: Harry J. Hillaker, program manager; Andrew Lewis, aerodynamics; Kenny Barnes, stabil-ity and control lead; and Jim Gordon, lead program engineer. (Lockheed Martin)
drag while providing enhanced lift. The final wing camber and twist combination used on the F-16XL aircraft prototypes showed superior performance compared to the standard F-16.
Drag was reduced during 1-g flight and in maneuvering flight at both high subsonic (Mach 0.9) and supersonic (Mach 1.6) flight conditions.17