overscan said:
The only source appears to be this article in the Journal Of Aircraft:
http://pdf.aiaa.org/jaPreview/JA/1985/PVJAPRE45221.pdf
Design Comparisons
With these inherent advantages of an oblique wing design
established, a direct comparison of the two designs on a common
mission can be made. The mission chosen will emphasize
the efficient loiter capabilities of the oblique wing design combined
with a supersonic dash to a combat condition. We chose
a hypothetical fleet air defense mission (Fig. 7), in which the
aircraft takes off from a carrier, cruises at the most efficient
condition to a station 300 n. mi. out, and loiters until a dash is
required to a combat location 100 n. mi. away. Following this,
the aircraft returns at best cruise altitude and velocity to the
carrier. Loiter time is 3 h for the baseline mission. The ground
rules chosen for this study, in addition to the common
mission, were that design criteria would be the same and common
technologies would be utilized for both aircraft. The only
difference in technology between the two designs (Table 2) is
the oblique wing itself. Both aircraft utilized advanced propulsion
systems optimized using a parametric deck to satisfy the
design requirements. Both aircraft carried the same weapons
and avionics suites, including 10 air-to-air missiles, and utilized
advanced materials wherever required, including composite
wings. The fuselage design (Fig. 8) was common to both
aircraft because of the avionics systems and the large number
of missiles required. As shown in Fig. 8, the missiles occupy
most of the available space on the underbody of the twinengine
design.
The two wing planforms are compared in Fig. 9. Maximum
leading-edge sweep was set at 65 deg, and an aspect ratio of
10.2 was chosen to maximize the loiter efficiency. These were
chosen as a starting point because NASA obtained a large
body of wind tunnel data on this planform in the early
1970s.5'6 Further studies confirmed that the aspect ratio could
be higher for mission efficiency but is limited by maximum
span considerations for carrier operations. The difference in
effective aspect ratio in the swept condition between the symmetric
and oblique wing designs is shown in Fig. 9. The symmetric
design has a minimum aspect ratio for supersonic flight
of 2.74; the oblique wing, 1.82. Volume distributions are compared
in Fig. 10 for the final-sized aircraft. The oblique wing
design exhibits much less volume at the center of the aircraft.
There is an overall increase in total volume on the symmetric
design due to the larger wing resulting from the sizing, the
overwing fairing required to close out the pivots, the glove required
for aerodynamic trim, and the larger engines required
because of the less efficient design. The result of this volume
distribution is illustrated in Fig. 11. The area of the wing on
the sized symmetric aft-sweep design is 649 ft2 compared to
583 ft2 on the oblique wing. Wave drag is approximately 26%
lower at the supersonic dash Mach number of 1.5. Taking all
the drag factors into consideration at Mach 1.6, there is a
substantial decrease at both 35,000 and 50,000 ft for the oblique
wing (Fig. 12). This is approximately an 11-21% decrease
in drag and results from all three components: friction drag
(because the aircraft itself is smaller and more efficient), wave
drag, and trimmed drag due to lift (because of the minimized
effects of aerodynamic center shift).
In carrier applications, takeoff gross weight can be severely
limited. Therefore, a valuable comparison is the useful load at
a constant takeoff gross weight representative of maximum
good design practice. Illustrated in Fig. 13 is a buildup by
component of the two designs at a constant gross weight. Once
again, it is apparent that the oblique wing design weights are
superior and that the total for the structure group is 14%
lower than that for the symmetric design. Because of the
greater efficiency due to lower drags, the propulsion group is
approximately 10% lighter than the symmetric design; and the
total weight empty for the oblique wing design is 11 % lower
than that of the conventional design, accounting for subsystems
and other miscellaneous weights that are approximately
the same for both designs. This decrease of 11% in
weight empty results in an increased useful load of 16% for
the oblique wing design, where useful load includes fuel and
weapons as well as the crew. The result of these weight and
performance advantages is shown nondimensionally in Fig.
14. The 100% design mission is the 400-mile radius mission
shown in Fig. 7. In scaling the radius, the cruise legs and the
supersonic dash are scaled by the same percentage. The aircraft
takeoff gross weight ratio compares to the design weight
used in Fig. 13. The advantage of oblique wings can be used in
either of two ways: 1) for a constant mission there can be a
17% gross weight reduction for the oblique wing design, or 2)
if maximum design takeoff gross weight is limited because of
carrier compatibility considerations, a 29% greater mission
radius can be achieved with the oblique wing design.
For a more severe (longer) mission, the variable-sweep
design becomes heavier more rapidly than the oblique wing
design, so that these differences are accentuated. Because of
such constraints in the naval application as landing speeds and
launch weight limits, the point is rapidly approached where a
more stringent requirement cannot be satisfied with a variable
aft-sweep design. A greater operating radius would require the
introduction of major new technologies into the aft-sweep
design before those same technologies would be needed for an
oblique wing.