SAWE Report - Cal Poly San Luis Obispo

5.2 Wing Planform
The next aspect of the wing that was considered was the leading and trailing edge sweep angles.
Because any edges on an aircraft reflect radar energy, the sweep angles of the edges of the wing
were chosen to minimize radar energy reflected back to the source, especially in the frontal
aspect of the aircraft where a specific RCS requirement is given by the RFP. To avoid reflecting
radar toward the front of the aircraft, the leading and trailing edges of the wing had to be highly
swept. In addition, the sweep angles could not be approximately 45º because a corner reflector
would be created. These requirements led to a diamond shaped wing planform with leading and
trailing edge wing sweeps of approximately 40º. Two initial designs were considered one having
a 40º swept leading edge and a 30º forward swept trailing edge and the other having matched
35.3º leading edge and trailing edge sweeps. A trade study was performed to select between
these two wing configurations by studying the effect of the two configurations on RCS and
aerodynamics. Figure 5.2 shows a comparison of radial sweeps of both configurations using
RadBase2. The return from the 40º and 35.3º leading edge sweeps can be clearly seen in the
plot. The leading edge spike on the matched leading and trailing edge configuration is
approximately 15 dB lower than the other configuration; however it is 5º closer to the frontal
aspect of the aircraft. The aerodynamic study of the two wing configurations indicated that
approximately 1,000 lb (454 kg) of additional fuel would be required due to the additional wave
drag of the lower leading edge sweep angle. Because of the aerodynamic benefits and because
the RFP only gives frontal aspect RCS requirements, the 40º leading edge and 30º trailing edge
configuration was chosen.
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