SAWE Report - Cal Poly San Luis Obispo

wing loading and thrust to weight ratio may be converted to wing area and thrust required. Once
this information is found the designer may start the configuration layout and choose a power
plant. In order to obtain the smallest aircraft, the design point should be at the highest wing
loading and lowest thrust to weight as possible on the constraint plot. As the design point moves
to the left on the constraint plot, the wing area increases. This yields a larger airframe. Large
airframes are expensive and cost more to maintain.
As the design point moves up on the constraint plot, the engines get bigger and heavier. This is
not desired as the aircraft will burn more fuel and have to fly at a higher lift coefficient for a
given Mach number. This would cause the fuel burn for a given mission and thus increase
operating costs. If the design point deviates from the lower right, an explanation is required.
The initial design point was chosen in the center of the design domain in order to allow for
aircraft growth. The design point was chosen away from constraint lines to make the aircraft
design performance less sensitive to changes in weight.
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0.9
0.8
Current Design
Point
Takeoff
Landing
ψ
Range
Thrust to Weight Ratio
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Initial Design
Point
Specific
Excess
Power
Specific
Excess
Power
40
60
80
100 120 140
Wing Loading, (psf)
160
180
200
Figure 2.2 - Constraint Plot
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