This study examines the role of different design constraints applied to the multidisciplinary design optimization of a strut-braced wing (SBW) transonic passenger aircraft. Four different configurations are examined: the reference cantilever wing aircraft, a fuselage mounted engine SBW, a wing mounted engine SBW, and a wingtip mounted engine SBW. The mission profile was for 325-passengers, Mach 0.85 and a 7500 nautical mile range with a 500 nautical mile reserve.
The sensitivity of the designs with respect to the individual design constraints was calculated using Lagrange multipliers. A design space visualization technique was also used to gain insight into the role of the different constraints in determining the design configuration. This design visualization technique uses a classic ‘thumbprint’ plot to represent the design space.
As expected, all the designs are very sensitive to the range constraint. The designs are also sensitive to the field performance constraints. The design visualization revealed that the second segment climb gradient constraint was a limiting factor in all the designs. It was also found that the wing mounted engines SBW and tip mounted engines SBW designs are more constrained than the cantilever wing optimum and fuselage mounted engines SBW designs.