The baseline mission is 250 passengers over a 9000 km range. For the reference subsonic transport with a cruise Mach number of 0 8 Table 5 show s a cruise lift-to drag ratio of about 18. the same can be said for the specific fuel consumption of 0.61, The wing has a typical dimensions for a conventional transport. Also the weight fractions arc very much like those of todays aircraft
A reference Mach number of 1.6 is chosen so the design would to easily meet future ozone layer depletion regulations and sonic boom corridor limitations. Choosing a higher Mach number would also make range, payload and Mach number variations difficult due to the high number of active constraints. At Mach 1.6 the OFW is clearly superior to the SWB. Interestingly enough, the enuse lift-to-drag ratio of the OFW is close to that of the SWB. The optimizer chose to improve the lift-to-drag of the SWB up to the level of the OFW at the expense of the structure The other explanation is that the size of the OFW could be reduced by increasing the thickncss-to-chord ratio and that this outweighed the decrease in lift-to-drag The absolute drag the OFW’ is still 16 less than that of the SWB! The structure of the OFW is also 14 lighter than for the SWB. In the case of the OFW. the lift-to-drag ratios of around 10.5 during cruise were achieved without a large structural penalty because of span loading and the fact that the OFW wing is much thicker. The OFW has similar TOC’s as the subsonic transport. Though both configurations arc not constrained by sonic boom or ozone layer depletion, they are both constrained by takeoff and sideline noise. Because of its better takeofT lift-to-drag ratio and lower w ing loading the OFW’ cuts back the engine at takeoff to meet the noise requirement The SW’B uses most of the suppression that is allowed. The price for suppression seems to be less than the price for the extra installation drag of a higher bypass ratio. The OFW mean sonic boom overpressure is only half of that of the SW’B The OW’B is not discussed as a reference aircraft because of its poor performance.