Variation of Range, Mach number and Payload

Range

Figure 101 shows that this OFW’ is able to achieve ranges of up to 6500 nm (12000 km). Span­loading enables the OFW’ to improve both range and TOC Лк OFW’ has has a similar reduction of TOC with range as the subsonic reference. Лк tnp cost due aircraft ground handling, baggage handling, administration and landing fees arc only w eakly dependent on range. As a consequence the indirect operating costs (IOC) per available scat km reduce with range. This effect is not so clearly visible for the SWB’s. Beyond 6000 km range the direct operating cost per available scat increases fast. And at 9000 km it increases faster than the decrease of the IOC’s. Relative to the subsonic reference the SWB seems to be most attractive for the transatlantic range. Beyond 11000 km us maximum takeoff weight snowballs, even with our aggressive technology assump­tions. The OWB even has problems making it across the pacific.

Mach number

Figure 102 shows the influence of the increase in speed from Mach 0.8 to 2.0 on TOC for the SWB’s and the OFW’s. The dominant influence is the price of wave drag added to super­sonic configurations. At supersonic speeds the increased specific airframe complexity increases the purchase price and therefore the direct operating costs. Over a wide range of Mach numbers the SWB’s and the OFW’s have similar lift-to-drag ratios and similar specific fuel consump­tions. The structural weights arc completely different. Both concepts have their minimum TOC at Mach 1.6. Mach numbers in excess of 2.0 arc probably not possible due to thermal stability problems with conventional fuels for trips in excess of 3 hours. In addition we found that a number of these designs were limited by as many as a dozen constraints at the same lime This is caused by incompatibility of low-speed and high-speed flight. The OWB is worse than the SWB except at very low supersonic speeds As we discussed before, the OWB improves more than the SWB if wc consider a lower range. Our calculations therefore agree with the 1977 Boe­ing High-Transonic Speed study by Kulfan. Neumann ct al. (365) that stated that the OWB is slightly superior to the SWB at Mach 1.2 and a 5500 km range. Our calculations however, do not support the claims made by the 1991 GE study of Elliot. Hoskins and Miller {360] that this configuration is superior to the SWB at 9000 km and Mach 2.4. Al Mach 1.8 the lift-to-drag of this configuration is already dow n to 7.5 because of excessive wave drag. In addition the struc­ture is very poor because of the single pivot that has to transfer all the loads.

Figure 102 TOC M a function of Mach number

Payload

The overall trend that the TOC’s reduce with increased payload is caused by die reduc­tion of the DOC’s per passenger km. with payload Maintenance costs, fuel burn and deprecia­tion do not nse (exactly) proportionally to the number of passengers transported. This effect is even a bit stronger for the supersonic transports. The larger area-ruled supersonic transports have a better cabin volume efficiency then the smaller ones. However, only supersonic configu­rations that are not highly constrained benefit from an increase in payload with respect to the subsonic transports. Because of the poor volume efficiency of the OFW configurations, the standard payload of 250 passengers may not be large enough. For the OFW a payload of 400 passengers is better It is not possible at this time to design a 400 passenger SWB SCT configu­ration since such an aircraft w ould have an excessive M^. How ever this study does seem to jus­tify the approach of the American HSCT teams (NASA. Boeing. MDD) (357) to transport the most passengers for a given The M^^ is for all practical purposes limited to 350 tons. At

higher takeoff weights the critical sideline noise constraint is no longer relaxed to accommodate heavier aircraft. Figure 103 shows the effect of increased payload on the TOC of the OFW. If we compare the 250 and 400 passenger OFW’s we find that the maximum takeoff weight has increased 33% while the payload has increased 60%. A detailed explanation of the improved economy of the oblique flying wing transport over the symmetric wing body is published in ref. 1371].

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