Contradicting requirements arc daily life for an engineer. But for a conventional SCT these four requirements really pose a design trap, mainly:
• high supersonic cruise performance requires
• a slender configuration with
subsonic leading edges (i. e. limited span) or very thin wings with leading edge flaps or variable geometry low engine diameters.
• low take-off noise requires
• large span with
round leading edges or leading edge flaps and large engine diameters.
At DA a screening of several promising configurations was performed, see Figure 21:
Figure 21 Search for a Viable Configuration
Remaining configurations were the conventional symmetric wing-body configuration at the left end. and the oblique flying wing (OFWj at the right end
The blended wmg-body lost for its poor slenderness. The optimizer simply concentrated the payload more and more at the center and spent more length for slenderness. So this configuration automatically transformed into the symmetrical wing-body.
The joined wing configuration has only limited span, does not provide enough fuel volume, does not provide space for an undercarriage and is structurally difficult, especially due to buckling.
The oblique wing-body combination is only interesting for rather small aircraft at low- supersonic speeds (57).
The extremely different aerodynamic requirements seem to prohibit a solution for the conventional symmetric wing-body, at least for large aircraft and long range Only limit performance of all disciplines’ technologies may reach the limit of viability. (Besides aerodynamics. severe pniblcms arc e g. weight, flutter, engines, long flexible fuselage, undercarriage» But this configuration has its merits for a smaller aircraft and shorter range, c. g. a 200 passenger transatlantic aircraft
The OFW is limited to large passenger aircraft, because profile height must be about
2.5 m or more. Therefore it is suited for SCTs with more than 250 passengers and for subsonic – aircraft with more than 400 passengers. The OFW provides variable geometry (aerodynamic – span) without large moving parts, and best supersonic performance It provides solutions to all the known problems of other configurations, like weight, noise, flutter, undercarriage, structural flexibility. In contrast it needs drag producing devices with controllable pitching moments to allow for a sufficiently steep descent and a short flare at touch down. Like with anything new there is still room for many new problems Also, the interfaces between the individual disciplines are strongly different from conventional (subsonic) aircraft.
Both a conventional solution at design limits or an unconventional OFW-solution pose a strong challenge for aerodynamics and the other disciplines The goal will only be met by new approaches using and further improving the techniques of Multidisciplinary Design Optimization (MDO).
Because both solutions require many new. unapproved technologies, flying technology demonstrators arc required in preparation of civil passenger traffic.