There is emphasis on fuel-efficient flight. Consideration of efficiency ”top-down” metrics show that we need to increase the Range parameter (Breguet Range Equation). However, for conventional configurations, we are reaching maturing technological stages. Structural technology has been exploited to a high level, using composites. Actively controlled structures may provide additional weight savings. So we need to continue to explore or re-visit more novel and unconventional layouts with challenging structures, materials and weight requirements. Some of these layouts can be achieved using modern analysis and test set-ups. A particular current interest is in design of moderate range aircraft. At moderate ranges, the aircraft fuel efficiency is higher. For example, a 3000nm range is 30-35% more fuel-efficient than a 6000nm range aircraft, Comparing with 9000nm aircraft, the 3000nm aircraft has 40-50% advantage. This has led to a propoal for Air to Air Refuelling for long ranges. The current moderate range aircraft (B737, B757, A300, A320) are of relatively older vintage and there is scope for newer and / or unconventional designs, perhaps incorporating twin-aisles. We consider unconventional concepts exploiting Joined Wing (JW) and Oblique FlyingWing (OFW). The Joined Wings Layout (JW) enables a high aspect ratio (AR) wing to improve L/D. Many configurational possibilities exist. We selected a layout similar to one on which useful experimental forces and moment data is available. Preliminary work on Aerodynamics and performance has confirmed possible benefits (15-20% higher L/D and hence Range Parameter). The JW is subject to non-linear aero-elastics and such aspects are not fully understood. The structural and weight benefits were quantified some time ago and these need to be confirmed with modern techniques. So there are challenges. Detailed understanding of aero-elastcs will allow an idea of the buckling modes on the rear wing. This may require strengthening and weight increases and may eventually entail planform changes. Further work is proposed in several areas e.g. detail configuration design bearing in mind the structural and aero-elastic constraints, the need for passive and active flow control and the incorporation of laminar flow. The Oblique Flying Wing Layout (OFW) has some inherent benefits e.g. Plank wing – Minimal twist – good “2- D suction”, Straight isobars, minimal wave drag (long overall wing). Structural advantages stem from simple box with torsional stiffness, without offset of loads (cf a conventional wing, starboard and port panels). Previous OFW attempts have been either supersonic or subsonic flying wings that can vary sweep in different parts of the flight envelope. These are only suitable for very large aircraft with a passenger cabin buried in the wing. Our interest is in smaller subsonic aircraft and so a separate cylindrical central fuselage is used. In 1976, Lockheed proposed a layout with a pivoting wing. This was capable of Mach 0.95 cruise. Admittedly, the fuel costs were lower and achieving a higher speed was considered more important. We review some features. However, we propose a fixed sweep OFW attached to the top of the fuselage (e,g. BAe146), avoiding pivot weight and complications, and limiting the cruise speed to about Mach 0.85. Preliminary work on Aerodynamics and performance has confirmed possible benefits (10-15% Range Parameter improvement). This in turn will imply weight reductions and efficiency enhancements. The stability and control issues are more complex. To some extent these have been resolved many years ago when NASA Ames undertook flights on the AD-1. Many interesting structural and integration aspects are posed. Amongst these are aspects such as structural divergence control over the forward swept panel. Techniques used on the X-29 by aligning fibres will need to be re-visited. Another aspect is the integration of propulsion structure, ei
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