The boeing team proposes a novel variable geometry wingtip control effector aimed specifically at very high aspect ratio/low sweep truss braced wings (TBW). Two boeing n+3 subsonic ultra green…

The boeing team proposes a novel variable geometry wingtip control effector aimed specifically at very high aspect ratio/low sweep truss braced wings (TBW). Two boeing n+3 subsonic ultra green aircraft research (sugar) configurations take advantage of TBW's. At cruise flight conditions the TBW may be subject to design requirements that distinguish them from more highly swept wings. High aspect ratio, short chord length and relative thinness of the airfoil sections all contribute to relatively low wing torsional stiffness. This may lead to aeroelastic issues such as aileron reversal and low flutter margins. Further, the geometry of a swept wing naturally provides strong stabilizing aerodynamic forces due to wing bending deformation under loads. Lacking this aerodynamic stiffening, low sweep wings may exhibit reduced divergence margins. In order to counteract these issues, high aspect ratio/low sweep wings may need to carry additional structural weight to provide high torsional stiffness. One very attractive option to provide roll control is to intentionally create wing twist. The NASA x-53 active aeroelastic wing (AAW) aircraft demonstrated this concept in flight testing. Boeing was lead contractor on x-53 so we fully understand that the primary advantage of AAW is that additional structural weight is not required to provide high torsional stiffness, in fact the additional weight is detrimental to the AAW approach. However, roll control by AAW works best in a fairly narrow range of dynamic pressure when forces generated by the control surface act through a moment arm to overcome the twist stiffness of the wing. At lower dynamic pressure, the twist loads are not sufficient to generate enough twist and at the aileron reversal speed, the ailerons provide no roll control at all. The proposed novel control effector is a variable sweep raked wing tip. At high speed the wingtip is in the raked (swept back) position providing dual, independent benefits. The drag reduction benefit of a raked wingtip is achieved, and in addition the control effector(s) are moved well AFT of the wing torsional axis. This provides a moment arm for forces generated by the control effector to apply wing twist and enable the AAW effect. At low speed the wingtip is unswept. This moves the aerodynamic center of the control surface loads forward to LIE on or very near the wing torsional axis. This allows the control surface to act very effectively as a conventional aileron by providing roll control forces while applying minimal twist loads to the wing. A key aspect of our concept is that high rates necessary for roll control can be provided by a high rate control effector such as leading or trailing edge flaps, conformal camber change of the wingtip, and/or twist of the wingtip itself. The large scale variable geometry (sweep) will change with flight condition and need much lower rate. Variable geometry will likely include sweep change, but other shape changes such as wingtip dihedral (winglets) and twist will also be investigated. Boeing has carefully selected a small, agile team that includes virginia tech for their experience with TBW aircraft, and nextgen aeronautics for their experience with development of morphing aircraft concepts. Both are team members on the boeing sugar phase II program. This program will draw directly on the designs and data generated in sugar phases i and II. Each of the three team members will develop a concept for variable geometry raked wingtips based on their unique experience. One of these concepts will be selected for a detailed performance investigation including extensive evaluation of aeroelastic response. Additional benefits will be considered such as active gust load alleviation, ride quality improvement and active buffet alleviation. Boeing is excited about the benefits of this synergistic application of AAW and adaptive structures/morphing technology to benefit high span low wing sweep configurations.