Tailoring Wing Structures for Reduced Drag Penalty in Off-design Flight Conditions

The induced drag penalty associated with off-design flight conditions is investigated. The investigation is limited to off-design flight conditions at a lower lift coefficient than the design lift coefficient. Two types of total angle of incidence distribution obtained at the design condition are studied. One is the distribution for elliptic spanloads and the other is the spanload distribution for straight-line wrapped surfaces. It is shown that the penalty may be significant as the structural deformation changes the total angle of incidence distribution and the spanload. The penalty is higher for the wing with the near optimal elliptic spanload at the design flight condition. The wing with straight-line wrapped surfaces does not have the minimum induced drag at the design condition. However, it is found to be insensitive to the structural deformation.