1. For joined wings that are optimally twisted to give minimum induced drag at a specified C L the induced drag at this 'design' CL may be canputed from Eq. (3). For off-design conditions the following approach is tentatively suggested, based upon Ref, 5. p.43. Increase CLy by 0.15 above the two-dimensional viscous airfoil value; put ex equal to e - 0.255, and equate the induced drag cmputed by the offset polar to the non-offset value at the design CL. Fuselage Interference: