Sorry, but couldn´t let it be - another super-glider. Well, instead of going forward I took a step back to Eppler´s E-403 airfoil (Boelkow Phoebus, 1966). These early laminar airfoils had obviously been designed for maximum laminar run length on any price. As a result, the laminar bucket is not as broad but deeper, max. airfoil-L/D is a bit worse but occurs at lower CL and therefore lower induced drag. Higher Re-numbers further reduce the disadvantage in viscous drag. The outcome was still a bit surprising to me, best L/D=113(!). However, the E-403 has less than 14% of relative thickness compared to over 17% of Wortmann´s FX-73. In order to be fair, one has to reduce aspect ratio to 92.3 (which is still very, very slender) getting a similar wing-spar and D-box, even though torsion due to pitching moment will be quite a bit stronger anyway. Due to another little rise in Re, the laminar bucket further narrows (but gets deeper). Thus, optimum CL significantly decreases again, which yields to even higher speed optimums despite of reduced wing loading. Therefore, as span loading is kept constant, induced drag will not increase due to lower aspect ratio. At last, best L/D for the bigger wing is only 3 points lower, still well over 110. Even traveling at very high speeds, you lose less than 0.1 m/s more. However, the narrow laminar bucket results in worse minimum sink rate, compared to the Wortmann-airfoil. This made me try positive flap settings. This worked very well even had a surprisingly positive effect on best L/D (more than 113 again), but with quite a steep decline when flying slower. The optimum is reached very close to the upper end of the laminar bucket. Another thing is transition on the pressure side. The pendulous abdomen of the E-403 causes an adverse pressure gradient followed by a laminar separation bubble (and turbulent reattachment, of course) at little more than 60% chord. By adding a (1-cos)-function to the pressure side I tried to stretch the belly and pressure distribution a bit downstream, with some kind of success. Knowing that some more camber might be helpful, I tried some "smart structure" or "morphing flap" at last, adding -1.5% to the camber line by a x^5-function over the chord length. The result was a max. L/D=117 @ 130kph. Not pleased with the steep characteristics of the new airfoil (max performance in a very narrow speed range), at last and very last I tried a flap again (hinged at 85%), but this time tending more to negative deflection for better high speed performance. Moreover, having a wing with more chord length and more camber more to the back, pitching moment will increase, leading to more torsion in the wing, more bending moment in the tail boom and additional work for the tail, which might cause a little extra drag as well. All this should be eased when "thinking positive: flaps negative". However, setting the flap at +2.5 degrees, a new optimum could be found: Max. L/D=118(!) @ 125kph as well as min. -w=0.29m/s @ 122kph. All in all it should be stated that L/D>100 should be practicably possible for a complete airplane when spending some serious effort in designing an airfoil for this special purpose, assuming that structural designers manage to handle a 2.7-ton-aircraft with an aspect ratio of about 100. As I still do not dispose of a suitable CAD-tool again, the image is actually still FX 73-170. However, absolute wing thickness is kept constant and therefore the picture won´t change anyway. XFoil 6.96 Grapher 2.03 AutoCAD 2002 Corel Photopaint 7 Notepad As the width of the complete image violates renderosity´s specifications, this is only the lft half. The right half will be postet later, you may put them both together (with an overlap of 500 pixels) if you want.