The glider I am designing has a mission requirement to fly for as much time as possible. It will fly in the low Re range of about 150,000 to 250,000.

While comparing different airfoils I am looking for a high value of Cl^3/2/Cd to get as high endurance as possible and a high Cl/Cd ratio.

Any other parameters I should consider in selecting the airfoil? I am currently considering Wortmann FX 63-137, E61, DAE-31 and Fx-74-c15-140. Any other airfoil suggestions would be appreciated.

  • $\begingroup$ How do those airfoils compare to other record setting airfoils? For example, en.wikipedia.org/wiki/Thomas_Knauff World glider records Single-place glider Out-and-return distance: 1,646.68 kilometres (1,023.20 mi), 25 April 1983, Schempp-Hirth Nimbus 3 Distance over a triangular course: 1,362.68 kilometres (846.73 mi), 2 May 1986, Schempp-Hirth Nimbus 3 Free distance using up to 3 turn points: 1,394.04 kilometres (866.22 mi), 1 June 1993, Schempp-Hirth Discus B $\endgroup$
    – CrossRoads
    Oct 15 '18 at 16:17
  • $\begingroup$ For human-carrying gliders, the task hasn't been duration since at least the 1940s -- tasks are cross-country speed over a defined course. $\endgroup$
    – Zeiss Ikon
    Oct 15 '18 at 16:42
  • $\begingroup$ Related, maybe a dupe? $\endgroup$
    – Pondlife
    Oct 16 '18 at 1:06

For a particular task of optimizing an airplane design for a specific point, you will need to consider the following characteristics, together with the endurance parameter:

  1. The pitching moment of the airfoil, (which will define the tail design, hence will affect weight and CG range and controllability)
  2. Tolerance to contamination and geometric impurities (especially CFD based methods may converge to non-robust shapes)
  3. Stall behavior (does it stall mildly or violently, as a wing)
  4. Wing weight (spar location, spar web thickness)
  5. Aeroelasticity (wing structural modes, static and dynamic aeroelastic properties)
  6. Manufacturability (if somebody will really build it!)

Many of these would require working on a conceptual or preliminary sizing task, where you would design a planform, twist, dihedral, tail volume, CG, mass estimation, aeroelasticity computations etc.

Number 1-2-3 could be more vital and would help pick an airfoil with less efforts than the others.


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