How to reproduce NASA/Langley airfoils for general aviation with long chord lengths? I have scaled a NASA/Langley LS(1)-0413 airfoil to a 90 inch chord length, and now the trailing edge is 0.5in. Any longer chord length would have a larger trailing edge thickness.


  (90in*(0.0071-0.0016)=.495in)


This doesn't seem right, I have not witnessed a non-supercritical airfoil with a trailing edge larger than a .25in.

First off, do long chord length wings using the low and medium-speed airfoils have thick blunt trailing edges? 

Secondly, if medium speed wings don't have blunt trailing edges how does industry taper the trailing edge? Is it assumed they will be rounded off, or sanded to a point? Should one remove from the bottom concave surface or remove from the top surface? Both will alter the exit angle of the airstream. 

Thirdly, is there an ideal length chord for the NASA/Langley low and medium-speed airfoils, e.g. do they really only apply to a 36in chord lenght? Does scale matter?
You are right, such a thick trailing edge is not right. It will add pressure drag unnecessarily – quick fix: Just taper the last 10 or 20 percent of the airfoil such that a thickness remains which is sufficient for structural reasons. You don't want a trailing edge that is as sharp as a knife edge. It has no stiffness left, so it will warp and will easily be damaged.

The more elaborate way: Do as if there would be a hinge at the nose and you close the two sides, just like scissors. That will leave the contour unchanged. The "hinge" location is ideally the center of the nose radius.

Tapering the last 10 or 20% will steepen the pressure rise there and will let the airfoil stall a tiny fraction of a degree earlier than with the unchanged surface contour.