Lot's of the first ones tried to copy the the birds, with everything beautifully rounded. Aero theory came to speculate that an ellipical shape was the ideal and thus we have the beautiful elliptical wing of the Supermarine Spitfire. Testing showed the actual shaping of the wing planform was a minor detail. Almost any plane designed since WW2 has had straight leading and trailing edges. The fancy ones have a straight taper with the tip about half as big as the root.
Simpler ones use a basic rectangle with lots of benefits possible with regards to assembly cost.
I've never seen an airplane wing that was triangular like a jib sail except for delta wings of old fighter designs or hang gliders. The sailmaker can control the draft of the sail fairly easily if the rig's structure is rigid enough. In Phil Bolger's 100 Rigs book I think he says that the thin plate airfoil is ideal and that the thicker streamlined shapes of the usual airplane wing ribs are not as good as the thin curved plate. Not sure where he got that info. My books all show the usual thicker streamlined shapes to be better in most ways.