drag, sail, induced and other.

It depends on which side you're talking about. On the flap, the entire windward side can have a laminar boundary layer, because the flow is accelerating all the way from the stagnation point to the leech. On the leeward side, there's very little opportunity for laminar flow, because of the leading edge suction peak.

On the main element, it depends on how the wing is constructed as well as the section shape. On the windward side, extensive amounts of laminar flow are possible. On the leeward side, the main element can be designed to have a rooftop pressure distribution with a flat or favorable pressure gradient to extend the laminar flow. Extending the laminar flow means pushing the maximum thickness aft, and perhaps making the section thicker.

It's probably unlikely that laminar flow will survive the crease at the junction between the smooth skin of the D tube and the film covering of the open bays. Roughness like the tape joint that bonds the film to the structure, or sponsor graphics, can also trip the flow.

All this is predicated on the notion that the freestream turbulence is low enough that any substantial amount of laminar flow is possible in the first place. That is by no means an assured proposition.

 

Thank for the precisions regarding the laminar flows.

Your E2 wing section combining an elliptical LE and flat contours reminds me the OPEN WING project from Steve Clark, which uses pultruded carbon arrow spars for the ribs.
If E2 is the weakest part of a wing. For an A-Cat which is more likely to capsize than a C-Cat or AC45, the above-mentionned combination could lead to a more reliable and cost-effective solution.

Thanks again

Erwan

 

I just reread this posting of yours and the one just preceding it. and I think I understand it a bit better.

But I have another question about the size of this flap. Would you venture to add any more suggestions about the size of the flap? Is there some relative % we might consider as appropriate for sizing the flap with respect to the leading element??

 

Most wingsails have flap chords in the range of 35% to 60% of the total chord. If you take the AC72s as an example, Artemis' first wingsail and ETNZ's wingsails were at opposite ends of that range. OTUSA's wingsails were in the middle.

What size flap you select depends on the design objectives and requirements. You can use programs like Javafoil or MSES to evaluate different candidate designs.