I'm using the Eppler 817 since it's what i've seen others doing. In my software it gives me great lift/drag ratios but as I'm not proficient in the field it's hard to argue for one versus another.
As far as AOA. The front wing should be 0 degrees. The rider controls the angle of attack. Of course if you make it a different angle, the rider will have to adapt, but that's not ideal. The angle that is important is the stabilizer. It's between 2-5 degrees relative to the front wing. You'll need to play around to find what works for your setup.
Of course this comes from a person that produced exactly 0 working wings so far
Hmmm... now I'm confused!
I was going to go for zero AOA on the front wing but when I looked at the Coefficient of lift vs AOA curve for the Eppler 817 it seemed to show almost zero lift at zero AOA (depending on the Reynolds number and Ncrit). So that makes me think I would have to put pressure on my back foot to increase the AOA and get some lift. However, my one and only go on a foil and advice I've heard given is that you need to get your weight over your front foot. So is the rear wing (stabiliser) creating a downforce that in turn is always trying to increase the AOA on the front wing? And this is why you need to keep weight on your front foot?... to balance the upward pitching moment generated by the rear wing?
And so... is having your front wing AOA at 2 degrees and the rear stabiliser at zero AOA the same as a front wing at zero and rear wing at -2 degrees???
I guess this is the balance we are aiming for and perhaps an answer to another thread on this forum about why you wouldn't put the mast directly above the centre of lift of the front wing... you need to create a sort of balance of moments either side of the mast and if the mast is directly over the front wing then there would only be a pitching moment from the rear stabiliser.
Another thing that had got me wondering was this article by a guy who clearly understands all the XFOIL analysis much better than I do...
In it he states...
Completely cavitation free operation is also not
possible above 22 knots for any of the foils, and
there is only about a one knot difference in the
cavitation speed over the design operating range
Referring to the NACA 63-209, Eppler 817 and his H105 design.
What happens when the foil cavitates? Surely people are hitting speeds over 22knots on Eppler and NACA foils out there or are the production foils using different profiles?
All this makes me think it's best not to think too hard and just try something and see what happens!