Airfoil selection for perpetual 5m solar eGlider

[quorneng]

I suspect the oversize fin area is a result of the plane having a low wing loading, a big span and being slow flying which results in a turn having a proportionally smaller radius than would be considered normal. This results in a more pronounced lift differential between the inboard and outboard wings. The inertia from the weight of solar panels spread all over the wing is likely to exacerbate this tendency. Unless the wing has significant dihedral (not ideal with solar panels) this can lead to a turn "auto tightening". The big fin and rudder are required to overcome this effect rather than for the needs of straight line lateral stability.
Just my own conclusion from my past full size glider flying.

 

[Piotrsko]

Prandtyl style wing twist would resolve the autotighten. How about a flat wing with small area diehederal tips. Unsure of the efficiency hit. I would call it washin but I usually get the term backward.

Old axiom in RC slope: you can never have too much rudder authority. Might not need it, but you cant add it inflight.

 

[WulfKeeper]

Thanks for your input @Piotrsko and @quorneng. I was leaning towards a similarly portioned fin. It occurs to be that the structure *inside* where the fin and fuse' merge doesn't have to be aero - only where the surface is exposed. I reckon I can design a strong/light internal merging but still make the 'skin' silky smooth

 

[Piotrsko]

Ever look at a super cub rudder to fuselage fairing? It's basically fabric since piper used 1930 style brute force rudder attachment.

 

[WulfKeeper]

Ever look at a super cub rudder to fuselage fairing? It's basically fabric since piper used 1930 style brute force rudder attachment.

Thanks again, Piotrsko! I found a great picture of the tail/rudder section on a website from a bloke restoring an original Super Cub. Yeah, very close to one of the options I was thinking about. I'll use that frame = tail as inspiration