Marks comments on Supra, Tom Kieslings Supras and leight weight high performance gliders:

It wasn't designed to fly at a particular wing loading. IMO if strength/stiffness are adequate, you cannot have an F3J competition glider that's too light. Ditto for TD. I would build a 35 oz Supra... if I could. The airfoils will still work OK.

A lighter glider launches faster for more available scoring time in the window, hangs longer, and lands slower for better landing control. If wind isn't a problem, I just don't see a downside to very low weight.

Yes, if there's wind and you have to add ballast, and then much of the low weight advantage over heavy gliders disappears. But the light ballasted glider has smaller moments of inertia than a pre-ballasted glider of the same weight. Low inertia improves handling and control, and signals lift better. Again, low unballasted weight is better.

Originally Posted by glderguy
That Icon, although not super light, had incredible hang ability. Just call me confused!
OK, so an 80 oz Icon floats well. But a 50 oz Icon would float much better. It's all relative. Going from 80 to 50 oz will increase still-air duration by a factor of 1.25 or so. Also, it will reduce the minimum turn radius by a factor of 0.625 which allows working smaller and lower lift. Altitude loss from a stall is also reduced by a factor of 0.625, which allows more agressive thermalling.
Originally Posted by glderguy
thought that perhaps some airfoils may work better at higher loadings or something like that, hence the good hang some of the heavier planes are capable of. Guess I was way off!
You're not completely off. If you're talking about a specific airfoil, then yes, performance will start to suffer if you go too light and go well below the airfoil's intended Reynolds number. For example, the MH32 works best at around 100 oz weight (assuming typical 3m glider aspect ratio). As you reduce the weight and the Reynolds number, the tips will start to suffer first. Things are still sorta OK at 70 oz. But on my 48 oz Supra, using the MH32 on the narrow tips would be a disaster. Instead, it has DLG-type airfoils out there. The center airfoil is closer to an MH32. This lets the wing tolerate extremely low weights without excessive L/D loss.
Originally Posted by davidleitch
And are they likely to suffer in a relative sense when ballasted up (or in my case used with an electric system)?
If you stick them on a 100 oz glider, then they will probably be a bit sub-optimal. How much penalty are we talking about? Dunno. I haven't run the numbers. But one thing's for sure -- going above an airfoil's intended Reynolds number is far less deleterious than going below. So my bet is that the "penalty" is miniscule.

But this may be a moot point. An electric glider naturally wants a larger Aspect Ratio than a winched glider. The absence of a hard-winching requirement makes the larger AR structurally feasible. And the larger AR offsets the larger weight, so Re won't change as much as it would otherwise