Is the s-4083 "de-thickened" to 6% a good idea on windy days with a weight about 355g ?

From : Don Stackhouse

For all you non-metricated readers out there, that's about 12.5 ounces, a fairly typical weight for many HLG's.

Matthieu, it's difficult to answer this question without a lot more info about the specific model in question. The choice of wing area, planform, twist distribution, any variations in airfoil section along the span, fuselage and tail design, priority for different flying conditions and the influences of your own flying style are just some of the parameters that affect the analysis. I will assume for the sake of discussion that the model you're discussing is within the average range for models of this type and try to make some general conclusions.

In general I am not impressed the 4083 airfoil. In my own analysis, in the performance I've observed in models using it, and in the feedback I've received from others who observed it in the field, it seems to be a fairly good airfoil at its design point. Unfortunately that design point is almost unusable for a hand-launch glider, and its off-design-point performance deteriorates rapidly the further away from that point you get. It has a very good max lift coefficient and L/D at that point, but this lift coefficient is so high that you get into some serious problems matching it to the model. It's basically a 1-speed airfoil, and that speed is not a useful one.

If you simply thin the 4083 the high speed problem actually gets worse. If you do a LOT of re-shaping you can get some improvements, but by the time you get something usable it isn't even remotely a 4083 anymore! There are other airfoils out there that seem to be working better in HLG's, and we have our own series that seem to work much better for us. In general, support for the 4083 seems to be on the wane.

I would also caution you to not get too fixated on any one parameter of the design process. Getting all the different variables in the design equation properly matched with each other is far more important than some currently popular hypothetical "optimum" selection for any one of those parameters. Wearing a pair of Michael Jordan's shoes can only improve your basketball skills if they fit your feet! With airfoils in particular, the needs of a wingtip are not the same as at mid-span or at the root. If you force yourself into using a single airfoil for the entire wing you will be forced to make compromises in other parameters to compensate. No single parameter should control the design, they should all be adjusted together to arrive at the best possible combination. Just as in most other sports, effective teamwork amongst all the players involved is the secret of a winning performance.

Don Stackhouse
DJ Aerotech