I see some planes with more ribs than others. Is this a trade off between better stiffness and airfoil shape vs weight? Is anything less than 3-1/2" spacing really necessary on a 600 sq. in. wing?

   3 and a half inches?  I don't know about that, most are more like 2" and I have considered adding half-ribs every inch to avoid "starved horse" problems.

     Brett

The sagged part is less than the intended airfoil thickness.  If you scientifically selected the airfoil, don't you want it everywhere?

The sagged part is less than the intended airfoil thickness.  If you scientifically selected the airfoil, don't you want it everywhere?

Hi Paul,
            I thought that may be the obvious answer but I have yet to see a model suffer from the lack of scientific airfoil in the bays.

Perhaps the "starved horse" ribbing helps to prevent span wise flow? Or an average between the minimum and maximum sections allows better for varying conditions?

Thanks.

The sagged part is less than the intended airfoil thickness.  If you scientifically selected the airfoil, don't you want it everywhere?

   I would not claim that my airfoil was carefully selected based on science! However, I want the things that are supposed to be straight to be straight, the curved parts curved and no "accidental" shapes. My turtledeck is a bit "starved horse" and I have often wanted to cut it off and make a new, correct replacement. So far I have resisted.

    Brett

There are plenty of real airplanes and lake freighters with the covering shrink over the ribs on the body (or hull).  But airplane wings are generally built to keep the airfoil true.  Stunters and combat planes have so much excess lift, you wouldn't know or care if it's efficient or not.  The only way to tell would be to build another plane with the wing sheeted to keep the airfoil true.

The sagged part is less than the intended airfoil thickness.  If you scientifically selected the airfoil, don't you want it everywhere?

You can select an airfoil scientifically.  But as Mike Selig at UIUC proved, building a wing with close enough tolerances to get realistic performance measurements is VERY difficult.  And when you do the differences are only apparent at the very extremes of performance.