michael

You may be seeing different profile shapes due to the type of curve your CAD person is using.

NACA didn't envision CAD programs when they created the coordinate tables for the airfoils. If they had, they would have given us the equation for the curves and not just the points. That way, every point would have been defined. Instead, they created the coordinate tables so draftsmen could lay out the points and fit a curve through them using a French Curve, spline or other drafting tool. You can almost bet that no two were ever created exactly the same.

Todays CAD tools are much more advanced. Unfortunately, most CAD users don't understand the mathematics behind the curves they are creating. Also adding to the confusion, not all CAD applications have the same name for a given mathematical definition. Long story short, you want the person to use Non-Uniform Rational B-Splines (NURBS). This will ensure two things, the curves pass through the points specified and secondly the curve will be smooth (i.e. no abrupt changes in curvature continuity).

Regards,

Patrick Flynn
Design Integration Manager
Honeywell Engines

Good luck with you ribs!
Mark Marino

I found these same airfoils in several on line data bases. I used Foilsim and plotted one that is a very good match to the CB-1 plans. I also found a very good aluminum spar at Carlson Aircraft supply. Did you increase the width of the airfoil at the front spar? I read a paper on the strength of the Kelly D wing and the author suggested an increased width at the front spar. How do you think this would work with the CB-1?

Michael
Nashville

The Bantam aluminum rib is the same as the CB-1, that is, the spar positioning and spacing within the rib is the same, the 1/4" capstrip space above and below the spar is still there allowing for spar inspection. I did put a riveted doubler across the tops and bottoms of the spars similar (well OK..the same as) to a Citabria rib making the Bantam rib virtually interchangable with the CB-1 wood rib. The spar dimensions are also the same height and width but with square tops and bottoms. As far as the width of the airfoil, do you mean the width of the rib? If you're talking rib width, the answer is there are several wider ribs in various locations (ie. Butt ribs) and also different aluminum thicknesses (ie. Wing walk ribs) where necessary.

Mark Marino

Michael