lml@lancaironline.net Mailing List Archive

How close are we to the designed airfoil?

I have a IV-P, not a Legacy but my airfoils are very close to design intent.

I CNC machined three templates that are accurate to design intent within .001". I made one template for the root, one for the flap/aileron split and one for the winglet split. I did not use feeler gages, but it was hard to see light under the 3/4" wide templates. I feel the three locations were within .03" of design intent and the leading edge was much closer than that.

Is it possible that we may have squeezed the wing too tight and made it too narrow or added too much micro and made it too blunt?
Can we get the correct airfoil by hand sanding?

I used a very long "long board". Three strips of sand paper long.

How do we know what the correct airfoil is - by eyeball?
Is there a better way?

I am thinking of "templating" my leading edges - getting a template that is the correct airfoil and attempting to get the leading edges as close to design as possible.

Does this make sense?
Am I wasting my time chasing 1 or 2 knots?
What is the best method of getting the correct airfoil?
Has anyone else done this?

While the airfoil shape is very close, I was able to measure incidence with the templates as well. The incidence was not as good as I would have liked.

Here are my actual incidence inspection results:

RH LH Spec

BL26.25 -1.764 -1.9705 -1.6

BL104 -.8033 -1.178 -.777

BL171 +.397 +.145 +.342

Washout 2.143 2.115 1.942

Results were obtained with a precision level .0005/ft and a sine bar. Therefore I'm pretty confident of the numbers.

By the way, I did the same thing for the horizontal. The top of the horizontal is not per design but the bottom is. The horizontal is actually an inverted wing rather than a symmetrical surface. I'm not smart enough to know what total effect this has.

Craig Berland

D. Brunner

N241DB

90% done 30% to go