A further explanation why the changes were made.
The original wing was not designed around using the intercostals (diagonals) to control twist. They were recommended after I started, and turned out to be key to the wing staying out of flutter. For the intercostals to work to their best potential, they need to be at 45 degree angles to the ribs. The old wing had them closer to 30 degrees, this angle for sure helped with twist, but it also puts added stress on the diagonals when loading gets too high. We saw this on an Alpha build when the wing entered flutter and several intercostals took damage. To get the correct angle we needed to move the spar forward, and move the ribs further apart.
Everything else was minor improvements that could be accomplished during the redesign.
The airfoil change is a little more cutting edge. When the wings are covered in film, the film will take a curve over the ribs, and sag into the space below. This is a catenary curve.
In the photo you can see the curve of the bubble surface between the rings.
This is the challenge of a film covered wing. The designer picks an airfoil based on published or calculated data, but when it is a film covered wing, the covering sags and the only place you have a chance at the accurate airfoil is on top of the rib, the rest is a very different shape. It would not be so bad if the curve was consistent along the entire rib, but it is not. You have a lot more sag in more curved sections of the airfoil, so the trail edge for example has very little curve, but the leading edge is very curved.
There are common construction methods to fight this, the obvious is sheeting the wing, or at least the front 40% of the wing, we do this on our Le Le wing. Half ribs can help fight the sag, we do a little of this on our Gentle Lady Evo design. Another method that was well intentioned is running stringers running from rib to rib, but stringers are a poor choice as they result in flat spots on the airfoil, thus they received the name of turbulators for all of the turbulence they create.
The AH-100 wing is different and can take advantage of this curve to give a more accurate airfoil for the majority of the film surface. By modifying the rib profile we can have a very accurate airfoil for the majority of the wing surface. Unlike the image above, the catenary curve for our films is nearly flat in the center and an initial heavy cuve near the rib. So the airfoil will be oddly shaped at the rib and slightly beyond it, but very quickly the rest of the surface will be much more accurate. And with our wider rib spacing on the new wing, we gain a more accurate airfoil for a higher percentage of the surface area.
Hope this helps to understand what we are doing with this wing.
How do I expect the new wing and the old wing to compare in flight? The new wing should be slower and create more lift, and the already gentle stall should be very gentle. Time will tell.
The first 40% of most any airfoil is very important to get right. This is where the airfoil does most of it work.
