Zoomie, your product looks good. Unfortunately my plane is a little smaller than 1/4 scale. It's more between 1/5 and 1/4 so I have to adjust my stiching accordingly. Also the WWI planes used 3 inch centers from what Hurri said. Not having the Windsock fabric special to see for myself I'll take his word for it. Comparing how the rib spacing works out at 3 inches and my photographs of the full size I would say 3 inches is correct. I did bookmark your page, I might use you product on another project in the future!