Research and Documentation
In many cases the best guide for a reproduction part is another airplane. The most original SC-W that I could find is the prototype SC that is located at the EAA Museum in Oshkosh, Wisconsin.
During January 2004 Ron and I arranged with the museum curator to visit and take detailed measurements of the aircraft. January in Wisconsin is pretty cold, fortunately the museum curator was kind enough to turn on the hangar heat for us!
Ron made measurements of all critical dimensions of the cowling, and created posterboard templates of the contour of the cowling, both along the long axis of the airplane and 3-D size of the bumps. To do the bumps, a template was made at every inch along the cowling. The tape shown in this photo was put onto the cowling to protect the polished surface from the posterboard edges:
Notice that the cowling is constructed of smaller segments with two bumps per segment. The segments are riveted together to make up the cowling. This is unusual construction, as most vintage cowlings are round and are "spun" from a single piece of metal that is flow-formed into a bowl shape. Spinnings are appropriate for round cowlings, but the Ryan cowling is not exactly circular except at the front opening. Fortunately the segmented construction will make reproduction by hand easier, since it allows for more "adjustment" room and is less awkward to work, since the panels are only about 18" x 36" each.