RE: Jim Pepino's YMF-5 Waco
You have heard of getting the cart before the horse, well, this is getting the horse before the cart. In the past I have always built the plane and then struggled with getting the cowl properly located and attached to the firewall. This time I started with the firewall while it could still be put down flat on the table.
A very good friend of mine (RCU screen name Gremlin Castle) did a very skillful job of turning my firewall assembly on his lathe. The actual firewall (F2) is 1/2" plywood with a spacer block that provides 2 degrees of right thrust. Of course, the spacer is offset to the left the correct amount so that the prop comes out in the center of the cowl.
Photo 1 shows the cowl in place with the holes cut for the muffler and spark plug lead.
Photo 2 shows the recessed T nuts for the cowl mounting tabs. They are recessed because some of the framework will glue over these T nuts. The firewall is 1/8" smaller in diameter than the curved balsa front. This is to allow the 1/8" balsa fuselage sheeting to be glued to the edge of the firewall for greater strength.
Photo 3 shows the mounting tabs. 1/8" x 1/2" hardware store aluminum.
Photo 4 shows the engine offset.
Photo 6 shows the large hole in the firewall. I put the hole there to allow me to fish out the fuel line for the engine and put it through the firewall.
Note: Look for the photo number reference in the bottom right corner of the photo.