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How to Size a Jet Exhaust Cone – Layout Method

This method is a bit simpler than the previous method.  It involves little math but may require the same clearing of the dining room table to make the layout.

It was sent in by Bruce Brown, club member, expert aerobatic pilot, retired sheet metal Journeyman and all ’round great guy.  I’ve flown aerobatics with Bruce for many years and when I want to know exactly how a maneuver is suppose to be flown I just watch him, usually followed by “Oh, that’s what it’s supposed to look like. . .”  

Bruce:  “If the cone adapter for the jet exhaust was your project then here’s how I would have done the layout, just as I did at work for 36 years. (Step 1) Draw a vertical centerline, then an outline of the fitting or “side view” of cone, bottom being the big end (D2) and the top (D1) centered above it by the length of the cone.  Then draw lines through the end points of D1 & D2 and extend them upward until they intersect. (Step 2) This is the point (Vertex) to then swing arcs through the same end points of (D1 & D2). Multiply D1 & D2 each x π to get their circumferences, which are also the arc lengths (Arc1 & Arc2).  With a flexible ruler, measure half the circumference (arc length/2) to each side of the centerline along the arcs drawn.  Then from the ends of the arcs, draw lines back to the Vertex. (Step3) You now have the pattern.”
I provided these drawings to help visualize the process.  I added the references in Bruce’s instructions above.  This is the adapter for my Jet Vision mentioned in the previous post.