I modeled the exhaust collector cone in CAD and then flattened it to give me a pattern of the holes as shown below:
I glued this on and then machined and ground out the material.
Below is a test fit of one of the bent tubes:
Next I grabbed a piece of scrap aluminum and made a fixture to hold the exhaust system in the proper position for silver soldering.
Below is the exhaust system ready to silver solder. Or so I thought.
In hindsight there is a bunch of stuff wrong with my fixture. And I found out the hard way.
- The 1/4″ plate that I used to secure the exhaust flange acts as a heat sink and wicks all of the heat away from flange as it is silver soldered. An excessive amount of heat was required to get the silver solder to melt, and it ended up just globbing up at the joint. I had to come back later, reheat and shake off the excess.
- I used thin strips of aluminum held together with very thin stainless steel wire to align the feeder tubes. The thin aluminum strips ended up melting and dribbling all over the collector tube and the thin stainless steel wire simply vaporized. Primarily due to excessive heat, see 1. above.
Below is the exhaust system as it sits now. It is functional and I may use it for initial engine checkout, but I have all the material for a couple more tries.
This is only the second time I have attempted silver soldering and I know that I need a better fixture and more practice.
One of the last remaining flying Boeing B-29s visited my air field this last week. This amazing aircraft holds a special place in my heart as my father regaled me with many SuperFort stories when I was a kid. He was in the Air Force and his time in the war was spent at forward Pacific island air bases keeping them flying.
