The plenum that we are fabricating was molded over the plenum of our chapter EAA tech counselor who has made three other plenums for RVs. His plenum was molded on the inside of the upper cowling which was used as the female mold. We measured between the side baffles and between the front and rear baffles. We then used the dremel fiberglass cutoff wheel to trim to those dimensions.
The inlet duct portions of the plenum should just clear the top of the upper cowling inlets. The trick will be how to seal the inlets and create a smooth explansion of the air as it enters. The plenum will move with the engine while the cowling remains fixed. I think rubber will be used to connect the plenum ducts to the inlets. I just don't know how yet!
Trimming the right inlet duct.
Trimmed plenum not yet attached is placed over the forward baffles tp check the trimming.
