RV-7 N890GF

I went back to the airport to finish up the plenum. Its fully cured and super strong. The core adds a significant amount of stiffness while keeping the whole thing very light.

I removed the top plastic and the whole plenum just popped right off. I then trimmed the excess material around the perimeter.

it took a few iterations, but I was able to get it to fit quite nicely. There are some gaps that I will fill, but the overall fit is going to be more than sufficient.

The core material being asymmetrical is one thing that does annoy me, but its mostly asthetic at this point. The plenum will get sanded smooth and then another thin coat of tinted epoxy and some paint to finish it off.

I spent a majority of the time today working on the inlets, trimming and fitting the plenum to better align.

I opened the gap up to 3/8″ to provide enough room for the gap seals that I will fabricate. I used some test material to check the fit, and it will work.

The left inlet needs some work on the outboard side. I will likely build up the plenum top again with some additional fiberglass. The height of the plenum lines up perfectly with the cowl inlet, but the gap is about 1/2″ instead of 3/8″.

Here is the upper inboard side of the left inlet, the gap here is much better. the test gap seal fits much nicer around this side. On the lower side I will have to work the seal around the filter, which will likely result in an odd shaped seal.

I’m waiting for a shipment of some AA3 .032 1″x1″ aluminum angle from Vans. I will rivet it to the baffles and then the plenum will screw to the angles.

There are a couple things I learned during this process:

1. I should have installed the angle brackets first, and then pour the foam to create the mold. Then I could use the angle brackets to perfectly align the foam, which would result in a perfect fit rather than a mostly perfect fit.
2. I would have used six layers of fiberglass and no core material (or maybe plan the shape a bit more). There are some voids around the core edges, which I can fix, but I think six layers would be more than strong enough for this application.
3. Get enough sand bags to apply enough even weight across the entire surface.

I’m sure there are other learnings, but these are top of mind from today. If I make another plenum, I would do it this way next time.