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Building a Sonerai Cowling

By Bill Evans, EAA 794228, Chapter 266

June 2020You may remember that Bill added his own design Hoerner wingtips to his Sonerai and upgraded the engine from a Jabiru 2200 to a 3300, requiring more fuel capacity and some other significant mods. Here is a day by day account of what he has been up to recently. — Ed.

Worked all week to get this far with the mold and now cowling. This shows the second (heavy) layer of cloth applied. Ran low on Epoxy, will buy more tomorrow. The cloth is all stuck on but not saturated. I used 1/32 inch beeswax sheet as a separation layer to ease cowling removal from the mold. 8 sheets of beeswax cost, say, $100. Three liters of epoxy cost $120, all the layers of fiberglas cost maybe half that. The rip-ply used to create a mold like exterior finish cost $25 per yard from the Boat House. It is Spinnaker rip-stopper nylon. Lovely stuff to use.


Work stopped – out of epoxy.

If I had it to do again I'd buy epoxy by the gallon. Hoping to finish the layup tomorrow. I joined the cowling halves, covered them in 1/32 beeswax sheet and have the first 2 layers of fiberglas cloth applied. It's a lot like work. One layer is 18 ounces. One more 6 ounce layer should complete it. I'm changing everything about it.

Spent 4-5 hours today laying up the third layer of fiberglas cloth. It is 6 ounces. With the mold inside it is all I can do to lift it. Most of the weight is resin, as it took almost three liters of epoxy. The middle layer is something like 18-20 ounces. It really drinks in the resin, however it also provides strength and thickness.


Cowling with plugs.

I used plastic wrap to cover the foam urethane plugs used to size the propeller shaft and cooling inlet openings. Once they are removed, the inlets are ready to use.


Rip-stop fabric taped in place.

The white and red stuff you see on the outside is Nylon rip-stopper fabric used in spinnakers. It costs $25 per yard. It allows any excess resin to soak through but does not bond to the fiberglas cloth. Once it is cured, you just rip it off. Results in a virtually perfect finish.


Planning to use Camloks to attach to firewall.

My friend Gord and I plan to locate the piano hinges on the sides, before cutting the cowling in halves, upper and lower. I'd like to use Camlok fasteners (1/4 turn) to attach the halves to the firewall. I just might find a use for the Hartwell latches inside the lower half to draw it into the firewall. Not sure I can conceal them entirely, but maybe.

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