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Model Airplane Construction: Firewall installation for a Zenoah G-38

Model Airplane Construction: Firewall installation for a Zenoah G-38

We always look for good techniques to share with our readers so I reached back to some of my Sopwith Camel Build-along posts. With this post we turn our attentions to the front end and work on the firewall installation. The techniques can be used with any RC model you want to modify so you can hang a gas engine on its nose.

So before installing the firewall with its proper down and right-side thrust offsets, I had to work on the engine installation and the soft-mounts and muffler clearance.


For 2 degrees of down and 2 degrees of right thrust, I offset the centerlines on the firewall 1/4 inch in the opposite directions, so the engine’s prop shaft would be centered in the cowling.


Here is the stock G-38 mount plate I have on the engine. To clear the soft-mount isolators so they would not touch the muffler box yet to be built into the model, I had to drill new holes in the lower section.


Also to allow the mount plate to set flat against the soft-mounts, I counter-sunk and installed flush attachment screws to secure the engine to the mount plate.


I then centered the mount plate with the offset centerlines and drilled out the holes for the isolators. The muffler clearance was transferred from the side view of the plans. This way, when the enclosure box is glued into place there is proper clearance for the mounting hardware and the muffler to fit into the box.


Here I am test fitting the engine and muffler. Plenty of clearance all the way around.


Here is the front of the firewall, As you can see, the soft mounts would not have cleared the muffler if I used the old mounting holes.


Next using the side views I installed the tristock backing strips for the firewall. They are also offset so the 2 degrees of right and 2 degrees of down thrust will be set when the firewall is glued into place.


With the fuselage upside-down, I slip the engine and firewall assembly into place.


A good fit and the thrust angles are correct. Remember the fuselage is upside down.


Before gluing the firewall in, I made sure the muffler would also fit and clear the compartment to be installed afterwards.


After removing the engine and soft mounts, I placed the fuselage on its side and epoxied the firewall into places. I used lead weights to make sure the glue joints fit snug against the back support tristocks strips.


Placing the fuselage upside down again, I glued in the front support strips. I checked the angles and centerlines during the whole process.


Here’s an aft view of the completed installation. The former shown here will be used to support the front of the fuel tank supports.

Remember, for great laser-cut parts, use Trillium Balsa (

That’s it for now. Now on to the landing gear attachment blocks. Stay tuned.

To go to the next installment (Part 4,) click  the link:

To see Part 2 of the build-along go to:



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