The O-360 typically comes with a vertical carburetor. On the XHawk it protrudes slightly through the bottom cowl. Upstream from it, we need an air intake that filters the air and can, at the pilot’s discretion, redirect warm air to the carb. The main options for the intake are the Bearhawk Aircraft heat box, Aircraft Spruce’s MA4-5 heat box (Part# 08-01630), and the Van’s FAB-360/540. This post is about the first one. At the time it did not come with any instructions and left install details entirely to the builder. ## Bearhawk Heat Box Generally speaking it fits the Patrol even tough it seems to rely on a filter size that is dimensioned for a six cylinder engine. This may turn out to be an advantage on dusty dirt strips. Part of the top filter is inside the cowl and needs a fairly aggressive inlet ramp to seal its frame to the cowl skin. ![[Air Intake-20241228155328949.webp]] I made the initial clearance hole as small as possible. Towards the front I needed all the material. Towards the rear I ended up removing quite a bit more of the cowl skin. ![[Air Intake-20241228155339586.webp]] In the side profile we can see how far the air intake cuts into the silhouette. This makes designing the enclosure challenging. ![[Air Intake-20241228155351515.webp]] The frontal view also reveals that the carborator and inlet are not on the center line. ![[Air Intake-20241228155400550.webp]] ![[Air Intake-20241228155434136.webp]] ### Mounting Bolts The heat box mounts to the carburetor via four head-drilled bolts (MS20074-04-03). The space to get them in is minimal. Widening the holes a bit may be necessary. ![[Air Intake-20241228155448426.webp]] ![[Pasted image 20241228155500.png]] ![[Air Intake-20241228155514357.webp]] Some holes needed a diagonal slant to help the bold slide in. ![[Air Intake-20241228155526865.webp]] ## Intake Enclosure The starting point of the enclosure is this 4x-folded aluminum sheet. My kit contained a part that was vaguely fitting (probably the from the the Bearhawk 4-Place). I needed to trim it and redo the end folds. ![[Air Intake-20241228202109547.webp]] ![[Air Intake-20241228202640242.webp]] Here is the oversized sheet metal piece from my kit with the cardboard mockup attached. ![[Air Intake-20241228192908118.webp]] Building this entire sub-assembly involves a lot of observation and contemplation. I generally like the process of solving these riddles. Having no authoritative instructions moves the task from a pure assemble job to a design activity. How do I make a solid enclosure with the materials and tools at hand? How do I keep it light and strong? What approaches reduce the amount of labor to a reasonable amount? I like this kind of thinking but the associated delays test my patience at times. ![[Air Intake-20241228202939809.webp]] The key to building the front-facing part of the enclosure is locating the seal towards the air filter. For this I built a frame from aluminum C-extrusions and taped it on with a temporary 10mm cardboard spacer. ![[Air Intake-20241228204900876.webp]] The point of the C-extrusion is creating a seal mounting point. The thinking here is that a fairly wide seal will be able to deal with significant lateral motion of the air filter, as expected during engine start. The setup allows me to customize the seal from high-flex Neopren strip as needed. ![[Air Intake-20250101122556022.webp]] ![[Air Intake-20250101122718169.webp]] ![[Air Intake-20241228205943856.webp]] The next step is about closing the gap between the frame and the rest of the enclosure. For this I cardboard-templated six sheet metal pieces as precisely as I could. ![[Air Intake-20241228211735427.webp]] These parts are fairly complex shapes that are difficult to get perfect. ![[Air Intake-20250101122915334.webp]] ![[Air Intake-20250101123008662.webp]] The remaining gaps I simply back-filled with epoxy. This is easy to apply when adding cotton fibers as a thixotropic agent (add as much cotton as it takes to stop the epoxy from dripping). ![[Air Intake-20250101123252712.webp]] As you can see the air intake adds a significant amount to the sky-bound force. ![[Air Intake-20250101124012276.webp]]