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Dans RV8
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Date:  11-22-2016
Number of Hours:  1.00
Manual Reference:  
Brief Description:  Straightening cowl seal path

The baffles are trimmed 3/8" to 1/2" from the cowl to allow the engine to move in its mounts. Without further sealing, airflow across the cylinders would be inadequate. Image 2 shows rubber seals attached to the aluminum baffles to fill the gap while allowing a little movement.

The RV8 baffle design has a joggle in the rear that woudl require two extra 90 degree turns (Red Arrow in Image 1). These are notorius sources of leaks. The RV8 design had four 90's. Getting rid of two is a big win.

I looked at the RV14 design (Figure 2) It has a filler to provide a straight run across the rear baffles. Due to the cut of the smaller RV8 cowling, thad design wouldn't work.

I came up with the idea of making a plastic filler part to put in the joggle (red arrow) to ease the transition with a couple of gentle bends. (Image 3). The first concern was the engine compartment temperature. Would the plastic melt? ABS melts at around 200 C. I found a great study on the RV Forum where several guys instrumented the engine compartment. While the cylinders can approach 200 C, the nearby parts are typically around 50C with peaks of around 70C. Plenty of headroom to use plastic. I also considered the possible failure mode. The seal will span the platic part, which is only 5 1/2" long. Shoudl the part melt, the seal will be mostly retained in place. Risk is certainly low enough to test.

I quickly designed this up in 3D CAD and started printing a part. The prototype took 3 hours of printing, but zero of my time.

I will take it to the airport for refinement tomorrow. I intend to add mounting holes, and may have to adjust the spline to match the baffle curve.

I am liking 3D CAD methodology!
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Joggle in Rear Baffle

Joggle in Rear Baffle

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Plastic part to straighten the path

Plastic part to straighten the path

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Printed Part

Printed Part

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