The Terrifying Tale of FrankenSnorkel !

[scsmith]

Originally Posted by scottmillhouse

Noted, I don't disagree but lot of things require compromises when building. We will see by my empirical testing in flight. My cover installation was to tie the snorkel, baffle assembly together as a solid unit with too little real estate to fit the filter. The x gave it the strength for a thin sheet to conform to the complex shape without buckling. I agree a sharp edge will not promote laminar flow but will act as a weir causing some turbulence. The question is does that cause any effect to the engine's needed airflow. In flight the inlet is pressurized so worse case is wide open throttle at redline during initial climb out. I believe there must be substantial excess flow capacity and area since the same filter is used for the 360 and 540 with two more cylinders by Vans web site.

It is not a matter of laminar vs turbulent flow, it is a matter of reduced effective flow area because of separated flow regions.

The only way you will be able to assess performance is a side-by-side comparison of MAP at the same time and same conditions. I know that my filtered flow drops the manifold pressure about 0.3 in. Hg compared to full ram flow at sea level take-off power. I suspect yours will drop the MAP a half inch or more.

[dtw_rv6]

I rebuilt mine twice when I built the airplane 10 years ago and I've never liked it. It was looking long in the tooth last fall, so I replaced the baffle ramp and did some re-glassing this summer. The primary goal here was to make the filter easier to service. I 3d-printed a set of molds, and here is the result. Its still not pretty, but I like it a lot more than what I used to have. Maybe I can finish out the perimeter with a rounded profile to incorporate Steve’s recommendation...

[DanH]

Originally Posted by scottmillhouse

I believe there must be substantial excess flow capacity and area since the same filter is used for the 360 and 540 with two more cylinders by Vans web site.

There is no excess. I think Steve's MP loss estimate will be pretty close.

[wjb]

Following the ghastly (and very educational) experiments outlined above, I too felt the need to fix my ill-fitting snorkel. The stock fiberglass ended up too far forward and too far outboard for my intake ramps:

Very tight to the front edge:


Not centered on the ramp or the inlet:


Hanging loose over the edge:


So, using all the VAF smarts I could scrape from DanH's fantastic fiberglass tutorials and other franken-doers, I decided to build a custom flange for the filter (apparently, the -14 already has this). MDF and insulation foam, covered with thin epoxy, wax, and PVA:



After layup, unmolding, and digging out the pink foam:



Fits the filter perfectly!


Nicely fits over the intake end of the snorkel:


However, the position is still wrong .. it needs to move back and inward:


Ok, doctors, time to prep for the "cut":



... stay tuned for part 2 ...

[wjb]

OK ... I made the cut; I'm committed now! After the original cut, I trimmed about a half inch off of the outboard section.


Time to bolt and cleco everything in place to fit the middle section:


It nests nicely now, wiht about a half inch of overlap. Note the corners cut off the filter flange ... I needed a bit of adjustability to get everything to line up properly.


Inside view looking in from the filter side


Time to prep to close the wound. Shaped and pressed into the servo side opening.


Trimmed off another ~1 inch from the filter side, plugged the hole with another piece of foam, and filled the middle. Slathered some pour-in-place urethane foam as a gap filler. I'm not looking for a perfect surface here, just a good substrate to hold the first plies of glass in place.


This foam is great; cures quickly and is VERY easy to shape. Sanded back the easy to access sections (front, bottom, back) and prepped for glassing. Top will be done after the initial plies cure and I can remove the assembly.


Two ply layup on ... quitting time for today.


Pulled the snorkel. Made and additional cut and added foam to get a better curve on the top side


More pour-in-place urethane foam to fill the gaps:


.. stay tuned for part 3 ..

[wjb]

The top now cured and shaped and ready for glassing. I added two more plies over the top, with about a 2 inch overlap on the seams. I Then added an additional two layers, a bit wider and longer that than the first set, with their seams 1/4 rotation around the neck from the original set.


Final bonding of the filter flange to the body. Everything now fits PERFECTLY!


All done and ready for painting:


Procedure complete; Snorkel better than new!


Thanks everyone for all the great tips and pointers that made this an enjoyable recreational-and-educational experience.

[DanH]

Well done Bill. Spend the time to prep and finish the outside for paint to match your exterior color scheme. You'll get a little kick every time you look at it.

Everyone needs at least one part which is their creation.