Ch 23 - Oil cooler fan - part #2

Shroud build up 

So… let me show you how I finished the shroud.

Starting with the top flange, I used four small blobs of hot glue to fix it to the main body, then I glassed the two together from the inside out.

Using scrap wood to suspend the assembly

Glassing the shroud from the inside out

To make sure the top flange would come out as flat as possible, I backed it with the 3D printed flange, and put some weight over it while it set.

Because I used EZ-poxy, I had the let the assembly cure overnight between every glassing cycle. 

Keeping the flange flat

The next morning I started by sanding the assembly down, and hot glueing the bottom flange to it. After making a small flox corner, I wrapped a continuous BID strip over the intersection (a few times over) glassing both flanges to the middle piece from the outside, and let it cure again.

Working on a flox corner

Glassing both flanges to the main body from the outside

Curing overnight

Looking at the part at this stage, it was pretty obvious that even though I had extended the bottom of the shroud vertically by about half an inch (13 mm) before the 3D lofting took place, this didn’t produce enough space to be able to insert the bolts, and even less for wrenching on them.

I created as much additional room as I could around the bolt locations by grinding fiberglass down, but it eventually became clear that the structure integrity would be come compromised and a different approach would be required.

Grinding back the glass to make room for the hardware

Unfortunately, this is not enough room to maneuver about with wrenches.

I decided to cut holes in the shroud over the bolt locations, and glass tiny domes big enough to account for bolts and wrenches.

Test fitting once again. Some of the holes already opened up.

The issue of the two bottom leaks had to be addressed at this point as well, so I used cardboard scraps to identify how much to modify the structure.

Obviously, these gaps needed to be filled.

Using a cardboard to measure the gap...

... I meant to say... gaps.

Next, I started cutting the bolt relief holes into the shroud.

Bolt and wrench relief cut into the shroud

A side view

As seen from the oil cooler side

I used plasticine to build up the structure of the relief domes…

Plasticine mold build up

Side view

… then I glassed over them.

Ready for glassing

Relief domes glassed

This modification worked as intended, creating just enough room to insert the bolts and tightening them.

Bolt relief created by the domes

Plenty of room for a wrench too

Lastly, I glassed a “skirts” to the front and rear sides of the shroud to close the gap with the oil cooler, and also used RTV silicone to seal it.

Marking the skirt depth

Sanding the bottom skirts

Sanding the top flange

RTV silicone where the skirts will seal

Forward skirt sealing over the silicone

Final bolted test fit

A quick epoxy wipe and we are done! Only 160 grams.

Here's the finished product!

Good fit, and no leaks.

This baby is ready for testing

Clearances from other items are good

Looking straight down on the installation (up is forward)

Next time I'll be walking you through the fan's bench testing process. This is a necessary step in order to gather data to help us make as good correlations and inferences as possible with the inflight gathered data.