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FAB Airbox & inlet filter

Graham

Active Member
Hi all,

I am installing the FAB airbox in my slow build RV6 with an O-320 engine.

In doing this I am having "fun" with vertical alignment of the FAB inlet with the airscoop inlet.
Initial trials with the airbox cleecod together indicated that I had to raise the inlet fwd end up which necessitated cutting the fibreglass airbox & re-glassing it. When I finally did this and bolted the airbox together with a filter installed I found that the airbox is 0.25" to 0.31" too high.

And yes I had both cowls installed when taking measurements. I suspect the fglass may have moved when setting and the cleecod assembly may have been too flexible. For the eagle eyed I have a "spare" filter on which I am learning how to do the cutouts on.

To alleviate this (& avoid re-cutting the fglass) I am proposing to pack the entire airbox assembly down by up to 0.31" by installing two 0.125" al packers between the airbox and the carb, and by thickening the Mount Plate from 0.063" to 0.125".

This will result in the air filter cutout being a lot shallower (approx 0.31") which means I can just trim the filter top rubber ring and not butcher the filter as Vans requires.
I do not like the vans filter butchering, it is not good design.

So my question is. Has anybody done this (or similar) and if so what has been their experience. Any other feedback also welcome.

Thanks in advance.
Graham Murphy
New Zealand.
 
In response to the initial post, I too needed to adjust the stock fiberglass airbox but doing so was actually pretty easy. I didn't do this until I had the lower cowl inlet glassed and ready, then used it to determine the position of the layups to support the adjusted front end of the airbox.

The only doctoring of the filter I needed to do was to provide two small relief areas in the top of the filter to clear the bolts holding the top plate to the engine.

This was for an updraft injected engine, but not sure there would be any significant differences.
 
I heavily modified my FAB.

Here are some pictures of what I did.

It has worked out very well but you should know that I also had to make a custom carb heat flapper valve.
 
I heavily modified my FAB.

Here are some pictures of what I did.

It has worked out very well but you should know that I also had to make a custom carb heat flapper valve.

Is the picture link locked?

Re-reading the original post, I think simply cutting the glass portion, bending the aluminum to the correct angle and re-glassing the joint would actually be easier... :)
 
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If you have a downdraft carb engine, long James cowl, and the Vans exhaust with the heat muff in front, good luck. You will find that you will have to cut the carb heat supply tube off the heat muff and point it straight ahead if you want to use the James FAB. I tried several different ways and just could not make it work.

After many hours trying, I am using the Vans FAB. I am still working on it, hopefully getting close to making it work.

Contact me if you want pictures.
 
Is the picture link locked?

Re-reading the original post, I think simply cutting the glass portion, bending the aluminum to the correct angle and re-glassing the joint would actually be easier... :)

Gill, try it now. It looks like the security changed when Google moved the pictures over from Picasa.
 
I Installed an O-320 in an O-360 cowl. To avoid total hacking up the FAB and to accommodate FI some day, I fabricated a 1" spacer, The interior of the spacer matched the the carb entrance diameter. I flew this configuration for 100 hours with no issues. At 100 hours I replaced the carb with FI and ditched the spacer.

Be sure to use safety wire on the bolts to keep them tight. It is a high vibration area and the spacer makes it easier to loosen up (assuming a non-metal spacer). I treated the safety wire as redundancy and didn't get it really tight. The FAB loosened up in under 10 hours. I then wired them very tight and no problems.

Larry
 
, and by thickening the Mount Plate from 0.063" to 0.125".

You should do this anyways. I have read several posts about cracking on that piece. I made of copy of the top plate in .063 and riveted it to the original. I also riveted on an angle for good measure. 220 hours and no cracks so far. I also believe that good alignment with the snout opening will also eliminate stress on this part.

Larry
 
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