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drain in FAB?

P

prkaye

Well Known Member
It occurrs to me as I work on the FAB that there is no palce for water to escape. If water gets in there, how can it get out, without getting sucked up into the engine?
I'm wondering why the plans don't call for us to drill a small water-drain hole in the bottom of the FAB (at least I haven't seen an instruction to do this). I suppose one drawback is that it would reduce the air pressure in the FAB...
 
Yeah, drain required. one inside the filter space, one outside the filter in my opinion. This is even more useful to let raw fuel out if someone pumps the throttle too much without the engine running.
 
Is this in the plans? I'll have to check-again. If not, what size drain-holes would you recommend?
 
The instructions (page 2 para. 6) say to drill two 1/8" holes at the lowest point of the bottom of the box, one inside and one outside the filter.
 
Yes, isn't it great that they mention the drains at the beginning of fabrication and later when it's time to position the holes they only discribe the inside hole with the optional drain tube. Got me in trouble as my partner said two were required and I said he was mistaken. Luckily he knew they mentioned at the beginning of the instructions. At least this is what was supplied with the RV-10.
Ron
 
Here's a little hint for finding the low spot. On my 3 (taildragger) :) I waited till I had mouned the fab with the a/c sitting on its gear, put an ounce or so of red dye in and let it settle and leave a stain mark or sight from underneath with a flashlight. Drill away
Tom
RV3 x 2.
 
Put the whole thing together, find where the filter sits, and put one on each side of the filter... done. There are a LOT of RV's out there flying without this, and only two out of three I know of lit on fire :).
 
osxuser said:
Put the whole thing together, find where the filter sits, and put one on each side of the filter... done. There are a LOT of RV's out there flying without this, and only two out of three I know of lit on fire :).
Click to expand...

Close but not exact.

Put one small hole (#30) in the aluminum plate that covers the bottom of the K&N air filter. Then put another #30 hole in the low point on the FAB.

This will allow any fuel to drain out of the carb, past the filter plate, into the FAB, and then drain out of the FAB.
 
All of a sudden

osxuser said:
Put the whole thing together, find where the filter sits, and put one on each side of the filter... done. There are a LOT of RV's out there flying without this, and only two out of three I know of lit on fire :).
Click to expand...

I feel warm and fuzzy all over..NOT!
 
Fire down below?

I have been debating about installing the filter bypass on my FAB. I am just completing it and need to decide.

I called a local RV-6A driver and asked if he had installed his. He originally did, but gas dripped from the throttle body down onto the plate and through the door gap onto the bottom of the cowl. During a engine start he had a FAB box fire. Fortunately as the engine started it extinguished the fire. He didn't know this until he inspected the FAB and found it damaged. He promptly removed the filter bypass valve and glassed in the bottom.

His recommendation was to glass in a piece of 1/4 aluminum tubing to the outside bottom of the FAB, drill the drain holes into the tube and run a hose to the lower firewall/cowl exit. Similar to the fuel pump overflow/pressure relieve vent tube run per the plans.

Food for thought...............

Paul
 
A Question

I have a question about the drain holes in the FAB. Are these holes for water that collects when the plane is parked on the ground? The reason I ask is that when the engine is running, isn't there so much engine suction that nothing will drain out the holes? Wouldn't engine suction induce airflow from outside to inside of the FAB through the holes?

Tom
RV-7A N175TJ Flying
 
The holes are actually to drain out FUEL that has pooled in the FAB when the engine is over primed. If you don't, the fuel will puddle, then if there is a backfire... it will ignite... ruining your whole day, and potentially part of your airplane.

Bill, I think your -9 might be different from the -6's I've worked on, because there is no plate at the bottom of the FAB, the filter just sits down in and gets clamped by pressure to the carb plate.
 
osxuser said:
Bill, I think your -9 might be different from the -6's I've worked on, because there is no plate at the bottom of the FAB, the filter just sits down in and gets clamped by pressure to the carb plate.
Click to expand...

I don't think the difference is between the -6 vs the -9. It has to do with the different engine. My (O-320) -6 has a metal plate like Bill's. The O-360 does not have the plate.
 
Mel said:
I don't think the difference is between the -6 vs the -9. It has to do with the different engine. My (O-320) -6 has a metal plate like Bill's. The O-360 does not have the plate.
Click to expand...

It isn't a difference between O-320 and O-360 but just basic version of FAB. I have a -9 with an O-320 and have a FAB without the extra lower plate. I think we just have different vintage airbox designs from Vans.
 
Weird, I've worked on quite a few different -6s of different vintages, and don't recall the plate in any of them, 320 or 360...
 
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