Drain Hole Diameter vs. Drain Time

[David Paule]

Since I hadn't seen any quantitative data for this, I decided to test it.

The test set-up was an empty 4 oz. can of chiles, set up on a rack in the kitchen sink so that I could have ready access to it. I’d fill the can from the faucet and start the clock when I moved the faucet away. This gave me a consistent timing set-up. I tried #40, #30, #19 , 3/16” and 1/4” holes.

Here’s the raw data:

#40 took 82 seconds
#30 took 52 seconds,
#19 took 30 seconds,
3/16” took 25 inches and
1/4” took 15 seconds.

Except for the 1/4” hole, all had at least some water remaining, generally .03 to .05 inches. The smaller holes had more variability for the time remaining, so I averaged the times. I did each at least twice.

Here’s a chart, with seconds on the vertical axis and hole diameter on the horizontal axis.



I'll probably use 3/16" or something between that and 1/4".

Worth noting is that my 1955 Cessna 180 has some nice snap-in fairings for its 1/4" drain holes. But they don't seem to be in the parts manual and I don't have a part number. They are roughly similar to the "seaplane" grommets AN231-4 used for fabric airplanes, but metal and they pop into the holes. With a decent glue, I'd imagine that the seaplane grommets would work but I didn't test any holes with them.

Dave

[PilotjohnS]

So what drain time is good enough?

[wirejock]

Which drain hole?
Fuse, or intake?

[David Paule]

Even the smallest hole I tried had a steady stream of water from it, until the water got to within maybe 1/4", when it started dripping. Should have mentioned that. The larger holes had less drip time and less water remaining.

You'll have to decide for yourself what size hole to use - but this at least gives you a basis for that decision.

Dave

[terrye]

"3/16” took 25 inches and" I think you mean 3/16" took 25 seconds?

I assume this is fuselage/wing water drain holes? My C-150 has approx 1/8" dia holes in the bottom skin on the aft side of each bulkhead. When they made the hole it looks like they took a 1/8" punch and levered it aft after they drilled the hole, I guess so it would suck out in flight.

To me, 3/16" or 1/4" water drain holes are just asking for wasp nests inside the structure, even if the plane is in a hangar.

[PilotjohnS]

Terry I think you have a point. I plan to use #40 drain holes unless someone has a reason to go bigger. .

[PaulvS]

Originally Posted by PilotjohnS

Terry I think you have a point. I plan to use #40 drain holes unless someone has a reason to go bigger. .

One reason to go bigger is to avoid the drain holes being blocked by dust and small pieces of dirt that will accumulate over time in the fuselage. At least that is a consideration in dusty regions of the world.

[Hangar 1271]

For no good reason whatsoever, I decided to see if your numbers made any sense. Since the time to drain is mostly influenced by area and head (I can't begin to determine the impact of turbulence on this) and, assuming the most accurate time is the 1/4 hole, the time to drain would theoretically be:

Hole Time
40 ____ 98
30 ____ 57
19 ____ 34
3/16 __ 27
1/4 ___ 15


Your numbers are reasonably close to these.

[David Paule]

Or you can get a can and try it yourself.

When I bought my C180, the interior was quite dirty. The plane was over 30 years old at the time and while the upholstery was fine, the belly and tailcone was loaded with the grease and debris that accumulates there. I stripped the interior, put the plane on grass and proceeded to spend a nice weekend scrubbing it out. I used a hose to rinse it, and found that virtually all the drain holes were clogged with grass and stuff. Several of those little snap-in drain things were misaligned. All that got fixed. I had water several inches deep at the bulkheads.... good draining can be important.

Dave

[stigaro]

Originally Posted by Hangar 1271

For no good reason whatsoever, I decided to see if your numbers made any sense. Since the time to drain is mostly influenced by area and head (I can't begin to determine the impact of turbulence on this) and, assuming the most accurate time is the 1/4 hole, the time to drain would theoretically be:

Hole Time
40 ____ 98
30 ____ 57
19 ____ 34
3/16 __ 27
1/4 ___ 15


Your numbers are reasonably close to these.

Heh, I did the exact same thing but chose the #40 as baseline due to less timing error on the 82 seconds. I get:

Hole Time
40 ____ 82
30 ____ 48
19 ____ 29
3/16 __ 22
1/4 ___ 13

Pointless, yes.