REFLECTOR: Rain and top fuselage naca

[Scott Derrick]

Sitting or flying the rain enters the plenum and drains down through the 
engine.

In flight I imagine some of the water exits out the rear openings.

I do have multiple drain holes in the lower cowling at the low points 
and a drain hole in the ram scoop/filter housing which is below the 
fuselage/rear cowling.

Interesting story about not having a drain hole in a low mounted intake 
scoop.  I was washing my plane last summer.  It was about 6pm and the 
airport was deserted. Finished washing and wiped it down with a shammey, 
got in and was going to taxi it back to the hanger. I was pretty 
aggressive in spraying it down with water and rinsing as it was really 
filthy.

I gave it a 3+(probably 5 I was distracted) second burst on the fuel 
pump for priming and hit the starter. It coughed but didn't start?   I 
gave it another shot and hit the starter, it made an odd muffled kind of 
sound and didn't start?  Hmmm... Not like it at all.  I bent out the 
door and down to look back and under saw a fluid dripping from the drain 
holes in the cowl which seemed OK, I had just sprayed it with water.

I gave it another short burst of fuel and hit the starter, still nothing.

Got out and walked back to the rear and bent down to see if that was 
water slowley dripping from a drain hole, I rested my hand on the intake 
ram scoop below the fuselage. IT WAS REALLY HOT!

I thought, SHIT THATS HOT! I touched it again to convince my unbelieving 
self that it really was hot, IT WAS!

I ran back to the front and opened the throttle, idle cutoff on mixture 
and held the starter on for about 30 seconds.  It actually coughed a few 
times at about the 15 second mark and seemed like it wanted to start.

I ran back to the rear and the intake was a bit cooler.  In a minute it 
was definitely cooling off. I removed the rear part of the scoop and it 
was partially black in side as was the servo intake tube. The filter in 
the front part of the scoop was partially melted. NOthing damaged but 
the filter thank god.

Without a drain hole the rear part of the scoop filled up with I don't 
know how much water, then when I gave it a shot of fuel(probably too 
much) some ran down and probably floated on top of the water.  That fuel 
ignited somehow, maybe a back fire!

I now have a 3/16 drain hole in the lower part of the scoop. I had not 
put one in because I was trying to seal it really tight for ram pressure 
in flight and sucking dust during taxi.  Now I sacrifice a minute amount 
of pressure during flight and probably don't get but a few specks of 
dust through that little hole during taxi...

live and learn..

Scott
-------- Original Message --------
Subject: REFLECTOR: Rain and top fuselage naca
From: Kevin Baker <flykb at verizon.net>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Date: 10/10/2011 04:55 PM

> Hi all
> As it's raining here in Dallas, finally.
> I was wondering about the naca scoops on top of the fuselage and rain/water getting into them.
> More importantly the small center air scoop.
> Are folks putting in water drains for rain or wash water to drain from? Or ?
>
> Thanks
> Kevin Baker
>
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