REFLECTOR: Rain and top fuselage naca

[Bob Jackson (Jax Tech)]

Kevin,

You will need a drain for the overhead NACA that pressurizes the overhead
cabin fresh air plenum, too.  We fashioned a kind of 'bowl' or intermediate
plenum directly beneath the fresh air NACA and then added a 3/8" drain line
down and out the bottom of the fuselage (with the bevel cut directed aft to
help it 'suck' out any moisture).

The main thing to take into account with the 'intermediate plenum' below the
NACA (if you're building a retract Velocity) is the fact that while the main
gear linkage is retracting, at one point in the cycle, the hinge point in
the linkage goes up to within just a few inches of the fuselage ceiling --
so you need to make sure the 'intermediate plenum' doesn't restrict the gear
linkage travel.  The intermediate plenum must be the low point of the fresh
air overhead plenum, and it's where the drain line must run from.

Bob Jackson
Turbo XL Velocity
N2XF

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Kevin Baker
Sent: Monday, October 10, 2011 8:49 PM
To: Velocity Aircraft Owners and Builders list
Cc: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Rain and top fuselage naca

Thanks Scott
What about the small naca scoop that goes into the cabin?
Did water drain into the cabin or fill up the back of the channel.
??

Thanks
Kevin

.

On Oct 10, 2011, at 19:33, Scott Derrick <scott at tnstaafl.net> wrote:

> 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
>>