REFLECTOR: NACA scoops

Wed Oct 19 10:57:35 CDT 2005

polite and subtle?? Are there two Scott Derricks' on this list?? :-)

I bought the premolded NACA's and ducts from the factory. I got the 
large size to accomodate the large engine, and they fit fine in my Std 
airframe.

I'm glad I got the pre-molded stuff. I have enough tasks(never ending) 
in my limited 1 to 2 days a week of working on the plane. They are 
relatively inexpensive and easy to install. I of course didn't have the 
premolded markings and indentations in the fuselage, but it was a simple 
task to make a template from the NACA's to transfer to the fuselage and 
firewall for cutting the holes out. I should get some pictures.

I had the engine on the firewall last month and started the induction 
system and turbo installation. It became apparent rather quickly that my 
newly mounted engine mount was sub-optimal for the induction plumbing. 
After trying to talk myself into believing I could make it work I 
finally gave up, pulled the engine and have started on a new mount. The 
problems were interference areas that would have made the induction 
plumbing a Rube-Goldberg affair. With just a few changes in the mount 
the plumbing changes to a simple and straightforward affair. And simple 
is the Prime directive. I just received all new metal and hopefully will 
be cutting and welding this weekend.

In the mean time I've started on replumbing my oil cooling system. 
Pulled out the huge and heavy high pressure rubber/steel braided lines 
from the pilot side duct. Using 5/8 copper tube one in each duct, with a 
secondary cooler/cabin heater under the rear seat. The copper lines are 
bonded(bolted and soldered) together in the front and rear and will also 
serve as the ground line from the battery to the engine compartment. 
This will nicely match the 1/0 AWG welding cable I have now for the 
positive wire. I also removed the cabin heating apparatus from the 
forward oil cooler duct to improve airflow through it. The mid body oil 
cooler/cabin heater is just about finished.

I also just finished the upper cowl receiving flange on the fuselage 
that will allow me to toss all those pesky fuselage cowl fasteners. The 
lip of the cowl now fits snugly between two receiving flanges, only 
screws will be where the cowl mates to the wings and where the upper and 
lower cowl meet behind the wings, they will be captive fasteners. No 
more nicks in my nice new Catto prop from errant cowl fasteners. Now to 
do the bottom cowl receiving flange.

I've almost finished fitting the cooling plenum to the IO520. this was 
the premolded plenum for a IO550. Luckily the factory makes it with a 
good bit of extra lengths where it is cut to fit and there was plenty to 
adapt it with out adding a hardly any glass to make up for the different 
head design(angle verses parallel valve.) and upper deck turbo plumbing.

I finally located all the required exhaust bends & fittings to relocate 
the turbo to a central and tighter location. Once I rehang the engine I 
can cut, fit and tack it together. Then send it to Custom Aircraft for 
final welding and testing. None of the turbo manufactures want to deal 
with a lowly homebuilder and the few aircraft turbo exhaust places don't 
either. I found the 4" V-Band flange and clamps from a large racing 
outfit, the 3" 321 stainless bends and slip joints from another racing 
shop and am having the large inlet and outlet flanges machined locally.

Of course, this has turned into a much larger project than I thought, 
but its been fun so far....

Got checked out in a local 172 rental so I can fly a bit. I didn't 
remember them as being so slow and under performing??

Scott

Greg Poole wrote:

>My understanding from previous posts and what I know of the factory's
>recommended NACA dimensions is that the size is different between the XL and
>STD purely because of the HP expected to be used in each model. In other
>words, you obviously need a bigger airflow for cooling & induction to the
>bigger engine than the smaller one - so there's more down sides to putting
>in the bigger ducts in the STD fuselage unless you are going to do a "Scott
>Derrick".
>
>Speaking of Scott...where and what has our mate got up to as he's been very
>quiet lately ....didn't realise how much I'd miss his polite and subtle
>posts!  What ya doin Scott?
>
>Greg in Sydney
>
>[mailto:reflector-bounces at tvbf.org] On Behalf Of Phil Hooper
>Sent: Wednesday, 19 October 2005 3:30 PM
>To: 'Velocity Aircraft Owners and Builders list'
>Subject: RE: REFLECTOR: NACA scoops
>
>Noel,
>
>I agree with Keith.  Get the pre-molded scoops from Sebastian.  I have the
>XL-RG and assume the scoops are the same.  The pre-molded parts make it
>easier and more accurate, still a lot of work, but you’ll get the right
>dimensions all around.  I would have to measure, but I think the final
>openings are 11” X 2” tall.  Be sure and allow ¼” to 3/16” along the top of
>the firewall to provide some strength for the cowling attach points.  
>
>Also, we discovered a potential problem.  My fuselage ( built in 2001) had
>the pre-molded markings-indentation, viz., where to cut the scoops.  The
>co-pilot side went fine, the air saw blade going through the skin flush
>against the firewall.  But when we cut the pilot side on the back, we went
>into the firewall.  At first I was alarmed, thinking the firewall was not
>aligned.  But the factory assured me that wasn’t possible because of
>notches;  the way it all comes together.  
>
>After a lot of examination, we concluded that the indentations on the
>factory mold are were in fact about ¼” further aft than the co-pilot side.
>The factory basically conceded this point meaning that fuselages birthed in
>this mold set will be the same.  I did some repair to rebuild the cut part
>at the top of the firewall still connected to the skin, and moved the rest
>of the cutout forward, mostly for looks.  I don’t think it’s critical.
>Lot’s of pix if anyone is interested.  
>
>Did anyone else have this fun experience?
>
>-----Original Message-----
>From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
>Behalf Of gattenby at gbronline.com
>Sent: Tuesday, October 18, 2005 8:02 PM
>To: reflector at tvbf.org
>Subject: REFLECTOR: NACA scoops
>
>
>On an downdraft standard fusalage, how deep are the NACA's?
>I've got cut lines drawn on the top, but I can't find
>instructions 
>on how deep do I make them drop down.
>My kit it old enough that I didn't get the premolded
>inserts.
>
>Noel
>3SUV103
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