REFLECTOR: Overhead NACA's

Sat Apr 18 08:40:32 CDT 2009

Terry,

I am assuming that you attached the photo on you last post, I see that you do have the exhaust exiting straight up on your engine, or at least the photo shows that you have cut holes in the plenum for your exhaust. I considered doing the same also but couldn't convince myself that the fiberglass plenum would survive the heat. Are you going to wrap your exhaust or what?

Andy

________________________________
From: Terry Miles <terrence_miles at hotmail.com>
To: bjb3013 at yahoo.com; Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Wednesday, April 15, 2009 4:28:05 PM
Subject: Re: REFLECTOR: Overhead NACA's

In electricity they will tell you the ground wire is every bit as important as the power wire.  The same applies to cooling.  It is not just the NACA shape and location, it is the tightness of the fit of your plenum and the routing and exit path for the air.  The cooling plenum shell parts in my kit were mistrimmed and the factory graciously replaced it.  It is still a lot of work.  I am grateful to M Collier for his advice and steady hand as I went along.  
Terry

From:reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Brent Bourgeois
Sent: Wednesday, April 15, 2009 13:15
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Overhead NACA's

Doug,
I have done a lot of work on my coolers and now have a system where I get 180-190 no matter how hard I run (or abuse) and regardless of OAT. The best thing you can do is a simple press study to see what you are dealing with. My experience has been that its almost never an inlet problem.  If you get the press low enough on the cooler outlet , at least 4 in/water difference, your oil will cool. 
Put a sense tube in front of the cooler and one behind, use an airspeed indicator to get mph, convert to inch/water. Get real numbers, make one mod at a time and make lots of notes.
Do this for engine cooling also. You may be surprised what works and what is BS
I have a STD RG with an IO-360 arm pit cooling, front and rear coolers.
Let me know If I can help

Brent
N61VB

--- On Wed, 4/15/09, Douglas Holub <douglas.holub at gmail.com> wrote:
From: Douglas Holub <douglas.holub at gmail.com>
Subject: Re: REFLECTOR: Overhead NACA's (was "Rudder Pedal stops")
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Date: Wednesday, April 15, 2009, 9:57 AM
I would remove the VGs in front of your NACAs to get the cylinder temperatures up to 360. ECI recommends that the cylinder temperatures be 400-425 in cruise for a parallel valve 4-cylinder Lycoming with 500 F redline.  If you've got an angle valve Lycoming I think the redline is lower, maybe 475?  My friend had a sticking valve on his engine, and the mechanic told him that it was because the cylinders were running too cool. His temps are in the low 300s.

Speaking of cooling, I've got a question for the collective, (especially for Al if you're out there.)  I need to run my engine below 75% power to keep the oil temperatures below 230 degrees on a 75 degree day like yesterday. My redline is 245. I went from a divergent wall NACA to a parallel wall NACA to a belly scoop. The oil keeps getting cooler, but I need another 20 degrees to be able to fly much in Texas in the summer time. My scoop has a 5 x 2 inch opening that smoothly diverges to the size of the oil cooler 2 feet later. In other words, it has an exansion plenum. Here's my question: I know that the drag will increase if I make the entrance larger and don't have an expansion plenum, but will cooling also increase? Or will the air spilling out of the entrance to the scoop just make things worse?

Doug Holub
Standard FG in phase I flight testing 
On Wed, Apr 15, 2009 at 9:33 AM, victor taylor <velocityoner at yahoo.com> wrote:
I converted my Velocity from the updraft cooling to the cut out home made naca vents on the top. My Velocity runs as cool as my Cessna 150 with temps running 310 cht and 190 oil. I had to add a small airfoil in front of the exhaust exit on the oil cooler after we test flew it. Also without the vortex generators in front of the nacas it will raise the cht by 50 degrees and the oil temp to 220. 

--- On Wed, 4/15/09, Lawrence J. Epstein, MD <ljepstein at hotmail.com> wrote:

From: Lawrence J. Epstein, MD <ljepstein at hotmail.com>
Subject: REFLECTOR: Overhead NACA's (was "Rudder Pedal stops")
To: "'Velocity Aircraft Owners and Builders list'" <reflector at tvbf.org>
Date: Wednesday, April 15, 2009, 7:45 AM 

You guys are "fastbuild" compared to me (13 years and counting). Mine is so old that NACA's hadn't been invented yet (not really) ( we had to walk uphill to school, both ways, in the snow, no shoes………)

Anyway…………..The factory sent me the templates and I cut them out myself (no opinion as to whether these are real NACA's or not). I cut everything except the forward most part and just pushed the skin down to the desired depth. I used 1/4" foam for the sides and covered them with bid. About 6-10 hours work.

Larry Epstein

From:reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of jerry at jlbent.com
Sent: Wednesday, April 15, 2009 8:22 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Rudder Pedal stops

Just to add to the challenge on the NACA ducts, you might want to consider the efficency of the factory design.  While they look like NACA ducts, they are not.  Andy Millin has spent a lot of time researching the topic and has a spreadsheet that does the calculations to produce the needed profile.  One very big difference (and maybe the most important) is that the factory solution does not have an airfoil on top of the opening.  Of course the amount of work needed to create a real NACA vs buying the factory pre-fab is not trivial.

I too am a SLOOOW builder and have a kit that did not come with the pre-fab'd NACA's.  Mine did not even have the NACAs drawn on the fuselage.  I had read Andy's information and decided to build my own.  Just let me say that one can get really obsessive about the details.  I would say that Brett and I have at least 50 hours of work on them.  Some is my learning curve.  Some is just ! the details.  We did the extra work to make the floor of the ramp flat, which is not what you get if you just cut the outline, build the side walls and call it done.

As of yet, I can not say that the true NACA will be better.  Hangar 18 suggest NACA's and believes they are better.  I do know that those in the Vari community think the Velo factory NACA are just wrong and will produce more drag and be less efficient than a proper NACA.  For the amount of work involved in both hands on construction and the amount of head scratching needed to build true NACA's, it is very hard not to go with the factory pre-fabs.

If you decide to go with the true NACA, let me know and we can talk details.  Maybe I can save you some time.

Jerry Brainard

 -------Original Message-------
From: Richard D. Wallace, Jr. 
Subject: Re: REFLECTOR: Rudder Pedal stops
Sent: Apr 14 '09 7:08pm

Noel:

I'm on the slow path also.  I got my kit for Christmas 2000.  My
fuselage has the NACA scoops outlined on the top also.  What do you
make the sides out of - BID?  Also what is the dimension on the
opening in the firewall?

Rick

On Tue, Apr 14, 2009 at 6:28 PM,  <gattenby at tulsaconnect.com> wrote:
> Rick.
>
> I'm taking the slow path to building an SUV as well (8 years and counting)
> I've not done the pedal things as I'm missing some parts. (got my kit 2nd
> hand)
>
> The NACA scoops can be bui! lt without the prefab inserts.
> My kit predated the inserts.  They weren't that big a deal.
> The kit had the lines drawn on the top, and I just cut them.
>
> If you need templates just let me know and I'll trace mine on paper.
>
> Noel
>
> On Tue, 14 Apr 2009 17:30:24 -0400
>  "Richard D. Wallace, Jr." <rdwallace57 at gmail.com> wrote:
>> Guys:
>>
>> I don't provide comments (lack of experience and I have
>>a single door,
>> fixed gear, dual yoke control SUV) but I do and have
>>read all e-mails
>> back and forth.  I seem to be just behind in
>>construction than some
>> and the need to ask questions is always unnecessary
>>because the
>> ! subject has already been discussed.  However, I have
>>come up with two
>> (2) questions:  1) do you need stops for the break
>>pedals so they are
>> not putting pressure on the master brake cylinder heads
>>when the
>> springs are pulling and your foot is not on the pedals?
>>and 2)  is
>> there a way to make the two (2) larger NACA scoops on
>>top and in the
>> back for the engine cooling from the existing fuselage
>>or do you
>> really need to buy the pre-fabricated ones from
>>Velocity?
>>
>> Thanks!
>>
>> Rick Wallace
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