REFLECTOR: Overhead NACA's (was "Rudder Pedal stops")

Scott Derrick scott at tnstaafl.net
Wed Apr 15 11:10:39 CDT 2009


just a thought.   course the only way to really know is to have two
pressure transducers, one in front and one in back.

You could use 1/4" clear plastic tubing and colored water to hook up a
couple poor man pressure gauges(manometer).

http://www.komar.org/faq/manometer/

There is a minimum differential for optimal cooling, which I don't know
off hand.

Scott


Douglas Holub wrote:
> The oil cooler is mounted on the engine side of the firewall, and I
> think the pressure is pretty low beneath the engine, but just to make
> sure I added an exhaust scoop for the oil cooler. I think the pressure
> was already low enough because I didn't notice any improvement with
> the exhaust scoop.
>
> Doug
>
> On Wed, Apr 15, 2009 at 10:33 AM, Scott Derrick <scott at tnstaafl.net
> <mailto:scott at tnstaafl.net>> wrote:
>
>     Doug, anyway to reduce the pressure on the back side of your oil
>     cooler?
>
>     Interesting about cylinder temps.  I had always thought "lower was
>     better".
>
>     Scott
>
>     Douglas Holub wrote:
>     > 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 <mailto:velocityoner at yahoo.com>
>     > <mailto:velocityoner at yahoo.com <mailto: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 <mailto:ljepstein at hotmail.com>
>     <mailto:ljepstein at hotmail.com <mailto:ljepstein at hotmail.com>>>/*
>     wrote:
>     >
>     >
>     >         From: Lawrence J. Epstein, MD <ljepstein at hotmail.com
>     <mailto:ljepstein at hotmail.com>
>     >         <mailto:ljepstein at hotmail.com
>     <mailto:ljepstein at hotmail.com>>>
>     >         Subject: REFLECTOR: Overhead NACA's (was "Rudder Pedal
>     stops")
>     >         To: "'Velocity Aircraft Owners and Builders list'"
>     >         <reflector at tvbf.org <mailto:reflector at tvbf.org>
>     <mailto:reflector at tvbf.org <mailto: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>
>     >         <mailto:reflector-bounces at tvbf.org
>     <mailto:reflector-bounces at tvbf.org>>
>     >         [mailto:reflector-bounces at tvbf.org
>     <mailto:reflector-bounces at tvbf.org>
>     >         <mailto:reflector-bounces at tvbf.org
>     <mailto:reflector-bounces at tvbf.org>>] *On Behalf Of
>     >         *jerry at jlbent.com <mailto:jerry at jlbent.com>
>     <mailto:jerry at jlbent.com <mailto: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 <mailto:gattenby at tulsaconnect.com>
>     >        
>     <http://mbox.jlbent.com/compose.php?to=gattenby@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
>     <mailto:rdwallace57 at gmail.com>
>     >        
>     <http://mbox.jlbent.com/compose.php?to=rdwallace57@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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