REFLECTOR: Oil cooler air flow

Wed Apr 15 18:59:33 CDT 2009

So assuming that the scoop is sufficiently out of the boundary area and that
the plenum is smooth inside, and has no bends and twists before it gets to
the oil cooler, and the entrance lip has a nice radius, are you saying that
an entrance that is one fourth the size of the oil cooler will cool better
than one that is half the size? Or just that there will be less drag?

Doug

On Wed, Apr 15, 2009 at 2:51 PM, Al Gietzen <ALVentures at cox.net> wrote:

>  Hi; Doug,
>
> Do you happen to have a photo of the scoop? Where is the cooler located?
> What size is the cooler core? Do you have any temp in/out measurements for
> air or oil?  Do you have any idea what the heat load to the cooler is? Is
> the scoop mostly outside the boundary layer?
>
> Just off the top of my head; the air will not flow through the core at
> anything approaching the speed of the plane, so a divergent plenum to slow
> the air, recover static pressure, and reduce the core pressure drop is
> essential. Typically for a roughly 3” thick core, you’ll want the scoop
> entrance to be close to 4 times smaller than the face of the core.  The
> shape of the plenum also matters.
>
> Contact me off-list if you like – alg3 at cox.net.
>
> Best,
>
> Al
>
>
> 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<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<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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