REFLECTOR: Oil cooler air flow

Thu Apr 16 20:58:38 CDT 2009

So a bigger scoop may not help, but no one knows for sure whether or not a
bigger scoop would ever actually reduce an oil cooler's ability to cool the
oil? (I'm not talking about my particular setup; I'm just talking in
general.)

On Thu, Apr 16, 2009 at 1:02 PM, Al Gietzen <ALVentures at cox.net> wrote:

>  Doug;
>
>
>
> Not having seen your setup, and having no data; no conclusion is possible.
>
>
>
> But, yes; it is possible that making the scoop too large can make things
> worse, or at the least, no better.
>
> The pressure drop across the core goes roughly as the cube of the flow
> velocity.  The maximum ram pressure you have at, say, 130 kts is about 11”
> H2O.  Take some losses in the duct, etc and you have less at the core, and
> reduce by whatever pressure you have at the exit. When the velocity is such
> that the pressure drop across the core exceeds the available pressure in the
> duct, air will spill around the scoop. When that happens the pressure at the
> scoop entrance may be lower than the available ram pressure.
>
>
>
> Al
>
>
>
> -----Original Message-----
> *From:* reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] *On
> Behalf Of *Douglas Holub
> *Sent:* Wednesday, April 15, 2009 4:00 PM
> *To:* Velocity Aircraft Owners and Builders list
> *Subject:* Re: REFLECTOR: Oil cooler air flow
>
>
>
> 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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> >
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