REFLECTOR: Vortex generators location for armpit cooling scoops

Brian Michalk michalk at awpi.com
Fri Aug 16 18:05:42 CDT 2013


I never really believed that a vortex generator worked, until I was 
flying in a 737 on a humid day and could see how a VG mounted on the 
engine nacelle cause a vortex that carried over the wing right above an 
aileron.

I've thought a lot about vortex generators for years and how in the 
world they accomplish what people claim.  People say they help the air 
stay attached to the wing.  Now, that's an odd claim, because they make 
turbulent air, and how does that keep it attached to the wing.

So yes, think of it as a mini tornado.  If we want to keep the air 
attached, think of it as adding pressure to the air that presses it 
against the wing.  Where does that pressure come from?  It comes from 
putting more air molecules in the place we want them, near the wing, 
which means that they come from somewhere else, meaning that somewhere 
else must have a vacuum because we took some molecules from that place.

The vortex generator makes a tornado.  It is a swirling mass of air, 
with the center of the vortex being a vacuum, and the mass of the 
molecules rotating about center, wanting to go in a straight line 
tangent to the rotation, but the vacuum keeps the molecules going in a 
circle.

So, the VG makes an area of vacuum, providing higher pressure some 
distance away from the vacuum.  I can visualize how this works on a wing 
to offset stall.

For a NACA duct, I can visualize the tornado, with it's side going right 
into the NACA inlet.

Anyway, this is how I see it in my mind.  I was baffled for years, and I 
hope this helps others see how they work.  If I'm totally wrong, I would 
like to know why.

Now, if I could ever figure out trailing edge fences, or the drag 
inducing right angle exhaust, I will be a happy man.

On 08/16/2013 11:02 AM, Laurence Coen wrote:
> Jeff,
> A vortex is like a tiny tornado.  Newton pointed out that things in 
> motion tend maintain direction and motion.  Air flowing over a curved 
> surface wants to go in a straight line so it tends to separate from 
> the surface. Vortex generators help the air stay attached and follow 
> the curve.  The way I picture my vortexes working is the upper one 
> spins CW and the lower CCW thus stuffing air down into the oil cooler 
> opening.  Of course if I actually knew all about aerodynamics I'd be 
> cruising at 300 kts on 4 gal/hr.  Never the less I saw a 10F drop 
> across the board in oil temp.  Placement was by sticking them where I 
> thought they would work.  No science at all.
> Larry Coen
> N136LC
>
> *From:* jeff findarle <mailto:flynfindarle at yahoo.com>
> *Sent:* Thursday, August 15, 2013 5:52 PM
> *To:* Velocity Aircraft Owners and Builders list 
> <mailto:reflector at tvbf.org>
> *Subject:* Re: REFLECTOR: Vortex generators location for armpit 
> cooling scoops
>
> OK, So I am trying to understand what is happening here 
> aerodynamically? Sorry, but I am new to all this. It looks like you 
> are trying to disturb the airflow over the fuselage to somehow help 
> air to the cooler? Is this correct and did you see any benefit from 
> it? If it is working, could you maybe take a pic with a measuring tape 
> depicting the distances from the openings. Would be greatly appreciated.
>
> TEAM JEFF,
> Jeff Findarle, GRI & Darin Heckel
> Realtor                     Realtor
>
> AllStar Realty
> 575 N main St.
> Heber City, UT. 84032
>
> Jeff's Cell 435-503-0514
> Darin's Cell 435-671-3957
> Off. 435-654-9440
> Fax 435-654-9437
>
> Distressed Property Experts, Short Sales a Specialty!
> Don't Lose it, Sell it!
>
>     ------------------------------------------------------------------------
>     *From:* Laurence Coen <lwcoen at hotmail.com>
>     *To:* Andrew Ellzey <ajlz72756 at yahoo.com>; Velocity Aircraft
>     Owners and Builders list <reflector at tvbf.org>
>     *Sent:* Thursday, August 15, 2013 10:18 AM
>     *Subject:* Re: REFLECTOR: Vortex generators location for armpit
>     cooling scoops
>
>     Andy,
>     There are no vortex generators in front of my armpit scoops (see
>     previous).  They are in front of my oil cooler inlet on the nose
>     and I attached a photo to give an idea of what they look like. 
>     They are made of angle aluminum and attached with silicone rubber
>     cement.  Something 1 1/4" tall should do it.  The ones in the
>     picture are 1" tall by 1" wide.
>     Larry Coen
>     N136LC
>
>     *From:* Andrew Ellzey <mailto:ajlz72756 at yahoo.com>
>     *Sent:* Wednesday, August 14, 2013 10:19 PM
>     *To:* Velocity Aircraft Owners and Builders list
>     <mailto:reflector at tvbf.org>
>     *Subject:* Re: REFLECTOR: Vortex generators location for armpit
>     cooling scoops
>
>     Larry,
>     So that is the question, how tall are your vortex generators, how
>     far out in front of the armpit scoops did you place them? Did you
>     make them, or buy them and if you bought them, where from. Can you
>     please send a photo.
>     Thanks,
>     Andy
>
>         *From:* Laurence Coen <lwcoen at hotmail.com
>         <mailto:lwcoen at hotmail.com>>
>         *To:* Velocity Aircraft Owners and Builders list
>         <reflector at tvbf.org <mailto:reflector at tvbf.org>>
>         *Sent:* Wednesday, August 14, 2013 6:25 PM
>         *Subject:* Re: REFLECTOR: Vortex generators location for
>         armpit cooling scoops
>
>         Andrew,
>         I have armpit scoops on my SR/RG that look just like yours. 
>         When I mounted them I was concerned about the boundary layer
>         and extended the scoops 3/4" out from the fuselage so the
>         entire scoop is outside the boundary layer.  I also added an
>         insert that looks like venturi that in theory should help with
>         pressure recovery.  The fact that I don't have cylinder head
>         cooling problems doesn't mean that it will work for you.  I am
>         down draft cooling a 220 HP Franklin.  I have vortex
>         generators ahead of my oil cooler inlet and that did lower my
>         oil temp.  If you try vortex generators I would suggest that
>         they be tall enough so they stick out of the boundary layer.
>         Larry Coen
>         N136LC
>
>         *From:* Andrew Ellzey <mailto:ajlz72756 at yahoo.com>
>         *Sent:* Wednesday, August 14, 2013 3:50 PM
>         *To:* Velocity Aircraft Owners and Builders list
>         <mailto:reflector at tvbf.org>
>         *Subject:* REFLECTOR: Vortex generators location for armpit
>         cooling scoops
>
>         I am still battling a high CHT at cruse on my # 5 cylinder on
>         my updraft IO-540-E1A5, 300HP Lycoming engine. I can do full
>         power climb outs in the pattern all day without any issue.
>         From everything that I have read on this subject on the
>         Reflector, this is common with the arm pit cooling. The higher
>         pitch angle in the pattern, and in a cruse climb, forces
>         plenty of cooling air into the scoops, but the cooling ability
>         drops off in level cruse fight attitudes. My question is, is
>         there anyone left on the reflector that is using the armpit
>         cooling, and do you have vortex generators in front of your
>         armpit scoops to help the airflow boundary layer adhesion to
>         this area forward of the armpit scoops? If you have vortex
>         generators, what size, location, did you make them, buy them,
>         can you send a photo, please.
>         I have swapped and calibrated my CHT probes, swapped the
>         lowest CHT cylinder fuel injector with my #5 injector. Nothing
>         helps, it seems to be tied with airflow into my scoops, or
>         airflow inside my lower cowling. If the addition of vortex
>         generators doesn't help, I will probably have to install some
>         additional baffling to redirect more air to the aft two
>         cylinders, #5, and #6. Cylinders 1, 2, 3, and 4 are getting
>         plenty of air, in fact they are running cooler than I like at
>         this time, but until I can get #5 CHT under control, I can't
>         lean my engine properly to know if I have adequate airflow for
>         all cylinders or not. Installing my gear doors seemed to help.
>         Photo attached showing my armpit cooling scoops. The
>         additional screws under the armpit scoops, attaches a mating
>         internal scoop that directs the airflow to my aft lower cowling.
>         Thanks again for your help,
>         -----------------------------------------
>         Andrew Ellzey
>         N151AJ 10 hours into Phase 1 testing
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