Reverse NACA duct

Can someone tell me where I can find more information on the design of a
reverse NACA duct?

--
Chris W

"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety."
-- Benjamin Franklin, 1759 Historical Review of Pennsylvania

On Fri, 24 Oct 2003 13:28:54 -0500, Chris W wrote:

Can someone tell me where I can find more information on the design of a
reverse NACA duct?

--
Chris W

Chris, what's a reverse NACA duct? My understanding is that they were
designed to work in one direction only, to bring in air with a minimum
of drag.

They don't work well, or at all, when placed on the fuselage or cowl
in a negative pressure area.

Thanks, Corky Scott

Corky Scott wrote:

Chris, what's a reverse NACA duct? My understanding is that they were
designed to work in one direction only, to bring in air with a minimum
of drag.

They don't work well, or at all, when placed on the fuselage or cowl
in a negative pressure area.

I had heard once that on some planes, a reverse or backwards NACA duct would
be installed in the aft part of the cockpit to improve ventilation by helping
suck air out of the plane. I also think I remember something about the
design being somewhat different.


--
Chris W

"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety."
-- Benjamin Franklin, 1759 Historical Review of Pennsylvania

"Chris W" wrote in message
...
Corky Scott wrote:

Chris, what's a reverse NACA duct? My understanding is that they were
designed to work in one direction only, to bring in air with a minimum
of drag.

They don't work well, or at all, when placed on the fuselage or cowl
in a negative pressure area.

I had heard once that on some planes, a reverse or backwards NACA duct
would
be installed in the aft part of the cockpit to improve ventilation by
helping
suck air out of the plane. I also think I remember something about the
design being somewhat different.


--
Chris W

As I recall, it was shaped rather like a raindrop, but with about 1/3rd of
the surface raised above the craft. The pointy end was pointed into the
wind, with the outlet in the downwind, rounded side. The object was to
create a low pressure area, then use it to get the bad air out. If only I
could remember where I read about it!
--
Jim in NC

In article , "Morgans"
writes:


I had heard once that on some planes, a reverse or backwards NACA duct
would
be installed in the aft part of the cockpit to improve ventilation by
helping
suck air out of the plane. I also think I remember something about the
design being somewhat different.


--
Chris W

As I recall, it was shaped rather like a raindrop, but with about 1/3rd of
the surface raised above the craft. The pointy end was pointed into the
wind, with the outlet in the downwind, rounded side. The object was to
create a low pressure area, then use it to get the bad air out. If only I
could remember where I read about it!
--
Jim in NC



I believe the guy who designed the Vision Aircraft did some work on this
several years ago and had some information on his web site at one time. I
don't know if it is still there or no.


Bob Reed
www.kisbuild.r-a-reed-assoc.com (KIS Builders Site)
KIS Cruiser in progress...Slow but steady progress....

"Ladies and Gentlemen, take my advice,
pull down your pants and Slide on the Ice!"
(M.A.S.H. Sidney Freedman)

Chris W wrote:

Corky Scott wrote:

Chris, what's a reverse NACA duct? My understanding is that they were
designed to work in one direction only, to bring in air with a minimum
of drag.

They don't work well, or at all, when placed on the fuselage or cowl
in a negative pressure area.

I had heard once that on some planes, a reverse or backwards NACA duct would
be installed in the aft part of the cockpit to improve ventilation by helping
suck air out of the plane. I also think I remember something about the
design being somewhat different.

--
Chris W

"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety."
-- Benjamin Franklin, 1759 Historical Review of Pennsylvania

About all that I can remember is that the NACA (or NASA, I don't recall) exit
ducts were essentially rectangular and that the exit ramp maintained a basically
constant width and faired smoothly into the larger surface.

I believe, but am not at all certain, that the exit lip protruded slightly and
was fairly sharp, as compared to the submerged inlet lip which was rounded.

There was considerable discussion of these duct entrances and exits from the
late 1960s until the early 1980s, and numerous examples appeared on
automobiles. Generally, the ones on real factory facing cars were well
designed, and the ones on street machines intended to look fast (such as some
Mustang models) were atrocious.

I couldn't find a solid reference to the exit ports of the submerged ducts, but
considerable work (originally classified, but now unrestricted access) appears
to have been done during the period from late in WWII through the end of the
1940s; and reports are referenced in 1945, 1497, and 1948.

I am not sufficiently motivated at this time to read through even the titles,
but further information is available at: http://naca.larc.nasa.gov/ and
http://naca.larc.nasa.gov/cit.html Reports made after 1958 are in another
directory.

On Fri, 24 Oct 2003 19:08:30 -0500, Chris W wrote:

Corky Scott wrote:

Chris, what's a reverse NACA duct? My understanding is that they were
designed to work in one direction only, to bring in air with a minimum
of drag.

They don't work well, or at all, when placed on the fuselage or cowl
in a negative pressure area.

I had heard once that on some planes, a reverse or backwards NACA duct would
be installed in the aft part of the cockpit to improve ventilation by helping
suck air out of the plane. I also think I remember something about the
design being somewhat different.


--
Chris W

"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety."
-- Benjamin Franklin, 1759 Historical Review of Pennsylvania


I had heard that too, so I contacted NASA about it. Spoke via E-mail
with one of the aerodynamicists. I told them I thought I understood
the principle of the NACA duct and that I'd like to use it to
facilitate removal of cabin air.

He replied that "obviously" I did NOT understand how NACA ducts
worked, or I would not be suggesting that I use one to draw the air
out of the cabin because that's not how they work.

So I meekly asked what might work, instead of a NACA duct and he
replied almost any opening would work, as long as it was placed in a
low pressure area.

You can create such a low pressure area by having a bump just in front
of the opening. The idea of a hollowed out tear drop was mentioned,
this would work. Or, just put a hole in the fuselage connected to the
exit duct aft of the cabin. That's a low pressure area as the
fuselage is narrowing to the tail at that point

Corky Scott

"Corky Scott" wrote in message
...
On Fri, 24 Oct 2003 19:08:30 -0500, Chris W wrote:

Corky Scott wrote:

Chris, what's a reverse NACA duct? My understanding is that they were
designed to work in one direction only, to bring in air with a minimum
of drag.

They don't work well, or at all, when placed on the fuselage or cowl
in a negative pressure area.

I had heard once that on some planes, a reverse or backwards NACA duct
would
be installed in the aft part of the cockpit to improve ventilation by
helping
suck air out of the plane. I also think I remember something about the
design being somewhat different.


--
Chris W

"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety."
-- Benjamin Franklin, 1759 Historical Review of Pennsylvania


I had heard that too, so I contacted NASA about it. Spoke via E-mail
with one of the aerodynamicists. I told them I thought I understood
the principle of the NACA duct and that I'd like to use it to
facilitate removal of cabin air.

He replied that "obviously" I did NOT understand how NACA ducts
worked, or I would not be suggesting that I use one to draw the air
out of the cabin because that's not how they work.

So I meekly asked what might work, instead of a NACA duct and he
replied almost any opening would work, as long as it was placed in a
low pressure area.

You can create such a low pressure area by having a bump just in front
of the opening. The idea of a hollowed out tear drop was mentioned,
this would work. Or, just put a hole in the fuselage connected to the
exit duct aft of the cabin. That's a low pressure area as the
fuselage is narrowing to the tail at that point

Corky Scott

Designing a quiet way to extract air might not be a problem in airplane
cockpits but in sailplanes, exhausting air from the cockpit is often very
noisy. (If it's noisy, I presume it to be draggy.)

The German glider designers are careful to add air intakes but usually
completely ignore air exits - the result is lots of noise but little air
flow through the cockpit.

A really quiet, efficient, low-drag air exit design would be very welcome.
I'm following this thread with interest.

Bill Daniels

In article ,
(Corky Scott) writes:


Can someone tell me where I can find more information on the design of a
reverse NACA duct?

--
Chris W

Chris, what's a reverse NACA duct? My understanding is that they were
designed to work in one direction only, to bring in air with a minimum
of drag.

They don't work well, or at all, when placed on the fuselage or cowl
in a negative pressure area.

Thanks, Corky Scott


The concept is to place it in the airstream in such a way as to result in
negative pressure at the opening.




Bob Reed
www.kisbuild.r-a-reed-assoc.com (KIS Builders Site)
KIS Cruiser in progress...Slow but steady progress....

"Ladies and Gentlemen, take my advice,
pull down your pants and Slide on the Ice!"
(M.A.S.H. Sidney Freedman)

Would a couple of NACA ducts work on the bootcowl of a Taylorcraft BC-12D to
bring in fresh cabin air? I understand a 337 would be required but would it
do the job better than have to fly with the windows slide back? Just
thinking of better ways of freezing my feet off this winter. RTL

--


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"Chris W" wrote in message
...
Can someone tell me where I can find more information on the design of a
reverse NACA duct?

--
Chris W

"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety."
-- Benjamin Franklin, 1759 Historical Review of Pennsylvania