Reverse NACA duct

"Robert Little" wrote in message
...
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


Oh, blasphemy and sacrilege! You would do that to the boot cowl of your
classic Taylorcraft?


Somebody's going to get this sooner or later and googling "inverted naca
duct" might bring something up. But my understanding is that the device
helps keep the boundary layer attached.


----------------------------------------------------
This mailbox protected from junk email by Matador
from MailFrontier, Inc. http://info.mailfrontier.com

"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

In article , Chris W writes:


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



I don't know of a specific design for one but I am simply mounting one on the
outside of the fuselage with the small end pointing into the airstream. The
air will flow around and over the duct and should result in a negative pressure
at the opening. Another option was one done by the guy who designed the
VISION. It was a small extending bulb with holes on the back side. Again, the
negative pressure on the down wind side results in a reverse flow.


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)

Reverse NACA duct ... Bad Idea!
Several years ago I read about someone installing a NACA scoop, pointed end
aft, to remove air from the cabin. I thought I would do the same for my
plane but first decided to test the idea. I built a NACA scoop and ran
high speed water through it in both forward and reverse directions. In
forward the water flowed as expected. In reverse the water exited at
nearly 90 degrees to the slip stream.
I believe a NACA scoop will just add drag, especially to fast
planes....Better to just use a ramped exit.

Russell Sherwood
Houston, TX



"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

"R&R Sherwood" wrote in message
...
Reverse NACA duct ... Bad Idea!
Several years ago I read about someone installing a NACA scoop, pointed
end
aft, to remove air from the cabin. I thought I would do the same for my
plane but first decided to test the idea. I built a NACA scoop and ran
high speed water through it in both forward and reverse directions. In
forward the water flowed as expected. In reverse the water exited at
nearly 90 degrees to the slip stream.
I believe a NACA scoop will just add drag, especially to fast
planes....Better to just use a ramped exit.

Russell Sherwood

I also remember someone else coming to that conclusion.

Try the "bump" or an adjustable "cowl type" flap.
--
Jim in NC

Back in the early 80's I was a co-op student (read,
engineer-in-training) at Fairchild-Swearingen. The group to which I
was assigned was studying the flow through the oil cooler for a PT-6
version of the Metro / Merlin line. They were using NACA-shaped ducts
on the sides of the nacelles to get the air into the plenum to cool
the oil.

It wasn't working, until I dug down into the original NACA references
to discover that the duct lip had a bump - not just a plain radius.

Sort of like this:


slipstream -------------

__________ ____________ surface _____
\ /
_________ | /
\__/ /
/
/
/
/
/
_________________


The lip helps create a low-pressure area inside the duct opening. I
don't think it would work in reverse, except perhaps by blind chance
(sort of like the Davis wing - it happened to be a high-aspect-ratio,
low-drag airfoil. Davis's elaborate equations tunred out to be so
much mathematical hogwash).

My opinion: You want a positive-flow outlet, poke a hole in an
existing low-pressure zone.

"Morgans" wrote in message ...
"R&R Sherwood" wrote in message
...
Reverse NACA duct ... Bad Idea!
Several years ago I read about someone installing a NACA scoop, pointed
end
aft, to remove air from the cabin. I thought I would do the same for my
plane but first decided to test the idea. I built a NACA scoop and ran
high speed water through it in both forward and reverse directions. In
forward the water flowed as expected. In reverse the water exited at
nearly 90 degrees to the slip stream.
I believe a NACA scoop will just add drag, especially to fast
planes....Better to just use a ramped exit.

Russell Sherwood

I also remember someone else coming to that conclusion.

Try the "bump" or an adjustable "cowl type" flap.

Corrie wrote:

Back in the early 80's I was a co-op student (read,
engineer-in-training) at Fairchild-Swearingen. The group to which I
was assigned was studying the flow through the oil cooler for a PT-6
version of the Metro / Merlin line. They were using NACA-shaped ducts
on the sides of the nacelles to get the air into the plenum to cool
the oil.

It wasn't working, until I dug down into the original NACA references
to discover that the duct lip had a bump - not just a plain radius.

You should've kept reading. The original NACA references specifically say *NOT* to use NACA-style
entrances for heat exchangers (oil coolers, radiators).

Russell Kent

Russell Kent wrote:

The original NACA references specifically say *NOT* to use NACA-style
entrances for heat exchangers (oil coolers, radiators).

Do they say why?

Dave 'yellow' Hyde