Today's Message Index:
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1. 07:29 AM - Re: Cabin fresh air exhaust (Area-51)
2. 11:36 AM - Re: Re: Cabin fresh air exhaust (Bud Yerly)
3. 12:37 PM - Re: Re: Cabin fresh air exhaust (Mike Christine Duane)
4. 06:02 PM - Re: Cabin fresh air exhaust (Area-51)
Message 1
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| Subject: | Re: Cabin fresh air exhaust |
An update today; had an evening free to ponder.
The 181 model received a reverse naca vent beginning aft of the door frames and
ending just forward of the fuel vents.
A free stream solution was dialed in for 100kt with a level attitude.
The results were pleasing. The exit vent caused the forward side vents to flow
a great deal more volume into the cabin. So the reverse naca vent works. It just
may not be located at the ideal position as it's trade off is additional Drag
and some acoustic related energy.
Porting through the D panel produced no benefits worth mentioning.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511334#511334
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| Subject: | Re: Cabin fresh air exhaust |
I would caution using the term reverse NACA duct.
The NACA duct with its isentropic sharp edged curvy entrance is an inlet de
sign not an exit. The vortex coming off the curvy sharp edged sides create
s a vortex guiding the boundary layer into the inlet. It is an excellent i
nlet. But not designed as an exit. It can work because of the discontinui
ty between the boundary layer and the surface will create a small vacuum.
There is no observed exit vortex aiding in the vacuum draw. The more effic
ient draw can be done using simply straight sides and about an inch or so e
xit ramp. It is easier to make also. However, to close it off, one has to
get cosmic on how to seal this type ramp in rain.
For an exit, a simple reverse ramp is all that is generally needed but the
best solution uses is a cowl flap design to rapidly build an exit vacuum dr
aft. Make as any cowl flap. The lip can seal if gasket material is used t
o make a reasonably watertight surface when closed. Ideally a duct connect
ed to a belly vent would be my first choice for reasonable weather tightnes
s but that just adds time, weight and a longer operating control mechanism
the farther it is from the cockpit. Its only advantage is the rain won=92t
get into the airplane.
The best air exit is always done at a low pressure area of the wing or fuse
lage. On the Europa, the wing is too hard to use but the top of the canopy
is not bad. One could use the area beside your elbow just above the wing
fairing as an exit area for a flap but I=92m not excited about that. The c
anopy (the back of the Thorp and other canopies had a flap that opened like
a cowl flap and drew the air out of the low pressure area just behind the
peak of the canopy glass. Of course, it leaked in the rain unless it incor
porated a seal. Anything behind the wing on the fuselage is basically stat
ic air pressure so not the best draw for the cockpit. Hence the vents in t
he D tube are limited in their ability to draw air but do work on trigear a
ircraft using ram inlet air from the cockpit as a way to flow air out somew
here. My 12AY air exit around the D panel is fair but not perfect by any m
eans. It is more of a pressure release than a true air draw area. Whereas
the small opening of the door seal just behind your head is a fair draw ou
t of the cockpit unless your doors fit nice and tight to the fuselage, then
that is not so great. (My pilot side vents air out better than the tight
fitting pax door. The door seal is the easiest to try. Simply pull the se
al off at the back and go fly. Hold a piece of paper to the gap and see ho
w it works. Mine is pretty fair on the pilot side only due to door fit.
One or more of our British friends added a vent to the top of the canopy ce
nter glassed area and had good air exit, but it leaked in the rain on the g
round also. No surprise there. Mono fliers found on grass the draw may ac
tually increase the amount of grass and dust drawn through the wheel well g
ear handle and airbrake levers on landing and takeoff. Nasty and dirty if
the vent is left open for takeoff and landing on dirt/grass.
What is the best solution? It is hard to say on a fully finished aircraft
. On trigears, the belly access hole can be used, and vents are put into t
he center tunnel which is more work. I don't care to do that but a one inc
h cowl flap on the bottom access door did seem to work as it sucks a piece
of paper and two 3 inch round vents in the sealed tunnel was somewhat useab
le. On Trigear conversions at the original Classic tail wheel, we cut the
wheel off and simply put in an exit duct around the hole for a draw. It lo
oked cool but I didn't see any advantage as I believe the exit duct simply
pulled air out of the flap drive holes.
USE CAUTION as installing cockpit air inlets near the leading edge of the w
ing tend to draw engine exhaust into the cockpit. I did a paper on that so
me time ago. Keep the vents high. Use some dark oil painted on the fusela
ge and fly and look at the flow. It goes from the exhaust up and over the
wing from the exhaust pipe on the XS unless the exhaust pipe is very long.
Finally, what has worked was just ram pressure. The ultimate vents and NAC
A vents are excellent inlets, but only two inlets aren=92t really enough in
a hot SE or SW US summer unless properly directed. I have two NACAs and
two Ultimate Vents. The NACA ducts have no flow direction which would be n
ice but the air impacts the pax and pilot legs only. So, the NACA air ente
rs and circulates around the legs and groin. Later I added Ultimate vents
in the windscreen side glass which directs air at the upper body and more i
mportantly the face. These are tolerable but I would like more air on my f
ace AND central body when doing pattern work. I have no issues with air ve
locity coming in using the D tube as it is effective as a ram air pressure
release of cockpit pressure. Putting in new fuselage ducting with vents in
the rear fuselage is out of my patience level anymore. I=92ll carry some
cool water and just wear shorts and a T shirt and close the vents when I ge
t up to altitude in summer. The oil tank and sun are sufficient warmth for
cruise at 10,500 in summer. I put on more clothes for winter. If I have
to go farther north in the winter or higher in altitude (which I have no in
tension to do) I=92ll buy a heated motorcycle suit and wear wool socks. I
have the available amps or will use the pocket batteries to warm me. We we
re always taught, dress for the worse conditions anticipated. Today, I sim
ply dress for cockpit comfort, and carry a jacket handy behind the seat and
pack some jeans as I go north.
Nice discussion, and it would be great to get more feedback from our hot we
ather fliers and get some fresh ideas. My last good idea was asking my wif
e to marry me. At least that mod to my life didn=92t take tweaking to get i
t to work right. Nothing works it seems in aircraft design and constructio
n without =93tweaking=94 to get exactly what you want, or need.
Best Regards,
Bud Yerly
-----Original Message-----
From: owner-europa-list-server@matronics.com <owner-europa-list-server@matr
onics.com> On Behalf Of Area-51
Sent: Thursday, August 24, 2023 10:29 AM
Subject: Europa-List: Re: Cabin fresh air exhaust
<mailto:goldsteinindustrial@gmail.com>>
An update today; had an evening free to ponder.
The 181 model received a reverse naca vent beginning aft of the door frames
and ending just forward of the fuel vents.
A free stream solution was dialed in for 100kt with a level attitude.
The results were pleasing. The exit vent caused the forward side vents to f
low a great deal more volume into the cabin. So the reverse naca vent works
. It just may not be located at the ideal position as it's trade off is add
itional Drag and some acoustic related energy.
Porting through the D panel produced no benefits worth mentioning.
Read this topic online here:
https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fforums.ma
tronics.com%2Fviewtopic.php%3Fp%3D511334%23511334&data=05%7C01%7C%7Ca2e88
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Message 3
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| Subject: | Re: Cabin fresh air exhaust |
=9CAcoustic related energy=9D? =C2-Do you mean =9Cnoise
=9D? LOL
Sent from the all new AOL app for iOS
On Thursday, August 24, 2023, 7:30 AM, Area-51 <goldsteinindustrial@gmail.c
om> wrote:
>
An update today; had an evening free to ponder.
The 181 model received a reverse naca vent beginning aft of the door frames
and ending just forward of the fuel vents.
A free stream solution was dialed in for 100kt with a level attitude.
The results were pleasing. The exit vent caused the forward side vents to f
low a great deal more volume into the cabin. So the reverse naca vent works
. It just may not be located at the ideal position as it's trade off is add
itional Drag and some acoustic related energy.
Porting through the D panel produced no benefits worth mentioning.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511334#511334
Attachments:
http://forums.matronics.com//files/5991deff_63b0_4b6f_bfbe_f8ef46ba77c4_156
.jpeg
http://forums.matronics.com//files/75525b6a_f13b_4b65_8f9a_3864f0e44cba_251
.jpeg
S -
WIKI -
-
=C2- =C2- =C2- =C2- =C2- -Matt Dralle, List Admin.
Message 4
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| Subject: | Re: Cabin fresh air exhaust |
Yes, fancy way of describing noise and padding out the content with exciting and
conversational inspiring fodder :)
Fully agree with all Bud's points. Somebody at the beginning mentioned a reversed
naca vent arrangement so that's what got reviewed but other exhaust arrangements
can be played with at some later stage. At this point it has been established
that providing a cabin exhaust vent to the outside improves flow through
capacity of cabin ventilation. Belly mounted exhaust vents downstream of the
rear cabin wall along with a vent at the wall is probably a suitable position
as the air flow is already a bit dirty from the cowling shape and mono undercarriage
and would assist sucking out any undesirable vapor or smoke should that
arise.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511344#511344
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