Cockpit Ventilation Synopsis (so far)

Tomorrow when I have more time I will post my synopsis on the
subject.

Paul

As promised (warned? but then encouraged...) here is my exhaust
project so far, which I felt I should post to it's own thread to not
hijack the OP's thread looking for more advice on other subjects...
Dick Butler was very helpful and inspiring early on, even encouraging
me to make it an article for soaring or something after reading up on
my 'discoveries', which I may do in the near future... so sorry if
it's old news by then to anyone who read it already on this group.
Also, it will be old news to several of you out there that I already
peppered with this drivel during my more active phase of this
project... At least while I'm sure most here read Soaring, I'm sure
most that read Soaring are not here... (make any sense?) Sorry I
don't have the accompanying pics posted to a public site yet, but for
anyone interested I can just email them directly to you until then.

disclaimer- I'm not formally trained in any of this stuff so this
information is based off my skin deep research and observations along
with my intuition. It is quite possible that I added 2 and 2 together
and came up with 5, but bottom line the exhaust vents I made do indeed
make my cockpit significantly more comfy and quiet.



Vented Exhaust Project Synopsis, Paul Hanson

What got me started on this project, was learning about the Mandl
Extractor by DG/LS: http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
, and the ensuing discussion about it here on ras which in turn led me
to the discovery of Dick Butler's dorsal vent on his highly modified
22 (ASW-22BL/Eta-Biter/The Beast/whatever you may call it, I believe
it's currently the highest measured performing sailplane in the
world...), via Dave Nadler's racing blog from Uvalde he posted in
that discussion:

http://www.nadler.com/public/Uvalde2...t_exterior.JPG
and
http://www.nadler.com/public/Uvalde2...it_cockpit.JPG ).

As mentioned previously then and now, UF flying out of Jean NV
(naturally a very HOT climate...), converted his aileron access hatch
on his Speed Astir he flies to have an adaptation of the Mandl
extractor built into which he kindly posted to that discussion and
this one,
( http://griderpirate.smugmug.com/gall...55235760_LUSmZ
) which came out rather well and he reported significant increase in
the flow of air through the cockpit (even with 101 dalmations and a
sheep in there... I had no idea Speed Astir's cockpits were so
large!). That's when the light actually went on in my head, cause my
ship, an SZD-59, has a rather large centrally located dorsal hatch on
it that would be perfect to play with, requiring very little faith in
my own abilities to conduct some testing...

I fly out of Avenal, with normal ground temps in the 85-115 degrees f
range, and with my 59's anemic ventilation system, spring/summer/fall
(especially summer!) flying is generally less than comfortable, so
any increase in cockpit comfort will be a "performance" increase for
me, but I do believe there is even a slight aerodynamic gain as well,
although I'm skeptical about LS's claimed 2 L/D points. I made a
Butler style arrangement (tunnel to follow...) and also a few attempts
at a 'tuned' Mandl style extractor, to make it as quiet (Mandl himself
describes his has having a slight rumble, which may or may not be due
to location...) and hence as efficient as possible. Since these are
based on a removable hatch on my ship, they can be changed out easily
and I'm currently doing subjective comparative testing of the two, and
if possible something more scientific down the road. The Butler hatch
required a mod to the forward lip of my hatch opening and is probably
too large to be adapted to most ship's little aileron control access
etc hatchy things and is probably better off centrally located on the
dorsal anyhow, but maybe not. The Mandl based design I came up with
will not require any mods to work on any SZD 59 or SZD 48-3, although
things with smaller hatches would probably only accept the MK I
version I made since it's shorter than my MKII with the larger/longer
bell mouth inlet based on my (again, skin deep) research of optimized
wind tunnel proportions... I don't think the Mandle exhaust vent would
be as sensitive to being asymmetrically located either.

My initial flight test on my Butler and Mandl hatch results were very
encouraging. It works! IT WORKS! IT TOTALLY EFFIN WORKS!! With the
forward intake NACA scoop and slider/popout window on my ship closed,
there was very little noticeable increase in noise at any of the
speeds I flew at (37-80kts on my first flight, but even up to VNE it's
still rather quiet. However once the forward vent was opened, I could
actually hear air flowing though it--for the first time ever! Normally
all it did was rumble before... Not only that, I could actually even
feel it too! (also for the first time...) When I opened the popout it
was the same pleasant surprise, with a very noticeable stream of
refreshing air, that sounded and felt very laminar (steady whooshing
sound with no rumble and not turbulent feeling). With just the little
circular popout scoop out and my forward vent open, I'm able to be
basically comfortable in the cockpit for entire fights. In no
configuration is the exhausting air exiting distracting. In fact, it
is much quieter in my cockpit since I'm now able to fly with my slider
window closed and my hand NOT scooped out the hole (my otherwise
'normal' mode of flying my 59...) in pale attempts to coerce the air
to enter. (it does not want to come in with nowhere to go out!) This
practice was especially lame at low altitude saves as well as
conditions where my left hand froze while the rest of me cooked. Many-
a-flight have I put my left hand on the stick to thaw and expose my
right hand (crossed over my chest) until I was evened out. BTW, it was
90 or so deg on the ground when I launched on my first test flight,
with a nasty inversion at ~3000msl (field elevation is 790', needless
to say very crappy soaring conditions only allowed a short test, but
I've flown a bunch with it since and I'm still very pleased with the
results...). It really is much quieter and much more comfortable in my
cockpit though, despite the intakes being open and despite the exhaust
hole too. What a welcome and wonderful relief! All this, AND it
increases the aerodynamic performance of the ship?!? Heck, I'd have
done it just to increase MY performance, even if there was an
aerodynamic disadvantage; however as Wil Shueman also proved in the
early 70's there is indeed an increase in performance to be had when
you give cockpit bleed/vent air somewhere constructive to go, so this
is not a new idea, just a newer and more optimized revisitation.

I have tested my (MK I...) Mandl extractor, both with and without a
honeycomb grill in the mouth, and I've tested my MKII a little too
(works killer...). The first incarnation, my MKI, has a small cup-
flange on the interior mouth of an otherwise normal length Mandl to
which I added a small radius to efficiently flare it open, providing a
slightly larger mouth and hence honeycomb grill than the normal mouth
size, increasing the grill's efficiency. This flange held the
honeycomb grill in place as well as add much strength. The newer
(MKII) version is much longer (extending it forward internally, the
exit portion itself is unchanged...) has a much larger bell mouth that
is nicely fared in, using the guidelines I established from wind
tunnels to determine geometric relationships as much as possible. I
did not get to fly very long with my MK I, but it seemed to make a
tiny bit more noise than my Butler exhaust, but the Mandl was still
completely effective at ventilation either way. The increased
perceived additional Mandl noise may or may not have even actually
existed, as those flights were mostly short and made in shearline
which makes any soaring noisier since the wind is shifting around
(which also really provided a new and unexpected cue to help model
the lift/sink I was flying in in all actuality...) so much as I circle
and fly in and out of mixing air. Also, and what I believe to be the
real culprit, is that those test articles have a thick lip at a
critical juncture (where extractor meets exterior), since it is a
fiberglass part that I simply taped to the inside of a mat-board
mockup of my hatch with the appropriate sized cutout but not fared in.
Ironically and quite unintentionally, the final shape I ended up on my
MKII, now looks (to me at least..) like a bulbous and rounded
variant of a NACA intake, but I assume very similar guidelines
probably underlie both designs for the same aerodynamic reasons. I
have pics of my MK I version in various stages in addition to a shot
of my Butler style extractor and the mod I had to do to the hatch's
lip (to my fuselage) to accommodate it. I will get more MK II pics
soon, as I am almost done contouring the bell inlet, getting ready to
mold it for reproduction. Overall, to my eye, ,it looks better than
the MKI and I'm pretty psyched about it, but who knows how much
difference it really makes in measured numbers... plus the MKI would
better fit most ship's small hatches. I will be making completed MKII
Mandl style hatches able to be adapted to any 59/48:3 without the need
for any mods, or with a tiny mod to use the slick flush latches I
acquired for the purpose (unfortunately SZD wants like $90 for their
not too slick latches so I got different ones for it...) or Butler
style hatches for them if anyone wants. I will also be making both
simple MkI and MKII exhaust parts for people to adapt to their own
ships in the manner they see fit, but will probably make some ready-
made version hatches for ships like ASW-20/19 and a few others.
Obviously the Butler arrangement is a little bigger commitment , with
the need to thin the forward lip on the hatch on a 59/48-3... or to
cut a much larger hole (surgery!) to accommodate it on other ships
without removable hatches. Perhaps smaller Butler vents would be
effective too... I haven't yet explored that region yet.

As mentioned, I have done a bit of research to establish rough
optimization guidelines for the bell mouth geometry on the Mandl as
well as the accelerator funnel/air straightener arrangement (which I
found analogous to a wind tunnel) that Butler used, and I cut and
pasted below what I shared with him on it after a most encouraging
phone conversation I had with him on the subject. Butler's untreated
vent (when it had no internal funnel...) was noisy to him, indicating
it was still kinda draggy (or more draggy than it *could* be at
least...). That's why Butler made the funnel in his ship, to both
accelerate and straighten the exit air to minimize it's impact in the
boundary layer and quiet the thing down which got me interested in the
honeycomb grills which I knew were used for that very purpose (the
straightening....). I put some thought and homework into it and came
up with a few refinements as well as guidelines (most notably the
honeycomb grill though, which is what really stumbled me into wind
tunnel guidelines as honeycomb grills are the key to them too... I was
just trying to figure out efficiency drops across the grills and found
much more than I was looking for) for making new ones on different
ships, should someone want to do such a thing...(note- it's even
duller from this point on...)

-Paul Hanson

PS. Feel free to make any suggestions, ask any questions, or give any
feedback. Of course also email me if you want me to keep you updated
on progress, I'll soon be testing a finished article of my MKII
version as well as making real glass articles of my Butler Extractor
as well, in addition to making a tunnel for the Butler arrangement.

PPS. In no other sport that I know of, can you so easily connect with
the 'superstars' and on top of that to have them be so darn kind. I
heart soaring!

PPPS. sorry for any non-sequiturs or repeated info, I'm trying to
adapt something I wrote last Dec aimed towards other 59/48-3 owners
into being currently relevant, and for any ships, not to mention the
lack of accompanying pics which add much to the storyline...


-------------------------------------------------------------------------------------------------------------------------------------------------------------------


Guidelines for Funnel Optimization: (copy/pasted from my email to DB)

It was quite by accident I wound up on a wind tunnel analogy though,
stumbled on while searching for measured effectiveness
and efficiencies inherent to honeycomb structures being used in air
straightening applications in the hopes of developing
some sort of guidelines to have a beginning place. Finding it stated
that a length (thickness of grill) of 6-8 times the cell width in so
many
places was encouraging, especially when I found it stated by
aerodynamicists in relation to wind tunnels. It was then that
my brain made the connection that your vent arrangement is essentially
a passive low speed wind tunnel.

Being a passive, reduced-pressure driven device has to change the
aerodynamic properties for establishing laminar flow in
the exit stream, but I'm almost sure most of the guidelines still
apply from normal active vacuum driven wind tunnels. I
had no intention of making a wind tunnel section for mine, but once I
studied up on it a little it seems quite a bit more
attractive. After a quick study of some pressure distribution charts
of sailplanes, I see why you chose that location for
your exit. Although it is optimally located in a low pressure area,
there is not enough length to apply most of the
guidelines for a laminar/deturbulating tunnel. Mine is located further
back, which unfortunately moves it out of the low
pressure hotspot, but at least affords me some linear length to
(theoretically) make a more optimized tunnel. For
the time being I will settle for the honeycomb in the exit and go
tunnel-less, which I'm sure will still work wonders for
straightening the flow, which is certain to at least quiet it a bit.


---------------------------------------------------------------------------------------------------------------------------


Honeycomb/Screen For 'Laminarization' of Exit Airflow (Laminator?) +
funnel considerations based on small wind tunnel
design


Use of aluminum honeycomb/screen to minimize turbulence/drag of the
exit air of the extractor vent, summarized guidelines:

1. Optimal length (aspect ratio) of honeycomb is 6-8 times the cell
width.
2. Any screens for further modification of airstream (probably not
necessary for this application)should be downstream of
the honeycomb, by ~.2 Diameters.
(diameter is calculated by surface area of opening on irregular shape
applied towards a circle)


Additional summarized (basic) design guidelines if using an
accelerator funnel arrangement: (to increases airflow while
decreasing turbulence-ie. noise/drag)

3. Accelerator funnel should begin with a parallel section (settling
chamber) of at least .5 Diameters in length immediately
behind the honeycomb grill, w/attn to transitions.
4. Optimal location for honeycomb/screens is mouth of funnel due to
increased surface area and therefore reduced
speed/pressure drops across honeycomb/screens(spaced ~.2 settling
chamber Diameters apart w/honeycomb
leading if screen is used)(note-for the sailplane cockpit arrangement,
may be necessary to put the
honeycomb/screen further downstream in funnel as to reduce risk of
damage to fragile aluminum honeycomb cells. Of course
titanium or stainless honeycomb is much tougher and could probably be
up front...)
5. Contraction ratio for funnels are typically between 6-9 (x surface
area)in small wind tunnels, and while longer
contraction lengths are preferable, the transitions and wall
smoothness is more important.
6. 45 deg fillets are beneficial in non symmetrical tunnels to reduce
separation in the corners, and 2D corner contractions
need 25% more length to achieve the same uniformity.
7. If there is a benefit to a velocity gradient to the exit air, this
can be achieved by angling 1 (or more) of the screens
until desired gradient is achieved

http://www.hexcel.com/NR/rdonlyres/5...Properties.pdf
(pg 30, note-
for this application the airflow will be WELL below the 2000cfm
minimum measured, probably closer to ~100-200cfm tops, so
the drag penalties will be far lower than the chart goes, but should
be easily deduced since the progression is linear)

http://www-htgl.stanford.edu/bradsha...eedTunnels.pdf

http://www-htgl.stanford.edu/bradsha...l/tscreen.html

http://www.me.berkeley.edu/fml/resea...nd_tunnel.html

http://www.vki.ac.be/facilities/pdf/l2b.pdf

http://www.vki.ac.be/facilities/pdf/l7.pdf

http://www.vki.ac.be/facilities/pdf/l6.pdf

http://www.vki.ac.be/facilities/pdf/wg1.pdf

http://tinyurl.com/6cpd54 (Godzilla is not very aerodynamic...)

Bumping this topic back up, as I would be interested if there was any more R&D done on these things, as well as any info on purchasing or fabricating one as a replacement for the aileron/spoiler hookup access hatch on my ASW-19. Paul, have you taken this any further along?

Thanks!

Rob