New Vent!

[sisu1a]

http://tinyurl.com/337bok7 ...I'm sure it works like a champ. Nice
work John/Hank/Dick!

[Andy[_1_]]

On Dec 6, 7:37*pm, sisu1a > wrote:
> http://tinyurl.com/337bok7* *...I'm sure it works like a champ. *Nice
> work John/Hank/Dick!

Looks nice but where do I put all the stuff that now sits in the over-
spar storage area? I don't think I want to discard my landout kit so
I can fit a vent system that has an unknown (to me) performance
advantage.

For me to be interested in a kit for the ASW-28 it would have to
extend the storage area aft so that, with the vent kit installed, at
least the same storage volume was still available, preferably more.
There is lots of room to extend backwards as is done in the 27's.
Unlike shorter pilots there in no room behind my seat and everything I
carry has to go just forward of, or over the spar.

Where can I find a picture of the installation looking aft into the
spar area?

Andy

[Mike the Strike]

On Dec 7, 7:56*am, Andy > wrote:
> On Dec 6, 7:37*pm, sisu1a > wrote:
>
> >http://tinyurl.com/337bok7**...I'm sure it works like a champ. *Nice
> > work John/Hank/Dick!
>
> Looks nice but where do I put all the stuff that now sits in the over-
> spar storage area? *I don't think I want to discard my landout kit so
> I can fit a vent system that has an unknown (to me) performance
> advantage.
>
> For me to be interested in a kit for the ASW-28 it would have to
> extend the storage area aft so that, with the vent kit installed, at
> least the same storage volume was still available, preferably more.
> There is lots of room to extend backwards as is done in the 27's.
> Unlike shorter pilots there in no room behind my seat and everything I
> carry has to go just forward of, or over the spar.
>
> Where can I find a picture of the installation looking aft into the
> spar area?
>
> Andy

An interesting gadget. However, wouldn't it be more logical to vent
nearer the rear of the fuselage, say in the lower tail?

Mike

[sisu1a]

>An interesting gadget. *However, wouldn't it be more logical to vent
> nearer the rear of the fuselage, say in the lower tail?>


Absolutely not... and this one of the major contributing factors to
why most glider's vent do not work. That's where designers have been
sticking them ever since Wil Shuman put one on his Libelle.

-Paul

[jcarlyle]

Paul,

The non-technical write-up at DG on the Mandl air extractor
experiments backs up your position ( http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
). But graph 7a in Prof. Boermans' paper ( http://frotor.fs.cvut.cz/doc/37.pdf
) suggests that the tail position is on a par with the pressure in
back of the wing.

-John

On Dec 7, 11:24 am, sisu1a > wrote:
> >An interesting gadget. However, wouldn't it be more logical to vent
>
> > nearer the rear of the fuselage, say in the lower tail?>
>
> Absolutely not... and this one of the major contributing factors to
> why most glider's vent do not work. That's where designers have been
> sticking them ever since Wil Shuman put one on his Libelle.
>
> -Paul

[Greg Arnold[_2_]]

Isn't there a lot of drag in a long, narrow tail boom that will restrict
the amount of air flowing to the tail? Also, how big of an exhaust
outlet can you put back there?

Also, I don't think the Boersmans graph shows pressure on the top of the
fuselage, where these outlets are located.



On 12/7/2010 8:40 AM, jcarlyle wrote:
> Paul,
>
> The non-technical write-up at DG on the Mandl air extractor
> experiments backs up your position ( http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
> ). But graph 7a in Prof. Boermans' paper ( http://frotor.fs.cvut.cz/doc/37.pdf
> ) suggests that the tail position is on a par with the pressure in
> back of the wing.
>
> -John
>
> On Dec 7, 11:24 am, > wrote:
>> >An interesting gadget. However, wouldn't it be more logical to vent
>>
>>> nearer the rear of the fuselage, say in the lower tail?>
>>
>> Absolutely not... and this one of the major contributing factors to
>> why most glider's vent do not work. That's where designers have been
>> sticking them ever since Wil Shuman put one on his Libelle.
>>
>> -Paul
>

[jcarlyle]

Greg,

I think the major effect on air exiting at the tail would be the total
area of tail vent. My LS8 tail has a lot of vent area (can't measure
it right now, but it's got to be 4 times the area of the inlet at the
nose). Even at that size, the interior diameter of the tail cone at
its narrowest has a much bigger area.

As for Boermans' graph, it's the total pressure around a "rotationally
symmetric body". I really have no idea from this graph what the
pressure is on the top or bottom of the fuselage, but somewhere (can't
find it now when I want it) I've seen a 3D colored pressure
distribution on a sailplane fuselage that clearly showed the pressure.
Unfortunately, I can't say where it showed the least pressure
appearing.

-John

On Dec 7, 11:52 am, Greg Arnold > wrote:
> Isn't there a lot of drag in a long, narrow tail boom that will restrict
> the amount of air flowing to the tail? Also, how big of an exhaust
> outlet can you put back there?
>
> Also, I don't think the Boersmans graph shows pressure on the top of the
> fuselage, where these outlets are located.

[sisu1a]

> The non-technical write-up at DG on the Mandl air extractor
> experiments backs up your position (http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
> ). But graph 7a in Prof. Boermans' paper (http://frotor.fs.cvut.cz/doc/37.pdf
> ) suggests that the tail position is on a par with the pressure in
> back of the wing.

Well I wish he would have told my glider that news, cause it
apparently didn't get the memo ;) My tail vent does not work -at all.
Like most gliders with tail vents... My forward located vent does,
like a champ. It also works on other gliders, and the difference is
not subtle.

Even if the pressures were equal, the forward spot still wins by a
long shot since the air doesn't have to travel such a long distance,
past obstacles, down a tapering duct (ducting adds significant static
resistance, a tapered one even more so, and bulkheads with holes in
them are dealbreakers...), and out an orifice that even if coupled to
the same differential pressure is not a shape that is as conducive to
generating low pressure (not efficiently anyhow...).

The low pressures being generated by these shapes are small. The
penalties of inefficient routing like the same old standard tail
configuration adds however are not. But as I understand it, the
pressure at the tail is kinda on a ship by ship basis. Some ships even
suck water up the tailpipe when blowing ballast, which is a pretty
good indicator of a poor choice for a 'low pressure' location. Also,
whenever I've looked at color coded pressure distribution charts I've
never seen it as hot at the base of the rudder as it is on the dorsal.
When I look at the Beorman graph however, I see a spike in pressure at
the tailvent location, up to +.175 or so... the numbers on the left
get smaller moving up... There *is an unexpected low pressure knee
back there, but it is well before the end of the tail where vents
would be and the same ducting/obstacle penalties still apply.

-Paul

[jcarlyle]

Paul,

Thanks! I knew you'd been experimenting, so I knew you agreed with
DG's findings. Sorry to say that I mis-read Boermans' graph, I
"assumed" the pressure was lower at the lower end of the Y axis.
<slaps forehead> So, if we agree that the tail vent would be located
at x=0.95 (not at 1.0, that's the end of the rudder), it should have a
pressure similar to the aft wing position, say, x=0.35.

My vent works pretty well on my LS8, but on my ASW-19 it was abysmal.
I was putting it down to the ASW having fairly small openings around
the rudder horns, as well as having those goofy NACA ducts under the
wing that reversed the incoming air before reversing it again at the
inside air vent. The LS has a nose intake, plus hefty openings around
the rudder, and it produces a nice air stream. Still, DG claims much
better venting by using the Mandl air extractor, as well a performance
gains.

-John

On Dec 7, 12:45 pm, sisu1a > wrote:
> Well I wish he would have told my glider that news, cause it
> apparently didn't get the memo ;) My tail vent does not work -at all.
> Like most gliders with tail vents... My forward located vent does,
> like a champ. It also works on other gliders, and the difference is
> not subtle.
>
> Even if the pressures were equal, the forward spot still wins by a
> long shot since the air doesn't have to travel such a long distance,
> past obstacles, down a tapering duct (ducting adds significant static
> resistance, a tapered one even more so, and bulkheads with holes in
> them are dealbreakers...), and out an orifice that even if coupled to
> the same differential pressure is not a shape that is as conducive to
> generating low pressure (not efficiently anyhow...).
>
> The low pressures being generated by these shapes are small. The
> penalties of inefficient routing like the same old standard tail
> configuration adds however are not. But as I understand it, the
> pressure at the tail is kinda on a ship by ship basis. Some ships even
> suck water up the tailpipe when blowing ballast, which is a pretty
> good indicator of a poor choice for a 'low pressure' location. Also,
> whenever I've looked at color coded pressure distribution charts I've
> never seen it as hot at the base of the rudder as it is on the dorsal.
> When I look at the Beorman graph however, I see a spike in pressure at
> the tailvent location, up to +.175 or so... the numbers on the left
> get smaller moving up... There *is an unexpected low pressure knee
> back there, but it is well before the end of the tail where vents
> would be and the same ducting/obstacle penalties still apply.
>
> -Paul

[[email protected]]

On Dec 7, 10:46*am, Mike the Strike > wrote:
> On Dec 7, 7:56*am, Andy > wrote:
>
>
>
>
>
> > On Dec 6, 7:37*pm, sisu1a > wrote:
>
> > >http://tinyurl.com/337bok7**...I'm sure it works like a champ. *Nice
> > > work John/Hank/Dick!
>
> > Looks nice but where do I put all the stuff that now sits in the over-
> > spar storage area? *I don't think I want to discard my landout kit so
> > I can fit a vent system that has an unknown (to me) performance
> > advantage.
>
> > For me to be interested in a kit for the ASW-28 it would have to
> > extend the storage area aft so that, with the vent kit installed, at
> > least the same storage volume was still available, preferably more.
> > There is lots of room to extend backwards as is done in the 27's.
> > Unlike shorter pilots there in no room behind my seat and everything I
> > carry has to go just forward of, or over the spar.
>
> > Where can I find a picture of the installation looking aft into the
> > spar area?
>
> > Andy
>
> An interesting gadget. *However, wouldn't it be more logical to vent
> nearer the rear of the fuselage, say in the lower tail?
>
> Mike- Hide quoted text -
>
> - Show quoted text -

I have an exit vent in the lower aft area of the fuselage of both my
'27 and '28. With all the other stuff done sealing rudder hinge,
elevator drive, horn splitters, etc, it improved negative pressure and
flow and resulted in less noise. This vent is a huge ass ache to put
in with the associated nozzle, has significant structural implications
requiring reinforcement, and simply, is not for the faint hearted.
The new vent on top is in a low pressure area which helps a lot with
getting flow and reduced cockpit pressure. It also takes an hour and a
half to install instead of about 10 hr. It's structural implications
are minimal. It slightly reduces available baggage storage in the top
center 4 inches.
Both my gliders will have rear vents closed this winter and '28 will
get top vent.
FWIW
UH

[Don Johnstone[_4_]]

Do you blokes suffer from major flatulence problems? Seems a lot of effort
to remove air from the cockpit but I could understand if the air was
contaminated in some way :-)



At 19:16 07 December 2010, wrote:
>On Dec 7, 10:46=A0am, Mike the Strike wrote:
>> On Dec 7, 7:56=A0am, Andy wrote:
>>
>>
>>
>>
>>
>> > On Dec 6, 7:37=A0pm, sisu1a wrote:
>>
>> > >http://tinyurl.com/337bok7=A0=A0...I'm sure it works like a champ.
>=A0=
>Nice
>> > > work John/Hank/Dick!
>>
>> > Looks nice but where do I put all the stuff that now sits in the
over-
>> > spar storage area? =A0I don't think I want to discard my landout
kit
>so
>> > I can fit a vent system that has an unknown (to me) performance
>> > advantage.
>>
>> > For me to be interested in a kit for the ASW-28 it would have to
>> > extend the storage area aft so that, with the vent kit installed, at
>> > least the same storage volume was still available, preferably more.
>> > There is lots of room to extend backwards as is done in the 27's.
>> > Unlike shorter pilots there in no room behind my seat and everything
I
>> > carry has to go just forward of, or over the spar.
>>
>> > Where can I find a picture of the installation looking aft into the
>> > spar area?
>>
>> > Andy
>>
>> An interesting gadget. =A0However, wouldn't it be more logical to
vent
>> nearer the rear of the fuselage, say in the lower tail?
>>
>> Mike- Hide quoted text -
>>
>> - Show quoted text -
>
>I have an exit vent in the lower aft area of the fuselage of both my
>'27 and '28. With all the other stuff done sealing rudder hinge,
>elevator drive, horn splitters, etc, it improved negative pressure and
>flow and resulted in less noise. This vent is a huge ass ache to put
>in with the associated nozzle, has significant structural implications
>requiring reinforcement, and simply, is not for the faint hearted.
>The new vent on top is in a low pressure area which helps a lot with
>getting flow and reduced cockpit pressure. It also takes an hour and a
>half to install instead of about 10 hr. It's structural implications
>are minimal. It slightly reduces available baggage storage in the top
>center 4 inches.
>Both my gliders will have rear vents closed this winter and '28 will
>get top vent.
>FWIW
>UH
>

[Morgan[_2_]]

Well, Paul isn't tooting his own horn with the experimentation he's
done, but I can attest to how well the extractor works that he has
built. He built a prototype for my ASW-20 that replaces the control
hookup hatch. The difference is incredible. I am able to fly with
the side window vents closed most of the time now, even when it's
pretty hot and we aren't getting that high. Not that heat has been a
problem for the last month or so. The whistling and air noise is so
significantly reduced that I found myself initially thermalling at 5+
knots higher airspeed than before, just because of the reduced audio
feedback. It took a bit to recalibrate to the reduced noise.

It's good enough that I was already considering modifying my Duo.
Especially if you live somewhere hot, the comfort is well worth it
regardless of if the performance impacts.

Morgan

[Eric Greenwell[_4_]]

On 12/7/2010 11:16 AM, wrote:

> I have an exit vent in the lower aft area of the fuselage of both my
> '27 and '28. With all the other stuff done sealing rudder hinge,
> elevator drive, horn splitters, etc, it improved negative pressure and
> flow and resulted in less noise. This vent is a huge ass ache to put
> in with the associated nozzle, has significant structural implications
> requiring reinforcement, and simply, is not for the faint hearted.
> The new vent on top is in a low pressure area which helps a lot with
> getting flow and reduced cockpit pressure. It also takes an hour and a
> half to install instead of about 10 hr. It's structural implications
> are minimal. It slightly reduces available baggage storage in the top
> center 4 inches.
> Both my gliders will have rear vents closed this winter and '28 will
> get top vent.

I got so much air from the front vent and eyeball vent on my ASH 26 E
(standard tail vents at the rudder cables) that I plugged up half the
duct work from the nose to make it easier to control. Still get tons of
air from the eyeball and scoop when I open them, so the air doesn't seem
to have any trouble getting out of the glider. I don't know where it is
leaving, however.

How low must the cockpit pressure be to assure myself the air isn't
going out the canopy/cockpit edge, gear doors or wing roots?

What is a good way to measure the cockpit pressure?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

[Grider Pirate]

On Dec 7, 1:49*pm, Eric Greenwell > wrote:
> On 12/7/2010 11:16 AM, wrote:
>
> > I have an exit vent in the lower aft area of the fuselage of both my
> > '27 and '28. With all the other stuff done sealing rudder hinge,
> > elevator drive, horn splitters, etc, it improved negative pressure and
> > flow and resulted in less noise. This vent is a huge ass ache to put
> > in with the associated nozzle, has significant structural implications
> > requiring reinforcement, and simply, is not for the faint hearted.
> > The new vent on top is in a low pressure area which helps a lot with
> > getting flow and reduced cockpit pressure. It also takes an hour and a
> > half to install instead of about 10 hr. It's structural implications
> > are minimal. It slightly reduces available baggage storage in the top
> > center 4 inches.
> > Both my gliders will have rear vents closed this winter and '28 will
> > get top vent.
>
> I got so much air from the front vent and eyeball vent on my ASH 26 E
> (standard tail vents at the rudder cables) that I plugged up half the
> duct work from the nose to make it easier to control. Still get tons of
> air from the eyeball and scoop when I open them, so the air doesn't seem
> to have any trouble getting out of the glider. I don't know where it is
> leaving, however.
>
> How low must the cockpit pressure be to assure myself the air isn't
> going out the canopy/cockpit edge, gear doors or wing roots?
>
> What is a good way to measure the cockpit pressure?
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
> email me)

In my case a water manometer* connected to the static system on one
side and open to cabin pressure on the other. All I need to do is get
around to it. I've been carrying thte bits and pieces in my trailer
for a couple years now, but I always think I'm going to fly 500k, and
don't want to carry stuff around (while I actually fly 'round the
patch all day).

*just a piece of clear vinyl tubing actually

[JS]

I experienced the reaction of several pilots to Paul's AS-W20 vent
mod, all positive. First saw this kit in Hank's shop. Looked at my
vent parts when I was up at Williams the other day.
To hopefully answer Andy's question: The largest part (the scoop
from the canopy rail to the hard mounted outer part) is removable.
Velcro onto the canopy frame and a ring of foam sealing the throat
where it slides into the outer part. It will take some room in the
baggage compartment, but not most of it.
In my 27 I won't be able to use much of the scoop, since there's an
"E" Oxygen bottle in the upper baggage compartment and currently an
APRS black box strapped on top of it.
Regarding flatulence, it's more about moving hot air (including that
I've generated in this forum) since many of us fly where it gets
bloody hot.
"More beans, Mr. Taggart?"
Jim

On Dec 7, 6:56*am, Andy > wrote:
>
> Looks nice but where do I put all the stuff that now sits in the over-
> spar storage area? *I don't think I want to discard my landout kit so
> I can fit a vent system that has an unknown (to me) performance
> advantage.
>
> Andy

[Kevin Christner]

> I have an exit vent in the lower aft area of the fuselage of both my
> '27 and '28. With all the other stuff done sealing rudder hinge,
> elevator drive, horn splitters, etc, it improved negative pressure and
> flow and resulted in less noise. This vent is a huge ass ache to put
> in with the associated nozzle, has significant structural implications
> requiring reinforcement, and simply, is not for the faint hearted.
> The new vent on top is in a low pressure area which helps a lot with
> getting flow and reduced cockpit pressure. It also takes an hour and a
> half to install instead of about 10 hr. It's structural implications
> are minimal. It slightly reduces available baggage storage in the top
> center 4 inches.
> Both my gliders will have rear vents closed this winter and '28 will
> get top vent.
> FWIW
> UH

What work needs to be done to fit these to other types? Reglass the
cockpit scoop to fit the inside of the fuselage shell?

2C

[Andrzej Kobus]

I assume this vent will not work with a fuselage tank installed,
correct?

[[email protected]]

On Dec 7, 7:20*pm, Kevin Christner > wrote:
> > I have an exit vent in the lower aft area of the fuselage of both my
> > '27 and '28. With all the other stuff done sealing rudder hinge,
> > elevator drive, horn splitters, etc, it improved negative pressure and
> > flow and resulted in less noise. This vent is a huge ass ache to put
> > in with the associated nozzle, has significant structural implications
> > requiring reinforcement, and simply, is not for the faint hearted.
> > The new vent on top is in a low pressure area which helps a lot with
> > getting flow and reduced cockpit pressure. It also takes an hour and a
> > half to install instead of about 10 hr. It's structural implications
> > are minimal. It slightly reduces available baggage storage in the top
> > center 4 inches.
> > Both my gliders will have rear vents closed this winter and '28 will
> > get top vent.
> > FWIW
> > UH
>
> What work needs to be done to fit these to other types? *Reglass the
> cockpit scoop to fit the inside of the fuselage shell?
>
> 2C

One done so far is for '24/27/28/29. It is molded to follow the inside
contour of the fuselage which has a lap joint.
To make one to fit another type, outer shape needs to be matched and
inner shape needs to be matched. Long answer
to say it probably won't be right. Other ships may follow- we'll see.
UH/LX

[[email protected]]

On Dec 7, 9:12*pm, Andrzej Kobus > wrote:
> I assume this vent will not work with a fuselage tank installed,
> correct?

Requires mod to fuselage tank. This is in prototyping and mold making
and will be available early next year. Probably not
as a home kit. It is much more complicated to install than the vent.
UH/LX

[Andy[_1_]]

On Dec 8, 5:48*am, wrote:

> One done so far is for '24/27/28/29. It is molded to follow the inside
> contour of the fuselage which has a lap joint.
> To make one to fit another type, outer shape needs to be matched and
> inner shape needs to be matched. Long answer
> to say it probably won't be right. Other ships may follow- we'll see.
> UH/LX

Any thought of making an extended baggage tray for the 28? There is
no reason it couldn't extend back like the 27 does. That would give me
back the forward of spar space that I would lose with the collector
plate. That forward of spar space is filled on my glider with 2 water
bottles, hand held radio, parachute bag, and canopy cover. (and the
essential landout deterrent - the stale peanut butter sandwich)

Maybe the reason my 28 is quiet is that all the space between my head
and the tail is stuffed full ;)

What measurements have been done on performance gains? I'd like to
see data for your 28 pre vent and post vent for sink rate at 90kts. I
won't spend $500 to reduce noise level or increase ventilation but I
would for a significant reduction in the sink rate at high speeds.

Andy

[Mike Ash]

In article >,
Don Johnstone > wrote:

> Do you blokes suffer from major flatulence problems? Seems a lot of effort
> to remove air from the cockpit but I could understand if the air was
> contaminated in some way :-)

Around here (northern Virginia) there's a month or two of summer where I
spend pretty much the entire flight with my hand stuck outside to get as
much air in as possible to try to stay cool. On one miserably hot day
this past July I had to cut a flight short as I began to seriously
overheat despite all my best efforts. I have one of Paul's extractors on
order and I'm hoping it'll make next summer much more pleasant.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon

[CLewis95]

from Paul (sisu1a):
>..... *But as I understand it, the
> pressure at the tail is kinda on a ship by ship basis. Some ships even
> suck water up the tailpipe when blowing ballast, which is a pretty
> good indicator of a poor choice for a 'low pressure' location.
>...

Paul (ALL)

I have this problem with my Genesis 2 (both water and "other" fluids).

Does this come from a "venturi" effect of air leaking from Horz/Vert
Stab Junction or poor Rudder Sealing? It amazes me how much gets
sucked back into fuselage. (Genesis has VERY short fuselage)

Another Genesis owner (DK) has experimented with an exit duct out the
fuse hatch over wings. ... comments Don???

Curt - 95

[[email protected]]

On Dec 8, 12:46*pm, CLewis95 > wrote:
> from Paul (sisu1a):
>
> >..... *But as I understand it, the
> > pressure at the tail is kinda on a ship by ship basis. Some ships even
> > suck water up the tailpipe when blowing ballast, which is a pretty
> > good indicator of a poor choice for a 'low pressure' location.
> >...
>
> Paul (ALL)
>
> I have this problem with my Genesis 2 (both water and "other" fluids).
>
> Does this come from a "venturi" effect of air leaking from Horz/Vert
> Stab Junction or poor Rudder Sealing? *It amazes me how much gets
> sucked back into fuselage. *(Genesis has VERY short fuselage)
>
> Another Genesis owner (DK) has experimented with an exit duct out the
> fuse hatch over wings. ... comments Don???
>
> Curt - 95
Likely due to pressure recoveing over the very short length of
fuselage and large reduction in cross section
over that length. High location closer to centerline would probably
better in order to avoid effects on root fillet
area.
Just speculating- It's cold here.
UH

[GliderDK]

>
> I have this problem with my Genesis 2 (both water and "other" fluids).
>
> Does this come from a "venturi" effect of air leaking from Horz/Vert
> Stab Junction or poor Rudder Sealing? *It amazes me how much gets
> sucked back into fuselage. *(Genesis has VERY short fuselage)
>
> Another Genesis owner (DK) has experimented with an exit duct out the
> fuse hatch over wings. ... comments Don???
>
> Curt - 95


I have had an air outlet on my Genesis2 for several years. It was
modeled after the outlet on DB's ASW-22. It seems to work very well.
Curt is correct that on a Genesis 2, dumped water ballast will enter
the fuselage thru the fairings over the rudder horns. These fairings
are suppose to be the air outlets. I have taken photos of that area
with tufts taped around the fairings. And indeed the tufts turn and
are sucked into the "outlets".

Don (DK)

[Bob Kuykendall]

On Dec 7, 12:47*pm, Don Johnstone > wrote:
> Do you blokes suffer from major flatulence problems? Seems a lot of effort
> to remove air from the cockpit but I could understand if the air was
> contaminated in some way :-)

At issue is that ventilation air tends to pressurize the cockpit, and
then leak out around the canopy perimeter. Anywhere that there is air
escaping through the canopy frame gap, that leak will trip the
boundary layer and increase drag. If you can keep the cockpit at lower
than ambient pressure, you run a good chance of maintaining laminar
flow across the gap between the fuselage and the canopy, which can
result in several more square feet of laminar flow than you had
previously.

I happen to think that many original designers got it right; that the
most effective vent is back at the base of the rudder, where it is
convenient to exhaust air around the rudder cable horns.
Unfortunately, something often got lost in translation, and most
production gliders allow too little exhaust area through the vertical
fin spar, causing inadequate ventilation flow and too much cockpit
pressure. They also offer many restrictions on the path from the
cockpit to the tailboom, which reduces the flow rate.

So I think that these trendy exhaust vents, while perhaps not the best
possible solution, are still a lot better than you can get without
removing the rudder and doing some relatively major surgery on the fin
spar.

Thanks, Bob K.
http://www.hpaircraft.com

[Grider Pirate]

On Dec 8, 11:20*am, Bob Kuykendall > wrote:
> On Dec 7, 12:47*pm, Don Johnstone > wrote:
>
> > Do you blokes suffer from major flatulence problems? Seems a lot of effort
> > to remove air from the cockpit but I could understand if the air was
> > contaminated in some way :-)
>
> At issue is that ventilation air tends to pressurize the cockpit, and
> then leak out around the canopy perimeter. Anywhere that there is air
> escaping through the canopy frame gap, that leak will trip the
> boundary layer and increase drag. If you can keep the cockpit at lower
> than ambient pressure, you run a good chance of maintaining laminar
> flow across the gap between the fuselage and the canopy, which can
> result in several more square feet of laminar flow than you had
> previously.
>
> I happen to think that many original designers got it right; that the
> most effective vent is back at the base of the rudder, where it is
> convenient to exhaust air around the rudder cable horns.
> Unfortunately, something often got lost in translation, and most
> production gliders allow too little exhaust area through the vertical
> fin spar, causing inadequate ventilation flow and too much cockpit
> pressure. They also offer many restrictions on the path from the
> cockpit to the tailboom, which reduces the flow rate.
>
> So I think that these trendy exhaust vents, while perhaps not the best
> possible solution, are still a lot better than you can get without
> removing the rudder and doing some relatively major surgery on the fin
> spar.
>
> Thanks, Bob K.http://www.hpaircraft.com

.... and as JS pointed out, many of us fly where it is REALLY hot, with
ambient temperatures of 43c, 110f, and closed cockpit temperature over
55c, 130f. It doesn't take long at that temperature to ruin an
otherwise great flying day.

[Matt Herron Jr.]

What keeps rain, wasps, mice, etc. from entering the vent hole when on
the ground?

[[email protected]]

On Dec 9, 3:11*am, "Matt Herron Jr." > wrote:
> What keeps rain, wasps, mice, etc. from entering the vent hole when on
> the ground?

We don't have mice running around on our launch grid and rarely grid
in the rain. Guess I just didn't think
about those problems.
UH

[Phil Jeffery[_2_]]

At 08:11 09 December 2010, Matt Herron Jr. wrote:
>What keeps rain, wasps, mice, etc. from entering the vent hole when on
>the ground?
>


Canopy cover?

[Francisco De Almeida[_2_]]

My two cents:

- complementing the post by Bob Kuykendal, and as an example, the air
passage though the tailfin spar of an LS8 is comprised of three small
holes with a combined area of barely 3 square inches. Added to the other
constrictions along the way, this means the ventilation pressure drop
occurs mostly after the cockpit. Thus, of course the cockpit will stay
significantly above ambient pressure in an unmodified LS fuselage.

- regarding the reingestion of ballast water (or pee...) at the end of the
tailboom, perhaps it is linked to lower pressures at the top end of the
rudder hinge? The location of the horizontal tailplane on the Genesis
would suggest suction occurs there.

- finally, and after applauding the designers of all these fine new
outlets, perhaps the next step is to locate the inlet in a neutral or even
a low pressure area? Why, you may ask? Because there is no reason in
principle to pursue the highest possible ventilation pressure drop.

With a nose inlet and a turtleneck exit, the total ventilation pressure
drop approaches twice the dynamic pressure of the outside free flow (i.e.
the pressure coefficients may approach +1 at the nose and -1 at the
turtleneck). The power lost to the ventilation flow is the product of this
pressure drop by the flow rate, e.g. at 100 kts a flow rate of 20
litres/second costs 30 Watts. This power is subtracted from the
performance of the glider.

If the inlet is located instead in a neutral pressure area (and the
cross-sections are suitably sized), the same cooling flow will cost only
15 Watts - and the cockpit will achieve an even lower pressure than
before, which is doubly good for performance!

Going further: an inlet may even be located in a moderately negative
pressure area (I envision exchanging the pop-out window for a small
naca-entry connected to a small eyeball vent). The Cp at this location is
about -0.7; with partial pressure recovery, perhaps we get -0.3 in the
cockpit. As the pressure at the turtleneck exit remains even lower, it is
still possible to create an effective airflow. Result: the most
energy-efficient ventilation possible.

Sounds counterintuitive, but should work and be easy to implement in a new
design (existing designs may be constrained by the impossibility of
increasing the cross-section of inlets).

[Francisco De Almeida[_2_]]

My two cents:

- complementing the post by Bob Kuykendal, and as an example, the air
passage though the tailfin spar of an LS8 is comprised of three small
holes with a combined area of barely 3 square inches. Added to the other
constrictions along the way, this means the ventilation pressure drop
occurs mostly after the cockpit. Thus, of course the cockpit will stay
significantly above ambient pressure in an unmodified LS fuselage.

- regarding the reingestion of ballast water (or pee...) at the end of the
tailboom, perhaps it is linked to lower pressures at the top end of the
rudder hinge? The location of the horizontal tailplane on the Genesis
would suggest suction occurs there.

- finally, and after applauding the designers of all these fine new
outlets, perhaps the next step is to locate the inlet in a neutral or even
a low pressure area? Why, you may ask? Because there is no reason in
principle to pursue the highest possible ventilation pressure drop.

With a nose inlet and a turtleneck exit, the total ventilation pressure
drop approaches twice the dynamic pressure of the outside free flow (i.e.
the pressure coefficients may approach +1 at the nose and -1 at the
turtleneck). The power lost to the ventilation flow is the product of this
pressure drop by the flow rate, e.g. at 100 kts a flow rate of 20
litres/second costs 30 Watts. This power is subtracted from the
performance of the glider.

If the inlet is located instead in a neutral pressure area (and the
cross-sections are suitably sized), the same cooling flow will cost only
15 Watts - and the cockpit will achieve an even lower pressure than
before, which is doubly good for performance!

Going further: an inlet may even be located in a moderately negative
pressure area (I envision exchanging the pop-out window for a small
naca-entry connected to a small eyeball vent). The Cp at this location is
about -0.7; with partial pressure recovery, perhaps we get -0.3 in the
cockpit. As the pressure at the turtleneck exit remains even lower, it is
still possible to create an effective airflow. Result: the most
energy-efficient ventilation possible.

Sounds counterintuitive, but should work and be easy to implement in a new
design (existing designs may be constrained by the impossibility of
increasing the cross-section of inlets).

[Francisco De Almeida[_2_]]

My two cents:

- complementing the post by Bob Kuykendal, and as an example, the air
passage though the tailfin spar of an LS8 is comprised of three small
holes with a combined area of barely 3 square inches. Added to the other
constrictions along the way, this means the ventilation pressure drop
occurs mostly after the cockpit. Thus, of course the cockpit will stay
significantly above ambient pressure in an unmodified LS fuselage.

- regarding the reingestion of ballast water (or pee...) at the end of the
tailboom, perhaps it is linked to lower pressures at the top end of the
rudder hinge? The location of the horizontal tailplane on the Genesis
would suggest suction occurs there.

- finally, and after applauding the designers of all these fine new
outlets, perhaps the next step is to locate the inlet in a neutral or even
a low pressure area? Why, you may ask? Because there is no reason in
principle to pursue the highest possible ventilation pressure drop.

With a nose inlet and a turtleneck exit, the total ventilation pressure
drop approaches twice the dynamic pressure of the outside free flow (i.e.
the pressure coefficients may approach +1 at the nose and -1 at the
turtleneck). The power lost to the ventilation flow is the product of this
pressure drop by the flow rate, e.g. at 100 kts a flow rate of 20
litres/second costs 30 Watts. This power is subtracted from the
performance of the glider.

If the inlet is located instead in a neutral pressure area (and the
cross-sections are suitably sized), the same cooling flow will cost only
15 Watts - and the cockpit will achieve an even lower pressure than
before, which is doubly good for performance!

Going further: an inlet may even be located in a moderately negative
pressure area (I envision exchanging the pop-out window for a small
naca-entry connected to a small eyeball vent). The Cp at this location is
about -0.7; with partial pressure recovery, perhaps we get -0.3 in the
cockpit. As the pressure at the turtleneck exit remains even lower, it is
still possible to create an effective airflow. Result: the most
energy-efficient ventilation possible.

Sounds counterintuitive, but should work and be easy to implement in a new
design (existing designs may be constrained by the impossibility of
increasing the cross-section of inlets).

[Papa3]

On Dec 9, 3:11*am, "Matt Herron Jr." > wrote:
> What keeps rain, wasps, mice, etc. from entering the vent hole when on
> the ground?

The same thing that keeps them from coming in through: the apple core
window, the nose vent, the spar carry through, the wheel well, ie.
nothing :-)

Look at it this way - when the ship's assembled and on the line,
there are lots of easier ways for varmints to get in. When it's
disassmbled in the trailer, there are huge holes where the wings used
to be.

[Andy[_1_]]

On Dec 9, 1:36*pm, Papa3 > wrote:
> On Dec 9, 3:11*am, "Matt Herron Jr." > wrote:
>
> > What keeps rain, wasps, mice, etc. from entering the vent hole when on
> > the ground?
>
> The same thing that keeps them from coming in through: *the apple core
> window, the nose vent, *the spar carry through, the wheel well, *ie.
> nothing *:-)
>
> Look at it this way - *when the ship's assembled and on the line,
> there are lots of easier ways for varmints to get in. *When it's
> disassmbled in the trailer, there are huge holes where the wings used
> to be.

Well rain could be an issue in flight particularly if all the inlet
vents are closed to keep the water out. Maybe the MkII version will
have a remote controlled closing flap.

I'm more interested in real performance numbers though. I don't mind
getting the back of my head wet a couple of times a year for a gain 50
fpm at 90 kts. 0.001 fpm at 90 kts and maybe it's not worth the risk
of getting wet.

Andy

[cernauta]

On Thu, 9 Dec 2010 13:27:59 -0800 (PST), Andy >
wrote:

>I'm more interested in real performance numbers though. I don't mind
>getting the back of my head wet a couple of times a year for a gain 50
>fpm at 90 kts. 0.001 fpm at 90 kts and maybe it's not worth the risk
>of getting wet.

If Francisco de Almeida's (Hi pal!) math is correct, and ventilation
at 100kts really costs 30W, then I believe we're talking about a
potential reduction in drag between 0,5% and 0,1%.

Well, my math isn't going to pass any tests...

aldo cernezzi