Fuselage Vents

[Ken Kochanski (KK)]

The performance claims look extremely good ... is this plausible ?

http://www.dg-flugzeugbau.de/mandl-absaugung-e.html

KK

[PMSC Member]

I love the timing. Right out of the XX playbook.


On Jul 30, 11:46 am, "Ken Kochanski (KK)" >
wrote:
> The performance claims look extremely good ... is this plausible ?
>
> http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
>
> KK

[Uncle Fuzzy]

On Jul 30, 8:46*am, "Ken Kochanski (KK)" >
wrote:
> The performance claims look extremely good ... is this plausible ?
>
> http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
>
> KK
Thanks for posting this!

Sounds plausible to me, but what do I know? I DO know that at 70
knots, opening the vent in my Speed Astir (AKA the 'Grob Solar Sauna)
will drive the altimeter down 100' instantly, so there is positive
pressure to deal with. I also know that I have a perfect spot to make
an 'experimental' vent that is completely removable. Increasing
airflow in the cabin is more important to me than the performance
gain.

[[email protected]]

On Jul 30, 8:46*am, "Ken Kochanski (KK)" >
wrote:
> The performance claims look extremely good ... is this plausible ?
>
> http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
>
> KK

Ventus mods have used a funnel behind the wheel well for years,
typically a 2" piece or pipe would form the exit.

Improvement here is the shape of the exit.

Regards

Al

[Go Soaring]

Yawn............See the below, 1972!! Wil Schuemann H301 Libelle

http://www.betsybyars.com/guy/soaring_symposia/72-modif.html


At 18:43 30 July 2008, wrote:
>On Jul 30, 8:46=A0am, "Ken Kochanski (KK)"
>wrote:
>> The performance claims look extremely good ... is this plausible ?
>>
>> http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
>>
>> KK
>
>Ventus mods have used a funnel behind the wheel well for years,
>typically a 2" piece or pipe would form the exit.
>
>Improvement here is the shape of the exit.
>
>Regards
>
>Al
>
>

[[email protected]]

Dear Uncle
If your altimeter changes indications when you open the vent, that
indicates your altimeter is not connected to STATIC. Best to check
you plumbing.

Guy Acheson, "DDS"



On Jul 30, 9:16�am, Uncle Fuzzy > wrote:

> Sounds plausible to me, but what do I know? �I DO know that at 70
> knots, opening the vent in my Speed Astir (AKA the 'Grob Solar Sauna)
> will drive the altimeter down 100' instantly, so there is positive
> pressure

[sisu1a]

On Jul 30, 8:17 pm, wrote:
> Dear Uncle
> If your altimeter changes indications when you open the vent, that
> indicates your altimeter is not connected to STATIC. Best to check
> you plumbing.

Or (dramatic pause) it means that someone (previous owner?) has chosen
the cockpit as the static source. If this is the case, I think Mr
Fuzzy just learned why it's an excellent BACKUP source and a poor
primary one (hint-use a pneumatic toggle to switch to cockpit static
only when your REAL static system is waterlogged/frozen) Use your
ships actual static system. It works better than the cockpit.

My 2 Pesos,
-Paul

[Uncle Fuzzy]

On Jul 30, 9:48*pm, sisu1a > wrote:
> On Jul 30, 8:17 pm, wrote:
>
> > Dear Uncle
> > If your altimeter changes indications when you open the vent, that
> > indicates your altimeter is not connected to STATIC. *Best to check
> > you plumbing.
>
> Or (dramatic pause) it means that someone (previous owner?) has chosen
> the cockpit as the static source. If this is the case, I think Mr
> Fuzzy just learned why it's an excellent BACKUP source and a poor
> primary one (hint-use a pneumatic toggle to switch to cockpit static
> only when your REAL static system is waterlogged/frozen) Use your
> ships actual static system. It works better than the cockpit.
>
> My 2 Pesos,
> -Paul

OR,
Uncle Fuzzy decided that he'd like his ALTIMETER to read the same
pressure as his FLIGHT RECORDER when the pneumatic switch is in the
CABIN position on his line to the Altimeter.

[Jim White[_3_]]

>Uncle Fuzzy decided that he'd like his ALTIMETER to read the same
>pressure as his FLIGHT RECORDER when the pneumatic switch is in the
>CABIN position on his line to the Altimeter.
>

Now there is a thought.... Open the air vent if you are close to airspace
to make the logger think you are lower, and fit an extraction vent if you
want that height record.

jim

[Uncle Fuzzy]

On Jul 31, 9:40*am, Jim White > wrote:
> >Uncle Fuzzy decided that he'd like his ALTIMETER to read the same
> >pressure as his FLIGHT RECORDER when the pneumatic switch is in the
> >CABIN position on his line to the Altimeter.
>
> Now there is a thought.... Open the air vent if you are close to airspace
> to make the logger think you are lower, and fit an extraction vent if you
> want that height record.
>
> jim

I'd think the relatively sudden increase (or decrease) in the delta
between the GPS altitude and the Baro altitude would raise suspicions.
I know I'd look at it if I saw a significant jump, and I'm not exactly
a rocket scientist.

[Soaring]

On Jul 30, 12:43*pm, " >
wrote:
> On Jul 30, 8:46*am, "Ken Kochanski (KK)" >
> wrote:
>
> > The performance claims look extremely good ... is this plausible ?
>
> >http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
>
> > KK
>
> Ventusmods have used a funnel behind the wheel well for years,
> typically a 2" piece or pipe would form the exit.
>
> Improvement here is the shape of the exit.
>
> Regards
>
> Al

Can someone e-mail more info on Ventus mods?
Thanks,

Andy

[Derek Copeland]

In that case, I suppose you would have to go onto oxygen a little bit lower
down with the fuselage extraction vent fitted!

At 16:40 31 July 2008, Jim White wrote:
>
>Now there is a thought.... Open the air vent if you are close to
airspace
>to make the logger think you are lower, and fit an extraction vent if
you
>want that height record.
>
>jim
>

[Ken Kochanski (KK)]

So assuming this is worthwhile ... what about putting extractors on
the back of the gear doors ... the door area is probably already
messing up the laminar flow ... and there are no structural issues ...
and yes, you would have to then allow fuse air to pass into the gear
well - I think most of the newer ships have this sealed up - and the
doors would have to be sealed, so you don't just pull air through the
door gaps ...

On Jul 30, 2:43*pm, " >
wrote:
> On Jul 30, 8:46*am, "Ken Kochanski (KK)" >
> wrote:
>
> > The performance claims look extremely good ... is this plausible ?
>
> >http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
>
> > KK
>
> Ventus mods have used a funnel behind the wheel well for years,
> typically a 2" piece or pipe would form the exit.
>
> Improvement here is the shape of the exit.
>
> Regards
>
> Al

[Uncle Fuzzy]

On Aug 2, 3:25*am, Derek Copeland
> wrote:
> In that case, I suppose you would have to go onto oxygen a little bit lower
> down with thefuselageextractionventfitted!
>
> At 16:40 31 July 2008, Jim White wrote:
>
>
>
>
>
> >Now there is a thought.... Open the airventif you are close to
> airspace
> >to make the logger think you are lower, and fit an extractionventif
> you
> >want that height record.
>
> >jim- Hide quoted text -
>
> - Show quoted text -

I made this vent to replace the access hatch for connecting my
controls
http://griderpirate.smugmug.com/gallery/3702283_9hEKD#355235771_pv8zu
Next weekend I will fly with a manometer to compare static to cabin
pressure with the 'normal' hatch, then the 'Mandl Extractor' hatch. I
can report subjectively that I was MUCH more comfortable in the
cockpit.

[DRN]

On Jul 30, 10:46 am, "Ken Kochanski (KK)" >
wrote:
> The performance claims look extremely good ... is this plausible ?
>
> http://www.dg-flugzeugbau.de/mandl-absaugung-e.html
>
> KK

I posted pictures of Dick Butler's air exhaust in my Uvalde blog.
You need to accelerate the air smoothly inside the fuselage
then direct it to exit parallel the exterior flow; these photos
show how Dick did it.

www.nadler.com

See ya, Dave "YO electric"

[sisu1a]

> I made this vent to replace the access hatch for connecting my
> controlshttp://griderpirate.smugmug.com/gallery/3702283_9hEKD#355235771_pv8zu
> Next weekend I will fly with a manometer to compare static to cabin
> pressure with the 'normal' hatch, then the 'Mandl Extractor' hatch. I
> can report subjectively that I was MUCH more comfortable in the
> cockpit.

Awesome! My SZD-59 is going to get one of these on it's booby hatch
now too, thanks for sharing!

-Paul

[Uncle Fuzzy]

On Aug 19, 6:42*pm, sisu1a > wrote:
> *> I made this vent to replace the access hatch for connecting my
>
> > controlshttp://griderpirate.smugmug.com/gallery/3702283_9hEKD#355235771_pv8zu
> > Next weekend I will fly with a manometer to compare static to cabin
> > pressure with the 'normal' hatch, then the 'Mandl Extractor' hatch. *I
> > can report subjectively that I was MUCH more comfortable in the
> > cockpit.
>
> Awesome! My SZD-59 is going to get one of these on it's booby hatch
> now too, thanks for sharing!
>
> -Paul

Speaking of thanks.... in characteristic style, I neglected to than
Bob Kuykendall for his advice regarding mold making, and DG for
publishing their findings in the first place. Does any other glider
manufacturer 'share' as much? This is an honest question. I've spent
quite a lot of time on the DG site, very little on any others.

[PMSC Member]

On Aug 19, 9:15 pm, Uncle Fuzzy > wrote:
> On Aug 2, 3:25 am, Derek Copeland
>
>
>
> > wrote:
> > In that case, I suppose you would have to go onto oxygen a little bit lower
> > down with thefuselageextractionventfitted!
>
> > At 16:40 31 July 2008, Jim White wrote:
>
> > >Now there is a thought.... Open the airventif you are close to
> > airspace
> > >to make the logger think you are lower, and fit an extractionventif
> > you
> > >want that height record.
>
> > >jim- Hide quoted text -
>
> > - Show quoted text -
>
> I made this vent to replace the access hatch for connecting my
> controlshttp://griderpirate.smugmug.com/gallery/3702283_9hEKD#355235771_pv8zu
> Next weekend I will fly with a manometer to compare static to cabin
> pressure with the 'normal' hatch, then the 'Mandl Extractor' hatch. I
> can report subjectively that I was MUCH more comfortable in the
> cockpit.

Nice work.

Now DB is a pretty smart guy, so chances are he has this figured out.
But I sure don't. I can't see how exhausting air into the low
pressure area that's responsible for producing aerodynamic lift is a
good thing. Perhaps the mass flow is trivial and doesn't matter as
long as the flow isn't spoiled. But we sure go to a lot of effort to
eliminate air leaks in this area and sealing surely does help....

[BB]

>
> I posted pictures of Dick Butler's air exhaust in my Uvalde blog.
> You need to accelerate the air smoothly inside the fuselage
> then direct it to exit parallel the exterior flow; these photos
> show how Dick did it.

OK, I need help to understand this from real aerodynamics geeks. I've
heard that these exits are placed in "areas of low pressure", and the
turtledeck sure looks like an obvious candidate for such an area. But
if you exhaust air there, surely you get separated or at least
disturbed airflow downstream of it. Just past "low pressure" is where
there should be "pressure recovery", and I would think venting air to
the low pressure point destroys the pressure recovery. For example,
the lowest pressure place possible would be right on the top of the
wing in the middle. But venting air there is obviously suicide. If
anything you want to suck air at that point to keep the boundary layer
attached. OK, if you've found a low pressure area where airflow is
already separated behind it, that would seem ok, which is what the
vents at the bottom of the rudder or through control horns do. But
otherwise, aren't you creating more drag than you reduce, by causing
separated flow downstream of the vent?

John Cochrane BB

[Uncle Fuzzy]

On Aug 20, 4:13*am, PMSC Member > wrote:
> On Aug 19, 9:15 pm, Uncle Fuzzy > wrote:
>
>
>
>
>
> > On Aug 2, 3:25 am, Derek Copeland
>
> > > wrote:
> > > In that case, I suppose you would have to go onto oxygen a little bit lower
> > > down with thefuselageextractionventfitted!
>
> > > At 16:40 31 July 2008, Jim White wrote:
>
> > > >Now there is a thought.... Open the airventif you are close to
> > > airspace
> > > >to make the logger think you are lower, and fit an extractionventif
> > > you
> > > >want that height record.
>
> > > >jim- Hide quoted text -
>
> > > - Show quoted text -
>
> > I made this vent to replace the access hatch for connecting my
> > controlshttp://griderpirate.smugmug.com/gallery/3702283_9hEKD#355235771_pv8zu
> > Next weekend I will fly with a manometer to compare static to cabin
> > pressure with the 'normal' hatch, then the 'Mandl Extractor' hatch. *I
> > can report subjectively that I was MUCH more comfortable in the
> > cockpit.
>
> Nice work.
>
> Now DB is a pretty smart guy, so chances are he has this figured out.
> But I sure don't. *I can't see how exhausting air into the low
> pressure area that's responsible for producing aerodynamic lift is a
> good thing. *Perhaps the mass flow is trivial and doesn't matter as
> long as the flow isn't spoiled. *But we sure go to a lot of effort to
> eliminate air leaks in this area and sealing surely does help....- Hide quoted text -
>
> - Show quoted text -
Thanks,
There's a link in the first post of this thread to an article on the
DG website that explains why they firgured there would be a
performance gain. DG placed their extractor behind and to the side
of the gear well. Mine is above and toward the rear of the wing
strictly because there was a control hookup access panel there,
allowing me to go back to original at any time. Perhaps not an ideal
location, but the only place I could put it without cutting my glider.
My motivation for the exhaust vent was comfort, and regardless of any
aerodynamic gains or losses, it certainly helps keep more comfortable
in the 100+ degree desert heat. Without the vent, I was hot even at
17,000 feet, with just the left side of my face cold where the canopy
vent blasted a thin stream of cold air.

[sisu1a]

On Aug 20, 4:13 am, PMSC Member > wrote:
> On Aug 19, 9:15 pm, Uncle Fuzzy > wrote:
>
>
>
> > On Aug 2, 3:25 am, Derek Copeland
>
> > > wrote:
> > > In that case, I suppose you would have to go onto oxygen a little bit lower
> > > down with thefuselageextractionventfitted!
>
> > > At 16:40 31 July 2008, Jim White wrote:
>
> > > >Now there is a thought.... Open the airventif you are close to
> > > airspace
> > > >to make the logger think you are lower, and fit an extractionventif
> > > you
> > > >want that height record.
>
> > > >jim- Hide quoted text -
>
> > > - Show quoted text -
>
> > I made this vent to replace the access hatch for connecting my
> > controlshttp://griderpirate.smugmug.com/gallery/3702283_9hEKD#355235771_pv8zu
> > Next weekend I will fly with a manometer to compare static to cabin
> > pressure with the 'normal' hatch, then the 'Mandl Extractor' hatch. I
> > can report subjectively that I was MUCH more comfortable in the
> > cockpit.
>
> Nice work.
>
> Now DB is a pretty smart guy, so chances are he has this figured out.
> But I sure don't. I can't see how exhausting air into the low
> pressure area that's responsible for producing aerodynamic lift is a
> good thing. Perhaps the mass flow is trivial and doesn't matter as
> long as the flow isn't spoiled. But we sure go to a lot of effort to
> eliminate air leaks in this area and sealing surely does help....

Ahhh, another victim of the all too common "equal path length theory".
Although a wing does generate a certain amount of reduced pressure on
it's upper surface and that does contribute to the lift, the
dominating force of lift rather comes from the thrust generated by the
air being flung down off the trailing edge for the wing. To account
for the actual physics of flight, one must also rely on Newtonian
physics coupled with Coanda Effect (http://en.wikipedia.org/wiki/Coand
%C4%83_effect ), since if you rely on Bernoulli alone a plane can not
fly inverted! See: http://www.eskimo.com/%7Ebillb/wing/airfoil.html
for much better explanation.

-Paul

[toad]

On Aug 20, 10:12*am, sisu1a > wrote:

> Ahhh, another victim of the all too common "equal path length theory".
> Although a wing does generate a certain amount of reduced pressure on
> it's upper surface and that does contribute to the lift, *the
> dominating force of lift rather comes from the thrust generated by the
> air being flung down off the trailing edge for the wing. To account
> for the actual physics of flight, one must also rely on Newtonian
> physics coupled with Coanda Effect (http://en.wikipedia.org/wiki/Coand
> %C4%83_effect ), since if you rely on *Bernoulli alone a plane can not
> fly inverted! See:http://www.eskimo.com/%7Ebillb/wing/airfoil.html
> for much better explanation.
>
> -Paul

Ahhh, another victim of the equating "Bernoulli" with "equal path
length theory" fallacy :-)

The "thrust generated by the air being flung down off the trailing
edge" that you refer to is simply the total difference between the
air pressure on the top surface and the bottom surface.

The top surface pressure is MUCH lower that ambient and the bottom
surface pressure is only a little higher that ambient, so most of the
lift is caused by the reduction of pressure on the top of the wing.

If you aren't using Kutta–Joukowski, then you are just making noise
about lift. See these articles. They will allow you to actually
calculate the lift !

http://en.wikipedia.org/wiki/Kutta_condition
http://en.wikipedia.org/wiki/Kutta%E2%80%93Joukowski_theorem

Todd Smith

Pilots should not be allowed to discuss aerodynamics without a
license !

[PMSC Member]

On Aug 20, 10:12 am, sisu1a > wrote:
> On Aug 20, 4:13 am, PMSC Member > wrote:
>
>
>
> > On Aug 19, 9:15 pm, Uncle Fuzzy > wrote:
>
> > > On Aug 2, 3:25 am, Derek Copeland
>
> > > > wrote:
> > > > In that case, I suppose you would have to go onto oxygen a little bit lower
> > > > down with thefuselageextractionventfitted!
>
> > > > At 16:40 31 July 2008, Jim White wrote:
>
> > > > >Now there is a thought.... Open the airventif you are close to
> > > > airspace
> > > > >to make the logger think you are lower, and fit an extractionventif
> > > > you
> > > > >want that height record.
>
> > > > >jim- Hide quoted text -
>
> > > > - Show quoted text -
>
> > > I made this vent to replace the access hatch for connecting my
> > > controlshttp://griderpirate.smugmug.com/gallery/3702283_9hEKD#355235771_pv8zu
> > > Next weekend I will fly with a manometer to compare static to cabin
> > > pressure with the 'normal' hatch, then the 'Mandl Extractor' hatch. I
> > > can report subjectively that I was MUCH more comfortable in the
> > > cockpit.
>
> > Nice work.
>
> > Now DB is a pretty smart guy, so chances are he has this figured out.
> > But I sure don't. I can't see how exhausting air into the low
> > pressure area that's responsible for producing aerodynamic lift is a
> > good thing. Perhaps the mass flow is trivial and doesn't matter as
> > long as the flow isn't spoiled. But we sure go to a lot of effort to
> > eliminate air leaks in this area and sealing surely does help....
>
> Ahhh, another victim of the all too common "equal path length theory".
> Although a wing does generate a certain amount of reduced pressure on
> it's upper surface and that does contribute to the lift, the
> dominating force of lift rather comes from the thrust generated by the
> air being flung down off the trailing edge for the wing. To account
> for the actual physics of flight, one must also rely on Newtonian
> physics coupled with Coanda Effect (http://en.wikipedia.org/wiki/Coand
> %C4%83_effect ), since if you rely on Bernoulli alone a plane can not
> fly inverted! See:http://www.eskimo.com/%7Ebillb/wing/airfoil.html
> for much better explanation.
>
> -Paul

I've got the basic Newtonian physics pretty well understood, actually,
but that is a good point. I think the popular misconception you refer
to is actually "equal transit time" not "equal path length" btw. And
if it turns out that I can be convinced that a turtle deck exhaust is
okay aerodynamically, I am absolutely going to steal your idea for my
ASW-20. Imitation, after all, is the sincerest form of flattery.

Intuitively it would seem that other low pressure areas on the
fuselage, typically behind the gear doors (DG) or near the tail (Wil
Scheumann, many others) would be a better pick. However, intuition
often leads astray in aerodynamics.

[Bill Daniels]

There's a lot of ways to look at this - and they all sort of work.

Putting aside for a moment the problem of designing a low drag air exit,
it's easy to see that creating a low pressure inside the glider is a good
idea. Anywhere there is a surface discontinuity (like the canopy or hinge
line) there is a likelihood of tripping the flow to turbulent. If air is
flowing out of this discontinuity it's the equivalent of a blowhole
turbulator. If you can reverse the flow with low internal pressure, it
becomes suction boundary layer control. If the low pressure extends to the
entire glider, you are sucking air in through control hinges. The potential
performance gain from this is significant.

Then, the "no free lunch" principle kicks in. Maintaining pressure
differentials in a leaky glider takes energy. Cleverly designing a low
energy cost air exit that takes advantage of low pressure areas is the key -
but it's not easy. I remember a professor saying that the main thing you
need to know about air scoops is they're ugly and usually don't work.

I expect to see many gliders festooned with ugly reverse scoops - some
functional, most not. Putting them on the lower fuselage just aft of the
thickest point has the advantage that you can't see them.

Then there is a 70 year old idea from Dr. Gus Raspet - suction fans. Thin
film solar cells are slowly creeping up in efficiency and down in cost.
Tiny, very efficient fans are found everywhere on electronics. Put a pan
fan on that access hatch powered with a stick-on solar panel. At a minimum
it'll help keep the cockpit cool on the ground.





"sisu1a" > wrote in message
...
> On Aug 20, 4:13 am, PMSC Member > wrote:
>> On Aug 19, 9:15 pm, Uncle Fuzzy > wrote:
>>
>>
>>
>> > On Aug 2, 3:25 am, Derek Copeland
>>
>> > > wrote:
>> > > In that case, I suppose you would have to go onto oxygen a little bit
>> > > lower
>> > > down with thefuselageextractionventfitted!
>>
>> > > At 16:40 31 July 2008, Jim White wrote:
>>
>> > > >Now there is a thought.... Open the airventif you are close to
>> > > airspace
>> > > >to make the logger think you are lower, and fit an extractionventif
>> > > you
>> > > >want that height record.
>>
>> > > >jim- Hide quoted text -
>>
>> > > - Show quoted text -
>>
>> > I made this vent to replace the access hatch for connecting my
>> > controlshttp://griderpirate.smugmug.com/gallery/3702283_9hEKD#355235771_pv8zu
>> > Next weekend I will fly with a manometer to compare static to cabin
>> > pressure with the 'normal' hatch, then the 'Mandl Extractor' hatch. I
>> > can report subjectively that I was MUCH more comfortable in the
>> > cockpit.
>>
>> Nice work.
>>
>> Now DB is a pretty smart guy, so chances are he has this figured out.
>> But I sure don't. I can't see how exhausting air into the low
>> pressure area that's responsible for producing aerodynamic lift is a
>> good thing. Perhaps the mass flow is trivial and doesn't matter as
>> long as the flow isn't spoiled. But we sure go to a lot of effort to
>> eliminate air leaks in this area and sealing surely does help....
>
> Ahhh, another victim of the all too common "equal path length theory".
> Although a wing does generate a certain amount of reduced pressure on
> it's upper surface and that does contribute to the lift, the
> dominating force of lift rather comes from the thrust generated by the
> air being flung down off the trailing edge for the wing. To account
> for the actual physics of flight, one must also rely on Newtonian
> physics coupled with Coanda Effect (http://en.wikipedia.org/wiki/Coand
> %C4%83_effect ), since if you rely on Bernoulli alone a plane can not
> fly inverted! See: http://www.eskimo.com/%7Ebillb/wing/airfoil.html
> for much better explanation.
>
> -Paul

[Bob Kuykendall]

On Aug 19, 7:34*pm, Uncle Fuzzy > wrote:

> Speaking of thanks.... in characteristic style, I neglected to than
> Bob Kuykendall for his advice regarding mold making, and DG for
> publishing their findings in the first place. *Does any other glider
> manufacturer 'share' as much? This is an honest question. *I've spent
> quite a lot of time on the DG site, very little on any others.

You're quite welcome, of course. Nice looking piece, I think you
nailed the shape! Interesting to see how your idea follows that of
Dick Butler--exhausting the vent air on top instead of on the bottom.

Now you get to experience the joys of sanding, filling, sanding, and
painting a 3D shape... Some folks ask me why I still mold on gelcoat,
why do I do that when others have made a practice of molding bare and
painting afterwards? My general answer is so that I can put the orange
peel and pinholes on the inside where nobody will ever know they're
there.

Thanks, Bob K.

[Uncle Fuzzy]

On Aug 20, 7:59*am, Bob Kuykendall > wrote:
> On Aug 19, 7:34*pm, Uncle Fuzzy > wrote:
>
> > Speaking of thanks.... in characteristic style, I neglected to than
> > Bob Kuykendall for his advice regarding mold making, and DG for
> > publishing their findings in the first place. *Does any other glider
> > manufacturer 'share' as much? This is an honest question. *I've spent
> > quite a lot of time on the DG site, very little on any others.
>
> You're quite welcome, of course. Nice looking piece, I think you
> nailed the shape! Interesting to see how your idea follows that of
> Dick Butler--exhausting the vent air on top instead of on the bottom.
>
> Now you get to experience the joys of sanding, filling, sanding, and
> painting a 3D shape... Some folks ask me why I still mold on gelcoat,
> why do I do that when others have made a practice of molding bare and
> painting afterwards? My general answer is so that I can put the orange
> peel and pinholes on the inside where nobody will ever know they're
> there.
>
> Thanks, Bob K.

LOL! The bodywork is tedious but simple. I can do that. Next time
I'm going to get REAL tooling resin! BTW, I am getting senile. AFTER
all the pain of making a fiberglass mold from the hatch, I realized I
could have pulled one on my vacuum form in minutes. I even have
several flavors of theromplastics on hand. D'oh! Mold rigidity is
achieved by filling the back of the mold with plaster of paris, which
I ALSO had on hand. Maybe an hour of hands-on work to produce the mold.

[PMSC Member]

On Aug 20, 10:35 am, toad > wrote:


> If you aren't using Kutta–Joukowski, then you are just making noise
> about lift. See these articles. They will allow you to actually
> calculate the lift !

Naw, they'll allow me to calculate the 2-D circulation, which I really
don't care about. And even DB has a finite wingspan :-).

> Pilots should not be allowed to discuss aerodynamics without a
> license !

We just do it to annoy :-).

How come you're not at R3?

-T8

[DRN]

On Aug 20, 8:19 am, BB > wrote:
> > I posted pictures of Dick Butler's air exhaust in my Uvalde blog.
> > You need to accelerate the air smoothly inside the fuselage
> > then direct it to exit parallel the exterior flow; these photos
> > show how Dick did it.
>
> OK, I need help to understand this from real aerodynamics geeks. I've
> heard that these exits are placed in "areas of low pressure", and the
> turtledeck sure looks like an obvious candidate for such an area. But
> if you exhaust air there, surely you get separated or at least
> disturbed airflow downstream of it. Just past "low pressure" is where
> there should be "pressure recovery", and I would think venting air to
> the low pressure point destroys the pressure recovery. For example,
> the lowest pressure place possible would be right on the top of the
> wing in the middle. But venting air there is obviously suicide. If
> anything you want to suck air at that point to keep the boundary layer
> attached. OK, if you've found a low pressure area where airflow is
> already separated behind it, that would seem ok, which is what the
> vents at the bottom of the rudder or through control horns do. But
> otherwise, aren't you creating more drag than you reduce, by causing
> separated flow downstream of the vent?
>
> John Cochrane BB

Careful ! A few points...

Do not confuse "separated" with "turbulent".
Separation is BAD.
Turbulent (non-laminar) is OK and less prone to separation in areas
aft of canopy for example. Modern gliders like yours and Antares
use turbulent (non-laminar) airfoils near the fuselage.

Lot's of "obvious low pressure" areas are not, for example
underneath fuselage (you have to look at the pressure analysis
for the particular fuselage).

What Dick did was add turbulent flow parallel to already
turbulent flow. The acceleration funnel is necessary to
avoid turbulence due to big speed mismatch.

Hope that helps...
Best Regards, Dave "YO electric"

PS: Great to see you in Uvalde !

[toad]

On Aug 20, 11:41*am, PMSC Member > wrote:
> On Aug 20, 10:35 am, toad > wrote:
>
> > If you aren't using Kutta–Joukowski, then you are just making noise
> > about lift. *See these articles. *They will allow you to actually
> > calculate the lift !
>
> Naw, they'll allow me to calculate the 2-D circulation, which I really
> don't care about. *And even DB has a finite wingspan :-).

You can't calculate the lift without the circulation :-)

>
> > Pilots should not be allowed to discuss aerodynamics without a
> > license !
>
> We just do it to annoy :-).

That works !

>
> How come you're not at R3?

Currently I am too poor.

>
> -T8

Todd

[PMSC Member]

On Aug 20, 1:37 pm, toad > wrote:
> On Aug 20, 11:41 am, PMSC Member > wrote:
>
> > On Aug 20, 10:35 am, toad > wrote:
>
> > > If you aren't using Kutta–Joukowski, then you are just making noise
> > > about lift. See these articles. They will allow you to actually
> > > calculate the lift !
>
> > Naw, they'll allow me to calculate the 2-D circulation, which I really
> > don't care about. And even DB has a finite wingspan :-).
>
> You can't calculate the lift without the circulation :-)

Based on the mass of my glider, I know the lift!


> > > Pilots should not be allowed to discuss aerodynamics without a
> > > license !
>

>
> > How come you're not at R3?
>
> Currently I am too poor.

Which just goes to show what we as pilots knew all along: it's the
circulation of *money* that creates lift :-).

Here's wishing you more of that.

Thanks for the Wiki links btw.

-T8