After all the threads on venting high pressure air overboard I thought
I would share this one with you.

I sealed up the ASW17 canopy and its nice and quiet now.
On Tow yesterday as I retracted the gear the pressure change was
enough to blow the hatch off the top of the turtle deck. I couldn't
figure out what the noise was at first thinking it was a gear door
who's bungy had broken or come unhooked.

I cycled the gear 2 - 3 times more so thinking it might be an animal
or rock or stuck in the gear well.
The noise continued until I performed a sharp pull up from 80 knots.

The rest of the flight was uneventful except there was more air noise
I attributed to a stuck gear door.
The glider had a slight resonance vibration again I attributed it to
the gear door.

Upon landing I was amazed to see the rigging hatch wedged in the
aperture retained by its lanyard and the remaining tape. It was
aligned 45deg. to the airflow which explained the vibration I was
feeling.

So now the fun part....
The ASW17 has a hatch that is exactly dead center of the fuz. so I am
now working on a replacement air exhaust hatch that will replace the
stock "non breathing" hatch. I am looking at a design like the ramp
style that Dick butler has on his ASW22.

More to follow.....

Al

On Sep 4, 7:53*pm, " >
wrote:
> After all the threads on venting high pressure air overboard I thought
> I would share this one with you.
>
> I sealed up the ASW17 canopy and its nice and quiet now.
> On Tow yesterday as I retracted the gear the pressure change was
> enough to blow the hatch off the top of the turtle deck. *I couldn't
> figure out what the noise was at first thinking it was a gear door
> who's bungy had broken or come unhooked.
>
> I cycled the gear 2 - 3 times more so thinking it might be an animal
> or rock or stuck in the gear well.
> The noise continued until I performed a sharp pull up from 80 knots.
>
> The rest of the flight was uneventful except there was more air noise
> I attributed to a stuck gear door.
> The glider had a slight resonance vibration again I attributed it to
> the gear door.
>
> Upon landing I was amazed to see the rigging hatch wedged in the
> aperture retained by its lanyard and the remaining tape. It was
> aligned 45deg. to the airflow which explained the vibration I was
> feeling.
>
> So now the fun part....
> The ASW17 has a hatch that is exactly dead center of the fuz. so I am
> now working on a replacement air exhaust hatch that will replace the
> stock "non breathing" hatch. *I am looking at a design like the ramp
> style that Dick butler has on his ASW22.
>
> More to follow.....
>
> Al

Al,

I think a reverse NACA duct is a better model to use. It will smooth
the transition more and accelerate the air to about equal to the speed
of the outside air for less drag. I would build one similar to the
one in the link but with a cover over about the first half with a
smooth transition toward the back.

http://www.appletreeauto.com/naca-duct-clear-3outlet9-1-4-pr-3425.html


Tim

On Sep 5, 10:03*am, Tim Taylor > wrote:
> On Sep 4, 7:53*pm, " >
> wrote:
>
>
>
> > After all the threads on venting high pressure air overboard I thought
> > I would share this one with you.
>
> > I sealed up the ASW17 canopy and its nice and quiet now.
> > On Tow yesterday as I retracted the gear the pressure change was
> > enough to blow the hatch off the top of the turtle deck. *I couldn't
> > figure out what the noise was at first thinking it was a gear door
> > who's bungy had broken or come unhooked.
>
> > I cycled the gear 2 - 3 times more so thinking it might be an animal
> > or rock or stuck in the gear well.
> > The noise continued until I performed a sharp pull up from 80 knots.
>
> > The rest of the flight was uneventful except there was more air noise
> > I attributed to a stuck gear door.
> > The glider had a slight resonance vibration again I attributed it to
> > the gear door.
>
> > Upon landing I was amazed to see the rigging hatch wedged in the
> > aperture retained by its lanyard and the remaining tape. It was
> > aligned 45deg. to the airflow which explained the vibration I was
> > feeling.
>
> > So now the fun part....
> > The ASW17 has a hatch that is exactly dead center of the fuz. so I am
> > now working on a replacement air exhaust hatch that will replace the
> > stock "non breathing" hatch. *I am looking at a design like the ramp
> > style that Dick butler has on his ASW22.
>
> > More to follow.....
>
> > Al
>
> Al,
>
> I think a reverse NACA duct is a better model to use. *It will smooth
> the transition more and accelerate the air to about equal to the speed
> of the outside air for less drag. *I would build one similar to the
> one in the link but with a cover over about the first half with a
> smooth transition toward the back.
>
> http://www.appletreeauto.com/naca-duct-clear-3outlet9-1-4-pr-3425.html
>
> Tim

But NACA ducts are usually used for inbound air not outbound...

There was another type I saw on a buddies ASH26 but can remember the
name of it began with an E.

Cheers

Al

On Sep 5, 11:08*pm, Al > wrote:
> On Sep 5, 10:03*am, Tim Taylor > wrote:
>
>
>
>
>
> > On Sep 4, 7:53*pm, " >
> > wrote:
>
> > > After all the threads on venting high pressure air overboard I thought
> > > I would share this one with you.
>
> > > I sealed up the ASW17 canopy and its nice and quiet now.
> > > On Tow yesterday as I retracted the gear the pressure change was
> > > enough to blow the hatch off the top of the turtle deck. *I couldn't
> > > figure out what the noise was at first thinking it was a gear door
> > > who's bungy had broken or come unhooked.
>
> > > I cycled the gear 2 - 3 times more so thinking it might be an animal
> > > or rock or stuck in the gear well.
> > > The noise continued until I performed a sharp pull up from 80 knots.
>
> > > The rest of the flight was uneventful except there was more air noise
> > > I attributed to a stuck gear door.
> > > The glider had a slight resonance vibration again I attributed it to
> > > the gear door.
>
> > > Upon landing I was amazed to see the rigging hatch wedged in the
> > > aperture retained by its lanyard and the remaining tape. It was
> > > aligned 45deg. to the airflow which explained the vibration I was
> > > feeling.
>
> > > So now the fun part....
> > > The ASW17 has a hatch that is exactly dead center of the fuz. so I am
> > > now working on a replacement air exhaust hatch that will replace the
> > > stock "non breathing" hatch. *I am looking at a design like the ramp
> > > style that Dick butler has on his ASW22.
>
> > > More to follow.....
>
> > > Al
>
> > Al,
>
> > I think a reverse NACA duct is a better model to use. *It will smooth
> > the transition more and accelerate the air to about equal to the speed
> > of the outside air for less drag. *I would build one similar to the
> > one in the link but with a cover over about the first half with a
> > smooth transition toward the back.
>
> >http://www.appletreeauto.com/naca-duct-clear-3outlet9-1-4-pr-3425.html
>
> > Tim
>
> But NACA ducts are usually used for inbound air not outbound...
>
> There was another type I saw on a buddies ASH26 but can remember the
> name of it began with an E.
>
> Cheers
>
> Al

Actually there are NACA designs for inlets and outlets. They would be
the best design to use for an outlet. Dick Butler's design is close,
but could use some slight modifications to improve the speed of the
exit airflow. In my opinion the Mandl Extractor is not the best
design to use. It has too great of an angle where the air rejoins the
outside airflow.

Hi Tim and Al, Perhaps it was just a pressure pulse which blew the cover
off. If you attatch a rear-facing duct you are likely to produce a
negative pressure difference, and an altimeter with an inboard static vent
would read higher than you are.

Perhaps the best initial solution would be to drill a 10-15mm hole in the
access cover, (or anywhere else really.) which depending upon the airflow,
would act as a static vent... neither increasing or decreasing the ambient
pressure.

I wonder if the pressure pulse was created by the closing of the u/c
doors, or because you where using the screen ventilation system, which
admits air onto the screen... Where is that supposed to go ?

Pete

At 06:14 06 September 2009, Tim Taylor wrote:
>On Sep 5, 11:08=A0pm, Al wrote:
>> On Sep 5, 10:03=A0am, Tim Taylor wrote:
>>
>> > > After all the threads on venting high pressure air overboard I
>though=
>t
>> > > I would share this one with you.
>>
>> > > I sealed up the ASW17 canopy and its nice and quiet now.
>> > > On Tow yesterday as I retracted the gear the pressure change was
>> > > enough to blow the hatch off the top of the turtle deck.

On Sep 7, 6:45*am, Peter Higgs > wrote:
>
> Perhaps the best initial solution would be to drill a 10-15mm hole in the
> access cover, (or anywhere else really.) which depending upon the airflow,
> would act as a static vent... *neither increasing or decreasing the ambient
> pressure.


On Sep 7, 6:45 am, Peter Higgs > wrote:
> Perhaps the best initial solution would be to drill a 10-15mm hole in the
> access cover, (or anywhere else really.) which depending upon the airflow,
> would act as a static vent... neither increasing or decreasing the ambient
> pressure.

I'm not sure I would want an "air spigot" pointing straight out of
the fuselage into the airstream - seems like unnecessary drag versus a
solution that lines the flow up with the external slipstream. The
reverse NACA duct has been shown to work well and it's my
understanding that it even produces a small amount of thrust.

As to altimeter readings - my altimeter is hooked to my tailboom
static ports. I'd recommend it as a general practice if you have
external ports available. My feeling is that any solution that vents
high-pressure fuselage air would yield a more accurate altimeter
reading than not venting but that the differences in any even aren't
that large.

9B

testing please ignore

$52? Here are some other sources for less expensive NACA ducts.
Black and Clear. These come with an intergral "exit" tube at the
larger end. Other sources don't have this tube, just an exit slot the
size and shape of the larger end. Google "naca duct".

Try racerpartswholesale dot com which has both black and clear lexan.

Replace "dot" with a period. Google is blocking this post for some
reason when it contains full URL's.

Thanks.

On Sep 8, 1:45*pm, ContestID67 > wrote:
> $52? *Here are some other sources for less expensive NACA ducts.
> Black and Clear. *These come with an intergral "exit" tube at the
> larger end. *Other sources don't have this tube, just an exit slot the
> size and shape of the larger end. *Google "naca duct".
>
> Try racerpartswholesale dot com which has both black and clear lexan.
>
> Replace "dot" with a period. *Google is blocking this post for some
> reason when it contains full URL's.
>
> Thanks.

Er Guys these are ducts that are inlet..

I need ones that are outlet...