Schleicher pneumatic tube plumbing question

On Dec 6, 9:39*pm, Tuno wrote:
To answer my original question more accurately ... the manual
indicates the routing of the pressures, but does not describe the
implementation. As it happens, my 29 has small (maybe 2.5 or 3mm OD)
tubing from behind the instrument panel to under the seatpan, where
they step up to the larger size using the same kind of insert adapter
found on my O2 system controller.

The tubes going aft from there do not hold a vacuum (with the multi-
probe thoroughly sealed and inserted). I'm wondering (after talking to
CH) if the O-rings in the multi-probe's receiver were damaged ...

2NO

What is it the engineers say? One test is worth a thousand theories.
I'd put the probe in place then apply pressure with a syringe as you
watch the airspeed indicator. No indication = massive leak or pinched
line. Open the canopy and see what it reads.........keep checking till
you find the problem. I'd leak test all lines while I was at it. I use
a separate ASI that is T'ed to the syringe then hooked to the line I'm
checking. All should hold 100 knots on the ASI for 60 seconds.
JJ

JJ's suggestion (from bucket loads of experience) mirrors the
instructions Reichmann put in the back of "Streckensegelflug". And
always a good idea to test thoroughly before altering.
Ted, in your first post you mention repair. If that repair was a
broken tail boom, there's a chance of a splice inside the fuselage to
keep you entertained.
Last leak like this I had turned out to be an almost hidden coupling
in the area where the tubing enters the instrument panel. Possibly a
failed fix of a previous problem!
Jim


On Dec 7, 5:57 am, JJ Sinclair wrote:


What is it the engineers say? One test is worth a thousand theories.
I'd put the probe in place then apply pressure with a syringe as you
watch the airspeed indicator. No indication = massive leak or pinched
line. Open the canopy and see what it reads.........keep checking till
you find the problem. I'd leak test all lines while I was at it. I use
a separate ASI that is T'ed to the syringe then hooked to the line I'm
checking. All should hold 100 knots on the ASI for 60 seconds.
JJ

This morning's trouble-shooting began by testing the tubes from the
seatpan back to the fin. With the multi-probe inserted and all holes
sealed, each tube (tested individually) held positive and negative
pressures. That was good news -- no problems hiding in the tail boom.

Next I tested each of the four tubes from the panel to the seatpan.
(Two are static -- one from the multi-probe (for the vario(s)) and one
from the tailboom (for the ASI and ALT).) Again, each tube tested with
positive results. This was encouraging because it demonstrated no
problems with any plumbing. It was disconcerting because of the big
question mark it left.

Next I reconnected the tubes under the seatpan and began testing each
tube from the instrument to the multi-probe. The first test or two
went well but I soon discovered that when the probe inlet was sealed
off without the probe, all tubes held pressure as a group, but if I
inserted the probe (with all inlets taped up), air blown into one tube
would exit the others.

This pointed, of course, to a problem with the probe or its
receptacle. The answer to the mystery can be found in the photographs
at www.justsoar.com/public/2NO/.

(I will resume typing in two minutes so you can examine the evidence
and see if you can figure it out yourself.)

.... DING welcome back.

The original multi-probe, an ESA-Systems model (http://www.esa-
systems.com/data/multis/mni-un.html), was badly mangled in the (ahem)
hard landing (as you can see in the photo with both probes). But if
you look closely at the photos, you'll see that the decal (with the
insertion "STOP" line) in the new probe is a full 3cm closer to the
aft end than the same decal on the original probe. Both probes have
the same ESA model number on the decals. Except for locations of the
decals and the gently used condition of the original, the two probes
are absolutely identical.

The fit is snug enough that just the decal is enough to firmly arrest
the insertion of the probe. I carefully measured the distance on the
original probe, removed the decal on the new one, and marked the
correct stop point with a wrap of gap tape. Inserting the probe, I
encountered some resistence with a cm to go, but that was just the
last O-ring, a gentle push and all was right with the world.

Dang this eggnog is good.

Big, big thanks to Cliff "CH" Hilty for driving down from Prescott to
assist me with the plumbing, that guy can take a cinder block and
fence post and make them fly.

~ted/2NO

On Dec 6, 9:39*pm, Tuno wrote:
To answer my original question more accurately ... the manual
indicates the routing of the pressures, but does not describe the
implementation. As it happens, my 29 has small (maybe 2.5 or 3mm OD)
tubing from behind the instrument panel to under the seatpan, where
they step up to the larger size using the same kind of insert adapter
found on my O2 system controller.

The tubes going aft from there do not hold a vacuum (with the multi-
probe thoroughly sealed and inserted). I'm wondering (after talking to
CH) if the O-rings in the multi-probe's receiver were damaged ...

2NO

Thank goodness it's December Ted. If the multi-probe got tweaked in
the accident then it's possible that the fittings are AFU, but I'd be
surprised if it actually happened. You might try just plugging the
entire fitting with the probe removed to at least eliminate the
possibility of a tubing leak inside the fin/tailboom. You'll need to
clamp the other lines too. I am curious about the procedure for
replacing the O-rings as it seems nearly impossible from casual
inspection. Any experts out there on how to do it?

I too have had the infamous Schliecher canopy hinge tubing kink
problem on a hot day in Arizona. The symptom was a zero indication on
climb and a wildly inaccurate airspeed. I think that means a kinked
static line. I used GY's cure - a 4" piece of 1" OD tubing split down
the side and wrapped around all the pneumatic tubes where they bend as
the canopy closes. I secured the tube with tie-wraps. It's still there
and working today. Turns out the desert temperatures make the tubes
just enough softer that they fold under the pressure when you shut the
hatch. Fixing it in 112 degrees and full sun may have been the
sweatiest experience of my life. I am perplexed but the change in
tubing size you describe Ted. Do you have to up-gauge the tubes at the
panel to fit the barb connectors on your instruments?

Best of luck - glad 2NO's back home.

9B

9B,

I assume by now you've read my post describing the problem.

My 29 has 3mm OD (polyethylene?) tubing going from the fore end of the
area under the glare shield to under the seatpan. After reading yours
and GY's accounts, my guess is that the factory addressed the problem
my using the smaller polyethylene tubing for this part of the glider,
which does much better under heat and stress than the larger tubing.

It came from the factory with adapters that step the smaller tubing up
to the larger size, both under the seatpan and behind the instr panel.
They're just like the connections on my MH EDS controller, where you
depress a flat ring to disengage the inserted tubing.

I'd like to know the proper nomenclature for that tubing and adapter.

Glider is back home and flies great!

2NO

On Dec 8, 11:46*am, Tuno wrote:
9B,

I assume by now you've read my post describing the problem.

My 29 has 3mm OD (polyethylene?) tubing going from the fore end of the
area under the glare shield to under the seatpan. After reading yours
and GY's accounts, my guess is that the factory addressed the problem
my using the smaller polyethylene tubing for this part of the glider,
which does much better under heat and stress than the larger tubing.


Interesting. I check in a few times a year to see what new tech notes
are out but didn't see one on this.

Anyone have a new 28 with this configuration?

Andy

On Dec 8, 11:19*am, Andy wrote:
On Dec 8, 11:46*am, Tuno wrote:

9B,

I assume by now you've read my post describing the problem.

My 29 has 3mm OD (polyethylene?) tubing going from the fore end of the
area under the glare shield to under the seatpan. After reading yours
and GY's accounts, my guess is that the factory addressed the problem
my using the smaller polyethylene tubing for this part of the glider,
which does much better under heat and stress than the larger tubing.

Interesting. *I check in a few times a year to see what new tech notes
are out but didn't see one on this.

Anyone have a new 28 with this configuration?

Andy

Jeez Ted - clearly the problem is that probe2 is bent at a 45-degree
angle. No way you will get good TE that way. I'd recommend you
straighten it out. ;-)

Glad you're back in the air.

9B

Andy:

I have the bent probe in the vice right now, under a space heater to
make the job easier. Using the unbent probe and one of those tacky
meeting room laser pointers as a guide. It is a tough like **cker but
like my son I'm going to tell it who's #1 when it comes to #2.

No way the glider will go as fast without the original probe!

B4 and after pix he
www.justsoar.com\public\2NO\May2008
www.justsoar.com\public\2NO\Dec2008

#2NO

On Dec 8, 11:19*am, Andy wrote:
On Dec 8, 11:46*am, Tuno wrote:

9B,

I assume by now you've read my post describing the problem.

My 29 has 3mm OD (polyethylene?) tubing going from the fore end of the
area under the glare shield to under the seatpan. After reading yours
and GY's accounts, my guess is that the factory addressed the problem
my using the smaller polyethylene tubing for this part of the glider,
which does much better under heat and stress than the larger tubing.

Interesting. *I check in a few times a year to see what new tech notes
are out but didn't see one on this.

Anyone have a new 28 with this configuration?

Andy

Jeez Ted - clearly the problem is that probe2 is bent at a 45-degree
angle. No way you will get good TE that way. I'd recommend you
straighten it out. ;-)

Glad you're back in the air.

9B

On Dec 8, 6:58*pm, Tuno wrote:
Andy:

I have the bent probe in the vice right now, under a space heater to
make the job easier. Using the unbent probe and one of those tacky
meeting room laser pointers as a guide. It is a tough like **cker but
like my son I'm going to tell it who's #1 when it comes to #2.

No way the glider will go as fast without the original probe!

B4 and after pix hehttp://www.justsoar.com\public\2NO\M...ic\2NO\Dec2008

#2NO

After is MUCH better.