Pneumatics Question

On 25 May, 15:13, wrote:
On May 24, 9:32*pm, jsbrake wrote:

Hi All,
Whenever I accelerate, my varios bump up and tell me I'm climbing,
then settle back to reality. *Any idea of what I need to look for to
fix this?
My setup:
Kestrel 19, two static ports in the tail boom, pitot and TE in the
fin. *The TE line is split under the seat using a Y connector and then
travels to two varios (a Winter mechanical and a 1990-era audio/final-
glide called a VariCalc). *Pitot and static lines are split behind the
panel using T connectors.
I replaced all the non-permanent tubing last year and they all seemed
to be leak-free.
Thanks!
-John

Next question is do they go down when you pull up. If both events
occur, you are somewhat over compensated.
Depending on the type of probe, this may be able to be tuned.
UH

To be pedantic what uncle Hank is saying is that in that case the
compensation is spot on and for comfort you need to be a tads under
compensated.
Your tube is a Braunschweig type commonly known amongst Anglo-Saxon
pilots as a Brunswick tube. They can be accurate but that is very
difficult to achieve by machining to a drawing. They usually need
calibrating by adjusting the length of tube distal to the lower slot.
The shape of the end is critical as it needs to be square and sharp
cornered. Not easy and devising the test bed be it bench or flight
test is pretty tedious.
The Brunswick is somewhat prone to yaw error. An Irving tube - the one
with two holes each facing 50 degrees away from the aft centre line is
less prone to yaw error and if accurately made to Frank Irving's
drawing will give the right amount of under-compensation without
calibration. If the degree of compensation proves to be your problem I
recommend you buy a commercially made Irving tube. You could spend all
summer messing around with a basically inferior tube. On no account
put in a Nick's tube with only one hole as they even more prone to yaw
error and poor compensation.

Slingsbys may have supplied commercially made Brunswick tubes so you
might have a good one if it is original.

Another source of confusing error is the use of long lengths of soft
silicon rubber tubing. (more than a few inches). Under varying 'G' it
deforms and causes air movement within the plumbing. PVC with a little
silicone grease and twist-wired at the joints is better if less sexy
and tedious to connect. A well made PVC joint left alone will last for
years.

If you want a bit of bed-time reading try "The influence of
acceleration on the sink rate of a sailplane and on the indication of
the variometer" by Frank Brozel; Technical Soaring; Vol X No1 p10.
Also anything you find by Frank Irving is always worth reading but I'd
have to do some deep research to give you any references so you are on
your own on that one.

UH: When I pull up, the varios go up... both of 'em.

There's about 2' of silcon tubing in the circuit, all of it at the
panel end. The second line of TE is silicon from the Y splitter that
I installed, so call that about 4' long. The pvc lines end at the
central pedestal where the hood and panel are removable, so there's
silicon, then a 5-way quick-connector and then silicon to the
instruments. I could probably remove about 4-6" of extra silicon, but
it gives me some "play" for being able to get at the quick-connect
without needing extra joints in my arms.

I'm not doing heavy g manoevers, maybe 1.5 g on a pull-up, perhaps
0.75 g on a push-over. The most g I normally pull is during
thermalling turns.

I think I recall reading in the aircraft notes about a Brunswick
tube. It appears to be factory made and the slots are well-defined.

. *Replaced the connector this year.

- the VariCalc has connections for all three lines; the Winter
mechanical connects to TE and capacity. *A problem in static shouldn't
affect both instruments.

Faulty multi-connectors can also cause your described symptom as well.
Check the O-rings well, and silicone grease is your friend.

Hmmm, this puts possible tailboom static issues back on the map and
your VariCalc could be cross-talking that or an internal pitot leak
error to your Winter. Run it once with cockpit static before getting
too fancy with time consuming ground testing. It's real easy and you
get to fly... Your vario isolation test will also be useful here, I
suggest unhooking (plug loose lines!) the VariCalc first.

-Paul

On 25 May, 17:29, jsbrake wrote:
UH: When I pull up, the varios go up... both of 'em.

There's about 2' of silcon tubing in the circuit, all of it at the
panel end. *The second line of TE is silicon from the Y splitter that
I installed, so call that about 4' long. *The pvc lines end at the
central pedestal where the hood and panel are removable, so there's
silicon, then a 5-way quick-connector and then silicon to the
instruments. *I could probably remove about 4-6" of extra silicon, but
it gives me some "play" for being able to get at the quick-connect
without needing extra joints in my arms.

I'm not doing heavy g manoevers, maybe 1.5 g on a pull-up, perhaps
0.75 g on a push-over. *The most g I normally pull is during
thermalling turns.

I think I recall reading in the aircraft notes about a Brunswick
tube. *It appears to be factory made and the slots are well-defined.

An up indication no matter which way you push or pull isn't a matter
of degree of compensation. A few inches of squashy tube won't make a
difference and it sounds like you have relatively modest quantities.

I am puzzled why different manoeuvres have the same effect. It
somewhat suggests multiple pathology.

Two questions ref egg sucking. Pneumatic netto was common in the
seventies, presumably there is no cruise/climb switch in the plumbing
to the Winter?
When you did your leak test did you connect to the Brunswick tube? If
so did you remember to put a piece of wire (about .020") up the slots
and into the plastic test pipe to stop the pipe sealing around the end
of the probe?

Make an exact diagram of all the plumbing. It helps enormously in
keeping track and thinking about what effect a leak at any position
will have.

On May 25, 1:23*pm, Peter Gray wrote:
On 25 May, 17:29, jsbrake wrote:





UH: When I pull up, the varios go up... both of 'em.

There's about 2' of silcon tubing in the circuit, all of it at the
panel end. *The second line of TE is silicon from the Y splitter that
I installed, so call that about 4' long. *The pvc lines end at the
central pedestal where the hood and panel are removable, so there's
silicon, then a 5-way quick-connector and then silicon to the
instruments. *I could probably remove about 4-6" of extra silicon, but
it gives me some "play" for being able to get at the quick-connect
without needing extra joints in my arms.

I'm not doing heavy g manoevers, maybe 1.5 g on a pull-up, perhaps
0.75 g on a push-over. *The most g I normally pull is during
thermalling turns.

I think I recall reading in the aircraft notes about a Brunswick
tube. *It appears to be factory made and the slots are well-defined.

An up indication no matter which way you push or pull isn't a matter
of degree of compensation. A few inches of squashy tube won't make a
difference and it sounds like you have relatively modest quantities.

I am puzzled why different manoeuvres have the same effect. It
somewhat suggests multiple pathology.

Two questions ref egg sucking. Pneumatic netto was common in the
seventies, presumably there is no cruise/climb switch in the plumbing
to the Winter?

It did have pneumatic netto, but the plumbing was removed before I got
the ship. I still have the brass fitting.

When you did your leak test did you connect to the Brunswick tube? If
so did you remember to put a piece of wire (about .020") up the slots
and into the plastic test pipe to stop the pipe sealing around the end
of the probe?

I removed the Brunswick and connected directly to the stub sticking
out of the fin. Air flows easily through the Brunswick.

Make an exact diagram of all the plumbing. It helps enormously in
keeping track and thinking about what effect a leak at any position
will have.

Straight runs from point of opening (fin for TE/pitot, 2 in boom for
static) to the pedestal. From there, it's silicon to the quick-
connect and then to the instruments. Pitot and Static are both T-
split in the panel, the TE is Y-split under the seat. Nothing else in
the circuit. Pitot goes to ASI and VariCalc; Static goes to ASI and
Alt; TE to the varios; Capacity to the mech vario. Basic setup,
matches what I found on W&W and Winter websites about connecting
plumbing to instruments.

In the case of using a mechanical and an electronic vario - capacity
and no capacity respectively - and a glider in which the tubing aft of
the panel is not that accessible, I wonder whether just teeing and
having a 7 foot length of tubing to the vario would isolate the TE
line enough to minimize mutual interference. I accept that this would
add volume to the system, which may be a problem, and that the handful
of tubing might be a problem for space behind the panel.

Would this be a workable solution?

*Pitot and Static are both T-
split in the panel, the TE is Y-split under the seat. *Nothing else in
the circuit. *Pitot goes to ASI and VariCalc; Static goes to ASI and
Alt; TE to the varios;

OK not static. Sounds like cross talk between your pitot and TE
through that VariCalc's internals. Still an easy test- unhook it and
fly.

-Paul

Get rid of the 4-way connector. They are unreliable, sometimes
causing cross-talk between paths. For peace of mind, use separate
connectors.

Bob


- then traced my original TE troubles to a leak in the 4-way connector
at the panel. *Replaced the connector this year.

On 25 May, 19:39, jsbrake wrote:
On May 25, 1:23*pm, Peter Gray wrote:



On 25 May, 17:29, jsbrake wrote:

UH: When I pull up, the varios go up... both of 'em.

There's about 2' of silcon tubing in the circuit, all of it at the
panel end. *The second line of TE is silicon from the Y splitter that
I installed, so call that about 4' long. *The pvc lines end at the
central pedestal where the hood and panel are removable, so there's
silicon, then a 5-way quick-connector and then silicon to the
instruments. *I could probably remove about 4-6" of extra silicon, but
it gives me some "play" for being able to get at the quick-connect
without needing extra joints in my arms.

I'm not doing heavy g manoevers, maybe 1.5 g on a pull-up, perhaps
0.75 g on a push-over. *The most g I normally pull is during
thermalling turns.

I think I recall reading in the aircraft notes about a Brunswick
tube. *It appears to be factory made and the slots are well-defined..

An up indication no matter which way you push or pull isn't a matter
of degree of compensation. A few inches of squashy tube won't make a
difference and it sounds like you have relatively modest quantities.

I am puzzled why different manoeuvres have the same effect. It
somewhat suggests multiple pathology.

Two questions ref egg sucking. Pneumatic netto was common in the
seventies, presumably there is no cruise/climb switch in the plumbing
to the Winter?

It did have pneumatic netto, but the plumbing was removed before I got
the ship. *I still have the brass fitting.

When you did your leak test did you connect to the Brunswick tube? If
so did you remember to put a piece of wire (about .020") up the slots
and into the plastic test pipe to stop the pipe sealing around the end
of the probe?

I removed the Brunswick and connected directly to the stub sticking
out of the fin. *Air flows easily through the Brunswick.

What that doesn't do is test the integrity of the joint between probe
and socket in the fin.

Originally Posted by jsbrake[_2_]

Hi All,
Whenever I accelerate, my varios bump up and tell me I'm climbing,
then settle back to reality. Any idea of what I need to look for to
fix this?
My setup:
Kestrel 19, two static ports in the tail boom, pitot and TE in the
fin. The TE line is split under the seat using a Y connector and then
travels to two varios (a Winter mechanical and a 1990-era audio/final-
glide called a VariCalc). Pitot and static lines are split behind the
panel using T connectors.
I replaced all the non-permanent tubing last year and they all seemed
to be leak-free.
Thanks!
-John

Hi John

Have a read of this article by Rudi Brozel of Ilec re compensation

http://www.nadler.com/sn10/Brozel_TE...n_20020510.pdf


ps is it Kilo Yankee

Cheers