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.