On Jul 2, 12:43*am, Darryl Ramm wrote:
On Jun 29, 8:16*pm, Bruno wrote:









Let the jokes begin...

My Cambridge L-Nav's backup battery ran low and I switched it out.
The settings got reset to default. *Now field elevation reads 4"
millibars too low. *For example, 6,200 feet the awos said pressure was
29.99 and my Cambridge read 29.54 for that elevation. *On start up my
LNAV showed 6,200ft at 29.54. *Never had problems before the battery
switch out. *Yes, have the manual and can get into config mode but
can't seem to find a way to adjust the error.

Now for compensation...
Many people thought my winglets were a desperate cry for compensation
but that is just the beginning of it. *My varios seem to be working
well but act completely uncompensated. *I have a TE probe in the tail
and as of this last winter the gaskets on them are nice and air
tight. *I know my two flasks for the varios are air tight as well.

When I pull up in a thermal the varios both show huge increases. *It
is usual for the varios to show over 10 knots in a pullup in a 3-4
knot thermal cruising at 80 knots. *Yeah, no compensation. *I read in
the LNAV manual that it has an electric TE compensation adjustment.
Anyone use this? *Does it work pretty well?

I have no idea what is wrong with the current system. *The plumbing is
all new as of last winter from the seat back forward. *I divided the
vario lines back by the seat back so they are not messing with each
other. *The best guess right now is the negative pressure line (TE) is
somehow not working/leaking/who knows what. *I did take out the metal
probe and blow in the holes and felt airflow through the end so at
least the probe is not blocked. *I am not using the ram air pressure
from the pitot but from the nose. *Could this be part of the problem?

Thanks for ideas,
Bruno - B4 - maybe this should have been posted anonymously

Maybe you should have changed one thing at a time...

By two varios you mean the cambride LNAV vario and a separate
mechanical vario?

Besides the compensation the varios appear to work OK?

Exactly what TE probe(s) do you have in the tail? A triple probe? An
ILEC single TE only probe? etc.

A very obvious possible problem is you have an uncompensated static
source connected to the varios - i.e. the line to the varios is just
open inside the cockpit. Its fallen off a fitting or broken/split etc.
Was this touched in away this could happen? Lines tugged on when the
changes were made behind the seat? Go back behind the seat again and
check things are still connected there properly. Did anybody do
anything silly like trying to high-pressure test the lines? You should
block one end and do a leak down test on that line. Ideally done with
something like a large syringe and manometer.

If you have a TE probe you should not need to use electronic
compensation (at least not for large errors).

Darryl

I'm going to repeat a suggestion I've made before to our instrument
designers. The "magic" of a TE vario is in the probe. The rest of
the system basically just displays what the probe 'sees'.

Does it make sense to measure a extremely tiny pneumatic signal with a
probe in the tail and send it 15 - 20 feet forward to the panel in a
potentially leaky and/or kinked age hardened plastic tube? Consider
that tube is buried in the fuselage structure where it is a nightmare
to replace/fix.

I think it would make much more sense to convert the pneumatic TE
signal to an electronic one right at the tip of the probe and relay it
to the panel via Bluetooth or other short range wireless technology.
The advantage would be a more accurate TE signal and much easier
installation/maintenance particularly for older gliders with leaky TE
plumbing.

The probe would have its own lithium cell for power which would last
at least a year. The probe would be turned on by the act of plugging
it into the fin and turned off by removing it. The panel instrument
and probe would be a "plug and play" system.