I'm 4" short and need more compensation...yes this is gliding related :)

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

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

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.

Thanks for the responses and ideas Darryl and Bill. I spent yesterday
afternoon with the glider. Following your suggestions Darryl I
started leak checking the total energy line first. After taking the
TE lines off the 2 varios I confirmed that indeed there was a massive
leak in the line somewhere. It would not hold pressure or suction for
even a second. I took the seat pan out and tracked the leak back to
the last possible bit of tubing before it disappears into the bulkhead
of the landing gear. It seems that in my enthusiasm to get the ship
ready when I first purchased it 6 years ago I was cutting into the
plastic covering that surrounds all the tubes and sliced my total
energy line up pretty good. Duh!!! That would explain why I never
experienced total energy in this glider. It was basically a static
line connected to the varios. A quick cut of the tubing and a single
splice later with a foot of new tubing and the line holds both air and
suction very well. No leaks whatever now. Yeah! Don't have to cut
into the tail like it was starting to look likely would happen. I am
really looking forward to flight testing the glider this next week.
Thanks again for the suggestions and helpful ideas.

The biggest problem solved. Now, anyone ever experience the Cambridge
LNAV problem I mentioned in the first post? It is reading about 4" of
millibars too low for the real pressure at a known altitude. Right
now that just means that I have another 400 feet for safely getting
home if I rely on the instrument. Not the end of the world but would
be nice to fix since I use this logger for my contest files.

Thanks again!
Bruno - B4

On Jul 3, 11:17*am, Bruno wrote:
Thanks for the responses and ideas Darryl and Bill. *I spent yesterday
afternoon with the glider. *Following your suggestions Darryl I
started leak checking the total energy line first. *After taking the
TE lines off the 2 varios I confirmed that indeed there was a massive
leak in the line somewhere. *It would not hold pressure or suction for
even a second. *I took the seat pan out and tracked the leak back to
the last possible bit of tubing before it disappears into the bulkhead
of the landing gear. *It seems that in my enthusiasm to get the ship
ready when I first purchased it 6 years ago I was cutting into the
plastic covering that surrounds all the tubes and sliced my total
energy line up pretty good. *Duh!!! *That would explain why I never
experienced total energy in this glider. *It was basically a static
line connected to the varios. *A quick cut of the tubing and a single
splice later with a foot of new tubing and the line holds both air and
suction very well. *No leaks whatever now. *Yeah! *Don't have to cut
into the tail like it was starting to look likely would happen. *I am
really looking forward to flight testing the glider this next week.
Thanks again for the suggestions and helpful ideas.

The biggest problem solved. *Now, anyone ever experience the Cambridge
LNAV problem I mentioned in the first post? *It is reading about 4" of
millibars too low for the real pressure at a known altitude. *Right
now that just means that I have another 400 feet for safely getting
home if I rely on the instrument. *Not the end of the world but would
be nice to fix since I use this logger for my contest files.

Thanks again!
Bruno - B4

Bruno

Altitude zero and gain adjustments are in the menus and the LNAV
manual describes how to set this. But you'll need to be able to pull
down/up the sensor pressure to do this. You could also just send it
off to ClearNav for a check and calibration or at least call them and
talk about what you are seeing. I don't think the altitude
calibrations are lost when you replace the internal battery. So I am
not sure what is going on.

Darryl

On Jul 3, 11:17*am, Bruno wrote:
Thanks for the responses and ideas Darryl and Bill. *I spent yesterday
afternoon with the glider. *Following your suggestions Darryl I
started leak checking the total energy line first. *After taking the
TE lines off the 2 varios I confirmed that indeed there was a massive
leak in the line somewhere. *It would not hold pressure or suction for
even a second. *I took the seat pan out and tracked the leak back to
the last possible bit of tubing before it disappears into the bulkhead
of the landing gear. *It seems that in my enthusiasm to get the ship
ready when I first purchased it 6 years ago I was cutting into the
plastic covering that surrounds all the tubes and sliced my total
energy line up pretty good. *Duh!!! *That would explain why I never
experienced total energy in this glider. *It was basically a static
line connected to the varios. *A quick cut of the tubing and a single
splice later with a foot of new tubing and the line holds both air and
suction very well. *No leaks whatever now. *Yeah! *Don't have to cut
into the tail like it was starting to look likely would happen. *I am
really looking forward to flight testing the glider this next week.
Thanks again for the suggestions and helpful ideas.

The biggest problem solved. *Now, anyone ever experience the Cambridge
LNAV problem I mentioned in the first post? *It is reading about 4" of
millibars too low for the real pressure at a known altitude. *Right
now that just means that I have another 400 feet for safely getting
home if I rely on the instrument. *Not the end of the world but would
be nice to fix since I use this logger for my contest files.

Thanks again!
Bruno - B4

Bruno

You mention using the "logger" for your contest files. The altimeter
in the LNAV is not used for the flight log in the GPS (Model 20 or
whatever you have attached). Those GPS devices have their own pressure
altimeters (they have to to avoid possible tampering).

Darryl