Cambridge 302 DDV woes - Help me PLEASE !!!

On 6 Oct 2003 22:44:20 -0700, (Jason Armistead)
wrote:

My club has a Cambridge 302 DDV (purchased in February/March 2003)
which oscillates wildly even when sitting on the ground. The needle
and audio are going haywire.

Have you checked that you are getting at least whatever the minimum
voltage ought to be at the vario terminals (not at the battery which
may be OK) Check the fuses, fuseholders, switches and wiring. The
German glider factories are good at building composite
structures(mostly anyway) not so good at electrical wiring, instrument
plumbing etc. If you did the wiring yourself(or your club did it)
that's an even better reason to check the above.

We have the latest firmware, V2.63, installed.

Audio and pointer responses on screens #4 anbd #5 are set at the
factory recommended 2.3 seconds value.

You mean the half second response touted in the advertising is
useless? Amazing!

I had a quick look at the IAS shown while flying, and at around 55 kts
on the mechanical ASI, the 302 screen #10 IAS was showing around 50
kts (somehow the accuracy seemed to improve when aloft). Because I
had a passenger in the back I really didn't spend much time fiddling.

The offset at zero airspeed can seem quite bad but due to pressure vs
airspeed being a square law relationship means that it gets better at
any reasonable speed - like above 40 knots.
For example if that offset shown is +13 knots on the ground, at 40
knots IAS you should see 42 knots. Not much of a problem.

Mechanical ASI's aren't as good as some people think.
The Winter ASI has a +/- 2 knots error band going to +/- 3 knots over
temperature and the 57mm Winter ASI is something I'd hope to find for
free in a Weeties packet. If you have one in a motor glider don't be
surprised when it stops working. I've seen the rubbing plate on the
capsule fall off of three of them.(All owned by the same person)

Are the ASI and the 302 running from the same pitot/static sources?

I doubt your problem is caused by the zero offset of the ASI sensor
unless the internal workings are truly bizarre. I guess that is
possible.

I want to know how to change the zero offset value (screen #10 ASI
reading), which is wrong. Can it be done without opening the 302 -
opening it will break the security seal and prevent it being used for
badge claims !!!

Which is why putting the logger into the vario is such a dumb idea.
Have you figured out yet that your glider is pretty useless while the
logger/vario is sent away for calibration? Or if you have to break
into the logger/vario to fix something you need to have it resealed so
the logger is actually of real use?


Mike Borgelt

"Peter" wrote...
Until my 302 broke down last week. The needle doesnt move and the
speaker only peeps during startup. No GPS on the serial line. Altitude
works though. Just UPS'ed it to the US

General comment to all with 302 problems. I had my 302 fail when I arrived at a
contest last season. On power up, 9 times out of 10 it wouldn't get past the
initial serial number screen. Those few times when it did start up, it acted
very strangely. I flew the practice day using a handheld GPS. I spent hours
looking at the wiring, and calling around to find a loaner. I finally noticed
that the temperature probe plug wasn't quite seated properly (about 1 mm of the
barrel was exposed above the connector). I pulled it out and pushed it in, and
the 302 magically started working again. Given that a slight tug is all that is
needed to unseat it, you may want to look at it carefully...

Marc

Jason;

A couple of months ago I had the same problem. I called and talked to
Cambridge and they suggested I look at the altitude readings on screen
#6. There are 3 alt readings on this screen: Flight Level, GPS, and
Pressure. Mine read FL=590 ft, GPS=600 Ft, and PR=6000 ft. The needle
and audio would make large up/down movements at random times. I
returned the 302 to the factory for repair.

Rich

Jason Armistead wrote:

My club has a Cambridge 302 DDV (purchased in February/March 2003)
which oscillates wildly even when sitting on the ground. The needle
and audio are going haywire.

We have the latest firmware, V2.63, installed.

Audio and pointer responses on screens #4 anbd #5 are set at the
factory recommended 2.3 seconds value.

Going to screen #10 (sensor readings) showed the Indicated Airspeed
(IAS) as
13 (knots / km ?) with the glider parked on the ground. See page 11
of the 302 DDV manual (February 2003, Firmware V2.6 edition

This is definitely WRONG !!!

Section 2.2.1 on page 4 of that same document says

"Proper DDV function depends CRITICALLY on correct airspeed
measurement. It
is REALLY important that pitot and static pressure connections are
correct." and so on.

So my take on this all is that while the vario thinks the glider is
moving when stationary (and the GPS input to it indicating contrary to
this) , it will NEVER give accurate readings.

The "ASI" value shown on screen 10 is supposed to be a "Airspeed
Indicator
zero offset (should be less than 1000)"

What the manual doesn't say is how to CHANGE that offset to fix up
problems such as the one we're seeing.

I had a quick look at the IAS shown while flying, and at around 55 kts
on the mechanical ASI, the 302 screen #10 IAS was showing around 50
kts (somehow the accuracy seemed to improve when aloft). Because I
had a passenger in the back I really didn't spend much time fiddling.

I want to know how to change the zero offset value (screen #10 ASI
reading), which is wrong. Can it be done without opening the 302 -
opening it will break the security seal and prevent it being used for
badge claims !!!

As we're in Australia, the idea of shipping the unit back to the USA
for repairs is not encouraging.

Can someone help me PLEASE !!!

Cheers

Jason A.
Southern Cross Gliding Club
Camden NSW

Rich Carlson wrote:

A couple of months ago I had the same problem. I called and talked to
Cambridge and they suggested I look at the altitude readings on screen
#6. There are 3 alt readings on this screen: Flight Level, GPS, and
Pressure. Mine read FL=590 ft, GPS=600 Ft, and PR=6000 ft. The needle
and audio would make large up/down movements at random times. I
returned the 302 to the factory for repair.

Thanks Rich, I will get someone to check this out. But, from what
I've seen the difference between pressure and GPS altitudes from
several IGC files we've downloaded is typically only a few hundred
feet if someone forgot to calibrate the pressure altitude on screen #2
on startup following a change in air pressure.

Marc Ramsey then wrote:

General comment to all with 302 problems. I had my 302 fail when I
arrived at
a contest last season. On power up, 9 times out of 10 it wouldn't
get past the
initial serial number screen. Those few times when it did start up,
it acted
very strangely. I flew the practice day using a handheld GPS. I
spent hours
looking at the wiring, and calling around to find a loaner. I
finally noticed
that the temperature probe plug wasn't quite seated properly (about 1
mm of the
barrel was exposed above the connector). I pulled it out and pushed
it in,
and the 302 magically started working again. Given that a slight tug
is all
that is needed to unseat it, you may want to look at it carefully...

More good advice thanks Marc. I must say that we've not had any
problems on power-up. Each time it just goes through the startup and
switches to screen #2 as per the manual.

Peter Cutting wrote:

I had a case of wild needle - discovered during launch on a comp day.
suspected rain in the static (it had rained plenty night before!). I
blew it out as quick as i could (loads of water came out). Re-light -
same problem. In desperation I went through the 302 settings and saw
that compensation was set to 95 or 105 (dont remember which). I had
been messing around with compensation a few days earlier and forgot
to
put it back to 100 - afterall its only 5% off 100 so the effect
should
be negligable anyway.

In desperation I set it back to 100 (ILEC tube) and the needle
settled
down noticeably so I could start the comp. That evenening I pumped
out the static for good measure (more water). The next day same
problem!! I checked the compensation and it had moved off 100 to the
earlier value all by itself!! Couldnt believe it. Anyway put it back
on 100 and no more problems since.

I have also seen some values not "stick" after being set up on the
configuration screens. Powering the unit off and on restored the
previous settings rather than the new ones. I think there must be a
glitch in how the 302 tries to write them to configuration EEPROM /
Flash. Maybe it's scheduled ever "X" seconds and we've turned the
unit off too fast. There's nothing in the manual about this, and
we've NEVER seen the settings come up randomly (which might suggest a
configuration memory corruption problem)

I think there might be a problem with water in the pressure / static
lines.

Can anyone suggest a good and proper (SAFE to instruments !) method
for testing, and if necessary clearing this ?

Mike Borgelt wrote:

Have you checked that you are getting at least whatever the minimum
voltage ought to be at the vario terminals (not at the battery which
may be OK) Check the fuses, fuseholders, switches and wiring. The
German glider factories are good at building composite
structures(mostly anyway) not so good at electrical wiring,
instrument
plumbing etc. If you did the wiring yourself(or your club did it)
that's an even better reason to check the above.

Good points Mike - the 302's internal voltmeter indicates 12.6 V,
which should be more than satisfactory. There's only a 0.2V dip when
the radio is transmitting, which again is OK. The wiring was done by
a couple of QANTAS LAMEs, so it certainly wasn't a hastily cobbled
together backyard job. They used all the right tools, ran the wiring
neatly, and connected it correctly.

Mikes other points about actual vs advertised response times, and the
problems of combined logger + vario instrumentation, I will take with
a grain of salt. All I will say is that it is good to see some healthy
rivalry in the glider instrumentation business !!!

Perhaps Mike, you'd like to suggest a suitable IGC/FAI approved
stand-alone logger unit. We're going to need a few for our other
gliders and are open to suggestions.

Once again, thanks to everyone for their posts. I will let you all
know when we find the cause of this rather bizarre 302 behaviour.

Regards

Jason Armistead

"Marc Ramsey" wrote in message news:mbCgb.8522 I finally noticed
that the temperature probe plug wasn't quite seated properly (about 1 mm of the
barrel was exposed above the connector). I pulled it out and pushed it in, and
the 302 magically started working again. Given that a slight tug is all that is
needed to unseat it, you may want to look at it carefully...

Marc


I had probe problems with my 302. It boots and works without the
probe connected but it will not boot with a failed probe. I assume
the partially seated 3 way plug is behaving the same as a failed
probe. I had 2 probe failures my first year with the 302. (Both were
exchanged under warranty so no complaint there)

Since the 302 will operate with disconnected probe I asked CAI to
explain why a probe failure should prevent boot. I also suggested they
change the firmware so it would report the probe failure but still
operate. I think that fell on stoney ground.

BTW the original 302 manual suggested use of silicone sealant to hold
the temp probe in place. I think tht was changed in later manuals. I
wonder if they found there was a corrosion problem.


Andy (GY)

In article ,
says...
I want to know how to change the zero offset value (screen #10 ASI
reading), which is wrong. Can it be done without opening the 302 -
opening it will break the security seal and prevent it being used for
badge claims !!!

I was told a while ago that the ASI zero offset is determined
automatically by the instrument whenever it is turned on, and does not
require any adjustment by the pilot.

--
-------
Eric Greenwell USA

On 7 Oct 2003 17:05:38 -0700, (Jason Armistead)
wrote:



Mike Borgelt wrote:

Have you checked that you are getting at least whatever the minimum
voltage ought to be at the vario terminals (not at the battery which
may be OK) Check the fuses, fuseholders, switches and wiring. The
German glider factories are good at building composite
structures(mostly anyway) not so good at electrical wiring,
instrument
plumbing etc. If you did the wiring yourself(or your club did it)
that's an even better reason to check the above.

Good points Mike - the 302's internal voltmeter indicates 12.6 V,


Right, so we have a suspect instrument and we are going to check the
voltage being delivered by relying on that instrument?
I suggest you borrow a good DVM and don't take the indicated voltage
for granted..


which should be more than satisfactory. There's only a 0.2V dip when
the radio is transmitting, which again is OK. The wiring was done by
a couple of QANTAS LAMEs, so it certainly wasn't a hastily cobbled
together backyard job. They used all the right tools, ran the wiring
neatly, and connected it correctly.

What was it: "trust but verify"?

Mikes other points about actual vs advertised response times, and the
problems of combined logger + vario instrumentation, I will take with
a grain of salt. All I will say is that it is good to see some healthy
rivalry in the glider instrumentation business !!!

Use all the salt you like but your vario/logger comes out of the
glider for calibration every two years and within a month of claiming
a World record as well. Hopefully the mail system doesn't lose or
break it delaying its return from the calibration lab as your glider
is without its main vario during this time .
(WARNING: the British Post Office appears to have a "chicken gun" as
used to test aircraft windscreens as part of its sorting system.)

I suggest you read the original advertising for the 300 series and ask
yourself if the promised stuff actually happens.
Much was made of the down to under half second response times and how
useful this was and how this was only possible with the technology
used in the 300 series..


Perhaps Mike, you'd like to suggest a suitable IGC/FAI approved
stand-alone logger unit. We're going to need a few for our other
gliders and are open to suggestions.

I'll happily sell you a bunch of Volksloggers. I have a batch about to
leave Germany and we may be able to increase the order and save some
shipping costs.

Mike Borgelt

On Thu, 9 Oct 2003 14:11:35 -0700, Eric Greenwell
wrote:

In article ,
says...
I want to know how to change the zero offset value (screen #10 ASI
reading), which is wrong. Can it be done without opening the 302 -
opening it will break the security seal and prevent it being used for
badge claims !!!

I was told a while ago that the ASI zero offset is determined
automatically by the instrument whenever it is turned on, and does not
require any adjustment by the pilot.


Hopefully there is a solenoid valve then that brings the pitot and
static to the same pressure during the power up cycle(you should hear
a click as it cycles). Otherwise there will be some interesting
effects in any reasonable wind, particularly in crosswinds.
Another method uses a pressure switch that switches mechanically at
some given airspeed thus telling the instrument what the sensor offset
is. Hopefully the pressure switch has a stable trip point.

The original CNAV had a solenoid valve in the airspeed measurement
system as did our B20 system back in the 1980's.
I think Peschges used the pressure switch in the VP2 at least.

Mike Borgelt