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