Cambridge 302 Question

I've have a Cambridge 302 in my glider. I have the setting at 0%
since I have the total energy probe fed into it, along with the pitot
tube and static port. The te tube is split just behind the cockpit as
recommended. The static and pitot are split or "t'd" behind the
instrument panel.

When I push hard forward to increase airspeed.....the cambridge VSI
goes up to 10knots positive.

Then when I pull back to bleed off airspeed.....the VSI goes down to
10 knots negative.

The manual says to increase the % , but doesn't say how much.

Another option is to not use the te tube and put it at 100%.

The te probe in my glider is located about 6 feet behind the wing spar
on the top of the fuselage. It's not the conventional spot on the
rudder.

Any thoughts? Recommendations?

wrote:
I've have a Cambridge 302 in my glider. I have the setting at 0%
since I have the total energy probe fed into it, along with the pitot
tube and static port. The te tube is split just behind the cockpit as
recommended. The static and pitot are split or "t'd" behind the
instrument panel.

When I push hard forward to increase airspeed.....the cambridge VSI
goes up to 10knots positive.

Then when I pull back to bleed off airspeed.....the VSI goes down to
10 knots negative.

The manual says to increase the % , but doesn't say how much.

Another option is to not use the te tube and put it at 100%.

The te probe in my glider is located about 6 feet behind the wing spar
on the top of the fuselage. It's not the conventional spot on the
rudder.

Any thoughts? Recommendations?

This may not be a factor at all, but if the tube is running under your
seat pan and is being squeezed by the underside of the seat pan, you can
get G induced inputs into the system. You push over and take the weight
off the tube, the tube expands which looks like big "up". You pull and
your weight sqishes the tube which looks like big "down". Not for sure,
but a possibility.

On Apr 19, 1:51*pm, wrote:
I've have a Cambridge 302 in my glider. *I have the setting at 0%
since I have the total energy probe fed into it, along with the pitot
tube and static port. *The te tube is split just behind the cockpit as
recommended. *The static and pitot are split or "t'd" behind the
instrument panel.

When I push hard forward to increase airspeed.....the cambridge VSI
goes up to 10knots positive.

Then when I pull back to bleed off airspeed.....the VSI goes down to
10 knots negative.

The manual says to increase the % , but doesn't say how much.

Another option is to not use the te tube and put it at 100%.

The te probe in my glider is located about 6 feet behind the wing spar
on the top of the fuselage. *It's not the conventional spot on the
rudder.

Any thoughts? *Recommendations?

Yep, pretty easy. Normally you would just change the % compensation
until it behaves as you want. But then normally you would need little
if any electronic compensation.

You say it's a fuselage mounted probe, there is nothing wrong per se
with fuselage mounted TE probes, Dick Johnson spent time trying to
point that out.

Presumably you have a mechanical vario and capacity flask on the other
side of the split TE line. Does that mechanical vario seem to behave
correctly? If so the problem is at the Cambridge 302, and that 302
should not need huge compensation adjustments (normally none).

Check the plumbing carefully, it might be as simple as you actually
have the static and TE lines crossed at the Cambridge (that would be
the first thing to check - don't rely on the color or the tubing etc.
(it might be spliced wrong you cant' see) really check there is a air
pressure connection by blowing gently onto (not into!) the TE probe).

Also simplify the problem. Block off any ports you really don't need.
Check all connections carefully, etc. Block the other side of the TE
line where it splits. Double check that the IAS and pressure altitude
on Cambridge all look OK (long shot but it may show up a problems).

If you start to suspect the Cambridge, try just sticking it on the
static line with 100% compensation and see what it does. But this
really should not be needed.

Darryl

On Apr 19, 4:27*pm, Darryl Ramm wrote:
On Apr 19, 1:51*pm, wrote:





I've have a Cambridge 302 in my glider. *I have the setting at 0%
since I have the total energy probe fed into it, along with the pitot
tube and static port. *The te tube is split just behind the cockpit as
recommended. *The static and pitot are split or "t'd" behind the
instrument panel.

When I push hard forward to increase airspeed.....the cambridge VSI
goes up to 10knots positive.

Then when I pull back to bleed off airspeed.....the VSI goes down to
10 knots negative.

The manual says to increase the % , but doesn't say how much.

Another option is to not use the te tube and put it at 100%.

The te probe in my glider is located about 6 feet behind the wing spar
on the top of the fuselage. *It's not the conventional spot on the
rudder.

Any thoughts? *Recommendations?

Yep, pretty easy. Normally you would just change the % compensation
until it behaves as you want. But then normally you would need little
if any electronic compensation.

You say it's a fuselage mounted probe, there is nothing wrong per se
with fuselage mounted TE probes, Dick Johnson spent time trying to
point that out.

Presumably you have a mechanical vario and capacity flask on the other
side of the split TE line. Does that mechanical vario seem to behave
correctly? If so the problem is at the Cambridge 302, and that 302
should not need huge compensation adjustments (normally none).

Check the plumbing carefully, it might be as simple as you actually
have the static and TE lines crossed at the Cambridge (that would be
the first thing to check - don't rely on the color or the tubing etc.
(it might be spliced wrong you cant' see) really check there is a air
pressure connection by blowing gently onto (not into!) the TE probe).

Also simplify the problem. Block off any ports you really don't need.
Check all connections carefully, etc. Block the other side of the *TE
line where it splits. Double check that the IAS and pressure altitude
on Cambridge all look OK (long shot but it may show up a problems).

If you start to suspect the Cambridge, try just sticking it on the
static line with 100% compensation and see what it does. But this
really should not be needed.

Darryl- Hide quoted text -

- Show quoted text -

I have all new tubing and new capacity flasks. The other two
mechanical VSI seem to work well. The cambridge works well
too....unless I push forward to speed up or pull back fast to slow
down.

Does the 100% compensation and the two static line system work ok?

SA

Sounds like s big leak in the system to me !
At 20:51 19 April 2009, wrote:
I've have a Cambridge 302 in my glider. I have the setting at 0%
since I have the total energy probe fed into it, along with the pitot
tube and static port. The te tube is split just behind the cockpit as
recommended. The static and pitot are split or "t'd" behind the
instrument panel.

When I push hard forward to increase airspeed.....the cambridge VSI
goes up to 10knots positive.

Then when I pull back to bleed off airspeed.....the VSI goes down to
10 knots negative.

The manual says to increase the % , but doesn't say how much.

Another option is to not use the te tube and put it at 100%.

The te probe in my glider is located about 6 feet behind the wing spar
on the top of the fuselage. It's not the conventional spot on the
rudder.

Any thoughts? Recommendations?

Its a big leak in the system is my guess
At 20:51 19 April 2009, wrote:
I've have a Cambridge 302 in my glider. I have the setting at 0%
since I have the total energy probe fed into it, along with the pitot
tube and static port. The te tube is split just behind the cockpit as
recommended. The static and pitot are split or "t'd" behind the
instrument panel.

When I push hard forward to increase airspeed.....the cambridge VSI
goes up to 10knots positive.

Then when I pull back to bleed off airspeed.....the VSI goes down to
10 knots negative.

The manual says to increase the % , but doesn't say how much.

Another option is to not use the te tube and put it at 100%.

The te probe in my glider is located about 6 feet behind the wing spar
on the top of the fuselage. It's not the conventional spot on the
rudder.

Any thoughts? Recommendations?

On Apr 19, 1:51*pm, wrote:
I've have a Cambridge 302 in my glider. *I have the setting at 0%
since I have the total energy probe fed into it, along with the pitot
tube and static port. *The te tube is split just behind the cockpit as
recommended. *The static and pitot are split or "t'd" behind the
instrument panel.

When I push hard forward to increase airspeed.....the cambridge VSI
goes up to 10knots positive.

Then when I pull back to bleed off airspeed.....the VSI goes down to
10 knots negative.

The manual says to increase the % , but doesn't say how much.

Another option is to not use the te tube and put it at 100%.

The te probe in my glider is located about 6 feet behind the wing spar
on the top of the fuselage. *It's not the conventional spot on the
rudder.

Any thoughts? *Recommendations?

Scott,

Go to screen 10 on the CAI 302 and note the indicated airspeed. You
may have the Pitot & static switched. Which mode are you in when this
happens climb or Cruise?

At TE probe requires that the Compensation be set at 0%. The Probe
supplies the Compensation.


Richard
www.craggyaero.com

On Apr 19, 2:34*pm, wrote:
On Apr 19, 4:27*pm, Darryl Ramm wrote:



On Apr 19, 1:51*pm, wrote:

I've have a Cambridge 302 in my glider. *I have the setting at 0%
since I have the total energy probe fed into it, along with the pitot
tube and static port. *The te tube is split just behind the cockpit as
recommended. *The static and pitot are split or "t'd" behind the
instrument panel.

When I push hard forward to increase airspeed.....the cambridge VSI
goes up to 10knots positive.

Then when I pull back to bleed off airspeed.....the VSI goes down to
10 knots negative.

The manual says to increase the % , but doesn't say how much.

Another option is to not use the te tube and put it at 100%.

The te probe in my glider is located about 6 feet behind the wing spar
on the top of the fuselage. *It's not the conventional spot on the
rudder.

Any thoughts? *Recommendations?

Yep, pretty easy. Normally you would just change the % compensation
until it behaves as you want. But then normally you would need little
if any electronic compensation.

You say it's a fuselage mounted probe, there is nothing wrong per se
with fuselage mounted TE probes, Dick Johnson spent time trying to
point that out.

Presumably you have a mechanical vario and capacity flask on the other
side of the split TE line. Does that mechanical vario seem to behave
correctly? If so the problem is at the Cambridge 302, and that 302
should not need huge compensation adjustments (normally none).

Check the plumbing carefully, it might be as simple as you actually
have the static and TE lines crossed at the Cambridge (that would be
the first thing to check - don't rely on the color or the tubing etc.
(it might be spliced wrong you cant' see) really check there is a air
pressure connection by blowing gently onto (not into!) the TE probe).

Also simplify the problem. Block off any ports you really don't need.
Check all connections carefully, etc. Block the other side of the *TE
line where it splits. Double check that the IAS and pressure altitude
on Cambridge all look OK (long shot but it may show up a problems).

If you start to suspect the Cambridge, try just sticking it on the
static line with 100% compensation and see what it does. But this
really should not be needed.

Darryl- Hide quoted text -

- Show quoted text -

I have all new tubing and new capacity flasks. *The other two
mechanical VSI seem to work well. *The cambridge works well
too....unless I push forward to speed up or pull back fast to slow
down.

Does the 100% compensation and the two static line system work ok?

SA

All new tubing and all new capacity flasks probably leak more often
than all old tubing and all old capacity flasks that have not had all
new fingers poking around in them :-)

Three varios? The TE line is split three ways beyond the seat and the
two mechanical varios have their own capacity flasks right? The reason
for splitting beyond the seat is just to give some line impedance so
that the flow to/from the capacity flasks does not significantly
affect the direct pressure reading 302.

The electronic compensation and a static source works very well on a
C302. I use that on mine, it provides a separate vario independent of
the TE. However it is only as good as the static and pilot sources. I
know Cambridge (Dave Ellis?) previously argued that a good TE probe
was better than electronic compensation, but I can't tell the
difference.

However your ships seems to have something going wrong and instead of
just changing things I personally would work out what the problem is
first.

I had misread the direction of the vario change when you said you
pushed/pulled. So the other poster's suggestion that you have a big
leak may be more likely. Does the behavior of you speed up/slow down
test depend on the cockpit vents being full open of closed. If you
were flying with the vents mostly open, speeding up could raise
cockpit/fuselage internal pressure, causing a false climb indication.
Has a tube fallen off somewhere? Is a right angle or "T" adapter
cracked or fallen apart entirely. Are any lines blocked off, are the
stoppers really secure/airtight? Do you have something else
misconnected somewhere so that the TE line is actually open to the
ambient cockpit pressure. Have you checked the tube has not fallen off
the TE probe? Try making the circuit as simple as possible and remove
any split behind the seat (in case you have a huge leak in a capacity
or other vario case - unlikely though - if those other varios seem to
work - but it is not clear if they actually show a climb when they
should or if you are just saying they don't show false speed relate
readings). If they don't show a climb when they should you could have
a huge leak on the mechanical vario side that (in a stretch) could
explain this. Is there an alt static source behind the panel, is it
accidentally open? Is it plumbed in the correct line?

You may be too close to the problem. Have somebody else sanity check
what you have done and how you have debugged it. Be prepared to buy
them a beer when they walk straight up point out the "obvious"
error :-)


Darryl

On Apr 19, 3:53*pm, wrote:
On Apr 19, 1:51*pm, wrote:



I've have a Cambridge 302 in my glider. *I have the setting at 0%
since I have the total energy probe fed into it, along with the pitot
tube and static port. *The te tube is split just behind the cockpit as
recommended. *The static and pitot are split or "t'd" behind the
instrument panel.

When I push hard forward to increase airspeed.....the cambridge VSI
goes up to 10knots positive.

Then when I pull back to bleed off airspeed.....the VSI goes down to
10 knots negative.

The manual says to increase the % , but doesn't say how much.

Another option is to not use the te tube and put it at 100%.

The te probe in my glider is located about 6 feet behind the wing spar
on the top of the fuselage. *It's not the conventional spot on the
rudder.

Any thoughts? *Recommendations?

Scott,

Go to screen 10 on the CAI 302 and note *the indicated airspeed. *You
may have the Pitot & static switched. *Which mode are you in when this
happens climb or Cruise?

At TE probe requires that the Compensation be set at 0%. *The Probe
supplies the Compensation.

Richardwww.craggyaero.com

To be clear, you can adjust the compensation when using a TE probe.
Normally a small percentage to correct compensation issues, but
usually not needed. The manual appears to say you *must* use 0 when
using a TE probe. But this is wrong. And the manual also contradicts
itself and explains you can do this tweaking. But none of that is of
course related to the problem described here.

Darryl

On Apr 19, 3:53*pm, wrote:
On Apr 19, 1:51*pm, wrote:



I've have a Cambridge 302 in my glider. *I have the setting at 0%
since I have the total energy probe fed into it, along with the pitot
tube and static port. *The te tube is split just behind the cockpit as
recommended. *The static and pitot are split or "t'd" behind the
instrument panel.

When I push hard forward to increase airspeed.....the cambridge VSI
goes up to 10knots positive.

Then when I pull back to bleed off airspeed.....the VSI goes down to
10 knots negative.

The manual says to increase the % , but doesn't say how much.

Another option is to not use the te tube and put it at 100%.

The te probe in my glider is located about 6 feet behind the wing spar
on the top of the fuselage. *It's not the conventional spot on the
rudder.

Any thoughts? *Recommendations?

Scott,

Go to screen 10 on the CAI 302 and note *the indicated airspeed. *You
may have the Pitot & static switched. *Which mode are you in when this
happens climb or Cruise?

At TE probe requires that the Compensation be set at 0%. *The Probe
supplies the Compensation.

Richardwww.craggyaero.com

And that was a clever suggestion - pitot and static swapped and the
302 in cruise mode and configured to be a super netto or netto vario
so the indicator relies on the airspeed....

Note to Scott - the altimeter display on the 302 home screen has
nothing to do with the static plumbing, it senses cockpit ambient
pressure, so is cannot help debug this question. So try what Richard
suggests.

Darryl