Cambridge 302 Question

On Apr 20, 12:05*am, Darryl Ramm wrote:
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

If that turns out not to be the problem a simple pressure check for
leaks is in order.

9B

On Apr 20, 7:52*am, wrote:
On Apr 20, 12:05*am, Darryl Ramm wrote:





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

If that turns out not to be the problem a simple pressure check for
leaks is in order.

9B- Hide quoted text -

- Show quoted text -

The pitot/static lines are correct. There is no leaks in the system.
All the lines and capacities are brand new now.

The Airspeed on page ten indicates correctly. It's within a couple
knots of the mechanical airspeed indicator adjacent to the cambridge.

My question is, how much %? The manual address this issue by
stating..."increase the % if this is happening".....but doesn't say
just how much.

I guess I can just try 10%, then 20%, then 30% and so forth. But
would much rather have a more educated attempt at setting this the
right way.

In addition to good advice from others, I'd start by taking the
mechanical vario off the system. The 302 is very fussy about sharing
lines with other instruments, and flow-based varios in particular. Get
the 302 working right on its own, then see if you can add the other
one back without making the 302 work worse. Also leak check the pitot
and static too. I had weird 302 problems twice that came down to leaks
in the ASI and ASI tubing.

John Cochrane

On Apr 20, 6:38*am, wrote:
On Apr 20, 7:52*am, wrote:



On Apr 20, 12:05*am, Darryl Ramm wrote:

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

If that turns out not to be the problem a simple pressure check for
leaks is in order.

9B- Hide quoted text -

- Show quoted text -

The pitot/static lines are correct. *There is no leaks in the system.
All the lines and capacities are brand new now.

The Airspeed on page ten indicates correctly. *It's within a couple
knots of the mechanical airspeed indicator adjacent to the cambridge.

My question is, how much %? *The manual address this issue by
stating..."increase the % if this is happening".....but doesn't say
just how much.

I guess I can just try 10%, then 20%, then 30% and so forth. *But
would much rather have a more educated attempt at setting this the
right way.

Electronic adjustment to TE compensation when I've tried it is a few
percent at most. TE probes should work very well. What you are
describing sounded like a significant problem, not something you tweek
electronic compensation to a TE for. You seem to be confident you
don't have any problems - you know you have no leaks - you have done a
leak-down test on all the lines? All your mechanical varios work
correctly right? They show climb etc. when they readings and readings
match (and they have separate capacities T-ing off behind the seat...
if they don't match then that might help show if one of the varios
themselves are leaking etc.)...

Have somebody else check your work. Try the static line at 100%
compensation. If that does not work send the 302 to Cambridge for
repair or try swapping with another to see if that works.

Darryl

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

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.


To answer you question directly - I don't believe you can fix the
problem you describe with electronic compensation. Here's why:

If I remember correctly an uncompensated vario reads climb when you
bleed off airspeed and sink when you accelerate. This is because with
static pressure only as the pressure source (no compensation) your
vario will indicate the altitude change irrespective of any associated
change in kinetic energy. Your description reads like the opposite, or
OVER-compensation.

I believe there also is an effect from the initial drag of adding lift
in a pullup (and presumably the opposite from reducing lift in a push-
over maneuver). That causes the uncompensated vario to show some small
altitude loss at the very beginning of a hard pullup (think of the
glider "mushing" a bit when you pull hard). This means that on a hard
pullup the vario would read momentarily down by 1 knot or so, then
read up until the speed stabilizes - all in still air, of course.

Putting this second effect aside for now, a pullup from 100 knots down
to 60 knots will gain you about 250 feet in about 10 seconds -
depending on the steepness of the pullup. That translates to 15 knots
average climb rate. You will see more climb rate early in the pullup
than at the end. If you were reporting 10 knots of positive climb rate
on a pullup then it would lead me to believe that you are getting
little or no total energy compensation and you should set the CAI 302
to 70% or so. This has two problems: First, you are reporting behavior
that indicates 70%+ OVER-compensation, not under. Second, I'd be hard-
pressed to recommend to someone that they put that much electronic
compensation on top of a TE probe since you are likely masking a big
problem.

Finally, you are asking for a specific answer to an insufficiently
defined problem. Without knowing the pullup profile the fact that you
are showing 10 knots on the vario doesn't really give enough
information to know how to set your instrument. I generated an answer
by assuming a profile - but I don't really know what kind of pullup
you used to generate this result. The glider matters too, but my
analysis ignores this detail in favor a of a simple energy conversion
relationship.

Hope that's helpful.

9B

On Apr 20, 9:09*am, wrote:
On Apr 19, 1:51*pm, wrote:

I generated an answer
by assuming a profile - but I don't really know what kind of pullup
you used to generate this result. The glider matters too, but my
analysis ignores this detail in favor a of a simple energy conversion
relationship.

Oh, and I generated an answer also based on the assumption that your
vario is behaving in a manner opposite to what you described - unless
I missed something in college physics.

9B