There are two problems with electronic pitot/static TE. The magnitude of
the compensation signal and its phase.

The first is commonly adjustable on the instrument, the second isn't.

Your pressure port and the combined flow resistance and capacity of
the tubing form a low pass filter. If the pitot and static system
filter time constants are greatly different you can get large transient
indications on the vario during pull ups or push overs.

So if you have a system that works adding another instrument and
connecting it to the static system will usually cause a problem.

Leaks will also cause problems, as would partially blocking the static
port with wax.(flow resistance increases.)

For optimum performance of electronic TE the pitot and static should be
on the same side of the TE(nose or tail) and the pitot should be twice
as far from the TE as the static is. (Former World champion Stig Oye
told me of this and a couple of minutes thought convinced me)

A combined pitot/static probe on the fin does not fulfill this
condition and still results in "g" change effects the same as a TE
probe but is more sensitive to pitch and sideslip than the common two
hole Irving pattern probe.

If you aren't having apparent problems with electronic TE you are lucky
or you've got your vario on a very slow response speed where the
unwanted transients are heavily damped.

If you are having problems you want to get a good handle on the physics
of what is going on

in order to fix the problem.

Mike Borgelt


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mborgelt
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