Henry Bibb wrote:
The compass in my plane decided to spontaneously emit fluid all
over the glareshield the other day, so I'm looking at options for
replacement.

I've Googled for opinions on the vertical-card vs whiskey issue,
and came away no wiser - anybody care to comment from fairly
recent experience?

This is for a VFR-only airplane without a DG.

Henry,

I just replaced our Precision Vertical Card compass with a SIRS unit so
this is still fresh in my mind.

You have basically three options:

1) Standard Airpath "whiskey" compass (About $175)
2) Vertical Card (Precision about $225)
3) SIRS Navigator (http://www.sirsproducts.com/ ($215)

I installed a SIRS because our 400+hour vertical card had developed
errors that had become uncorrectable, it tended to stick occasionally in
turns, and my avionics shop refused to install and warranty a new
vertical card due to MANY customer complaints and warranty claims.

As I see it, the chief benefits of the SIRS unit over the Airpath a

1) The rotating mass is smaller, and they use a lens to make the card
appear as large as required by the TSO. The smaller mass reduces the
acceleration/turning effects. I've seen this first hand.

2) Clear silicone fluid Vs. Kerosene. I don't know if the silicone
fluid will discolor over the years, or whether it really damps the card
oscillations, but at least if it leaks I won't have a flammable liquid
running down into my radio stack.

3) The lighting is LED. LEDs draw less power for the light they produce
and simply won't burn out in the operational lifetime of the compass (if
not the airplane). One less thing to worry about.

4) And, for what it's worth, SIRS Navigation produces high-grade
compasses for many industries, and a different model of this compass is
used as the standby in the Concorde.

Hope this helps,

-Doug

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Doug Vetter, CFIMEIA

http://www.dvcfi.com
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