to HSI or not to HSI

Dave Butler wrote:
Please excuse the hijacking of this religious/political forum to raise a
question about flying.

My partners and I are faced with a decision. What would you do?

We plan to update our outdated panel with a GNS480. The CDIs currently
installed are not compatible with the GNS480, so one of them will be
replaced.

We could replace the existing CDI with a compatible one for $2000.

We could install a non-slaved NSD360 HSI instead for $3500.

If we install the HSI, the no-longer-used CDI hole can be used for the
electric AI that's been waaaay over on the other side of the panel.

I think I know what we will do (go for the HSI), but I'm collecting
opinions.

Is the NSD360 likely to become a maintenance headache?

In the electronic age, does it make sense to install an
electromechanical aid to situational awareness?

Thanks,

Dave


One thing, if you get the NSD360, make sure that it meets precession spec.
I got one, and after hearing about how the electric coupling made it precess
much lower than the standard DG it replaced, I noticed that it wasn't any
better. I chalked it up to sales hype.

A year or so later, the unit died, and had to go in for service. It was a
simple belt fix, that had to go back to the manufacturer, Century. They
fixed it, and then told me that it was seriously out of spec for precession,
that it would take about %50 of the price of the unit to fix it.
I told them that it had been that way when it left their plant when new.

I ended up getting it repaired on my own dollar, fortunately not at
Century, who have lost me as a customer from now on.

Dave Butler wrote:

Brenor Brophy wrote:

liberal snippage

This quote is from the Avionics West article at
http://avionicswest.com/articles/kno..._autopilot.htm
This HSI, slaved or not, MUST have BOTH vacuum and electrical inputs
in order to operate. In other words, if you lose vacuum or the
electrical system, this HSI compass card will quit!


Can anyone confirm the statement above from Avionics West? I consider
them a reliable source of information, but this seems counterintuitive
to me. In case of electrical failure, why is the heading information not
still available? Is the compass card not mechanically connected to the
gyro?

Obviously, I can see that the navigation information would not be
available in case of electric failure, but the quote specifically says
the compass card will quit.

Thanks,

Dave


The compass card is electrically connected to the gyro. Thats why either
a vacuum out or electrical out can kill it.

THe solution is pretty simple. Move the old DG over and keep it when installing
the new HSI.