to HSI or not to HSI

FWIW, the GNS480 displays an electronic HSI on its NAV page. I also plan to upgrade my panel with the GNS480, but after spending $11K on the GPS I can't justify spending more on a HSI that doesn't add that much extra. The NSD360 was the cheapest HSI I could find but after some research it seemed like a problem instrument. This quote is from the Avionics West article at http://avionicswest.com/articles/kno..._autopilot.htm

"The most popular Cessna HSI today is the Edo-Aire NSD-360 series. Cessna installed these units in thousands of single and multi-engine aircraft. This compass system is slaved in most cases, but be advised there are many non-slaved NSD-360's in the field. Even with a slaved NSD-360, you must set the compass card once the aircraft is running. After that if everything is working as it should, you shouldn't have to set the compass card again. 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! Expect to pay between $300-500/year to keep your NSD repaired. Sure, you may not need a repair for several years but when your unit does, it really hits the ole pocket book "

This next quote is from an AVWEB article at http://www.avweb.com/news/reviews/182525-1.html

"Not long thereafter, my vacuum-driven NSD-360 HSI started acting up. On several occasions, the slaved heading gyro suddenly wound up 20 or 30 degrees in error, causing the autopilot to take me on an unplanned off-route excursion each time. Although I subsequently diagnosed the problem as being a clogged central vacuum filter, it reminded me that the NSD-360 was a pretty vulnerable instrument, and one that had required (and would continue to require) overhauls every few years at a cost of around $2,800 a pop. Somehow, that made the $8,000 price of the Sandel seem a lot more reasonable. "

So that finished me on the NDS360 and all the other HSI's were way too expensive. I'm going to keep my DG and get a new MD200 CDI to go with the GNS480.

-Brenor

"Dave Butler" wrote in message ...
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We plan to update our outdated panel with a GNS480.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

Brenor Brophy wrote:
FWIW, the GNS480 displays an electronic HSI on its NAV page. I also plan
to upgrade my panel with the GNS480, but after spending $11K on the GPS
I can't justify spending more on a HSI that doesn't add that much extra.
The NSD360 was the cheapest HSI I could find but after some research it
seemed like a problem instrument. This quote is from the Avionics West
article at http://avionicswest.com/articles/kno..._autopilot.htm

"The most popular Cessna HSI today is the Edo-Aire NSD-360 series.
Cessna installed these units in thousands of single and multi-engine
aircraft. This compass system is slaved in most cases, but be advised
there are many non-slaved NSD-360’s in the field. Even with a slaved
NSD-360, you must set the compass card once the aircraft is running.
After that if everything is working as it should, you shouldn’t have to
set the compass card again. 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!
Expect to pay between $300-500/year to keep your NSD repaired. Sure, you
may not need a repair for several years but when your unit does, it
really hits the ole pocket book "

This next quote is from an AVWEB article at
http://www.avweb.com/news/reviews/182525-1.html

"Not long thereafter, my vacuum-driven NSD-360 HSI started acting up. On
several occasions, the slaved heading gyro suddenly wound up 20 or 30
degrees in error, causing the autopilot to take me on an unplanned
off-route excursion each time. Although I subsequently diagnosed the
problem as being a clogged central vacuum filter, it reminded me that
the NSD-360 was a pretty vulnerable instrument, and one that had
required (and would continue to require) overhauls every few years at a
cost of around $2,800 a pop. Somehow, that made the $8,000 price of the
Sandel seem a lot more reasonable. "

So that finished me on the NDS360 and all the other HSI's were way too
expensive. I'm going to keep my DG and get a new MD200 CDI to go with
the GNS480.


Thanks for the great references, Brenor... and thanks to everyone who replied,
though I won't attempt to apply individually to each.

Dave

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

On Fri, 12 Nov 2004 10:35:54 -0500, Dave Butler
wrote:

Is the compass card not mechanically connected to the gyro?

Bingo!

That's why precession is minimal with this unit. I believe it is called
"electro-optical" coupling, but don't ask me to explain it :-)


--ron

Dave Butler wrote in
:

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

True. I have a non-slaved NSD 360. If I start the engine and have
vacuum, the AI works properly, but the HSI will show a "heading" warning
flag, and will not function as a DG (ie, I can taxi around, making turns,
but the compass card on the HSI will not show the turns) until I apply
power to the avionics bus. It doesn't make any sense to me; I cannot
understand why a vacuum powered gyro will not function as a DG without
electrical power, but that's the way it is.

It's true. Several years ago when we (the group that owned the Bonanza 36 I
was a member of) decided to replace our maintenance-hog Narco HSI, we chose
the King KNS-55 HSI because it worked on the electrical system only (no
vacuum). That meant that a vacuum failure left the HSI, turn coordinator,
and S-Tec autopilot working which would be pretty much a non-event.
Electrical failure would leave the backup DG (the DG that was replaced by
the original HSI was still in the panel) operating.

"Dave Butler" wrote in message
...
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

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.