to HSI or not to HSI

Dave,

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

Never realized that there is something like a _nonslaved_ HSI, but one never
stop learning ;-) Does that mean you have to handle it like a DG an
twist-the-knob regulary? I'm used to slaved HSI for a while now a found the
slaving one of the biggest improvements when moving up from a DG. Have you
considdered a slaved one? What's the additional cost (may be a lot, taking
into account the flux-gate, sync, installation, etc...)?

Best Regards

Kai

On Thu, 11 Nov 2004 13:36:08 -0500, Dave Butler
wrote:

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?

I've had a non-slaved NSD360 since 1986. It has been down for maintenance
once.


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

That depends on how big your wallet is :-))

I find it very useful for flying back courses; and it is more useful for SA
than is a plain CDI.

However, since installing my CNX80, I have found myself referring to the
ground track vs desired track information (on the GPS) more frequently than
to the CDI in order to fine tune my heading.


--ron

Michelle P wrote:
Dave,
My NSD 360A ran fine for about 9 years then just died. I sent it back to
the factory. Told me nothing wrong. Lousy service. I have an old soon to
be rebuilt NSD360A for sale. Interested? I upgraded to a Sandel.

Thanks, Michelle. We are a little shy of buying stuff from other than our local
avionics shop since we like having warranty service. I'll present your offer to
my partners, though.

Dave

Michelle

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We plan to update our outdated panel with a GNS480.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




--
Dave Butler, software engineer 919-392-4367

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

Michael wrote:
Dave Butler wrote

Actually, if your primary AI is vacuum and the secondary is electric,
you can simply remove the T&B and install the second AI in its place.
AC91-75 permits the replacement of the T&B with a second AI, as long
as the power source for the 2nd AI is different from the power source
for the 1st AI. So really, being able to free up the hole should not
factor into your decision.

Yeah, thanks for reminding me about that.


Some people love HSI's, some hate them, some are indifferent. I've
flown several planes with HSI's and I'm indifferent. It's OK. A DG
with CDI is also OK. About the only time an HSI really has an
advantage is when you're flying reverse course on a localizer. Other
than in training, I do not believe I have ever had to do that.

Happens fairly often here. Fayetteville, NC (FAY) has a localizer back-course
approach that seems often to be the approach of choice. I often use it for
practice approaches and occasionally "in anger".

Dave

My order of preference would be
IFR GPS
Autopilot
HSI

And an HSI without slaving lacks one of its better features.
Consider that an autopilot, if ALL ELECTRIC, will give you much safety
in IMC. You loose your vacuum, you still have autopilot. Autopilot is
nice for VFR also, as is a panel mount GPS.

All these gadgets need maintenance.

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:

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

"Ben Jackson" wrote in message
news:mkXkd.397609$D%.109302@attbi_s51...
In article ,
Richard Hertz no one@no one.com wrote:
Can you explain why that is the one advantage (BC)/revers on localizer,
and
why that is so?

An HSI is like a CDI you can spin around. When shooting a back course
it is effectively upside down, cancelling out the reverse sensing.

Yes, thanks.
But there is no such thing as "reverse-sensing" on the localizer. If
perhaps the current common teaching of localizers and CDI was corrected then
we that selling point of HSI is dropped.

The CDI needle points to the color sector you are in. On some (older) nav
heads the blue and yellow sectors were indicated. So, no need to look for
reverse sensing/etc, just look at the approach chart, look at the needle and
you will know where you are relative to the course. Nothing could be
simpler.


--
Ben Jackson

http://www.ben.com/

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.