The International Cessna^® 170 Association

Tom Rogers at Avionics West wrote an article about the problems of the vertical card compass years ago, and how turning it upside down during installation frequently ruins it. Tom was no amatuer and operated a fine, well-respected avionics shop. I think he knew what he was doing, and certainly knew the numbers of units he returned for warranty. Now that Tom has died, his older articles have been removed from their website, as now they focus primarily on GPS sales.

This subject was also discussed at the Cessna Owner site: http://www.cessnaowner.org/forums/topic.html?id=3569

I hope the Precison folks solved the matter, but it was definitely not a "myth".

One of the primary things that convinced me to buy a B model was that I wanted it to go camping. The B model can accept an extended baggage compartment that, when filled with the light stuff, will allow a lot more room in the main part of the cabin. Trust me, it does make a big difference.

If turning it upside down can damage the unit, how on Earth do you get them shipped?
There is no way USPS is going o be so careful as to not turn a ox upside down.
Sounds like superstition to me.

Well, get out your Ouiji-board and grab some needles/pins for your VooDoo dolls. Here's the original article (from the PilotsOfAmerica website*) describing the "myth" Precision claims never occured:

From the Avionics West of Tennessee website

http://www.avionicswest.com/articles.htm

How about the Vertical Card Compass? Well for years I slammed the vertical card compass because in nine out of ten aircraft they wouldn’t fall into calibration. The problem is industry wide, in most cases they are worthless. (Sure, I heard about a friend of a friend that had one that worked properly but I never met anyone personally who did.) It became a policy in our shop to refuse to install the vertical card compass because of the problems we encountered. We found problems with this compass in every aircraft regardless of the manufacturer. They oscillated and had gross errors on some headings. Finally one day I was sitting around with nothing to do so I thought I’d try to find out why the vertical card compass didn’t work as it should. After all, they meet TSO C7c-1 but why don’t they work in the aircraft. The first thing I did was disassemble a vertical card compass. The quality of the machine work inside was great. I found a basically square magnet with a gear on it suspended in a gimbal. Another gear was attached to a shaft and turned the compass card. Real basic stuff. I noted that if I rotated this compass in certain directions the card would oscillate it slightly shook the case. Ten degrees difference in heading and the oscillation would cease.. I blame this on the square magnet, maybe a different design would help. But I still didn’t see any reason the vertical card compass would not properly swing. As I moved this compass around in open air, I found this compass seemed to point in properly. So out to the hanger we go looking for an innocent victim to install the compass in. In the corner sat a lonely C-172 waiting to be worked on. We pulled the little Cessna out and checked the wet compass that was already installed. We found this compass was accurate within +/- two degrees. So out came the factory Airpath and in went the vertical card compass. We found during our swing that on "North" through "East" was right on but between 120 and 240 we had over forty degrees of error and no way to adjust it out! My first words were "Typical vertical card compass". We removed the suspect compass and found that now it didn’t track properly out of the aircraft as it did prior to installation. What happened? Did the installer drop it or did it get magnetized? Now we disassemble the case again and find the magnet had come out of the gimbal. Our question was, "why?" We thought that since this vertical card compass was "used", maybe it was already in the failing mode and finally bought the farm. Now I have to figure out what is going on. The parts department now orders a new PAI-700/28 vertical card compass to the tune of $366.50. It arrived in a couple days and I walked around outside to verify the thing appeared to track correctly and it did. This time I personally installed the vertical card compass in the 172 and to the compass rose we went. This time I found errors of thirty degrees in the 60-120 area. So out came the vertical card compass and in went the trustworthy wet compass. As before, the wet compass was working fine. As I walked outside with the recently purchased compass I now found that the thing had different readings than before when I pointed it in the same direction! We disassembled the new vertical card compass and found the magnet had partly separated from the gimbals, much like the first compass that failed! " What gives?" we questioned. We completely disassembled the vertical card compass and found the magnet was held in the gimbal by small pin but the top of the magnet just floated on its gimbals. We carefully reassembled this compass. For some reason the installer was pointing to the inside of the vertical card compass showing me why he thought the compass failed. As he got closer with the screwdriver the magnet pulled out of the top gimbal again. What this told us was that anytime you install the vertical card compass with normal "magnetic" tools you run a high risk of pulling the magnet out of the gimbal therefore causing the compass to fail. Again we properly assembled the vertical card compass and installed the case with a brass "non-magnetic" screwdriver. We installed it in the Cessna again using the brass non-magnetic tool. We found this compass now would come within three degrees of the proper magnetic heading. This was great. What we found was that probably in prior installations we used steel screw drivers that destroyed the compass before we had finished the installation! I flew the Cessna and found on some heading the compass card had a little oscillation but even with this little problem the vertical card was superior to the wet compass. We were all happy that we finally solved the problem on why vertical card compasses usually don’t work. Then someone said, "What if the pilot lays a flashlight near the compass"? We did and as my luck would have it the compass now had gross errors on some headings. We removed the vertical card and reinstalled the wet compass much to my disappointment. I think that if the top gimbal had a small recessed hole and the top of the magnet had a pin to help hold the magnet in the gimbals better this thing would work but we can’t change the design.

The vertical card compass has some advantages over the wet compass. It looks like a directional gyro and you turn toward the number you want to go to instead of backward like you do with the wet compass. The vertical card compass doesn’t have the lead and lag problems associated with the wet compass. The down side of course is the vertical card compass is prone to problems and large errors. I am determined to find a way to make the vertical card compass work in our Cessnas. You haven’t heard the last on this subject!

*http://www.pilotsofamerica.com/forum/ar ... 12380.html

It makes sense that Precision would have addressed those old issues by now with improved design.
If that's the magnet I'm looking at rivetted at the bottom.... it's different than the troubled-one described (as being square, and held/suspended by a solitary pin.)

Be aware that PAC is not the only mfr of vert. card compasses. Falcon made a knock-off as did a chineese mfr I can't recall just now. The original complaints were specifically about the PAC early model.

gahorn wrote:It makes sense that Precision would have addressed those old issues by now with improved design.
If that's the magnet I'm looking at rivetted at the bottom.... it's different than the troubled-one described (as being square, and held/suspended by a solitary pin.)

Be aware that PAC is not the only mfr of vert. card compasses. Falcon made a knock-off as did a chineese mfr I can't recall just now. The original complaints were specifically about the PAC early model.

Beside the more-familiar display of a vert card, there also exists the disposal of the original-type fluid and those occasional leaks.

George, didn't Hamilton also have a vertical card compass that looked almost, but not exactly, like the Precision one? I don't see the Hamilton listed in Spruce. I put a Precision one in my C-140A and my current plane has one also.

170C wrote:George, didn't Hamilton also have a vertical card compass that looked almost, but not exactly, like the Precision one? I don't see the Hamilton listed in Spruce. I put a Precision one in my C-140A and my current plane has one also.

My early experiences in aircraft maintenance was with a now-defunct company called "Precision Aeromotive" owned by "Pappy" Lane. It was primarily an engine shop but also sold other related services and parts.
As he neared the end of his career, he spun-off the unrelated parts business which became a small supply-house at the northwest end of Hobby Airport. They called themselves "Precision Air Parts" and later was consolidated into "Precision AirMotive"...the compass mfr'r.

The person known as "Ham" Hamilton I never met nor heard of until recently. Here's a pic or two of what you were thinking of perhaps:

I was able to find the following info:

'The Hamilton HI-400 Vertical Card Compass was invented by a man known as "Ham" Hamilton at Hobby Airport in Houston Texas in the early 1970s. He owned a small aircraft instrument repair shop known as Hamilton Instruments at Hobby Airport. I knew "Ham" at the time because I was an avionics technician working for Associated Radio Service Company, also at Hobby Airport. "Ham" brought his prototype into our shop and showed it to us. It was a great invention. The model number "HI-400" stands for Hamilton Instruments-400.
Hamilton later sold his invention to Precision Airmotive, also at Hobby Airport."

blueldr,

Thanks for your last post. I believe I have decided on one of the B models on my list. Still not sure which B but at least a decision on a B has been made at this point. I like the extended baggage area idea. I'm thinking this is something that you can get access to without having to install an exterior baggage door...right? I appreciate the input.


Justin

juredd1 wrote:...I like the extended baggage area idea. I'm thinking this is something that you can get access to without having to install an exterior baggage door...right? I appreciate the input.


Justin

SURE! All you need is a long track-system and a belly-creeper or skidplate!

(Of all the un-original things done to my airplane....the baggage door was the one I like BEST.)

Justin, I've never had an extended baggage area so I can only go on getting into the standard area.

Could you get to an extended area it without a baggage door. Sure but first you'd have to climb into the regular baggage area which is not an easy feet.

If you have the hat rack that covers the baggage area you would have to fold down the seat then low crawl over it in to get to the back. If you remove the rack over the baggage area you can reach over it to the baggage area but getting to the extended area would be a struggle. Oh and if you get that '55 you just can't remove the rack because the rear seat latches to it unlike the early models I think '53 and earlier. But this could be overcome somehow.

I think most people with an extended baggage area don't have the rear seat installed at all.

Tie one end of a long piece of string to your sleeping bags and the other to your rear seat.
Then just toss the bags back as far as you can throw

Okay, okay....I get the point, it's a long way back there. As always thanks for providing some enjoyable reading.

I have a three year old I could toss her back there to retrieve the goodies until I can swing a baggage door. Hey it's an option.

Justin,
Don't let these "Straight C-170" and "A model" guys influence you. They will NEVER tell you how many times they have cried themselves to sleep.
It's just like the old Packard Automobile slogan, "Ask the Man Who Owns One". (That's probably from before you were born. If you don't know about Packard automobiles, think "P-51 Mustang Airplane engines").