Autopilot 400

[Sten]

Hi, I was adviced by "gmas@inreach.com" to move to this list, from skymaster@yahoogroups, where I just posted the following. So, here goes...
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Hi Guys,

I've bee lurking on this list for a while, searching for a decent 337 for sale. Well, yesterday I brought home a 1970 Reims/Cessna 337F that I purchased in Denmark! And the deal also includes an additional almost complete 337 partly disassembled, with engines and everything (but props). Even a cargo pod!

Lots of small problems to fix on my new ship. A few taken care of already, like PTT u/s, and LH Main Tank Gauge not working.

Next on the list is the 400 A/P that is totally dead. Circuit breaker is OK, but nothing happens when I switch it on. The A/P head off/on switch gets voltage, but that's it! Read about the computer of the 400 series that frequently loses the power supply. Actually looked everywhere for the computer, but cant find it! Logical place would be the avionics bay behind the fire wall, but not so. Maybe I don't have one?

Any hint or tip would be highly appreciated!!

Cheers!

Sten Svensson, Sweden

[SkyKing]

Sten,

Welcome to the ranks of Cessna Skymaster owners!

I believe you'll find your 400A computer up ABOVE the headliner in the aft area of the cabin. It's either mounted next to the ELT on the right side or directly across from it. If you have a 400 DME, the electronics for it are also located in the same general area.

Have you ordered the Service and Parts manuals from Cessna yet? They will offer you an excellent source of reference materials to restore things and to properly maintain it.

Have fun!

SkyKing

[Sten]

Hi, Thanks for the info. I opened the headliner and found it right away. That is, found it’s bracket and connectors. Box was gone. There is one square- and one round connector, and a static pressure(?) tube.

Probably need a new box. What are my chances of finding a functional one at reasonable cost?

Is there a second hand source for manuals?

Cheers!
/Sten

[Bob Cook]

I have a complete set of manuals for the 400 series.

IS yours an "A"?
Does it have the flight director?

KEVEN has a source for one perhaps he can jump in.

They are a good autopilot. find the serial number and model in the orig. equip list.

regards

bob

[MikeZ]

Sten: if you can swing it, I'd scrap the 400 and put in an S-Tec, even the lowest end model. I know its more money, but in the long run if you want to keep the plane its worth it.

I flew with the 400 series for 10 years, and every year or two had to put lots of money into it. It wasn't that accurate, and had a bad habit of making "excursions", wild hard wingovers. I was able to handle it but my passengers got freaked. Not to say that yours will do the same.

I'm told by a friend that runs Autopilot central that S-Tec has a huge market share, but that their repair shop only gets less than 5% of its business taking care of that brand of autopilot.

If you're going to do real IFR flying, this is not an area to scrimp on. Good luck.

Mike Zinn

[Dale Campbell]

Mike is right. If you need as many parts as it sounds. The S-Tec is your best choice. I spent over $6,000 getting my 400 working right in my 337H. If I knew that in advance, I would have put that money in a S-Tec, like I had in my old ship I sold. I never had a problem with the S-Tec..

[Sten]

Bob, Mike, Dale,

Several options, it seems… :-)

The 400 has no flight director, and no heading bug. Heading is set on a knob on the control head.

Actually, I do have a S-Tec 50 that only spent about one year in a Reims Rocket (Cessna 172). Everything is there, servos, gyros, etc., but it’s a 14 Volt system, and my 337 is 28 Volt.

I can probably add a converter to take care of the voltage, bu it’s a major job to install the S-Tec, as I have no manuals, servo brackets or –cables.

Was thinking that if there are a lot of 400 computer boxes around I could get one real cheap to test the system. Maybe not a good idea?

Further opinions welcome!

/Sten

[Keven]

Sten:

I'm in the middle of the same process you're in right now. You need to determine whether you have a 400 or 400A. Then you need to determine which year it is. I've got a non-working 400 pre 1968 model which is COMPLETELY different than the later model.

Availability is another problem. If you have a post 1968 model, which you almost surely do, then I've got a source for you at a very good cost. E-mail me and I'll put you in touch with the guy. I couldn't use the one he has for sale because it wasn't the right model for my bird.

I'm also debating about putting in an S-TEC and just being done with it. But then again, $$$. However, if I could find a reasonably priced 400 computer, then it's worth it for me to at least try and see if I can make it work for awhile. On the flip side, the thought of not hand flying on every 2-3 hour trip I make each week is starting to sound pretty appealing to me:)

Let me know if I can help.

Keven
________
Festique (http://www.girlcamfriend.com/cam/Festique/)

[Guy Paris]

Sten,

I have a 77 G with a 400A. When I first got the bird some 10 yrs ago, the A/P worked ok but would not couple to the loc or the gs. I had an OLD TIMER look at it, he took out the comp. box did some repairs to some of the card in it. We re installed it, he did some in flight adjustments roll rates etc. It has worked ok since. The trick is to find some one who still has the test equipment for the Cessna type. There is a shop close to me that still has it. Some times when they do a retro fit they save good componets. Recently got a elect. trim actuator from them. With the 400A there is no F/D and no annunciation, eg: LOC. capture or GS. capture. One has to pay good attention to what is going on.. When ever any asks as to my flying time I respond... about 4 thousand hours, and about 16 thousand watching George, that was the A/P nick name. (the four and sixteen is just a guess)....Guy ....old72driver....

[Sten]

Wow, I’m amazed by the amount of knowledge an engagement on this board! Thanks all for helping out.

It appears I need some assistance to recognize exactly what kind of Navomatic System I have. The best way would probably be for me to post a couple of pictures here. What is the Board Policy concerning attached photos?

Further, if I go with the S-Tec 50 I already have, is there anyone who has an installation manual that I can acquire a copy of? Also interested to know if the Navomatic servo brackets and control wires can be used with the S-Tec servos, where to position the control head and the other components, etc.

I have a complete set of manuals and brackets, etc. for C172, if someone is interested.

Thanks! /Sten

[SkyKing]

Sten,

There's an even easier method of determining 'which' box you should have installed, as well as other installed equipment, and that is to contact either Reims/Cessna or Cessna in Wichita and secure a copy of the Original "Weight & Balance and Installed Equipment Data" list for your specific tail number (as it came from the factory). This data will list a "Control Number" that specifies every component installed.

If unable to contact Reims/Cessna, I would try the Cessna Technical Support Department in Wichita, Kansas at (316) 517-5800.

BTW, you'll find a whole slew of 400 avionics items in Trade-A-Plane. E-Bay is another source under "Avionics".

Good luck on your project!

SkyKing

[kevin]

Sten,

In response to your question, the message board will allow one photo to be attached per message. You can post as many of these messages with photo as you wish, there is no specific limit.

Kevin
webmaster

[Burt Benson]

I have a complete 400A autopilot for sale. It was removed from a 1976 337G.

Burt

[Sten]

Really! How much?
/Sten
sten@stonab.se

[GMAs]

Sten... this is the place to be if you own a skymaster... smile... glad to see you made it over... I think you will find this to be a very informative group...

As to your autopilot... call S-tec and they will work with you... they can take your old one and convert it over to 24 volt... and they have the plans and items that you need to make it work... its much better... the 400 is like a 1960 VW Bus... while it will run down the road.. it's slow and old and hard to find parts for anymore... and the ones that are subed... are not the same... so it never really does work as good ... while your 50 is like a modern corvett... good fast and less trouble... technology has come a long way since the 400... and after you get through getting the transistors to working.. the caps and other parts are going to start having problems too... its just better to upgrade... call S-tec they are a good company to work with and they will get you set up... I am sure... as the actuators for the old autopilot will come out and the new ones go right back in where the others were... kinda thing... even use some of the wireing from the old ones...smile...

Good luck and fly safe.. G.>M>. GMAs.

[Bob Cook]

GMAS

You are only telling 1/2 the story. They are two different animals..... one is a role rate (s-tec) and the 400 is a pitch/roll autpilot that has its input from the AI and DG. The S-TEC is a rate of change device that gets its input from the turn and bank.

Big difference.

I do not see 737 / DC8 autopilots being replaced with new ones, and these are far older than most 400 series autopilots. BTW mylar caps do not dry up or become leaky. The power supplies were the weak side of things and you need some good support equipment to set them up or diagnose problems with them. There are still good service people that support the 400 series autopilot and there are lots of parts around from those who have been convinced a new autopilot is necessary.

The 400 was and is a good autopilot if serviced properly. The aircraft does not need to change direction BEFORE the autopilot senses the change.

Each case is different and must be subjectively analized. If the 400 is working properly it is a damn good autopilot. I can do fully coupled approaches with mine and I have not seen a hiccup yet. Let's me more objective.

my two cents.

Bob

[Sten]

Hi,

I called S-Tec Friday afternoon and talked with Scott Howard. Can’t say he was over enthusiastic about the idea to modify my 50-system that came out of a C172, to fit the 337. Also said installation had to be done by a S-Tec dealer. I told him we have our own maintenance shop, and if it can be done, the 50 will be installed here with or without their support.

Anyway, after a lengthy discussion he explained their part # system. He also faxed a parts list for the 337 S-Tec 50-System.

The computer is fairly easy to modify, it’s just a matter of “replacing a few resistors”. The servos are different, as there is a specific servo speed for each aircraft. It has to be the right servo, and they are “very expensive” to modify!

The gyros are all the same except for the turn coordinator voltage, and the lamp voltages if so equipped.

For most Skymasters, the Computer part # is 0132-0-7, Roll Servo # 0106-R9, and Pitch Servo # 0108-P4. These are the numbers for a 28 volt system. The 14 volt part # ‘s change only the first four digits, the dash # of the computer and servos remain.

So, I’m still as confused as ever! Seems also to be some different opinions about the excellence of the original 400 System!

Next, I will have a look at the dash numbers of the 50 System I have. And try to locate a manual of the 400 System in the aircraft, so I can construct a test device to check the servos.

If the 400 servos are OK, I’ll probably try to find a good computer for the existing system. If not, and the dash numbers are right, it will be a winter project to install the 50-System!

Comments appreciated!

/Sten

[MikeZ]

Like any other item of complicated electromechanical equipment, what Bob said is true, like if it ain't broke, don't fix it.

I think the more appropriate way to look at it for Sten and others facing the same issue is one of putting good money after bad.

Even if one bought the S-tec on credit, I'd wager that the payments would be less than the ongoing repair and maintenance costs for the old (renovated) 400 autopilot. Not to mention downtime and aggravation.

So its a personal decision after all.

[skymaster]

howdy: recommend you talk with ron hitchcock exec. autopilot in sacramento ca. he can check your boards. a dealer can exchange servos . currently he is working on my s-tec 65. the servo test is being performed by a local s-tec dealer. Ron's electrical and bench testing abilities are superb. j

[Sten]

Skymaster,

Thanks for the tip, but the logistics of sending the servos away for testing gets a little complicated as I'm in Sweden...

I have a home brew tester for S-Tec servos. It plugs in to the servo connector and tests the servo in the wing/fuselage.

I'm now looking for the schematics for the Navomatic 400 so I can test primarily the servos, but also the control head. If they are OK, I'll try to find a good computer box...

/Sten