Autopilot Servo

The inop autopilot on my 1966 337A is a "Navomatic 400" Is this the same thing as an ARC 400 or ARC 400A? Where do I look on the unit itself (logs and original equipment list is with A&P making entries)?

Thanks,

Keven
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Wellbutrin Class Action

[Bob Cook]

Keven

There is the 400 and 400A, also the 400A with IFCS. The one you have should have three switches down the right side. In the original equipement list is the part number for the computer. should be a 535-xxx mod ?

Then I know which one you are talking about. The computers are all basically the same with the same servos. There was a major change around 75 when they upgraded the system. All autopilots were made by ARC / American Radio Corp. Believe Cessna owned these guys at the last. they made good stuff (some of it anyway).

What's the problem and I will tell u where to look.

Bob

[Ron Ball]

The 1966-A would have, if stock the 400[ No 3 swithces down the right side] Has center turn knob for directional control. I have a 1967-B with this 400 unit. Also, have a 1973 -G [pressureized] with the 400A [ has the 3 swithed, white rocker switches, down right side. They are not the same.

[Pete Somers]

I have been reading the various messages about the 300 nav-o-matic in Paul's 67 T337B.

The servo is the old version which you undo 4 screws, the 2 at the bottom are easy but the 2 upper ones are hard to get to, then the servo splits at and angle and you remove the whole servo which has the electronics,motor, followup and clutch leaving just the drive assy in the wing so that the a/c can be flown with this part removed.
That does make fault finding alot easier!
The computer is part of the control head (the 2 boards that were mentioned).
I pretty sure that the you will find the drive transistors u/s you will be best to replace them all.

You will need to recenter the servo before you secure it back in the wing.

If the servo is not the problem try diconnecting the plug on the AH and see if that cures the problem.

Pete

Ron, Bob, et al,

Here's the way my 66' 337A "Navomatic 400" appears on its face:

From left to right and top to bottom:

Top left is a vertical dial labeled "up down" and below that is a yellow light labled "trim"

Next and to the right, top is a round dial which on top of the dial reads "push heading omni" and the dial itself reads "pull turn"

Below this on the bottom of the panel are three toggle switches from left to right which read "Alt On", "Omni Hdg" and "On Off"

And to the far right on top is a round dial which reads "Heading" and has numbers on the dial itself (like a DG).

From what Ron said in his last post, it appears that I probably have an ARC 400, not the ARC 400A.

Bob, in response to your last post to me, my problem is that when the headliner was off, I discovered that I had NO SERVO, that, naturally, poses a problem for using the AP.

The question now is can I use Burt's Servo (and other parts if necessary) from his 400A on my bird?

Bob, you'll be able to see this first hand next week if all works out well for OSH. But any help from you all before then to get the wheels in motion would be most helpful.

Let me know.

Thanks,

Keven
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Voyeur Xxx

[Bob Cook]

Keven

Are you telling me you have no computer? There are no servos in up in the headliner, just the flap motor. The elevator servo is in the port boom at the back and the trim servo is in the starboard boom (copilots side). The aileron servo is in the wing.

If you do not have the computer then you must be very careful trying to mate a new one in it's place. You will need to go thru a complete alignment of the servos and computer in the aircraft including flight test.

This is not good news. I can probably find someone with the expertize to help do this reserection.

Why not meet me in Buffalo and fly to Osh together? Why take two aircraft? Its less than 2 hr flight north of Greensboro to IAG.
I am rather open when I come and go. Maybe drop in and Grab Larry on the way <G>, if nothing more he can buy us lunch...... there are 3 empty seats.

It would be nice to know the serial number and model number of the computer from the original equipment list. BTW there are differences in the wiring harness between revisions (yrs).

fyi

bob

Bob:

Yes, I THINK that's what I'm telling you that I don't have a computer, not servo. An A&P (not my normal one) who helped with chasing down a leak when the headliner was off mentioned to me that he noticed that I didn't have a servo while he was poking around. That's where I got that info. He obviously mispoke, and I obviously was too ignorant to inquire further.

However, the fella I bought the plane from told me that there was no computer because he had removed it to have it looked at, and never put it back because he didn't know what he was going to do, repair/replace, etc. Then he lost his medical, and couldn't find where he put it in his warehouse (he owned a Chevy dealership) so it was lost in a sea of parts. That's the story I got, don't kill the ignorant messenger

Concerning flying in to OSH together, I'm all for it! Problem is that I'm just not sure that we'll be able to coordinate. I'm meeting a client in Cinci before I head on to OSH. My original plan was to have the client meeting, spend the night with my sister and her family in Cinci, and then get up early and head straight to OSH. Of course, I have not even spoken to my sister yet to see if she's going to be in town. If not, I was going to head to OSU to see my dad. I don't know how far out of your way Blue Ash or OSU is for you. I'd be at one of those two places.

I would further complicate your life by needing to be back in SC (GSP) to pick up a friend around lunch on Friday to head to Charleston. So I'd have to get back to my plane Friday a.m. sometime (a little over 2 hours for me from Ohio to GSP).

It would be nice if it could work out, but I understand if you can't accomodate my bizarre schedule!!! It would be particularly nice to have Larry buy us lunch

I'll post or e-mail the info on the serial and model # on the computer, hopefully later today, so we can see what I'm looking at.

Thanks again,

Keven
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Ship Sale

[Bob Cook]

I go into Blue Ash all the time or Lunkin when the wx folds.
Could meet u there but KIAG would be same or shorter for you and you could leave the AC in my hanger.

I was planning on going to Quincy (UIN) so I might need to change plans. Let's see what unfolds by Friday.

Re autopilot, think you will need a computer to start. I know we could probably get it running again but how long and how much is the 1M$ question.

Need to look at the servos, connectors and make sure everything else is still in place. Also the control head is compatible with the computer. There are differences. I am inclined to suggest an STEC if the existing harness and control head is not compatible. Depending on who is doing the work you can pay for the STEC in labour.

There are tons of these computers out on the market and only a handfull of people that know the system. TOOO bad they lost the computer.

Bob

[Ron Ball]

Yes, you have a 400, not 400A. They are completely different. I have both. Probably alot of units out there, collecting dust. Probably call Auto pilot central or others and get one they have gone thru and repaired.

[Paul Sharp]

Well here's the latest: Went to the A/C this morning with my brother-in-law, who's good with electronics. Armed with the info from Bob, we checked and did have voltage on the reference lead (C - 10 volts). The potentiometer seemed to be OK. But we found 2 bad transistors (Q6 and Q7 if I remember rightly now - anyway I tossed them so I can only replace the bad ones by filling the empty sockets). Picked up 2 new transistors which are now NTE121 (or whatever those 3 letters are) of the newer brand.

Bob helped with schematics and much other advice, including via phone. I really owe him a lot more than a steak dinner but would be willing to buy one of those whenever he's ready as some sort of small thanks for a whole bucketload great expert help! And thanks to others here who've chimed in and helped, too.

[Bob, BTW re: the two screws that seemed to be shorting out the two transistors that were insulated from the heat sink - when I tried to put them back I found that what was happening was that the collectors of each of them were supposed to be connecting via the screws, which went through insulating shoulder washers on the sink and into studs on the back side which had wires on them; so while the cases are still isolated from the heat sink they are making contact on the back as part of the circuitry. Anyway, I'm putting it all back together the way it was with the 2 new transistors, and plan on reinstalling in the A/C tomorrow.]

I use the A/P regularly, although not heavily. But there are times when it is really a boon, such as when plans change in IMC and you have to study a new chart, long straight courses that you don't want to hand steer, etc. Without at least a "heading George" (which a single-axis A/P amounts to), I would tend to like any particular plane a lot less.

[Paul Sharp]

Well, plugged in the servo electronics and it promptly blew the breaker, twice. So took stuff back out and came back to the bench. Found a couple of fried resistors (they might have caused the problem originally, although can't tell). Getting some new transistors (expensive fuses....).

Noted that the turn coordinator isn't working. Don't know if it's related to the servo not being connected or not. Mine does seem to be a little different since the O.E. List says something to the effet that the A/P is interconnected with the gyro and etc. Also I suppose there is supposed to be a breaker for the turn gyro but I couldn't find one (other than the A/P breaker as mentioned above) that was blown. Could it have one inline or something? Or is it possible gone south?

Sigh.... This might turn out to be an expensive project.