My aircraft (Socata ST-10, built 1971) is factory-equipped with a Badin Crouzet autopilot. It basically consists of pneumatic bellows that actuate the ailerons and works either as a wing leveller or follows the heading bug from the DG. Here is a picture of the control unit:
According to an article I found online Link, my setup was part of a “scalable” autopilot system that Badin Crouzet offered in these days.
In the past few weeks, my autopilot started to work unreliably – sometimes doing unmotivated banks, sometimes tracking with 10 or 15 degrees offset and so on …
Unfortunately, my workshop knows nothing about this obviously rare autopilots. Does anyone here have experience with them?
I am sending off some emails to people who were “around” the relevant era, including some who used to work for Air Touring, the then distributor of that aircraft.
It looks like this is a normal electronic autopilot but using vacuum actuators instead of the traditional DC brush motor driven servos.
I guess the actuators would have been operated by proportional-control valves, which might be very similar to the valves used in precision hydraulic systems e.g. vehicle suspension which is fully synthethised in software (no springs). I was involved in projects in the late 1970s where the then Dowty Controls used to make such valves. They had two solenoids (one to drive the piston one way and one to drive the piston the other way) and they provided proportional control. However in your case it might be just open/close valves if the “servo” is organised to integrate the signal. Pneumatics don’t normally provide precision positioning like hydraulics do.
If you find a good electronics engineer, and the schematics, it should be possible to troubleshoot this stuff.
If it was me, I would start by
Searching US Ebay for “Badin Crouzet” reveals that Castleberry Instruments in Texas (an excellent mechanical instrument service shop, which I have used multiple times) might know about the stuff. I have emailed my contact there.
Don’t forget to look to the pneumatics as well. Once worked on one of these (in a Rallye), it was obviouse that it didn’t work as the rubber membrane and bellows had dry cracks in them, a small crack could lead to similair issues as you described.
Now if you pronounce Badin Crouzet on English you get – Bad in Cruise
Sorry, couldn’t resist
The feedback I have received thus far is all along the same lines: nobody could fix these things.
That I think leaves the best option as getting an electronics engineer to troubleshoot it, discreetly i.e. off the books That is how a lot of avionics problem fixing is done – it is called “necessity”.
The French company disappeared after some takeovers. The old name, Crouzet, is still very much around, making switches, relays, etc, and a French speaking person could start working on this in France. This stuff was made in the 1970s/1980s so they cannot all be retired or dead yet. I would at least try to get the maintenance manuals (which should contain the schematics / circuit diagrams).
Thank you Peter. I’m now also in contact with a gentleman in Germany who is well connected in the Rallye world and hope he can provide me with some recommendations.
Will report the outcome, in case somebody else encounters the same troubles.
I’ve owned 2 Robins with Badin APs, neither worked. Even when they were still supported they were very unreliable. I stripped out mine years ago to lighten the load on the control cables. I’m amazed that you have a 1971 aircraft with a Badin AP that still works!
I’m amazed that you have a 1971 aircraft with a Badin AP that still works!
That reminds me of a funny line I saw somewhere else, when one poster asked who he could contact to get his PA28 analogue clock to actually work. Some helpful person said ‘why – to make it unique ?’. My PA28 clock doesnt work either of course, however the I am happy to say the original Century IIB A/P does at least still work fine, which isnt bad for a 70’s piece of kit.
Posts moved from here
Joe_90 wrote:
There definitely was one for the Rallye 235
If you mean “Badin Crouzet” analogue, vacuum driven AP then I wouldn’t recommend it. Spend hundreds of man hours trying to get mine to work and despite having factory documentation including mechanical drawings and electronic schematics the results are far from perfect. I have 2 spare units sitting on shelf but just gave it up.
Badin Crouet was installed in many French built airplanes in early 70s: Rallyes, Jodels, even Cessnas
I was wondering if it would be possible to get somewhat simplified STC for a modern AP to replace the Badin Crouzet. After all, mechanical “interfaces” could probably be reused and after reading installation manual of Trutrak Vision I guess that it could be easily configured to mimic operation of the old AP. Vision retails for $2000.
Question: How to generate paperwork to legally install a low cost AP as a replacement of Badin Crouzet?
This is interesting. Some time ago @blueline posted above and he was struggling to get some info. If you still have the factory documentation, @Robin_253, I am sure he would be really interested. I would also much appreciate this for my avionics manuals collection 
What aircraft is this for?
@wigglyamp should know if there is a process for this.
