Badin Crouzet is basically a collection of very old transistors, light bulbs, diaphragms, photo resistors and vacuum valves
My thinking was that If this thing worked well 40 years ago then today with enough of time and resources one can get it to work. But I sort of failed. Glass is half full half empty though because it kind of works but having spend so much time troubleshooting this I lost my believe in overall reliability of this system.
I would be extremely happy to say goodbye to all this stuff and get something modern and reliable.
I believe the electronic part of documentation is kind of generic, the mechanical actuators are customized for particular make and model.
Peter, you could probably make a number of Robin owners happy.
The HR100 had this as a factory option and apart from one owner with a Century I, there seems to be no AP with STC for this great tourer.
:-)
An STC is obviously possible for “anything” but you need to be sure that enough people will dig into their pockets.
And that is always the problem in GA. I could recount many examples of this. One was a TB20 turbocharger STC (to make a TB20 into a TB21, but with a supposedly better turbo) where Tornado Alley wanted $200k for the STC. For 10 owners, a “great deal” at $20k each plus the turbo – much cheaper than selling up and buying another can of worms plane which somebody prob90 sold for a “reason” 
How many were interested in the end?
One – the one who originally proposed it. Maybe some others popped up with “interest” but for sure nothing happened.
Most avionics shops who develop STCs sell them for a long time afterwards, for 1k-3k, to other avionics shops. Sometimes less, sometimes more…
Actually, a Basic FAA STC can be approved by EASA for 233 EUR – the caveat is it applies only to a single plane. But at that price… See Application for validation of FAA STC classified as Basic and limited to one s/n
From here
I don’t understand the above but an autopilot installation is nontrivial because the feedback control loop behaviour needs to be tweaked on test flights, all around the corners of the loading and speed envelope. I would be amazed if this was possible as a “basic STC”.
Could an STC be created based on proving that a new device works exactly like another one which was approved for a particular aeroplane?
Badin’s operation is dead simple: tilt the gyro and one of two light bulbs becomes darkened by a diaphragm attached directly to the gyros’ axis. This in turn will triger a vacuum valve which through a pneumatic actuator will act on ailleron’s steering cable. There is no rocket science here. One needs only a with a vacuum cleaner and 12 V battery to learn how the whole thing works. It would be trivial to reverse engineer Badin’s way of working and probably not very difficult to re-create that on a digital AP. Question is if this excercise would be acceptable for EASA to allow installation of new AP in place of Badin?
I don’t know but my feeling is that you would have to engage an EASA 21 company to do this. It will cost you thousands just to get started, I am sure. I embarked on one job years ago and it was going to cost 2k just to get the 21 company to look at it.
Anything to do with autopilots is difficult, which is why we see so few retrofit products on the market. STEC have most of the market but they did their “certification” in the old days when not much due diligence was required and their autopilots are often unstable in some installations.
It would be a fun DIY project 
but a lot more work than might appear.
I would get rid of the pneumatic stuff because it is difficult to get accurate position control with air actuators. In fact I would buy one of the homebuilt-market autopilots and install that. Some of them have somewhat reasonable servos, and the rest is just consumer electronics. Obviously this would be illegal but would be much less work than building something yourself entirely, which would be just as illegal. And you would get the pitch axis too, which is really nice to have – fly a coupled ILS, etc.
Thanks @Peter for bringing the recent posts to my notice. I had some changes in my flying in the past 6 months and have therefore visited less often.
Unfortunately, my research into Badin Crouzet Autopilots led me to exactly the same results back then – nobody knows anything about them, nobody can fix them, nobody has spares. I haven’t found anyone who actually has a working example.
While in the US this whole AP retrofit business is being made much easier just now, I fear this won’t be of much use for those of us who own EASA aircraft which never got an FAA STC.
I bet you that the certified version of the Trutrak won’t be the current price. It is not in anybody’s interest to totally bomb out the market
I have 2 Robin HR100s – Both had Baudin Cruzet APs. One of the autopilots is in bits in a box and the other one is still installed but the aircraft wasn’t airworthy when I bought it, so I have never seen one working. There are EASA Century AP mods for the Robin in existence (Century I & II).
They (the BC A/Ps) are generally regarded as unreliable, as Ted P mentioned. If it was working from 1971 until recently, you have been incredibly lucky!
If you isolate what is wrong with it I may have the bit you can have (free)
