Let’s not be unfair, very often S-TEC is the only option on the market. In the GDR, people were looking forward to receiving their Trabant many years after placing the order
Ha. S-TEC55X, the Trabant of the autopilot world..
Well I have to say my S-TEC in a C172 does everything I need it do and is a huge help when single pilot IFR. Yes it is old technology but is far better than the Navomatic in my last aircraft. Recent trip was middle England to south of France (with of course a stop for customs!) and a/p took us all the way there and back quite faultlessly.
You bet it’s better than the steam driven Navomatic. Just don’t rely on it completely. My S-TEC in the Warrior, although a good and reliable A/P (and only five or six years old) once stalled the plane enroute when the altitude hold tried to fight some unusual thermal updrafts (at least that was my theory later). That was VFR and I watched with amusement, but i would not want that to happen in IMC …
It might be better than the Navomatic 200/300 but surely not better than the Navomatic 400 which is attitude-based.
>>Mooney Driver, sorry to hear you are getting to know the STEC55X. It is sure to disappoint.
Jesse,
well, it is the only system I could actually go for. Not much else in the retrofit market which has an STC for the M20C.
One motivation behind that was however that it can be upgraded to a DFC 90 should that STC ever materialize. That is why I went for the 55x and not the cheaper 30 or 50, apart from the fact that neither of those has a flight director. At the aero, S-Tec also reduced the price for anyone interested in a 30 they offered the 55x instead with a discount of about 5000$.
Why do you think it is bound to disappoint? In which way is it worse than say the KFC150/200, which btw have no STC for my plane? Or what should I have gone for instead?
the other way to interface an old analog autopilot is via a Sandel SN3500 EHSI, which can convert ARINC429 roll steering data into analog deviations
That is exactly what the Aspen does too. I once had the chance to talk to one of the guys who came up with it and he said, what they wanted to achieve was that the Aspen could serve any vintage Autopilot with HDG only with a GPSS steering signal, so that is what they do, they translate the signals to get the AP to think there is a DG sending heading bug signals.
The only way to burn more AVGAS faster than in a Cessna 421 is to set an AVGAS delivery truck on fire…
Or buy an Antonov 2 :)
My favorite AN2 story is when it got here the first time to ZRH and the fuel truck arrived. After fuelling more than 1000 liters of Avgas (the An2 can load 1200 liters) we asked for some oil, to which the delivery truck produced a 1 ltr bottle. The Hungarian mechanic made a big show of climbing up on the engine and emptying that bottle, then calling down “thanks, now can we have another 29 of these please?” The looks on the face of the delivery truck driver was quite priceless.
It was a joke. It is certainly better than nothing but just not a particularly strong autopilot. If that is all you can fit legally then the decision is made. If you get a DFC-90 upgrade path eventually then that is a great autopilot.
The 55X works but from what I have seen it has a tendency to “snake around” in light turbulence. A while ago I had a flight in an SR22 and it was very obviously doing this. Whereas the KFC225 would be steadier than the best hand flying, in those conditions, and very accurate vertically in smooth air (stable within 10ft).
I am certain that STEC never flight tested most of the models on their STC. The flight tests take a lot of time because you have to do it in all corners of the loading envelope and at all speeds from Vs to Vne.
You then have to make sure there is sufficient control loop stability margin at all those points – in crude control theory you make sure that the loop gain is below unity before the phase shift reaches 180 degrees and in practice you need to have a hefty margin there, and more so on the ancient analog autopilots which use poorly-stable electrolytic capacitors in the time constants (which was always known to be a stupid practice but avionics doesn’t seem to attract good electronics engineers).
Honeywell /King did the testing correctly, apparently, on their KAP and KFC units, but they cost a lot more (I think a KFC225 was about $40k, end user list price) and have very few STCs.
I cannot understand why Avidyne don’t throw some money at some contractor and get them to generate a load of STCs. I am sure there are plenty of shops who would like to own the STCs 
Hmmm, wait, I forgot that Avidyne don’t have any money to throw at anybody, do they…? But Garmin clearly do, so their reluctance to enter the market must have a different motive.
I cannot understand why Avidyne don’t throw some money at some contractor and get them to generate a load of STCs. I am sure there are plenty of shops who would like to own the STCs Hmmm, wait, I forgot that Avidyne don’t have any money to throw at anybody, do they…? But Garmin clearly do, so their reluctance to enter the market must have a different motive.
I spoke to a guy from Garmin who investigated doing retrofit STCs for the GFC700. The conclusion was that it was too expensive and there would be no return on investment. Too many different STCs for too many airframes, too much money per airframes.
I believe Avidyne identified the only opportunity with critical mass (Cirrus with S-TEC 55X) and executed on that.
Doesn’t seem to say anything about STCs, and unfortunately you need an STC for an autopilot.
